Unit 6: Human Physiology

Question 1

What is the purpose of exocrine glands?

Answer 1

• food particles are too big to be absorbed through intestine walls of digestive system
• food particles need to be digested to soluble molecules that can pass through the membranes in the intestinal tissues
• to do that, exocrine glands of the digestive system secrete enzymes that hydrolyse large molecules into smaller molecules

Question 2

Define the digestive system

Answer 2

digestive system = complex tube from mouth to anus

Question 3

What are the two types of organs in the digestive system

Answer 3

• the organs that make the tube are usually called the organs of the digestive tract or alimentary canal
• organs that secrete chemicals into the tube are called accessory organs

Question 4

Draw a diagram of the digestive system

Answer 4

https://file.notion.so/f/f/e52fcf8a-d6ea-4a2d-a3c3-d8bce0c54560/cb3f85ac-4f39-4183-921a-9a1167a341b6/Untitled.png?id=3cf4af86-a088-45d7-a09f-bba6dc61c810&table=block&spaceId=e52fcf8a-d6ea-4a2d-a3c3-d8bce0c54560&expirationTimestamp=1714953600000&signature=oyH1djvUhB_W8d1rOgdH68bkU2AMLj5KXQU-ZJXnuQg&downloadName=Untitled.png

Question 5

Give the steps for digestion

Answer 5

1. in the mouth, you chew food and it’s mechanically mixed with salive
2. saliva has the enzymes amylase that start the digestion of starches (carbohydrates). saliva also moistens the mixture to make it easier to swallow
3. the bolus (food mixture) enters the oesophagus (also called the gullet) and then moves to the stomach through peristalsis
4. longitudinal and circular muscles work antagonistically, meaning opposite to each other. when one contracts, the other relaxes. the longitudinal muscle contracts to widen the lumen of the alimentary canal while the circular muscle contracts to constrict lumen
5. in the stomach, food is churned with acid. the food and acid mixture is called chyme (pronounced kime). stomach acid kills bacteria and starts digestion of proteins and continues digestion of carbohydrates
6. food enters small intestine. first section is called the ‘duodenum’ (meaning twelve fingered cuz that’s how it looks). Here, the acid from the stomach needs to be neutralised so enzymes in the small intestine can function properly. These enzymes have an optimum pH of neutral to alkaline, and some digest fat and lipids while others digest carbohydrates, and others digest proteins. By the end, the digestion has been completed and the digested products are absorbed by the last section of the small intestine which is the ileum. Most digestion happens in the small intestine

Question 6

Define Peristalsis

Answer 6

Peristalsis = wave of contraction and relaxation of the longitudinal and circular muscles of the alimentary canal, by which contents are forced along the tube

Question 7

What are the accessory organs and what do they each do

Answer 7

• pancreas secretes amylase, lipase, and protease (aid in digestion of starch, lipids, and proteins respectively) into the small intestine
• liver secretes bile to emulsify lipids
• gall bladder stores bile

Question 8

Why is bile not an enzyme

Answer 8

bile isn’t an enzyme. it breaks large lipid globules into smaller lipid globules (emulsify). bile doesn’t facilitate hydrolysis reactions like enzymes.

Question 9

Where is the small intestine located and how long is it

Answer 9

small intestine is muscular tube of about 6-7 metres long in humans that lies between stomach and large intestine

Question 10

What are the three sections of the small intestine

Answer 10

Duodenum, jejunum, and ileum

Question 11

What lies on the surface of the small intestine and why

Answer 11

inner surface of the small intestine is covered with villi, which increase surface area by 30-60 fold, which is essential for absorption

Question 12

What are the tissue layers of the small intestine from outside to inside

Answer 12

• serosa — outermost layer with connective tissue in contact with body cavities
• longitudinal muscles — responsible for peristalsis
• circular muscles — responsible for peristalsis
• submucosa — connective tissue supporting mucosa that has large vains and arteries, giving rise to the capillary bed of the mucosa
• mucosa — innermost layer forming soft lining of the tube comprised of epithelium (lines the lumen of the digestive track), connective tissue, and smooth muscle (villi form part of this layer)

Question 13

What happens in the small intestine

Answer 13

• in the small intestine, food is broken down to monomers that can easily be absorbed by the villi and taken up by the lymph or blood
• first large food is broken into smaller units, then the smaller units are broken down into these monomers

Question 14

What produces enzymes for the small intestine

Answer 14

pancreas and wall of the intestine produce necessary enzymes and secrete them into the lumen (centre space) of the small intestine

Question 15

What digestive enzymes are made by the acinar cells of the pancreas?

Answer 15

• amylase — breaks starch down into maltose
• endopeptidase aka trypsin — breaks down proteins into smaller polypeptides
• lipases and phospholipases — break down lipids and phospholipids to fatty acids and glycerol (both produce both). in phospholipids, they also break into a phosphate.

Question 16

How does pancreatic juice get to the small intestine

Answer 16

the pancreatic juice with the enzymes is then carried through the pancreatic duct to the duodenum, where it’s released into the lumen of the small intestine

Question 17

Which enzymes complete digestion in the small intestine following pancreatic enzymes

Answer 17

• nucleases — break down DNA and RNA
• Maltase: break down maltose into glucose
• lactase — breaks lactose down into galactose and glucose
• exopeptidases — break down small polypeptides into single amino acids
• dipeptidases — break down a dipeptide into two amino acids

Question 18

Where do the monomers in the small intestine go?

Answer 18

the monomers in the small intestine are then absorbed into the blood or lymph

Question 19

What happens to cellulose in the digestive system

Answer 19

cellulose remains undigested as the enzyme cellulase (which breaks down cellulose) isn’t produced by humans

Question 20

Where does the absorption of food molecules take place and what is required?

Answer 20

actual absorption of food molecules takes place in the small intestine, across the epithelium. transport proteins are necessary for this absorption and so is a large surface area. The capillary network and the lacteal carry absorbed nutrients away from the intestine.

Question 21

How is SA of small intestine increased

Answer 21

SA of small intestine is increased by presence of villi which are the location of absorption of all the monomers produced by the digestive processes in the small intestine

Question 22

Draw a villi

Answer 22

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Question 23

What are epithelial cells

Answer 23

epithelial cells are where absorption happens. each epithelial cell has projections of the plasma membrane that protrude into the lumen of the small intestine. the projections are called microvilli, which further increase the surface area

Question 24

What do goblet cells do

Answer 24

goblet cells make mucus

Question 25

What is the lamina propria

Answer 25

lamina propria is the connective tissue of the villus

Question 26

Define absorption

Answer 26

absorption = taking in of digested food substances and minerals and vitamins from the lumen of the small intestine into the blood

Question 27

Which molecules are directly absorbed by villi

Answer 27

• molecules directly absorbed by the villi:
  
  • bases and phosphates from nucleic acids
  • fatty acids and glycerol
  • amino acids
  • monomeric carbohydrates, like fructose, glucose, galactose, and ribose
• vitamins and minerals in food can be absorbed without further digestion.

Question 28

What are the end products of digestion used for

Answer 28

once end products of digestion are distributed around the body through the circulatory system, they can be used by cells for anabolic processes or for respiration. these uses are called assimilation

Question 29

What happens to contaminants in the blood stream

Answer 29

• food might have contaminants or poisons which contain ethanol (including alcohol, beer, or spirits)
• most contaminants can pass directly into the blood. the liver can detoxify some of them. but if they can’t be broken down by the liver, they can be secreted in the urine

Question 30

What happens to medical drugs in the digestive system

Answer 30

most medical drugs are taken directly into the blood and broken down by the liver

Question 31

What are microvilli

Answer 31

microvilli are hairlike folds in the membrane of the epithelial cells of the villus, which is where absorption takes place by means of facilitated diffusion, passive, and active transport

Question 32

What two pathways can absorbed molecules follow

Answer 32

to be absorbed into blood, molecules have to pass into capillaries of the villus. fats are absorbed into the lymph, which circulates in the lacteal in the centre of the villus.

Question 33

What is the process to be absorbed into the body

Answer 33

1. substances to be absorbed move from the lumen into the epithelial villi
2. amino acids and monosaccharides move from villi into capillaries and monoglycerides move into the lacteals

Question 34

Define lacteal

Answer 34

Lacteal is the specific term for the lymph system

Question 35

What are the four modes of absorption in the digestive system and when are they used

Answer 35

1. Simple diffusion — when molecules are small and hydrophobic so they can pass through the phospholipid bilayers. this occurs usually with the products of lipid digestion
2. facilitated diffusion — fructose, glucose, and hydrophilic monomers are moved by protein channels. This still requires a concentration gradient
3. Active transport — needed when concentrations are lower in the lumen of the small intestine. movement needs to occur against a concentration gradient. glucose, amino acids, and some mineral ions are transported out of the lumen in this way, which needs ATP. the cells of the epithelium have many mitochondria that can synthesis ATP for this process
4. Pinocytosis — draws in small droplets of liquid surrounded by a small section of the phospholipid membrane. most likely to occur with fat droplets in the lumen of the small intestine

Question 36

How does starch get digested

Answer 36

• starch digestion starts when you start chewing your food
• amylase is an enzyme present in saliva
• once saliva and food have been mixed, amylase starts to break down the alpha-1, 4 glycosidic bonds that connect glucose monomers in amylose and amylopectin. 1 and 4 refer to the carbon atoms in the glucose molecules that are joined by the bond
• end products of starch breakdown by amylase are maltose, a dimer of glucose connected by a-1, 4 bonds, and maltotriose, which is made of three glucose molecules connected by a-1, 4 bonds
• amylopectin also has a-1,6 glycosidic bonds. but those can’t be broken by amylase
• branching of polymers are caused by the a-1,6 glycosidic bonds in amylopectin molecules
• • after the initial catalytic breakdown by amylase, di- and tri- saccharides from starch molecules are still too big to pass through membranes, so they need to be further broken down into monomers (monosaccharides) before absorption
• what enters the small intestine from starch is a mixture of maltose, maltotriose, and dextrins
• three enzymes immobilised in the epithelial cells of the small intestine, maltase, glucosidase, and dextrinase, break down these three molecules into glucose, which can be absorbed by villi

Question 37

What are dextrins

Answer 37

• dextrins — small polymers with the a-1,6 glycosidic bonds.

