topic 6 Flashcards
1
Q
A
2
Q
what is peristalsis ?
A
peristalsis is the contraction of circular and longitudinal muscle layers
3
Q
what is the function of peristalsis in the small intestine?
A
to mix the food with enzymes and move it along the gut.
4
Q
what is the function of the pancreas?
A
to secrete enzymes into the lumen of the small intestine.
5
Q
what are the main enzymes present in pancreatic juice?
A
amylase, lipase, endopeptidase
6
Q
amylase
A
starch->maltose
7
Q
lipase
A
triglycerides-> fatty acids + glycerol
or
triglycerides-> fatty acids + monoglycerides
8
Q
nucleases
A
DNA and RNA -> nucleotides
9
Q
maltase
A
maltose -> glucose
10
Q
lactase
A
lactose -> glucose + galactose
11
Q
sucrase
A
sucrose -> glucose + fructose
12
Q
proteases/peptidases
A
proteins/polypeptides -> shorter peptides
13
Q
dipeptidases
A
dipeptides -> amino acids
14
Q
what do enzymes do?
A
they digest most macromolecules in food into monomers in the small intestine.
15
Q
describe the path of digestive enzymes from the pancreas to the small intestine
A
- synthesised in pancreatic gland cells on ribosomes on the rER
- processed in the Golgi apparatus
- secreted by exocytosis
- flow through pancreatic duct and into small intestine
16
Q
what type of reactions are macromolecules->monomers
A
hydrolysis
17
Q
what are the two functions of the villi in the small intestine?
A
- to increase the surface area of epithelium over which absorption is carried out
- to absorb monomers formed by digestion as well as minerals and vitamins
18
Q
draw out a labelled diagram of a villus
A
check
19
Q
list 6 substances absorbed by the villi in the small intestine
A
- glucose, fructose, galactose and other monosaccharides
- amino acids
- fatty acids, monoglycerides, glycerol
- bases (from nucleotides)
- mineral ions (eg Ca, K, Na)
- vitamins
20
Q
to be absorbed into the body, nutrients must pass from the —– of the small intestine to the ——- or ——- in the villi
A
lumen; capillaries; lacteals
21
Q
what happens before nutrients pass into the lacteal/capillaries of the villi?
A
they must first be absorbed into epithelium cells
22
Q
describe how triglycerides are absorbed from the small intestine into the villi.
A
- triglycerides are digested into fatty acids and monoglycerides
- monoglycerides are absorbed into villus epithelium cells by simple diffusion
- fatty acids are absorbed by facilitated diffusion (via fatty acid transporters)
- inside the epithelium cells, fatty acids + monoglycerides form triglycerides, which cannot diffuse back out.
- triglycerides + cholesterol + phospholipids + protein -> lipoprotein particles
- these are released into the interstitial spaces of the villus by exocytosis
23
Q
describe how glucose is absorbed from the small intestine into the villi
A
- Na-K pumps in the inwards-facing part of the plasma membrane pump Na ions by active transport from the cytoplasm to the interstitial spaces inside the villus and K ions in the opposite direction
- there is a low concentration of Na ions inside villus epithelium cells
- sodium-glucose co-transporter proteins in the microvilli transfer a Na ion and glucose molecule together from the intestinal lumen to the cytoplasm of the epithelial cell (facilitated diffusion).
- glucose channels allow the glucose to move from the cytoplasm to the interstitial spaces inside the villus and into the blood capillaries.
24
Q
why can glucose not pass through the plasma membrane of the villus epithelium via simple diffusion?
A
because it is polar and therefore hydrophilic
25
mouth
- mechanical digestion of food by chewing and mixing with saliva (contains lubricants and enzymes)
26
oesophagus
- movement of food by peristalsis from the mouth to the stomach
27
stomach
- churning and mixing with secreted water + acid which kills foreign pathogens in food
- initial stages of protein digestion
28
small intestine
- digestion of lipids, carbs, proteins, nucleic acids
- neutralisation of stomach acid
- absorption of nutrients
29
pancreas
secretion of lipase, amylase, and protease
30
liver
secretion of surfactants in bile to break up liquid droplets
31
gall bladder
storage and regulated release of bile
32
large intestine
- re-absorption of water
- further digestion by symbiotic bacteria (especially of carbs)
- formation and storage of faces
33
describe the 4 layers of the wall of the small intestine
- serosa (outer coat)
- muscle layers (longitudinal muscle and inside it circular muscle)
- sub-mucosa (tissue layer containing blood and lymph vessels)
- mucosa (lining of SI, with epithelium that absorbs nutrients)
34
describe the processs of starch digestion
Starch can exist in one of two forms – amylose (linear, only 1,4) or amylopectin (branched, 1,4+1,6)
The digestion of starch is initiated by salivary amylase in the mouth and continued by pancreatic amylase in the intestines
Amylase digests amylose into maltose subunits (disaccharide) and digests amylopectin into branched chains called dextrins (it cannot break 1,6 bonds)
Both maltose and dextrin are digested by enzymes (maltase) which are fixed to the epithelial lining of the small intestine
35
how and why are the products of the digestion of starch transported to the liver?