Question 38

What happens to excess glucose

Answer 38

any excess glucose is taken by the liver and converted into glycogen and converted into glycogen, the animal equivalent of starch

Question 39

What is dialysis tubing

Answer 39

dialysis tubing (AKA Visking tubing) is partially permeable cellulose tubing with microscopic pores that lets water, small molecules, and ions to pass through freely, but doesn’t allow the movement of large molecules. dialysis tubing is used in separation techniques. dialysis enables the removal of small molecules from macromolecules in solutions based on differential diffusion

Question 40

Define the term dialysis

Answer 40

dialysis — separation of smaller molecules from larger molecules in solutions by selective diffusion through a partially permeable (selectively permeable/semipermeable) membrane

Question 41

How is dialysis tubing used as a model of the small intesting

Answer 41

• the medium outside representing the blood into which digested products are absorbed
• tubing represents the epithelium of the small intestine
• the high concentration of glucose solution inside the tubing is what is usually observed after a starchy meal has been fully digested
• since the size of glucose molecules is small enough to pass through the pores of the tubing, it will diffuse from a region of higher concentration (in the tubing) to a region of lower concentration (in the beaker)
• • movement of glucose mimics absorption of glucose via the epithelial cells
• if the water in the beaker was tested for glucose, the result would be positive since the water mimics blood
• if starch solution was added into the tubing through the capillary tube, and samples of water in the beaker were tested for presence of starch at intervals of 10 minutes, a negative result would always be found. starch molecules are too big to pass through the pores of dialysis tubing. same thing would happen in small intestine. starch and other complex undigested models aren’t absorbed

Question 42

How can the presence of starch be tested

Answer 42

• brownish-orange = no starch
• black-blue = starch is present

Question 43

What is a shortcoming of dialysis tubing

Answer 43

shortcoming of dialysis tubing is that it can only account for absorption by diffusion or osmosis, not by active transport

Question 44

Who was william harvey and what did he do

Answer 44

Before Harvey’s Findings: Scientists followed Galen’s beliefs, who believed Arteries and veins were separate blood networks (except where connected via invisible pores), veins pumped natural blood (believed to be produced by the liver), and arteries pumped heat (produced by the heart) via the lungs (for cooling).

William Harvey: English physician who proposed arteries and veins were part of a single connected blood network, but did not know of the existence of capillaries. He also proposed arteries pump blood from the heart to the lungs and body tissues, and that veins return blood to the heart from the lungs and body tissues. This helped explain how body temperature and pH are stabilised in the process of homeostasis.

Question 45

What is blood made of

Answer 45

Plasma, white blood cells, red blood cells, and platelets

Question 46

Define blood plasms

Answer 46

Plasma: Liquid portion which carries dissolved substances such as proteins, hormones, carbon dioxide, glucose, and vitamins and minerals

Question 47

Define white blood cells

Answer 47

White blood cells: part of the immune system, help defend body from disease. Process of phagocytosis to engulf foreign particles/microbes.

Question 48

Define red blood cells

Answer 48

red blood cells: Contain iron-containing hemoglobin proteins to transport oxygen. Iron is recycled. Produced in bone marrow. No nuclei or mitochondria. Also able to pick up CO2 for removal. Bioconcave shape increases the sa:v for exchange of materials. Shape also allows for easier passage in capillaries.

Question 49

Define platelets

Answer 49

platelets (cell fragments): involved in mechanisms that clot blood when blood vessels break. Injury triggers the production of fibrin. Fibrin forms a solid mesh to close the wound.

Question 50

Define the heart

Answer 50

Definition: Four chambered organ consisting of two sets of atria and two sets of ventricles.

Question 51

Define atria

Answer 51

Atria: Like reservoirs. Collect blood returning to the heart through veins.

Question 52

Define ventricles

Answer 52

Ventricles: Like pumps. Expel blood from the heart at a high pressure through arteries.

Question 53

Define systemic circulation

Answer 53

Systemic circulation: Process through which the left side of the heart pumps oxygenated blood around the body

Question 54

Define pulmonary circulation

Answer 54

Pulmonary Circulation: Process through which the right side of the heart pumps deoxygenated blood to the lungs.

Question 55

Define the myocardium

Answer 55

Myocardium: Thicker muscular wall on the left side of the heart, since it pumps blood further

Question 56

Draw a heart diagram

Answer 56

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Question 57

What are the four heart chambers

Answer 57

• Two atria (sing. atrium) are smaller chambers near the top of the heart that collect blood from the body and lungs. They pull blood into the heart.
• Two ventricles are larger chambers near the bottom of the heart that pump blood to the body and lungs. They push blood from the heart.

Question 58

What are the heart valves

Answer 58

Heart Valves(ensure one way flow):

• Tricuspid and bicuspid Atrioventricular valves (between atria and ventricles): bicuspid valve on the left side, tricuspid valve on the right side. Connect atriums to ventricles.
• Pulmonary and aortic Semilunar valves (between the ventricles and arteries): Aortic valve on left side, pulmonary valve on right side. Connect the ventricle to artery.

Question 59

What are the blood vessels

Answer 59

• Vena cava (inferior and superior) feeds into the right atrium and returns deoxygenated blood from the body
• Pulmonary artery connects to the right ventricle and sends deoxygenated blood from the heart to the lungs
• Pulmonary vein feeds into the left atrium and returns oxygenated blood to the heart from the lungs
• Aorta extends from the left ventricle and sends oxygenated blood around the body

Question 60

Give the steps of circulation

Answer 60

1. Right side of the heart (Pulmonary circulation)
   
   1. Blood enters the heart through the inferior and superior vena cava, with oxygen-poor blood from body tissues flowing into the right atrium
   2. The atrium contracts, and blood flows from the right atrium into the right ventricle through the open tricuspid valve
   3. When the ventricle is full, it begins contraction. Increased pressure of blood against the tricuspid valve forces it shut, preventing blood from flowing backwards into the atrium
   4. As the ventricle contracts, blood leaves the heart through the pulmonary valve into the pulmonary artery and flows to the lungs where it’s oxygenated.
2. Left side of the heart (Systemic circulation)
   
   1. Pulmonary vein carries oxygen-rich blood from the lungs into the left atrium of the heart
   2. The atrium contracts and blood flows from the left atrium into the left ventricle through the open bicuspid (aka mitral) valve
   3. when full, the ventricle begins to contract. The increased blood pressure against the bicuspid valve causes it to close, preventing blood from flowing backwards into the atrium while the ventricle contracts.
   4. As the ventricle contracts, blood leaves the heart through the aortic valve, into the aorta and to the blood.

Question 61

What signals regulate the heart rate

Answer 61

• Nerve signals from the brain can trigger rapid changes
• endocrine signals can trigger more sustained changes
• changes to blood pressure levels or CO2 concentrations (and therefore also blood pH) will trigger changes in heart rate

Question 62

What controls the pacemaker

Answer 62

pacemaker is under autonomic control from brain, specifically the medulla oblongata (brain stem)

Question 63

What regulates heart rate

Answer 63

• Two nerves connected to the cardiovascular centre in the medulla oblongata in the brain, can regulate heart rate by signalling to the SA node to either speed it up or slow it down.
  
  • The cardiac accelerator nerve tells the heart to beat faster.
  • The vagus nerve tells the heart to slow down

Question 64

What does the cardio vascular centre do

Answer 64

Cardio vascular centre monitors the blood pressure, pH, and carbon dioxide concentration of blood, to determine whether impulses should be sent along the cardiac accelerator nerve or vagus nerve.

Question 65

Why is the speed that the heart slows down after activity a measure of fitness

Answer 65

Application: Increased activity means more respiration, causing a greater need for oxygen and increased production of waste products (i.e. CO2). Increased CO2 in the blood will decrease the pH, which will make the cardiovascular centre send impulses along the cardiac accelerator nerve to the sinoatrial node to increase heart rate. As the heart pumps faster, more oxygen is sent to body tissue, and more carbon dioxide is removed. Once activity stops, impulses are sent along the vagus nerve. The speed at which the heart rate slows down is a measure of your fitness.

Question 66

Define Hormones

Answer 66

Hormones Definition: Chemical messengers released into the bloodstream that act specifically on distant target sites (i.e. the heart)

Question 67

What is adrenaline

Answer 67

Adrenaline (aka epinephrine)(called the ‘flight or fight’ hormone) is a hormone secreted by the medulla of the adrenal glands located above the kidneys. Strong emotions can cause it to be released into the bloodstream. It increases heart rate by stimulating the SA node to emit electrical signals at a faster rate, as well as increasing the conduction speed of impulses generated by the SA and AV nodes. Other than that, it also increases muscle strength, blood pressure, and sugar metabolism, to prepare the body for immediate action of vigorous physical activity.

Question 68

Define atheromas

Answer 68

Atheromas definition: Fatty deposits caused by high blood concentrations of low density lipoproteins (LDL) in the arterial wall next to the endothelial cells.

Question 69

Define thrombosis

Answer 69

Thrombosis: Forming of a clot in the blood vessel that can entirely block the blood vessel. If the blocked artery happens to be a coronary artery, the cells in that part of the heart will die resulting in a myocardial infarction (heart attack).

Question 70

Define coronary arteries

Answer 70

Coronary arteries: Blood vessels surrounding the heart that nourish the cardiac tissue. If occluded, the region of heart tissue nourished by the artery will die and cease to function.

Question 71

Define Angina

Answer 71

Angina: Pain caused by restricted flow of blood in a coronary artery due to the heart cells being deprived of oxygen and nutrients.

Question 72

Define Atherosclerosis

Answer 72

Atherosclerosis definition: The hardening and narrowing of the arteries due to deposition of cholesterol.

Question 73

Define stenosis

Answer 73

Stenosis definition: Narrowing or restriction of a tube or blood vessel or valve that reduces blood flow

Question 74

Define atherosclerotic plaques

Answer 74

Atherosclerotic plaques: Lesions in the artery which form as the smooth lining progressively degrades

Question 75

What is an acute myocardial infarction

Answer 75

Heart attack

Question 76

What are the steps to a coronary occlusion

Answer 76

1. Atheroma’s develop in the arteries and significantly cause stenosis in the lumen
2. Restricted blood flow increases pressure in the artery, damaging the arterial wall
3. Damaged region is repaired with fibrous tissue which significantly reduces the elasticity of the vessel wall
4. Atherosclerotic plaques form as the lining of the artery degrades
5. If a plaque ruptures, a blood clot is triggered, forming a thrombus which restricts blood flow
6. If the thrombus is dislodged it becomes an embolus and can cause a blockage in a smaller arteriole

Question 77

What are the consequences of Atherosclerosis and its treatment

Answer 77

• blood clots which can cause CHD when occurring in coronary arteries. Myocardial tissue requires oxygen and nutrients transported via coronary arteries in order to function. If a coronary artery becomes completely blocked, an acute myocardial infarction will happen.
  
  • Treatment: By-pass surgery or creating a stent

Question 78

What are the risk factors for a coronary occlusion

A GODDESS

Answer 78

• Age: Blood vessels are less flexible when older
• Genetics: Having hypertension predisposes individuals to developing CHD
• Obesity: Being overweight places strain on the heart
• Diseases: Certain diseases increase risk of CHD (i.e. diabetes which can cause high blood glucose concentrations). Certain infections with bacteria such as Chlamydia pneumoniae can also play a role.
• Diet: Diets rich in saturated fats, salts, and alcohol increase the risk
• Exercise: Sedentary lifestyles increase the risk
• Sex: Males are at a greater risk due to lower estrogen levels
• Smoking: Nicotine causes vasoconstriction, raising blood pressure

Question 79

Draw a labeled diagram of the cardiac cycle

Answer 79

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Question 80

Define the cardiac cycle

Answer 80

Definition: Describes series of events taking place in the heart over duration of a single heart beat.