via the hepatic portal vein; excess glucose is absorbed by liver cells and converted to glycogen for storage
36
37
what is the function of the arteries?
convey blood at high pressure from the ventricles to the tissues of the body
38
what are artery walls composed of?
muscle and elastic fibres
39
name the 3 layers of arteries
- tunica externa: tough outer layer of connective tissue
- tunica media: thick layer containing smooth muscle and elastic fibres made of the protein elastin
- tunica intima: a smooth endothelium forming the lining of the artery
40
what is the role of the arterial muscle and elastic fibres?
to assist in maintaining blood pressure between pump cycles
41
systolic pressure
the peak pressure reached in an artery
42
diastolic pressure
the minimum pressure inside an artery
43
role of elastic fibres in the maintenance of blood pressure
1. systolic pressure pushes the wall of the artery outwards, widening the lumen and stretching elastic fibres in the wall, thus storing potential energy
2. at the end of each heartbeat the pressure in the arteries falls sufficiently for the stretched elastic fibres to squeeze the blood in the lumen.
This mechanism saves energy and prevents the diastolic pressure from becoming too low.
44
role of muscle fibres in the maintenance of blood pressure
VASOCONSTRICTION
circular muscles in the wall form a ring so when they contract, the circumference is reduced and the lumen is narrowed, blood pressure increase
45
why do arterioles have a particularly high density of muscle cells?
so that they can respond to various hormone and neural signals to control blood flow to downstream tissues
46
artery:
- diameter
- relative thickness of wall and diameter of lumen
- number of layers in wall
- muscle and elastic fibres in wall
- valves
- larger than 10µm
- relatively thick wall and narrow lumen
- 3
- abundant
- none
47
what is the role of capillaries?
to allow exchange of materials between cells in tissues and the blood in the capillary
48
general role of arterial muscle fibres in walls
help to form a rigid arterial wall that is capable of withstanding the high blood pressure without rupturing
49
general role of arterial elastic fibres in walls
allow the arterial wall to stretch and expand upon the flow of a pulse through the lumen
50
give 2 tissues that do not contain capillaries
tissues of the lens and cornea in the eye- these must be transparent
51
state and explain the adaptations of capillaries
- very small diameter which allows passage of only a single red blood cell at a time (optimal exchange)
- capillary wall is made of a single layer of cells to minimise the diffusion distance for permeable materials
- surrounded by a basement membrane which is permeable to necessary materials
- may contain pores to further aid in the transport of materials between tissue fluid and blood
52
describe plasma and tissue fluid
plasma is the fluid in which blood cells are suspended; tissue fluid contains oxygen, glucose, and all other substances in blood plasma apart from large protein molecules which cannot pass through capillary wall
53
describe the process of absorption from capillaries into tissues
fluid flows between the cells in a tissue, allowing the cells to absorb useful substances and excrete waste products as the tissue fluid then re-enters the capillary network
54
describe how capillary structure may vary depending on its location in the body and specific role
- wall may be continuous (eg nervous tissue in blood-brain barrier) with endothelial cells held together by tight junctions to limit permeability of large molecules
- In tissues specialised for absorption (e.g. intestines, kidneys), the capillary wall may be fenestrated (contains pores)
- some capillaries are sinusoidal and have open spaces between cells and be permeable to large molecules and cells (e.g. in liver)
55
Arteries split into ? which in turn split into ?, decreasing arterial pressure as total vessel volume is ?