Question 81

What are the two periods of the cardiac cycle

Answer 81

Systole and Diastole

Question 82

Give the steps of the cardiac cycle

Answer 82

1. Atrial contraction begins (atrial systole)
2. Atria eject blood into ventricles (atrial systole)
3. Atrial systole ends, AV valves close (sound)
4. Isovolumetric contraction of the ventricles (ventricular systole)
5. Ventricular ejection
6. Semilunar valves close (second sound)
7. Isovolumetric relaxation of the ventricles (ventricular diastole)
8. AV valves open, passive ventricular filling occurs.

Question 83

How are the atrium and ventricle affected by the different parts of the cardiac cycle

Answer 83

• Atrial systole: Atrium contracts, ventricle relaxes
• Ventricular systole: atrium relaxes, ventricle contracts
• Diastole: Atrium relaxes, ventricle relaxes

Question 84

What is the direction of blood flow throughout the phases of the cardiac cycle

Answer 84

• Atrial systole: From atrium to ventricle
• Ventricular systole: From ventricle to aorta
• Diastole: Into atrium and ventricle

Question 85

What happens to the valves through the different phases of the cardiac cycle

Answer 85

• Atrial systole: AV open, aortic closed
• Ventricular systole: AV closed, aortic open
• Diastole: AV open, aortic closed

Question 86

Define an isovolumetric contraction

Answer 86

Isovolumetric contraction: Term for an event occurring at the beginning of systole, during which the ventricles contract with no corresponding volume change. Makes the pressure in a heart chamber rise so blood can be forced into the artery in a one-way direction.

Question 87

What happens during systole in the cardiac cycle

Answer 87

• Returning blood will flow into the atria and ventricles since the pressure in them is lower due to the volume of blood
• When the ventricles are almost 70% full, the atria will contract (atrial systole) which increases the pressure in the atria and forces blood into the ventricles
• As the ventricles contract, the ventricular pressure exceeds the atrial pressure. AV valves then close to prevent backflow, making the first heart sound (ventricular systole)
• with both sets of heart valves closed, pressure rapidly builds in the contracting ventricles (isovolumetric contraction)
• When ventricular pressure exceeds blood pressure in the aorta, the aortic valve opens and blood is released into the aorta

Question 88

What happens during diastole in the cardiac cycle

Answer 88

• Ventricular pressure falls as blood exits the ventricle and travels down the aorta
• When ventricular pressure drops below aortic pressure, the aortic valve closes to prevent back flow (second heart sound)
• When ventricular pressure drops below the atrial pressure, AV valve opens and blood can flow from the atria to the ventricle
• Aortic pressure remains high as muscle and elastic fibres in the artery wall maintain blood pressure

Question 89

Define myogenic

Answer 89

Myogenic: The muscle can generate its own contractions. Signal for compression arises within the organ, originates in the muscle; not controlled by neurons. Neurons don’t need to tell it to compress.

• Contraction of the heart is myogenic, meaning signal for cardiac compression arises within the heart itself

Question 90

What are the steps to a heart beat

Answer 90

1. Sinoatrial node sends out an electrical signal that stimulates contraction as it’s propagated through the walls of the atria
2. Signal passes through the interatrial septum to reach the atrioventricular node.
3. Signal is relayed from the AV node through a bunch of His located in the interventricular septum to the top of the ventricle (top of the heart/apex is the bottom-most part where two ventricles meet in a point-like shape)
4. At the top of the ventricles, the signal spreads from the bundle of His (aka atrioventricular/AV bundle) to the ventricles through the Purkinje fibres located in the wall, causing ventricular contraction.
   - These events ensure there’s a delay between the atrial and ventricular contractions, resulting in two heart sounds. This allows time for the ventricles to fill with blood, following atrial contractions to maximise blood flow.

Question 91

What is the myocardium

Answer 91

Myocardium Definition: Heart muscle tissue

Question 92

Define the sinoatrial node

Answer 92

Sinoatrial Node: Specialised cluster of cardiomyocyte cells in the wall of the right atrium which direct contraction of heart muscle cell. Initiates each heartbeat and sets the heart rate, so it’s often called the primary pacemaker. ‘Fires’ (sends electric signals) at regular intervals to cause the heart to beat with a rhythm of 60-70 beats per minute for a healthy, resting heart.

Question 93

What natural pacemakers do we have

Answer 93

• Normal Sinus Rhythm: 60-100 bpm Cardiac Contractions
• If SA Node fails, second pacemaker AV Node maintains contractions at 40-60 bpm
• If SA Node and AV Node fail, tertiary pacemaker which is a bundle of His may coordinate contractions at rate of 30-40 bpm

Question 94

What is the structure of an artery

Answer 94

Arteries have thick walls and narrow lumens because they transport blood at high pressure
Inside to outside:
* Tunica media (smooth mucles
* Tunica intima (endothelial cells)
* Tunica externa (elastin and collagen)

Question 95

What is the structure of veins

Answer 95

Veins have thin walls with wide lumens and valves because they transport blood at low pressure
Inside to outside:
* Tunica media (smooth muscle)
* Tunica intime (endothelial cells)
* Tunica externa (elastin and collagen)

Question 96

What is the structure of capillaries

Answer 96

Capillaries have walls that are only a single cell thick because they exchange materials between blood and tissue

Question 97

What is the difference in functions of the three vessels

Answer 97

• Arteries send blood from the heart
• Veins send blood to the heart
• Capillaries allow material from blood to exchange with tissues

Question 98

What is the difference in pressure of the three blood vessels

Answer 98

• Arteries have low pressure
• Veins have high pressure
• Capillaries have low pressure

Question 99

Difference in lumen diameter between the 3 blood vessels

Answer 99

• Arteries have narrow lumens
• Veins have wide lumens
• capillaries have extremely narrow lumens (1 cell/5 micrometres wide)

Question 100

Difference in wall thickness between the blood vessels

Answer 100

• Arteries have thick walls
• Veins have thin walls
• Capillaries have extremely thin walls (single cell thick)

Question 101

Difference in wall layers between three blood vessels

Answer 101

• Arteries have the layers tunica adventitia, tunica media, and tunica intima
• Veins have the layers tunica adventitia, tunica media, and tunica intima
• Capillaries have one layer of endothelial cells

Question 102

Difference in tunica media between three blood vessels

Answer 102

• Arteries: Thicker
• Veins: Thinner
• Capillaries: Absent

Question 103

Difference in Muscle and Elastin fibres of three blood vessels

Answer 103

• Arteries have thick layers
• Veins have thin layers
• Capillaries have none

Question 104

Difference in valves of three blood vessels

Answer 104

• Arteries have no valves
• Veins have valves at intervals
• Capillaries have no valves

Question 105

Difference in diameter between three blood vessels

Answer 105

• Arteries can be greater than 10mm
• Veins can be greater than 10 mm
• Capillaries are between 2 and 10 micrometers

Question 106

What is the function of arteries

Answer 106

Function: To convey blood at high pressures from the heart to the tissues of the body and lungs

Question 107

What is the aorta

Answer 107

Aorta: Main and biggest artery which connects the heart with the rest of the body. It exerts a systolic pressure of 120-200 mm Hg.

Question 108

What is systolic blood pressure

Answer 108

Systolic blood pressure: Highest pressure experience by arteries when the heart contracts

Question 109

What is vasoconstriction

Answer 109

Process where circular muscles around the arteries resist the outward pressure and constrict during systolic blood pressure.

Question 110

What is diastolic blood pressure

Answer 110

Lowest pressure experienced by arteries when heart relaxes between beats

Question 111

What is vasodilation

Answer 111

Process where the smooth muscles surrounding arteries relax during diastolic blood pressure

Question 112

What are arterioles

Answer 112

Smaller forms of arteries that branch off to supply blood to organs, limbs, etc. They have a higher muscle density and are more susceptible to the hormonal and nervous control of vasoconstriction and vasodilation.

Question 113

What is the stroke volume

Answer 113

Volume of blood pumped out of the left ventricle in the heart during each heartbeat/contraction

Question 114

What is cardiac output

Answer 114

Volume of blood the heart pumps through the circulatory system in a minute

Question 115

What is the importance of vasodilation and vasoconstriction

Answer 115

Note: Vasoconstriction and vasodilation directly control the flow of blood through the body. They also play a role in regulating body temperature and are involved in slowing down the flow of blood when someone is severely wounded.

Question 116

What is the structure of an artery

Answer 116

• narrow lumen to keep high blood pressure (80-120 mmHg)
• thick wall with outer layer of collagen to prevent artery from rupturing under high pressure
• Arterial wall has inner layer of muscle and elastic fibres to maintain pulse flow (can contract and stretch)
• Muscle and elastic fibres help maintain blood pressure between pump cycles

Layers:

1. Tunica intima: Part facing the lumen is lined with endothelium. In direct contact with the blood in the lumen. Includes endothelium that lines the lumen of all vessels and forms a smooth, friction-reducing lining.
2. Tunica media: Thickest layer. It’s the middle coat made up of smooth involuntary muscle cells and elastic fibres arranged in three layers.
3. Tunica adventitia (AKA Tunica externa): Outermost coat. Tough layer made of loosely woven collagen fibres that protect the blood vessel and anchor it to surrounding structures.

Question 117

Describe the pressure of blood in arteries over time

Answer 117

Blood flows in bursts, and not continuously.

Question 118

Define pulses

Answer 118

Pulses: Repeated surges in the arteries through which blood flows from the heart upon ventricular contraction. The blood flows at a high pressure, and the muscle and elastic fibres help maintain the pressure between pumps.

Question 119

Define arterial muscle fibres

Answer 119

Muscle Fibres: Help make a rigid arterial wall capable of withstanding the high blood pressure without rupturing. They can also contact to narrow the lumen, increasing the pressure between pumps, helping maintain blood pressure through the cardiac cycle.

Question 120

Define arterial elastic fibres

Answer 120

On the arterial wall and are formed from elastin protein, which are stretched at every heartbeat when there’s high pressure.

Question 121

Define elastic recoil in artery’s

Answer 121

Artery returns to its normal size when pressure exerted on arterial wall is returned to the blood. Helps push blood forward through the artery, and maintain arterial pressure between pumps.

Question 122

What are capillaries

Answer 122

Capillaries are found when arteries split into arterioles, which then split into capillaries, decreasing arterial pressure since the total vessel volume is increased. Capillaries then fuse together to form venules, which fuse together to form veins. Arteries branching into capillaries ensures blood is moving slowly, and all cells are near a blood supply.

Question 123

What is the function of capillary’s

Answer 123

Function: Exchanging materials between cells in tissues and blood travelling at low pressure through diffusion or active transport. After this material exchange has occurred, tissue fluid is mostly reabsorbed into capillaries, which drains into venules.

Question 124

What is the structure of capillaries

Answer 124

• Small diameter (5 micrometres wide), allowing passage of only a single red blood cell at a time, resulting in optimal exchange
• Capillary wall is made of a single layer of cells, to minimize the diffusion distance for permeable materials
• Surrounded by a basement membrane, which is permeable to necessary materials
• Can contain pores to further help in transportation of materials between tissue fluid and blood
• Rather leaky walls, allowing easy exchange of materials

Tissue fluid/Interstitial Fluid: Liquid part of blood that passes through the capillary wall. Mainly composed of water, sugars, salts, fatty acids, amino acids, coenzymes, hormones, and waste products from the cells.

How capillary structure changes depending on its location in the body and specific role:

• A capillary wall might be continuous with endothelial cells held together by tight junctions to limit the permeability of large molecules
• In tissues specialized for absorption (intestines, kidneys, etc.), the capillary wall might be fenestrated (have pores)
• Some capillaries are sinusoidal and have open spaces between cells and be permeable to large molecules and cells

Question 125

Describe blood flow in capillaries

Answer 125

• Blood flows through capillaries slowly and at low pressure, to allow for maximal material exchange
• high blood pressure in arteries is dissipated by extensive branching of the vessels and the narrowing of the lumen
• Higher hydrostatic pressure at the arteriole end of the capillary forces material from the bloodstream into the tissue fluid. material leaving the capillaries at body tissues include oxygen and nutrients which are needed by cells for respiration.
• lower hydrostatic pressure at the venule end of capillary lets materials from the tissues to enter the bloodstream. materials that enter capillaries at body tissues are carbon dioxide and urea (wastes produced by the cells)

Question 126

What is the function of veins

Answer 126

Function: Collecting blood from the tissues and conveying it at low pressure to the atria of the heart.

Question 127

What is the structure of veins

Answer 127

• Very wide lumen to maximise blood flow for more effective return
• Thin wall with less muscle and elastic fibres, since blood flows at a very low pressure (~5–10 mmHg)
• Since pressure is low, veins have valves to prevent backflow and stop the blood from pooling at the lowest extremities

Question 128

Describe the flow of blood in veins

Answer 128

• Low blood pressure which can make it hard for blood to move against the force of gravity. Veins have numerous one-way valves in order to maintain blood circulation by preventing backflow
• Veins typically pass between skeletal muscle groups, which facilitate venous blood flow via periodic contractions. When skeletal muscles contract, they squeeze the veins and cause blood to flow from the site of compression. Veins typically run parallel to arteries, and a similar effect can be caused by the rhythmic arterial bulge created by a pulse.
• Blood flow in veins is helped by pressure exerted by skeletal muscles. When you move, the muscles squeeze the veins like a pump. Patients that are immobilised for long periods of time or are in a coma need manual manipulation of the muscles to help the flow of blood, prevent blood boils, and bed sores.
• Valves close to prevent backflow. Valves in veins ensure that blood flows in one direction only, towards the heart, by preventing backflow.

Question 129

What are the sections of the immune system

Answer 129

• Non-specific immune system (involves phagocytes)
• Specific immune system (lymphocytes + antibodies)

Question 130

What is the body’s primary defence

Answer 130

Primary defence against infection: Preventing entry of organisms and viruses that cause disease

Method of Primary Defence: Skin, Mucous membranes

Question 131

What is the structure of the skin

Answer 131

• Pores for sweating
• hair follicles
• sebaceous glands (produce oils called sebum to keep skin supple and at a slightly lower pH. oil and low pH both act as growth inhibitors for certain bacteria.)

Question 132

What are mucous membranes

Answer 132

Mucous membranes: Protect body in parts open to outside world. Made up of a surface layer of epithelial cells over a deeper layer of connective tissue. Produce a sticky mucus for lubrication and protection, that contains glycoproteins and lysozymes, which are enzymes that attack the bacterial cell walls. Both of them have antiseptic properties (properties discouraging or preventing the growth of microorganisms). The mucus itself also forms a barrier and traps organisms which can be killed by white blood cells found in the mucous membranes.

Question 133

Outline the process of blood clotting

Answer 133

1. Blood vessel is damaged (initial cut)
2. Platelets release chemicals
3. First reaction triggers second reaction by producing a required chemical for the second reaction
4. Continues through series of several reactions with up to 12 factors. Each reaction takes an inactive protein in blood called a clotting factor and activates it
5. Conversion of fibrinogen to insoluble fibrin. Reaction is catalyzed by enzyme ‘thrombin’ which itself was activated through the cascade of reactions
6. Network of fibres that trap red blood cells and platelets form a soft scab to prevent the entry of pathogens into the body as well
7. Scab hardens, forming protective layer
8. Skin heals under protective layer

Question 134

Define fibrinogen

Answer 134

Fibrinogen: Soluble and inactive clotting factor in blood

Question 135

What is the most common cause of hemophilia

Answer 135

Most Common Cause: Missing clotting factor VIII (7)

Question 136

What is a thrombus

Answer 136

Thrombus: Clot formed in a vessel which remains where it was formed

Question 137

What is a coronary thrombus

Answer 137

Thrombus formed in coronary artery

Question 138

Define atherosclerosis

Answer 138

Atherosclerosis: Narrows lumen of arteries, slows down blood flow, ultimately increasing chance of a thrombus occluding a coronary artery, leading to certain parts of the heart not receiving oxygen and nutrients, causing that part of the heart to die, and a heart attack.

Question 139

Define angina

Answer 139

Angina: Chest pain caused by a thrombus reduces the amount of blood reaching heart muscles instead of stopping it completely, causing heart muscles to not get enough oxygen-rich blood.

Question 140

What is the process of thrombosis of coronary arteries

Answer 140

1. Plaque in artery walls rupture lining of the vessel
2. Clot that began at site of rupture can grow larger and completely block artery

Question 141

What factors increase the risk of clot formation

Answer 141

• smoking
• obesity
• hypertension
• diabetes

Question 142

What is our second line of defence

Answer 142

Second Line of defence by immune system is activated when pathogens enter the body and cause disease.

Function: Recognizes proteins and other molecules on pathogens as foreign, triggering an immune response.

Question 143

Define an antigen

Answer 143

Any molecule that enters the body and triggers an immune response

Question 144

Define a white blood cell

Answer 144

Also known as leukocytes. Blood cells with immune function.

Question 145

What are the types of leukocytes

Answer 145

Macrophages aka phagocytes

Question 146

Define a pathogen

Answer 146

Pathogen: Disease-causing virus/microorganism. Examples: viruses, bacteria, protozoans, prions, fungi.

Question 147

Define a macrophage/phagocytes

Answer 147

AKA: Phagocytes because one main function is phagocytosis

Function: Engulf pathogen that entered the body. Once inside the phagocyte, enzymes secreted by the lysosome will digest the pathogen.

Location: Lymph nodes or blood

Question 148

Define amoeboid motion

Answer 148

Amoeboid motion: Process of movement for phagocytes, which involves the extension of pseudopods.

Question 149

How do phagocytes showcase non-specific immunity

Answer 149

Phagocytes can squeeze past leaky endothelial cells of capillaries and invade tissue where infection occurs, i.e., in a small wound in the skin. This is an example of non-specific immunity to diseases, since phagocytes can respond equally well to a variety of organisms.

Question 150

What is the sequence of destruction of pathogens by phagocytes

Answer 150

1. Chemical recognition
2. amoeboid motion (extension of pseudopodia)
3. endocytosis
4. enzymatic digestion

Question 151

Define an antibody

Answer 151

Antibody: Large protein with variable regions produced by the body that will bind to an antigen. Molecules produced by immune system in response to the detection of antigens. A Protein molecule made by lymphocytes with a specific structure. They recognise antigens

Question 152

Define an antigen

Answer 152

A molecule or entity that enters the body and triggers an immune response. Often found on the surface of a pathogen.

Question 153

Define a lymphocyte

Answer 153

Lymphocyte: Type of white blood cell responsible for production of antibodies

Question 154

Define a B lymphocyte

Answer 154

B lymphocyte: Also known as a B cell. Have capability to recognize millions of antigens through the receptors on their surfaces, which are essentially an antibody attached to its cell surface as an integral protein so that the antigen binding site points outwards.

Question 155

What happens when a B cell recognizes an Antigen

Answer 155

1. Clonal selection: B cell divides repeatedly through mitosis to make many copies of the B cell that can recognise the antigen
2. Most B cells become plasma cells which make and secrete large quantities of the antibody for the antigen to circulate in the blood
   
   1. Antibodies may bind to the antigen, allowing phagocytes to recognize then destroy the pathogen
   2. Antibodies may bind to proteins in the coat of a virus, preventing the virus from entering the other cells
3. Some B cells become memory cells, a long-lived pool of cells capable of responding quickly to the antigens in case of re-encounter. They remain in the bloodstream and lymph nodes for a long period of time, allowing the next antibody production be quicker. The next antibody production is called specific immunity.
4. When infection is overcome, the number of plasma cells which produce the antibodies will decrease

Question 156

Define a T lymphocyte

Answer 156

T Lymphocyte: Also called a T helper cell. Is important in helping B cells complete their function of making antibodies. Once antigen is recognized by T helper cell, the immune system is activated to fight against the antigen. It triggers production of antibodies and activates macrophages and killer T cells, which engulf and destroy the antigen.

Question 157

What is an APC

Answer 157

APC: Antigen Presenting Cell which is a special type of white blood cell that traps the antigen and presents it to the T helper cell.

Question 158

Define HIV

Answer 158

Definition: Human immunodeficiency virus. Infects and stops T helper cells from functioning. Infected T helper cells are destroyed. Since they’re needed to activate B cells to produce antibodies, infections with HIV cause a loss in the ability to produce antibodies, which can lead to the development of AIDS (acquired immune deficiency syndrome). HIV Causes an overall reduction of active lymphocytes, including T cells and B cells. Activated T cells decrease as infected T helper cells are destroyed and activated B cells decrease since there are less T helper cells to cause their activation.

Composition: Retrovirus with RNA as genetic material. Once it infects a cell through the proteins on its surface, it makes a DNA copy from its RNA, with the help of enzyme called reverse transcriptase. cDNA produced is inserted into the host cell’s genome.

Cure: Infection can be slowed down or stopped with the use of antiviral drugs targeting reverse transcriptase activity.

Question 159

What are the symptoms of HIV

Answer 159

• High fever
• Chills
• Pneumonia
• Headaches
• Loss of appetite
• Mood swings
• cough with sputum or phlegm
• Shortness of breath
• Pleuritic chest pain
• Hemoptysis
• High heart rate
• Joint pain
• Nausea
• Vomiting
• Clamminess
• Blueness
• Muscle fatigue
• Muscle aches

Question 160

What happens if HIV is left untreated

Answer 160

Will develop into AIDS, which is a range of diseases normally only seen in severely immuno-suppressed patients, i.e. fungal pneumonia and Kaposi sarcoma (form of skin cancer).

Question 161

How is HIV transmitted

Answer 161

1. Sexual intercourse
2. Transfusion of infected blood
3. Sharing hypodermic needles by drug users
4. Pregnancy, birth, or breastfeeding (mother to child)

Question 162

Define antibiotics

Answer 162

Any substance produced by a microorganism that can inhibit growth of other microorganisms. Normally require low concentrations to be effective, however, with uncontrolled use in hospitals and agriculture, resistance has become widespread and routinely effective concentrations must be increased to higher dosages.

Question 163

How do antibiotics function

Answer 163

Block processes in prokaryotic but not eukaryotic cells. Target bacterial cell wall and membrane formation, ribosome function, or DNA replication, transcription, and translation slowing down or stopping growth of bacteria. Can be used to treat bacterial infections in humans and animals without harming body cells, as they are eukaryotes.