The branching of arteries into capillaries therefore ensures blood is moving ? and all cells are located near a blood supply
After material exchange has occurred, capillaries will pool into ? which will in turn collate into larger ?
arterioles; capillaries; increased;
slowly;
venules; veins
56
describe the flow of blood in capillaries
1. blood flows through the capillaries very slowly and at a very low pressure in order to allow for maximal material exchange
2. The higher hydrostatic pressure at the arteriole end of the capillary forces material from the bloodstream into the tissue fluid
3. The lower hydrostatic pressure at the venule end of the capillary allows materials from the tissues to enter the bloodstream
57
what is the role of veins?
to collect blood at low pressure from the tissues of the body and return it to the atria of the heart
58
capillary:
- diameter
- relative thickness of wall and diameter of lumen
- number of layers in wall
- muscle and elastic fibres in wall
- valves
- around 10µm
- extremely thin wall
- only one layer, tunica intimate which is an endothelium consisting of a single layer of very thin cells
- none
- none
59
why is the hepatic portal vein unusual
it carries blood from stomach and intestines to liver, not back to the heart
60
adaptations of veins
- very wide lumen (relative to wall thickness) to maximise blood flow for more effective return
- thin wall containing less muscle and elastic fibres as blood is flowing at a very low pressure
- pressure is low so veins possess valves to prevent backflow and stop the blood from pooling at the lowest extremities
61
why do veins typically pass between skeletal muscle groups?
as they facilitate venous blood flow via periodic contractions; it would otherwise be difficult for the blood to move against the downward force of gravity
62
describe how valves in veins work
- if blood starts to go backwards, it gets caught in the flaps of the pocket valve, which will with blood, blocking the lumen of the vein
- when blood flows towards the heart, it pushes the flaps to the sides of the vein so the pocket valve opens
63
vein:
- diameter
- relative thickness of wall and diameter of lumen
- number of layers in wall
- muscle and elastic fibres in wall
- valves
- variable but much larger than 10
- relatively thin wall with variable but often wide lumen
- three layers
- small amounts
- present in many veins
64
what is meant by the term 'double circulation'?
in humans there is a separate circulation for the lungs:
- pulmonary circulation, to and from the lungs
- systemic circulation, to and from all other organs including the heart muscles
65
why do humans have double circulation?
blood capillaries in the lungs cannot withstand high pressures so blood is pumped to them at relatively low pressure; after passing through the lung capillaries, pressure is still low so blood must return to the heart to be pumped again before it goes to other organs
66
draw and label a diagram of a heart
67
The contraction of the heart is called ? while the relaxation of the heart is called ?
systole; diastole
68
Atrial systole is the period when
Ventricular systole is when
the atria are contracting
the ventricles are contracting
69
Functions of atrial and ventricular systole
Atrial systole forces blood from the atria into the ventricles
During ventricular systole, blood is forced from the ventricles into the pulmonary artery and aorta
70
Initiation of the heartbeat by the sinoatrial node
1. the heart beat is initiated by a group of cells in the wall of the right atrium called the sinoatrial node (SAN)
2. the cells of the sinoatrial node depolarise, reversing the charge across their membranes
3. Depolarisation of the cells in the sinoatrial node sends an electrical signal over the atria, causing them to contract in atrial systole
4. The electrical signal then reaches a region of non-conducting tissue which prevents it from spreading straight to the ventricles; this causes the signal to pause for around 0.1 s
This delay means that the atria can complete their contraction before the ventricles begin to contract
5. The electrical signal is carried to the ventricles via the atrioventricular node (AVN), a region of conducting tissue between atria and ventricles
6. The signal then travels to the base of the heart via conductive fibres in the septum known as the bundle of His
7. it is then carried through conductive fibres called Purkyne fibres which spread around the sides of the ventricles, causing contraction of the ventricles from the apex, or base, of the heart upwards
8. Blood is forced out of the heart into the pulmonary artery and aorta
71
why is the sinoatrial node is considered to be the pacemaker of the heart?
because it initiates the heart beat and so controls the speed at which the heart beats
72
why is the heart considered myogenic?
it will beat without any external stimulus from other organs or the nervous system
73
how can heart rate be increased or decreased?
with signals from branches of two nerves originating in the cardiovascular centre, a region in the medulla of the brain
- signals from one of the nerves cause the pacemaker to increase the frequency of heartbeats
- signals from the other decrease the rate
74
low blood pressure, oxygen concentration and pH suggests that
High blood pressure, oxygen concentration and pH suggests that
the heart rate needs to speed up to increase the flow rate of blood to the tissues, deliver more oxygen and remove more CO2
the heart rate may need to slow down
75
what is the function of epinephrine?