Question 164

Whats the relation between fungi and antibiotics

Answer 164

Fungi: Most antibiotics are isolated from saprotrophic fungi, since fungi often secrete antibiotics to inhibit growth of competing bacteria. An example is penicillin.

Question 165

What is the relation between viruses and antibiotics

Answer 165

Viruses: Viruses are not affected by antibiotics, since they are not living and do not have their own metabolic processes. Viruses infect living cells and make use of the cells own metabolic processes to spread the viral infection.

Question 166

How does resistance to antibiotics change over time

Answer 166

Natural selection favours the spread of resistance, so if a mutation causing resistance to an antibiotic occurs in a bacterium, after several generations a strain of bacteria will evolve with genes that have resistance to the antibiotic. This has occurred many times with many different type of bacteria. However, some bacteria have exchanged genes coding for antibiotic resistance and developed resistance to several. Some bacteria have become resistant against all known antibiotics, making them lethal. These include tuberculoses and some STDs (i.e. gonorrhoea and chlamydia).

Question 167

What is chlamydia

Answer 167

Chlamydia causes a build-up of scarring that can block the fallopian tube and prevent fertilisation

Question 168

How was penicillin discovered and tested

Answer 168

Discovered by Fleming in 1928

Testing: Done to ascertain if the molecule would be effective in fighting human infections by Howard Florey and Ernst Chain in the early 1930s.

1. On Mice
   
   1. They infected eight mice with Streptococcus, a bacterium causing pneumonia in mice. They were kept under identical conditions, but four were given an injection of penicillin. The ones injected stayed alive, but the others died within 24 hours. This gives a strong indication that penicillin may have played a role in the recovery of mice
2. On humans
   
   1. proceeded to test penicillin on very sick patients with infections. Most of them survived
3. Commercial production
   
   1. In the 1940s and allowed testing on more and more patients, eventually confirming it as a very effective weapon against infection

Question 169

Define physiological respiration

Answer 169

Transport of oxygen to cells within the tissues where energy production occurs. It is comprised of three distinct processes: Ventilation, gas exchange, and cell respiration.

Question 170

Define ventilation

Answer 170

The active exchange of air between the atmosphere and the lungs. In humans, it is achieved by the act of breathing.

Question 171

Define gas exchange

Answer 171

The passive exchange of oxygen and carbon dioxide between the alveoli and bloodstream via passive diffusion.

Question 172

Define cell respiration

Answer 172

The release of ATP from organic molecules. It’s enhanced by the presence of oxygen.

Question 173

What is gas exchange dependent on

Answer 173

• concentration gradient of oxygen
• concentration gradient of carbon dioxide

Question 174

What is ventilation

Answer 174

Definition: The exchange of air between the atmosphere and the lungs. In humans, it is achieved by the act of breathing: bringing fresh air into your alveoli and removing the stale air.

Purpose: Maintaining a concentration gradient of oxygen and carbon dioxide in between air in the alveoli and blood flowing in adjacent capillaries. The longer air remains in the alveoli, the lower the concentration of oxygen in the air, decreasing the concentration gradient that drives the diffusion of oxygen into the blood. Ventilation removes the lower oxygen air and replaces it with fresh higher oxygen air. This ensures oxygen continuously diffuses into the blood from the alveoli. The exchange of gases that occurs at the alveoli is called gas exchange and is directly dependent on ventilation. gas exchange is a passive process.

Question 175

Define breathing/ventilation rates

Answer 175

The number of breaths, including both inhalation and exhalation, taken per minute. Between 12-20 times/minute is normal for adults, but can increase to 30-40 times/minute when running at full speed.

Question 176

What happens during inspiration and expiration

Answer 176

Inspiration:
* External intercostal muscles contract
* internal intercostal muscles relax
* Diaphragm contracts (drops)
* Abdominal muscles relax
* Pressure in lungs decreases while volume increases, air enters

Expiration:
* Internal intercostal muscles contract
* External intercostal muscles relax
* Diaphragm relaxes (rises)
* Abdominall muscles contract
* Pressure in lungs increases while volume decreases, air escapes

Question 177

What are the two gas laws

Answer 177

• The pressure of a gas is directly related to the number of molecules that occupy a certain volume(when volume is larger the pressure is lower). The flow of gas then is always from an area of high pressure to an area of low pressure.
• When a gas is compressed, its volume decreases and pressure rises.

Question 178

What is the pathway for oxygen entering the body

Answer 178

mouth/nasal passage → trachea → two bronchi → bronchioles → alveoli (oxygen, reverse for CO2)

Question 179

What muscles are involved in ventilation

Answer 179

• External intercostals contract to make the ribs move up and out during inspiration
• To move ribs back down and in, the internal intercostals contract during expiration

These are antagonistic muscles. Diaphragm muscles are also antagonistic (contract to increase volume of thorax, other muscles contract to move diaphragm back up during exhalation).

Question 180

How are the lungs structured for ventilation

Answer 180

The lungs are a ventilation system, as they continually cycle fresh air into the alveoli from the atmosphere, meaning O2 levels stay high in alveoli, diffusing into the blood, while CO2 levels stay low, diffusing from the blood.

Structure: Large surface area to increase the overall rate of gas exchange

Question 181

Give the steps of the respiratory system

Answer 181

1. Air enters through the nose or mouth and passes through the pharynx to the trachea
2. Air travels down the trachea until it divides into two bronchi which connect to the lungs
3. Right lung is composed of three lobes, while the left is only comprised of two (due to position of the heart)
4. In each lung, bronchi divide into many smaller airways called bronchioles, increasing the surface area
5. Each bronchiole terminates with a cluster of air sacs called alveoli, where gas exchange with the blood stream occurs.

Question 182

Define breathing

Answer 182

The active movement of respiratory muscles that enable the passage of air into and out of the lungs.

Question 183

What is the mechanism of breathing according to Boyle’s law

Answer 183

When gas is compressed (volume decreases), pressure rises. In the lungs, when breathing in, the thorax (chest) expands, and the pressure in the lungs is lowered, ensuring the thoracic pressure is lower than atmospheric pressure. This causes air to rush into the lungs. When breathing out, the thorax gets smaller, the pressure rises, and air is forced out of the lungs.

Question 184

What happens physically during breathing

Answer 184

• Respiratory muscles contract to change the volume of the thoracic cavity, and hence alter the pressure in the chest. Since muscles only do work via contraction, different groups are required to expand and contract chest volume. Changing chest volume creates a pressure differential between the chest and atmosphere, with air then moving to equalise.
  
  • Muscles that increase the volume of the chest cause inspiration (since chest pressure<atmospheric pressure)
  • Muscles that decrease the volume of the chest cause expiration (since chest pressure>atmospheric pressure)
• Atmospheric pressure is lower at high altitudes, meaning a greater increase in chest volume is required before a pressure differential is formed, making it harder to breathe at high altitudes
  
  • The body will adapt mechanisms to improve oxygen uptake under these conditions which is why athletes often undertake high altitude training prior to competitions

Question 185

What muscles are responsible for inspiration and what is the process

Answer 185

Responsible muscles: Diaphragm, external intercostals, some accessory muscles.

Process:
1. Diaphragm muscles contract, causing the diaphragm to flatten and increase the volume of the thoracic cavity
2. External intercostals contract, pulling ribs upwards and outwards (expanding chest)
3. Additional muscle groups might help pull the ribs up and out

Question 186

What muscles are responsible for and what is the process of expiration

Answer 186

Responsible muscles: Abdominal muscles, internal intercostals, accessory muscles

Process:
1. Diaphragm muscles relax, causing the diaphragm to curve upwards and reduce the volume of the thoracic cavity
2. Internal intercostal muscles contract, pulling ribs inwards and downwards, reducing breadth of chest
3. Abdominal muscles contract and push the diaphragm upwards during forced exhalation
4. Additional muscle groups help pull the ribs downwards

Question 187

Define lung cancer

Answer 187

Lung Cancer Definition: the uncontrolled proliferation of lung cells, leading to the abnormal growth of lung tissue (tumour). The abnormal growth can impact on normal tissue function, leading to a variety of symptoms according to size and location. The tumours can remain in place (benign) or spread to other regions of the body (malignant).

Question 188

Why is lung cancer the most common cause of cancer-related deaths

Answer 188

• Lungs are vital to body function and thus the abrogation of their normal function is detrimental to health
• Lungs possess a rich blood supply, increasing the likelihood of metastasis

Question 189

What are symptoms of lung fcancer

Answer 189

• Coughing up blood
• Cough that does not go away
• Wheezing
• Shortness of breath
• Respiratory distress
• Weight loss
• Accumulation of fluid in the chest
• Loss of appetite
• Fatigue
• Repeated problems with pneumonia or bronchitis
• Can cause chest pain, difficulty swallowing, and heart complications, if the cancer compresses adjacent organs

Question 190

causes of lung cancer

Answer 190

• Asbestos dust particles lodge in the lungs and can’t be broken down
• Smoking
• Passive smoking (second-hand smoking)
• Air pollution (diesel exhaust fumes contain many carcinogens)
• Radon gas: If there’s a higher concentration of Radon gas, it emits alpha particles, which can cause mutations when inhaled

Question 191

Define emphysema

Answer 191

Definition: Lung condition caused by the long-term exposure to cigarette smoke and other pollutants. It gives rise to an inflammatory response in the lungs, resulting in a narrowing of the small airways and breakdown of lung tissue. Alveoli also become less elastic, making ventilation more difficult. Also results in increased protease activity, which breaks down the alveolar wall, creating one larger air space instead of many tiny ones, reducing the surface area of the lungs and resulting in a smaller amount of oxygen reaching the bloodstream. The proteases are normally inhibited by alpha-1-antitrypsin.

Note: A small proportion of emphysema cases are due to a hereditary deficiency in alpha-1-antitypsin due to a gene mutation

Question 192

What are symptoms of emphysema

Answer 192

• Shortness of breath
• Phlegm production
• Expansion of the ribcage
• Cyanosis
• Increased susceptibility to chest infections

Question 193

How does ventilation change in response to physical activity levels

Answer 193

1. ATP production via cellular respiration produces carbon dioxide as a waste product, and may consume oxygen aerobically.
2. Changes in blood CO2 levels are detected by chemo sensors in the walls of the arteries which send signals to the brainstem
3. As exercise intensity increases, the demand for gas exchange, leading to an increase in levels of ventilation

Question 194

How does exercise influence ventilation

Answer 194

• Increase ventilation rate: greater frequency of breaths allows for a more continuous exchange of gases
• Increase tidal volume: Increasing the volume of air taken in and out per breath allows for more air in the lungs to be exchanged

Question 195

What are the methods to measuring ventilation

Answer 195

• Simple observation (counting number of breaths per minute)
• Chest belt and pressure meter (recording the rise and fall of the chest)
• Spirometer (recording the volume of gas expelled per breath)

Question 196

Define spirometry

Answer 196

Spirometry definition: Involves measuring the volume/flow at which air can be inhaled or exhaled. A spirometer is a device that detects the changes in ventilation and presents the data on a digital display. A simpler method to perform spirometry involves breathing into a balloon and measuring the volume of air in a single breath (volume can be determined by submerging the balloon in water and measuring the volume displaced; 1ml=1 cm3).

Question 197

Define tidal volume

Answer 197

The amount of air that enters or leaves the lungs in a single breath at rest. Average tidal volume is 500 ml.

Question 198

Define alveolus

Answer 198

Definition: Air sacs of the lung where gaseous exchange takes place. Oxygen concentration in the alveoli is higher than the concentration of oxygen in the blood that flows past it. Carbon Dioxide however, is less concentrated in the alveoli and has higher concentrations in the blood.

Question 199

Draw a diagram of an alveoli

Answer 199

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Question 200

What is the function of alveoli

Answer 200

Function: The gradient, the thin walls, and moisture of the alveoli and the short distance to the capillaries, facilitate gas exchange by diffusion. Each molecule diffuses based on its concentration gradient, not a constant amount.

Question 201

What is the strucutre of alveoli

Answer 201

• Thin epithelial layer (one cell thick) to minimise diffusion distances for respiratory gases
• Surrounded by rich capillary network to increase capacity for gas exchange in blood
• Roughly spherical in shape, in order to maximise available surface area for gas exchange
• Lined by a layer of liquid to create a moist surface conducive to gas exchange with the capillaries as dissolved gases are better able to diffuse into the bloodstream. It’s easier for oxygen to diffuse across the alveolar and capillary membranes when dissolved in liquid. However, the lining also creates a tendency for the alveoli to collapse and resist inflation.

Question 202

How does surfactant contribute to alveolis

Answer 202

https://file.notion.so/f/f/e52fcf8a-d6ea-4a2d-a3c3-d8bce0c54560/81ee79bf-ce68-4e28-a800-b21ffcf38e11/Untitled.png?id=f9c78589-9584-4641-af4d-f21528333166&table=block&spaceId=e52fcf8a-d6ea-4a2d-a3c3-d8bce0c54560&expirationTimestamp=1715040000000&signature=NAKA1BaxNnRFagYDzZcGrAax-bv8QZItIMCLfxkIW7M&downloadName=Untitled.png

Question 203

Define surface tension

Answer 203

Surface tension: The elastic force created by a fluid surface that minimises the surface area via cohesion of liquid molecules.

Question 204

What are the types of alveolar cells

Answer 204

Type 1 and Type 2 Pneumocytes

Question 205

What are pneumocytes

Answer 205

Alternative name: Alveolar cells

Definition: Cells that line the alveoli. Comprise of the majority of the inner surface of the lungs.

Types: Type I pneumocytes, type II pneumocytes

Question 206

What are type 1 pneumocytes

Answer 206

• Function: Involved in process of gas exchange between alveoli and the capillaries
• Structure: Squamous (flattened) in shape and extremely thin (0.15 micrometres), to minimise diffusion distance for respiratory gases
• Connected by occluding junctions, preventing leakage of tissue fluid into the alveolar air space
• Amitotic and unable to replicate

Question 207

What are type 2 pneumocytes

Answer 207

• Function: responsible for secretion of pulmonary surfactant, which reduces surface tension in the alveoli. As an alveoli expands with gas intake, the surfactant becomes more spread out across the moist alveolar lining, increasing surface tension and slowing the rate of expansion, ensuring all alveoli inflate at roughly the same rate.
• Structure: Cuboidal shape and many granules for storing surfactant components
• Only comprise around 5% of the alveolar surface but are 60% of the total cells
• Can differentiate into type 1 if required

Question 208

What is a pulmonary surfactant

Answer 208

Water-based solution containing phospho-lipoproteins. They create a moist surface inside the alveoli to prevent the sides of the alveoli from sticking to each other by reducing surface tension. It also increases the speed at which gases dissolve, helping gas exchange.

Question 209

What is the speed of nerve impulse

Answer 209

80-120 metres/second

Question 210

Draw a neuron

Answer 210

https://file.notion.so/f/f/e52fcf8a-d6ea-4a2d-a3c3-d8bce0c54560/d4056153-f786-4940-94b1-f11a3a0bb74c/Untitled.png?id=e986172d-f927-45fb-b107-15db9c32b3d8&table=block&spaceId=e52fcf8a-d6ea-4a2d-a3c3-d8bce0c54560&expirationTimestamp=1715040000000&signature=GnvAnxZiugu-P4OW2RIb94hRD28U0e6nDf42LfY-NeY&downloadName=Untitled.png

Question 211

What is a neuron

aka, amount, function

Answer 211

Alternative Name: Nerve Cell

Amount: 80-90 billion in a human body

Function: Transmitting signals in the form of electrical impulses

Nervous System: Used for communication throughout the body and communication within the brain, generating higher brain functions.

Question 212

What is the structure of neurons

Answer 212

• Axons
  
  • Some are coated with a myelin sheath, which is an insulating layer that speeds up transmission of a nerve impulse. This is made of compacted layers of the Schwann cell membrane (mostly lipid, but also has several proteins. help maintain structure and compaction of myelin and adhesion of the sheath to the axon)
• Gap between adjacent Schwann cells is called the node of Ranvier. A nerve signal propagated along a myelinated axon can move at speeds of up to 120 m/s, whereas in the case of an axon which isn’t myelinated, the speed can be as slow as 1 m/s. Myelin sheath forces nerve signals to jump from one node of Ranvier to the next, accounting for the faster speed of impulse transmission, called saltatory conduction of nerve impulses.

Question 213

What is a propagated signal

Answer 213

It moves down the length of the axon towards the terminals.

Question 214

What is the resting potential in a neuron

Answer 214

Definition: A Neuron has a sodium (NA+) and potassium (K+) ion gradient across the membrane. When a neuron isn’t transmitting a signal, it has more sodium on the outside than inside, and more potassium on the inside than outside. There are also some proteins with a negative charge located inside the neuron. The ion gradient causes an electrical imbalance, known as the resting potential.

Function: A Sodium-Potassium pump transfers potassium ions into the cell and sodium ions out (so dum get out). For every turn of the pump, 3 sodium ions are transferred out of the neuron, but only two potassium ions are transferred back into the neuron, resulting in an overall loss of positive ions and the development of the negative resting membrane potential of -70 mV.

Note: The membrane is more permeable to potassium ions than sodium ions.

Types of channels: Sodium and potassium ion channels are passive, since the movement is driven by the concentration gradient. Sodium potassium pump is active, requiring energy in the form of ATP to move the ions against their concentration gradient.

Question 215

What is the action potential of a neuron

Answer 215

When neurons send electrical messages it happens through a pattern of changes in the membrane potential. When stimulated, neuron can become depolarised. Depolarisation is caused be opening of sodium channels, allowing rapid influx of Na+ ions (passive movement) into the cell. Since there’s a concentration gradient across the membrane (more outside), this is a rapid change. Membrane potential of -70 mV changes quickly to positive value of around 30 mV. Once an area of the neuron is fully depolarised, the change in potential causes voltage-gated potassium channels to open. As a result of the channels opening, potassium ions that are at a higher concentration in the neurons diffuse out, and result in a decrease in membrane potential, which is a process called repolarisation. The potassium ions stay open until the potential becomes as negative as the resting potential. However, in many cases, the potential becomes more negative than the resting potential for approximately 2 ms, which is called hyperpolarisation. This is because not all potassium channels close immediately after the resting potential is reached. After hyperpolarization, that part of the neuron enters a refractory period and can’t be depolarised (to make an action potential) since the sodium channels are inactivated. Once depolarised to about -50 mV(the threshold potential), the depolarisation will rise rapidly to +30 mV, and the action potential will occur, meaning a nerve impulse is sent. Depolarisation over the threshold causes an action potential, called the all or nothing principle. If a neuron doesn’t reach a threshold potential of around -50 mV, the neuron won’t depolarise enough to send an impulse. If it reaches the threshold, there’s a positive feedback effect in the membrane, and nearby sodium channels open to further depolarise the neuron and instigate action potential.

Example: When touching something, the dendrites of a neuron in the tip of fingers will become depolarised

Question 216

How are neurons voltage-gated

Answer 216

Voltage-gated: The trigger to open the protein channels is a membrane potential of 30 mV.

Question 217

What is an oscilloscope trace of a neuron

Answer 217

Oscilloscope trace of neuron shows a graph of the membrane potential values in mV, as it would appear on the screen of an oscilloscope.

Question 218

What is an oscilloscope

Answer 218

Device that registers electrical voltages and displays them on a screen as time passes

Question 219

Define the threshold potential for a neuron

Answer 219

Threshold potential: Minimum level to which membrane potential must be depolarized to trigger an action potential. The threshold potential varies between -55 mV and -40 mV.

Question 220

Define the all or nothing principle for a neuron

Answer 220

All or nothing principle: Neurons can not be depolarised without the threshold potential of around -50 mV.

Question 221

How do depolarisation and repolarisation of a neuron happen

Answer 221

Depolarisation: Na+ channels open, Na+ diffuse to the inside of the neuron

Repolarisation: Na+ channels close and K+ channels open, allowing K+ to diffuse out

Question 222

Draw a membrane potential graph for a neuron

Answer 222

https://file.notion.so/f/f/e52fcf8a-d6ea-4a2d-a3c3-d8bce0c54560/c196bee0-fc22-4921-96cd-d826a83ea9e4/Untitled.png?id=f90c5b8a-11b5-4368-af73-bc92a12a2649&table=block&spaceId=e52fcf8a-d6ea-4a2d-a3c3-d8bce0c54560&expirationTimestamp=1715040000000&signature=IdbkzSRamLvwgUEtn1cBro7XlbASSt6NMWUHB1FsXX8&downloadName=Untitled.png

Question 223

What is the process for propogation of nerve impulses

Answer 223

When sodium from the part of the axon that was depolarised previously diffuses to the right, it makes the membrane potential in that area less negative. When the membrane potential reaches the threshold point, sodium channels open and let more sodium flow into the cytoplasm of the axon and cause depolarisation. Increased sodium ion concentration in the cell disturbs the concentration gradient that normally exists, and establishes a new concentration gradient. Inside the cell, the sodium concentration is high because it just diffused into the cell, therefore it will diffuse to the right and left inside the axon because that’s where the sodium concentration is still low. On the left side of the axon, the sodium channels are inactive as they’re in the refractory period, so no depolarisation can occur. To the right, the increased sodium depolarises that part of the axon and makes a new action potential, which repeats itself until the end of the axon is reached.

Question 224

Define nerve impulses

Answer 224

Action potentials propagated along axons of neurons. Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential.

Question 225

Define synapses and their structure

Answer 225

Synapses: Connections between neurons and other things like neurons, glands, muscles, and receptors (sensory cells).

Structure: A presynaptic neuron and a postsynaptic neuron, with a gap of 20 nm between. The gap prevents movement of a nerve signal from one neuron to another.

Question 226

What is a neurotransmitter

Answer 226

Neurotransmitter: Chemical diffusing from the presynaptic neuron to the postsynaptic neuron, allowing electric signals in a presynaptic cell to ensure that another nerve signal is propagated in the postsynaptic neuron. It is a crucial factor in the transmission from one neuron to the next. There are about 40 neurotransmitters in the body. Acetylcholine and noradrenaline are two often found in synapses connecting nerves and muscle fibres.