controlled by the brain, and increases the heart rate to prepare for vigorous physical activity because of a threat/opportunity
76
what responds to the secretion of epinephrine by the adrenal glands?
the sinoatrial node
77
describe Harvey's discovery of the circulation of the blood with the heart acting as the pump
- demonstrated blood flow through larger vessels is unidirectional, with valves to prevent back flow
- showed the rate of flow through major vessels is too high for blood to be consumed in the body after being pumped out by the heart; it must therefore return to the heart and be recycled
- showed the heart pumps blood out in arteries and returns it in veins
- predicted presence of numerous fine vessels
78
describe the events leading up to occlusion of the coronary arteries
1. Low density lipoproteins (LDL) containing fats and cholesterol accumulate in the artery wall of the coronary artery.
2. phagocytes are then attracted by signals from endothelium cells and smooth muscle. The phagocytes engulf the fats and cholesterol by endocytosis and grow very large.
3. Smooth muscle cells migrate to form a tough cap over the atheroma. The artery wall bulges into the lumen narrowing it and thus impeding blood flow.
79
describe the possible effects of coronary artery occlusion
Coronary occlusion is a narrowing of the arteries that supply blood containing oxygen and nutrients to the heart muscle.
Lack of oxygen (anoxia) causes pain, known as angina, and impairs the muscle's ability to contract, so the heart beats faster as it tries to maintain blood circulation with some of its muscle out of action.
The fibrous cap covering atheromas sometimes ruptures, which stimulates the formation of blood clots that can block arteries supplying blood to the heart and cause acute heart problems.
80
give 6 factors that increase risk of atheroma
- high blood concentrations of LDL (low density lipoprotein)
- chronic high blood glucose concentrations, due to overeating, obesity or diabetes
- chronic high blood pressure due to smoking, stress or any other cause
- consumption of trans fats, which damage the endothelium of the artery.
- infection of the artery wall with Chlamydia pneumoniae
- production of trimethylamine N-oxide (TMAO) by microbes in the intestine.
81
define atherosclerosis
the development of an atheroma - plaque, or fatty tissue that blocks arteries
82
describe the pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle using a diagram
0.0-0.1 seconds
The atria contract causing a rapid but relatively small pressure increase, which pumps blood from the atria to the ventricles, through the open atrioventricular valves.
The semilunar valves are closed and blood pressure in the arteries gradually drops to its minimum as blood continues to flow along them but no more is pumped in.
0.1-0.15 seconds
The ventricles contract, with a rapid pressure build up that causes the atrioventricular valves to close.
The semilunar valves remain closed.
0.15-0.4 seconds
The pressure in the ventricles rises above the pressure in the arteries so the semilunar valves open and blood is pumped from the ventricles into the arteries, transiently maximizing the arterial blood pressure.
Pressure slowly rises in the atria as blood drains into them from the veins and they fill.
0.4-0.45 seconds
The contraction of the ventricular muscles wanes and pressure inside the ventricles rapidly drops below the pressure in the arteries, causing the semilunar valves to close.
The atrioventricular valves remain closed.
0.45-0.8 seconds
Pressure in the ventricles drops below the pressure in the atria so the atrioventricular valves open.
Blood from the veins drains into the atria and from there into the ventricles, causing a slow increase in pressure.
83
84
describe the body's primary defence mechanism
the skin and mucous membranes form a primary defence mechanism against pathogens that cause infectious disease
85
skin
- outermost layer is tough and provides a physical barrier against the entry of pathogens and physical/chemical damage
- sebaceous glands are associated with hair follicles and secrete sebum, which maintains skin moisture and slightly lowering skin pH, which inhibits the growth of bacteria and fungi
86
mucous membranes
thinner and softer type of skin found in airways and reproductive organs
- the mucus secreted is a sticky solution of glycoproteins and traps pathogens, which are either swallowed or expelled, acting as a physical barrier
- also has antiseptic properties due to the presence of the anti-bacterial enzyme lysozyme
87
how are cuts in the skin sealed?