Question 227

What are the steps in propagation of a nerve signal

Answer 227

1. Neurotransmitter is synthesised and stored in vesicles of the presynaptic neuron
2. Action potential reaches the presynaptic terminal
3. Depolarisation of the presynaptic terminal causes opening of voltage-gated calcium 2+ channels
4. Influx of calcium 2+ through channels
5. Ca 2+ causes vesicles with neurotransmitters to fuse with a presynaptic membrane
6. Neurotransmitter is released from presynaptic neuron into the synaptic cleft via exocytosis
7. Neurotransmitter binds to receptor molecules on postsynaptic membrane
8. Opening/closing of postsynaptic ion channels (i.e. if Na+ channels are opened, Na+ ions will enter the postsynaptic neuron and depolarise it, possibly initiating an action potential)
9. Membrane potential of postsynaptic neuron changed (i.e. depolarised if sodium channels are opened). This affects whether the postsynaptic cell may have an action potential.
10. Retrieval of vesicular membrane from plasma membrane in the presynaptic neuron

Question 228

What is the postsynaptic potential

Answer 228

Postsynaptic potentials: Changed in postsynaptic membrane potential. When many excitatory postsynaptic potentials occur in a neuron at once, they might add up to initiate an action potential, and information is passed from one neuron to the next. The propagation of an action potential across a synapse involves the depolarisation of the presynaptic neuron, which triggers a cascade of reactions that lead to the release of a neurotransmitter into the synapse.

Question 229

What is acetylcholine and what is its role in synapses

Answer 229

Acetylcholine: Choline and acetyl group. In presynaptic cell, it’s combined by the enzyme choline acetyl transferase and then stored in vesicles. When the acetylcholine is released into the synaptic cleft by exocytosis and diffuses across to the postsynaptic cell, it binds briefly to the receptors on the postsynaptic neuron. This causes sodium ion channels to open and the postsynaptic membrane to be depolarised. If the threshold is reached an action potential will occur. Once the neurotransmitter is released, an enzyme called acetylcholinesterase breaks the neurotransmitter down into choline and acetate. The choline is reabsorbed by the presynaptic cell and used again, while the acetate is recycled in the presynaptic knob.

Note: Secretion of acetylcholine by neurons at synapses by exocytosis ensures the action potential is propagated to the postsynaptic neuron. The timely reabsorption of acetylcholine ensures the intensity and duration of the signal being sent is controlled.

Question 230

What is modulation

Answer 230

Modulation: Modulating the message means controlling the intensity and duration of the signal across the synapse. This can happen through reabsorption of the neurotransmitter by the presynaptic neuron, which is how antidepressants work. Modulation can also occur when enzymes in the synapse break down a neurotransmitter like in MAOIs.

Question 231

What are SSRIs

Answer 231

SSRIs (Selective serotonin reuptake inhibitors): Antidepressant drugs that prevent presynaptic neurons from absorbing the neurotransmitter serotonin from the synapse, allowing it to affect the postsynaptic neuron for a longer period of time.

Question 232

What are MAOIs

Answer 232

MAOIs (monoamine oxidase inhibitors): Antidepressants. Monoamine oxidase is an enzyme that breaks down serotonin. When it’s inhibited by these types of antidepressants the serotonin is able to affect the postsynaptic neuron for a longer period of time.

Question 233

What are neonicotinoids

Answer 233

Neonicotinoids: Derivatives of nicotine used as insecticides. Neonicotinoids can bind to nicotinic acetylcholine receptors in cholinergic synapses. Once a neonicotinoid enters the nervous system, it irreversibly binds with receptors, preventing acetylcholine from binding. Acetylcholinesterase also can not break down the compounds

Question 234

What are cholinergic synapses

Answer 234

Synapses that use acetylcholine as the neurotransmitter

Question 235

What is the effect of neonicotinoids

Answer 235

Effect: Synaptic transmission is permanently blocked; the nerve signals can’t be propagated to the postsynaptic nerve. If in the brain this can result in paralysis or death.

Effect per species: Binding of neonicotinoids to receptors is not as strong as in insects. Thus, humans and other mammals are less affected by these compounds than insects. Most of the cholinergic receptors in insects are also located in the brain, making neonicotinoids useful insecticides.

Question 236

What is imidacloprid

Answer 236

Type of insecticide that’s a neonicotinoid. It has an annual turnover of over 1 billion dollars.

Question 237

What is the effect of neonicotinoids on bee populations

Answer 237

Bee populations are lower due to a casual relationship with exposure to neonicotinoids.

Question 238

What are the standard blood glucose levels and how are they maintained

Answer 238

Blood Glucose Levels: Need to be kept within 70-130 milligrams/decilitre for most people so that your blood has a certain osmotic balance, and cells of your body (especially brain cells) have an ample supply of glucose for cellular respiration. If sensors detect blood glucose levels are above or below the limits, two hormones are secreted.

Insulin and Glucagon: Produced by the Islets of Langerhans in the pancreas. Responsible for maintaining and controlling blood glucose concentrations.

Question 239

What is insulin

Answer 239

Insulin: Secreted when blood glucose is higher than normal. It’s produced and secreted by the beta-cells of islets of Langerhans in the pancreas. It causes the blood glucose levels to fall by stimulating glucose uptake into muscles and liver cells, where it’s converted into glycogen.

Question 240

What is glucagon

Answer 240

Glucagon: Secreted when blood glucose is lower than normal. It’s produced and secreted by the alpha-cells of islets of Langerhans in the pancreas. It causes the blood glucose levels to rise by stimulating glycogen hydrolysis to glucose in the liver, which releases glucose into the blood.

Question 241

What are the two types of pancreatic function

Answer 241

The pancreas has exocrine AND endocrine functions. As an exocrine gland (gland associated with a duct) it secretes enzymes that help in digestion, while as an endocrine gland (ductless gland) it secretes hormones that regulate blood sugar levels.

Question 242

What is the difference between glucagon and glycogen

Answer 242

Glucagon is a protein-based hormone released from the pancreas. Glycogen is NOT a hormone; it’s a carbohydrate found in the liver that is in the form that glucose takes when stored there.

Question 243

What is diabetes

Answer 243

Diabetes mellitus: Blood glucose levels are consistently too high, and urine has elevated glucose levels.

Symptoms: Frequent urination, increased thirst, hunger

Question 244

What happens if diabetes is left untreated

Answer 244

If untreated: Serious long-term complications can occur such as heart disease, kidney failure, and retinal damage

Question 245

What are the types of diabetes

Answer 245

• Type 1 Diabetes: Results from body’s failure to produce insulin. This is sometimes referred to as insulin-dependent diabetes mellitus (IDDM) or juvenile diabetes
  
  • Treatment: Injecting insulin into the body daily
• Type 2: Results from insulin resistance which is a condition where the body cells fail to use insulin properly. This was previously referred to as non insulin-dependent diabetes mellitus (NIDDM), or adult-onset diabetes because it usually starts later in life.
  
  • Treatment: Eating food with low levels of carbohydrates, frequent but small meals, strenuous exercise, losing weight.

Question 246

What is thyroxin

Answer 246

Definition: Main hormone that regulates metabolism and body temperature

Overall Effect: To activate nuclear transcription of large numbers of genes for synthesis of enzymes, structural proteins, transport proteins, and other substances in almost all cells of the body. Therefore, increasing metabolic activities of almost all body tissues.

Effects List:

• Increased rate of utilisation of foods for energy
• Increased breathing rate to obtain oxygen and get rid of carbon dioxide
• Increased rate of protein synthesis and protein carabolism
• Increased number and size of mitochondria in most cells of the body
• Increased growth rate of children and adolescents
• Growth and development of the brain during fetal life and for the first few years of post-natal life
• Enhanced carbohydrate metabolism
• Enhanced fat metabolism

Note: All of those effects are regulated by the level of thyroxine produced. Too much or too little will affect the normal functioning of the body

Question 247

How does thyroxin affect body temperature

Answer 247

Body Temperature: When body’s metabolic rate increases, the rate of cellular respiration also increases, producing a large amount of heat. Thus, elevated thyroxine production accounts for increased body temperature. When body temperature is too high, thyroxine level is thus decreased, and vice versa.

Question 248

Where is thyroxine produced

Answer 248

Production: In thyroid gland. Requires 4 iodine atoms and amino acid tyrosine. If there’s not enough of these, a goitre may be developed.

Question 249

What is hyperthyroidism, hypothyroidism, and a goitre

Answer 249

Hyperthyroidism: Body makes too much thyroxin

Hypothyroidism: Not enough thyroxin

Goitre: Enlargement of the thyroid gland

Goitre treatment: Supplementing diet low in iodine with iodine tablets

Symptoms of thyroxine deficiency:
- Fatigue
- Depression
- Forgetfulness
- Feeling cold
- Constipation
- Impaired brain development if in young children

Question 250

What are the adipose tissues

Answer 250

Adipose Tissues: Fatty tissues mainly composed of fat cells (adipocytes) that are specialised in the synthesis and storage of fat globules/lipids

Question 251

What is leptin

Answer 251

Leptin: Hormone produced and secreted by cells in adipose tissues

Question 252

What factors control blood leptin concentration

Answer 252

• Food intake
• The amount of adipose tissues in the body

Question 253

Where are leptin receptors and how does appetite inhibition occur

Answer 253

Leptin Receptors: Found in the hypothalamus of the brain

Appetite inhibition: Occurs when leptin binds to leptin receptors

Question 254

What happens to leptin and appetite when fat mass decreases or increases

Answer 254

When fat mass decreases: the level of plasma leptin falls (only a few of the leptin receptors bind to leptin in the hypothalamus) so appetite is stimulated until the fat mass is recovered. There’s also a decrease in body temperature and energy expenditure is suppressed

When fat mass increases: Leptin levels increase and appetite is suppressed until weight loss occurs.

Question 255

What is the function of leptin

Answer 255

Regulation of energy intake and fat stores so weight is maintained within a narrow range.

Question 256

What is the relation between leptin and obesity and how was it found

Answer 256

Mice: Strain of mice was discovered in the 1950s with a mutation that made them greedy. They quickly became obese and had a mass of up to 100g whereas the normal range was 20-25 g. These mice were homozygous for the ob (obese) allele. Mice with two of these recessive alleles could not produce leptin, thus having no appetite inhibition. They were then injected with leptin and their body mass reduced by 30% in a month.

Humans: A small subset of humans are also homozygous for the ob allele, and are frequently obese. In a double-blind trial (no one know if they had placebos or the real leptin drug, including researchers), some participants did lose body mass but others gained it. Those that lost it quickly regained it after the trail was stopped. These are very disappointing results compared to the mice.

Reasons for difference between mice and humans:

• Obese people have very high leptin levels in their blood, meaning that receptor cells in the hypothalamus might no longer be sensitive and responsive to leptin.
• The exact mechanisms by which leptin activates hypothalamic neurones to suppress appetite is not fully understood yet

Question 257

What is melatonin and how is it made

Answer 257

Melatonin: Hormone that controls the internal clock of your body; your internal circadian rhythm. Melatonin levels are high at night and low during the day.

Synthesis: Produced in pineal gland from the amino acid tryptophan and its production is dictated by light. Exposure to light has a negative effect on the release of melatonin.

Question 258

What is the pineal gland

Answer 258

Small endocrine gland found near the centre of the brain between two hemispheres. It’s reddish-gray and shaped like a pine cone about 0.8 cm long.

Question 259

Why can we maintain a day/night cycle independent of external cues

Answer 259

Human brains can maintain a day/night cycle independent of external cues due to melatonin level cycles. However, without external cues, the day/night cycle is slightly longer than 24 hours, so it slowly shifts away from the actual night and day cycle. The reason those with external cues don’t shift away from the cycle is because of certain receptor cells in the retina that signal dawn and dusk to the pineal gland.

Question 260

How do impulses from the retina regulate melatonin levels

Answer 260

Impulses from retina: first channeled to a group of cells in the anterior hypothalamus, which are called the suprachiasmatic nuclei (SCN). The SCN then pass on information to the pineal gland. The pineal gland adapts melatonin concentrations to coincide with a normal 24-hour cycle.

Note: Melatonin receptors are also present on neurons of the suprachiasmatic nuclei of most species, implying the possible involvement of a negative feedback loop in the regulation of melatonin

Question 261

What are the effects of melatonin

Answer 261

• Internal temperature drops
• Receptors in the kidney cause decreased urine production

Question 262

How do estrogen and progesterone affect embryonic development

Answer 262

Embryo: All embryos in the uterus start out as female

Estrogen and Progesterone: Two hormones that are continually present during pregnancy because the mother’s ovaries and placenta keep secreting them. They start the embryo on the path to becoming a female, with the gonads developing into ovaries.

Question 263

How does sexual distinction occur

Answer 263

Male and female reproductive systems have a similar pattern of development. Sexual distinction only occurs as a result of the influence of hormones. The first sign of development of reproductive organs happens during the 5th week and sexual distinction of the external genitalia becomes apparent in the 10th to 12th week.

Question 264

Draw a diagram of the female reproduction system

Answer 264

https://file.notion.so/f/f/e52fcf8a-d6ea-4a2d-a3c3-d8bce0c54560/513edcf9-067d-4ab3-9930-4d60b672ecb0/Untitled.png?id=69af44aa-185d-4ad6-8586-274e6b19edf1&table=block&spaceId=e52fcf8a-d6ea-4a2d-a3c3-d8bce0c54560&expirationTimestamp=1715040000000&signature=3z3Rm71-_v-cIu1uvkwhRUokUI75LXkWy0zFnwDcg-o&downloadName=Untitled.png

Question 265

What are the organs of the female reproductive system

Answer 265

Ovary: Produces estrogen, progesterone, and ovum (eggs)

Fallopian tubes (oviduct): Collect eggs from the ovary and carry them to the uterus

Uterus: Place for the gestation(development) of the embryo and fetus

Cervix: Blocks entry to the uterus during pregnancy and dilates during birth

Vagina: Canal connecting cervix and outside of body. Forms birth canal and is the receptacle for penis during heterosexual intercourse

Vulva: External parts for the production of the internal reproductive system

Question 266

What happens if an embryo has XY chromosomes

Answer 266

Protein named testis determining factor (TDF) is coded for by the SRY gene on the Y chromosome. This triggers the development of testis. TDF is a DNA-binding protein that regulates transcription of a number of genes that are involved in the differentiation of the gonads into the testis. This happens around week 8 of pregnancy. Once testis have developed, they start producing testosterone. This triggers the development of male genitalia. During puberty, testosterone production increases further, giving rise to the secondary male sexual characteristics such as pubic hair, penis enlargement, and deepening of the voice. Testosterone is also responsible for triggering the production of sperm.

Question 267

Draw a diagram of the male reproductive system

Answer 267

https://file.notion.so/f/f/e52fcf8a-d6ea-4a2d-a3c3-d8bce0c54560/a78b79ee-8392-4be0-ac45-8e55f7bbb393/Untitled.png?id=39fe48f3-1110-4a76-b974-b1e709ab6ed0&table=block&spaceId=e52fcf8a-d6ea-4a2d-a3c3-d8bce0c54560&expirationTimestamp=1715040000000&signature=VZn8ybAT9GLdkOn9djAOM14IrZoaPi76et6FxZCfR3A&downloadName=Untitled.png

Question 268

What are the organs of the male reproductive system

Answer 268

Testis: Sperm and testosterone production

Epididymis: Store sperm until ejaculation

Sperm duct: Transfers sperm during ejaculation

Seminal vesicles: Produce an alkaline, sugar-rich fluid (fructose) that provides sperm with a source of energy to help them move

Prostate gland: Produce an alkaline fluid, rich in proteins, which with seminal vesicle’s secretion and sperm makes semen

Urethra: Transfer semen during ejaculation and is the passage of urine during urination

Penis: Becomes erect during sexual arousal. Penetrates vagina during heterosexual intercourse to deposit semen close to the cervix.

Question 269

Define the menstrual cycle

Answer 269

Definition: Cyclic and periodic change in ovarian and pituitary hormones that control when a women is fertile. This occurs between the onset of puberty and the end of menopause. It also controls the timing of menstruation and the release of blood and tissue from the uterus through the vagina

Question 270

Define puberty

Answer 270

Phase of adolescence when the individual reaches sexual maturity and becomes capable of reproducing. It’s accompanied by the maturation of genital organs, development of secondary sexual characteristics, and the first occurrence of menstruation in females (in humans and some primates).

Question 271

Define menopause

Answer 271

Phase in woman’s life around age of 45-50 when menstruation stops.

Question 272

What are the phases of the menstrual cycle

Answer 272

1. Follicular(1st 14 days): Formation of follicles in the ovary which each contain one egg during its development until ovulation
2. Luteal(2nd 14 days): Transformation of a follicle into a corpus luteum once ovulation has taken place around day 14

Question 273

Define menstruation

Answer 273

Marks the start of the menstrual period. Lining of the uterus is shed and bleeding starts. Menstruation normally lasts around 3-5 days. If fertilisation doesn’t happen, the corpus luteum breaks down, resulting in a decrease in the level of progesterone and estrogen. With a drop in the progesterone level, the thickened lining of the uterus can’t be maintained anymore, and breaks down. As a result, the extra layers of the endometrium lining, the unfertilised egg, and a small amount of blood, pass through the vagina. This lasts 3-5 days. While menstruation is happening, the amount of estrogen in the blood falls, reducing the inhibitory effect of estrogen on FSH secretion. The pituitary gland then increases its output of FSH, a new follicle starts maturing, and the cycle starts again.

Question 274

What are the hormones controlling the menstrual cycle

Answer 274

Luteinising hormone (LH) and follicle-stimulating hormone (FSH) (secreted by pituitary gland); Estrogen and progesterone (secreted by ovaries).

Question 275

What is the follicular phase of the menstrual cycle

Answer 275

FSH causes several follicles in the ovary to begin to develop, and usually only one matures. As it develops, it secretes estrogen which stimulates the uterine lining (endometrium) to thicken with mucus and a rich supply of blood vessels. These changes last about 10 days and prepare the uterus for a possible pregnancy. The endometrium is where a fertilized ovum will implant in order to further develop during pregnancy.

Question 276

Define ovulation

Answer 276

A high level of estrogen in the blood (produced by the follicle) causes the pituitary gland to reduce secretion of FSH(negative feedback) and begin secretion of LH(positive feedback). The decrease of FSH then decreases the production in estrogen. When the concentration of LH in the blood reaches a threshold, ovulation occurs, meaning one mature follicle (a Graafian follicle) ruptures, and releases a mature egg. Ovulation occurs around the middle of the menstrual cycle.

Question 277

What is the luteal stage of menstruation

Answer 277

After ovulation, LH causes the ruptured follicle to fill with cells, which forms the corpus luteum (yellow body). It secreted the hormone progesterone, which maintains the continued growth of the endometrium. The corpus luteum also produces estrogen, which accounts for the rise in this hormone level after ovulation. As the concentration of estrogen and progesterone rise to a threshold, they inhibit the secretion of FSH and LH respectively (negative feedback). Luteal stage lasts 14 days.

Question 278

What are the hormones of the menstrual cycle (include where their made, when they rise, and their function)

Answer 278

• Progesterone
  
  • Produced: Ovary
  • Rises: Start of luteal phase
  • Function: Promotes thickening and maintenance of the endometrium
• Estrogen
  
  • Produced: Ovary
  • Rises: Peaks near end of follicular phase
  • Function: Stimulates repair of endometrium and increase in FSH receptors on ovary cells
• FSH
  
  • Produced: Pituitary
  • Rises: Starts near end of the cycle
  • Function: Stimulates development of follicles and production of estrogen by the follicle wall
• LH
  
  • Produced: Pituitary
  • Rises: Suddenly during end of follicular phase
  • Function: Stimulates completion of meiosis in the oocyte, and thinning of the follicular wall, so that ovulation can occur. After ovulation, it stimulates the development of the remaining part of the Graafian follicle into the corpus luteum by causing an increase in the number of follicle cells, which secretes estrogen (positive feedback) and progesterone.

Question 279

Define IVF

Answer 279

Definition: Artificial fertilisation. The fertilisation (joining of the sperm and egg) takes place in vitro (glass)

Question 280

What are the steps of IVF

Answer 280

1. Egg production stimulated by hormone therapy
   
   1. Woman is given drug(s) to suppress her natural cycle by suspending her normal secretion of hormones. She can administer them herself in the form of a daily injection or nasal spray. This happens for about 2 weeks.
   2. FSH and LH are injected at a higher dose than normal for around 12 days to stimulate production of a number of ova (egg cells), called superovulation. The clinic monitors progress throughout by vaginal ultrasound scans and possibly blood tests
2. Between 34 and 38 hours before eggs are due for collection, the woman is given a hormone injection to help them mature. This is likely to be human chorionic gonadotrophin. Eggs are then usually collected from the ovaries by using ultrasound guidance while the woman is sedated. A hollow needle is attached to the ultrasound probe and used to collect eggs from the follicles in each ovary
3. A sperm sample is collected from the man and checked for viability
4. Eggs are mixed with sperm and cultured in the lab for 16-20 hours after which they are checked for signs of fertilisation. Sperm can also be injected directly into the egg. The eggs then grow into embryos and fetus’ in the laboratory incubator for up to 6 days. This is monitored by an embryologist and the best embryos will be chosen for transfer. The remaining ones are frozen for future use.
5. If the woman is under age of 40, one or two embryos are implanted in the uterus at the right time in her menstrual cycle. But if she’s older than 40 years, a maximum of 3 can be used. The number of embryos transferred is restricted due to risks associated with multiple births.

Question 281

What did Harvey find for investigating in Sexual Reproduction

Answer 281

Philosophers and physicians in Harvey’s day believed in Aristotle’s theory, where the man produces a seed which develops into an egg, which then develops into an embryo with the help of menstrual blood.

Harvey: Used a scientific approach by observing and dissecting female deer in the mating season to see if small embryos could be found immediately after fertilisation. He said that the seed and soil theory put forward by Aristotle couldn’t be true because there were no small embryos in the uterus of female deer after fertilisation. However, he couldn’t fully explain how development occurred, since he couldn’t see any embryo until many weeks after fertilisation.