1. platelets aggregate at the site forming a temporary plug
2. they release clotting factors that trigger off the cascade of reactions involved in the clotting process
3. this cascade results in the production of thrombin, an enzyme, which converts the soluble protein fibrinogen into the insoluble fibrin
4. the resulting clot is initially a gel but if exposed to the air dries to form a hard scab
88
Use of phagocytes in defence
- ingestion of pathogens by phagocytic white blood cells gives non-specific immunity to diseases
- they engulf of pathogens by endocytosis and digest them with lysosomes (enzymes)
89
Use of antibody production in defence
Production of antibodies by lymphocytes in response to particular pathogens gives specific immunity
90
define an antigen
any chemical that stimulates an immune response
91
define a specific immune response
- the production of one type of antibodies specific to a particular pathogen's antigens by lymphocytes
92
describe the steps of antibody production
1. antigens on the pathogen stimulate cell division of the small group of lymphocytes that produce the appropriate antibody
2. plasma cells (large clones of lymphocytes) are produced within a few days and secrete large quantities of the antibody
93
describe the role of antibodies
antibodies are large proteins that have two functional regions: a hyper variable region that binds to a specific antigen and another that helps the body fight the pathogen by
- making it more recognisable to phagocytes
- preventing viruses from docking to and entering host cells
94
some of the lymphocytes produced during an infection are not active plasma cells but instead become
memory cells
95
immunity to a disease involves
either having antibodies against the pathogens or memory cells that allow rapid production of the antibody
96
describe the function of antibiotics
block processes that occur in prokaryotic cells but not eukaryotic cells. For example, bacterial DNA replication, transcription, translation, ribosome function and cell wall formation.
97
what is the issue with widespread antibiotic use?
some strains of bacteria have evolved with genes which confer resistance to antibiotics and some strains have multiple resistance
98
why can viral diseases not be treated using antibiotics?
Being non-living, they rely on the host cell's enzymes for ATP synthesis and other metabolic pathways. These processes cannot be targeted by drugs as the host cell would also be damaged.
99
medical name for a blood clot
thrombus
100
coronary thrombosis is
the formation of blood clots in the coronary arteries - this can be a fatal condition.
101
give 4 things that increase the risk of coronary thrombosis
coronary occlusion, damage to the capillary epithelium, hardening of the arteries, rupture of an atheroma
102
Effects of HIV on the immune system and modes of transmission
Production of antibodies by the immune system is a complex process and includes different types of lymphocyte, including helper T-cells. The human immunodeficiency virus (HIV) invades and destroys helper T-cells. The consequence is a progressive loss of the capacity to produce antibodies.
In the early stages of infection, the immune system makes antibodies against HIV. If these can be detected in a person's body, they are said to be HIV-positive.
HIV is a retrovirus that has genes made of RNA and uses reverse transcriptase to make DNA copies of its genes once it has entered a host cell. The rate at which helper T-cells are destroyed by HIV varies considerably and can be slowed down by using anti-retroviral drugs. In most HIV-positive patients antibody production eventually becomes so ineffective that a group of opportunistic infections strike, which would be easily fought off by a healthy immune system.
A collection of several diseases or conditions existing together is called a syndrome. When the syndrome of conditions due to HIV is present, the person is said to have acquired immune deficiency syndrome (AIDS).
AIDS spreads by HIV infection. The virus only survives outside the body for a short time and infection normally only occurs if there is blood to blood contact between infected and uninfected people. There are various ways in which this can occur:
- sexual intercourse, during which abrasions to the mucous membranes of the penis and vagina can cause minor bleeding
- transfusion of infected blood, or blood products such as Factor VIII
- sharing of hypodermic needles by intravenous drug users.
103
Florey and Chain experiments
Florey and Chain tested penicillin on infected mice
Eight mice were injected with hemolytic streptococci and four of these mice were subsequently injected with doses of penicillin
The untreated mice died of bacterial infection while those treated with penicillin all survived – demonstrating its antibiotic potential
104
what is the function of ventilation?
it maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries
105
draw a labelled diagram of an alveolus
pg311
- type 1 pneumocystis in alveolus walls
- phagocyte
- network of blood capillaries
- type 2 pneumocystis in alveolus walls
106
give 4 ways of monitoring ventilation in humans at rest and after mild and vigorous exercise
1. ventilation rate
- observation of number of times air is exhaled and inhaled in a minute
- data logging with inflatable chest belt that is placed around the thorax
2. tidal volume
- one normal breath is exhaled through a delivery tube into a vessel and the volume is measured. it is not safe to use this apparatus for repeatedly inhaling/exhaling air as the co2 concentration will rise too high
- spirometers measure flow rate into and out of lungs and from these measurements lung volumes can be deduced
107
structure and function of type 1 pneumocytes
extremely thin alveolar cells that are adapted to carry out gas exchange
- located in epithelium, in wall of alveolus
- flattened cells
- distance over which co2 and o2 have to diffuse is very small, which increases the rate of gas exchange
108
structure and function of type 2 pneumocytes
secrete a solution containing surfactant that creates a moist surface:
- allows oxygen to dissolve and diffuse to blood
- provides area from which co2 can evaporate into the air and be exhaled
hydrophobic heads face the water and the hydrophobic tails face the air:
- reduces surface tension and prevents water from causing the sides of the alveoli to adhere when air is exhaled from lungs, helping prevent the collapse of the lung
109
give a flow diagram describing airways for ventilation
nose/mouth -> trachea -> two bronchi -> lung -> tree-like bronchioles -> groups of alveoli
110
give the structure and function of trachea and bronchi
rings of cartilage in their walls to keep it open even when air pressure inside is low or pressure in surrounding tissues is high
111
structure and function of bronchioles
smooth muscle fibres in their walls, allowing the width of these airways to vary
112
draw a diagram for inspiration
- ribs upwards and outwards
- air in
- diaphragm down
113
draw a diagram for expiration
- ribcage inwards and downwards
- air out
- diaphragm up
114
describe the basic physics involved in ventilation
- if particles of gas spread out to occupy a larger volume, the pressure of gas becomes lower
- if gas is compressed to occupy a smaller volume, the pressure rises
- if gas is free to move, it will flow from regions of higher pressure to regions of lower pressure
115
describe the process of ventilation and how pressure is linked with it
1. muscle contractions cause pressure inside the thorax to drop below atmospheric pressure
2. air is drawn into the lungs from the atmosphere (inspiration) until lung pressure has risen to atmospheric pressure
3. muscle contractions then cause pressure inside the thorax to rise above atmospheric, so air is forced out from the lungs to the atmosphere (expiration)
116
muscles can be in two states
contracting and relaxing
117
contracting
- muscles do work
- exert a pulling force (tension) that causes a particular movement
- become shorter
118
relaxing
- muscles lengthen passively
- pulled into an elongated state by the contraction of another muscle
- do not exert a pushing force (compression) while relaxing so do no work
119
describe an antagonistic pair of muscles
when one muscle contracts and causes a movement the second muscle relaxes and is elongated by the first . the opposite movement is caused by the second muscle contracting while the first relaxes
120
why are antagonistic pairs of muscles needed?
muscles can only cause movement in one direction. if movement in opposite directions is needed at different timed, at least two muscles will be required
121
draw a table for
diaphragm, ribcage
inspiration, expiration
p315
122
draw a table for
volume and pressure changes, movement of diaphragm, movement of ribcage
inspiration, expiration
p.316
123
causes of lung cancer
- smoking: tobacco contains many mutagenic chemicals.
- passive smoking
- air pollution from diesel exhaust fumes, nitrogen oxides from all vehicle exhaust fumes, smoke from burning coal, wood, or other organic matter
- radon gas: radioactive gas that leaks out of rocks like granite. accumulates in badly ventilated buildings so people inhale it
- asbestos, silica, some other solids if dust or particles of them are inhaled, in construction sites, quarries, mines, or factories
124
consequences of lung cancer
- difficulties with breathing, persistent coughing, coughing up blood, chest pain, loss of appetite, weight loss, general fatigue
- may lead to secondary tumours
- chemotherapy or radiotherapy
125
emphysema
Emphysema is a lung condition whereby the walls of the alveoli lose their elasticity due to damage to the alveolar walls
- The loss of elasticity results in the abnormal enlargement of the alveoli, leading to a lower total surface area for gas exchange
- The degradation of the alveolar walls can cause holes to develop and alveoli to merge into huge air spaces (pulmonary bullae)
126
theories for formation of emphysema
in smokers, the number of phagocytes in the lungs increases and they produce more elastase.
- phagocytes inside alveoli normally prevent lung infections by engulfing bacteria and produce elastase, a protein-digesting enzyme, to kill them inside the vesicles formed by endocytosis.
- alpha 1-antitrypsin (A1AT) is an enzyme inhibitor and prevents elastase and other proteases from digesting lung tissue.
- genetic factors affect the quantity and effectiveness of A1AT produced in the lungs
127
symptoms of emphysema
- irreversible, chronic disease
- low oxygen saturation in the blood and higher than normal co2 concentrations.
- patient lacks energy
- shortness of breath
- ventilation laboured and more rapid than usual
128
volume and pressure changes
- inspiration
- expiration
volume in thorax increases and pressure consequently decreases
volume in thorax decreases and pressure consequently increases
129
movement of the diaphragm and abdomen wall muscles
- inspiration
- expiration
inspiration:
- diaphragm contracts and so it moves downwards and pushes the abdomen wall out
- muscles in the abdomen wall relax allowing pressure from the diaphragm to push it out
expiration:
- diaphragm relaxes so it can be pushed upwards into a more domed shape
- muscles in the abdomen wall contract pushing the abdominal organs and diaphragm upwards
130
movement of the ribcage for the external intercostal muscles and internal intercostal muscles
- inspiration
- expiration
inspiration:
- the external intercostal muscles contract, pulling the ribcage upwards and outwards
- internal intercostal muscles relax and are pulled back into their elongated state
expiration:
- external intercostal muscles relax and are pulled back into their elongated state
- internal intercostal muscles contract, pulling the ribcage inwards and downwards
131
Difference between nervous and endocrine system
endocrine system consists of glands that release hormones; nervous system consists of nerve cells called neurone
132
What is the function of neurons?
to transmit electrical impulses
133
draw a diagram of a standard neuron
134
dendrite
short branched nerve fibres, for example those used to transmit impulses between neurone in one part of the brain or spinal cord
135
axons
very elongated nerve fibres, for example those that transmit impulses from the fingers to the spinal cord
136
how are nerve fibres adapted?
they are myelinated, which allows for saltatory conduction
137
saltatory conduction
in myelinated nerve fibres the nerve impulse can jump from one node of ranvier to the next
138
describe myelin
- consists of many layers of phospholipid bilayer
- deposited by Schwann cells, which grow round and round the nerve fibre
139
node of ranvier
gap between the myelin deposited by adjacent Schwann cells.
140
why is saltatory conduction faster than continuous transmission?
action potential to be conducted much faster and prevents the loss of the electrical signal through the cell membrane.
141
define resting potential
the potential difference or voltage across the membrane of a neuron that is not transmitting a signal
142
why is there a resting potential?
due to the imbalance of positive and negative charges across the membrane
143
describe resting potential and how it is maintained
- sodium-potassium pumps transfer sodium and potassium ions across the membrane. Na+ ions pumped out and K+ ions pumped in. The number of ions pumped is unequal - when 3 Na+ ions are pumped out, only two K+ ions are pumped in, creating concentration gradients for both ions
- the membrane is about 50x more permeable to K+ ions than Na+ ions, so K+ ions leak back across the membrane faster than Na+ ions. As a result, the Na+ concentration gradient across the membrane is steeper than the K+ gradient, creating a charge imbalance
- there are proteins inside the nerve fibre that are negatively charged (organic anions) which increase the charge imbalance
144
define an action potential
a rapid change in membrane potential, consisting of:
- depolarisation - a change from negative to positive
- repolarisation - a change back from positive to negative
145
value of resting potential
-70mV
146
describe depolarisation
due to the opening of sodium channels in the membrane, allowing Na+ ions to diffuse into the neuron down the concentration gradient. The entry of Na+ ions reverses the charge imbalance across the membrane, so the inside is positive relative to the outside. This raises the membrane potential to a positive value of about +30mV
147
describe repolarisation
happens rapidly after depolarisation and is due to the closing of the sodium channel and the opening of potassium channels in the membrane. This allows K+ ions to diffuse out of the neuron, down their concentration gradient, which makes the inside of the cell negative again relative to the outside. The potassium channels remain open until the membrane has fallen to a potential close to -70mV
148
why does it take a few milliseconds for the neuron to be able to transmit another nerve impulse?
the diffusion of potassium depolarises the neuron, but does not restore the resting potential as the concentration gradients of sodium and potassium ions have not yet been re-established.
149
define a nerve impulse
action potentials propagated along the axons of neutrons
150
why does the propagation of the action potential happen?
because the sodium ion movements that depolarise one part of the neutron trigger depolarisation in the neighbouring part of the neuron
151
what is the function of the refractive period after a depolarisation?
prevents propagation of an action potential backwards along an axon
152
describe how local currents, or propagation of the action potential, come about
1. depolarisation of part of the axon reduces the concentration of sodium ions outside the axon and increases it inside
2. depolarised part of the axon therefore has different sodium ion concentrations to the neighbouring part of the axon that has not yet depolarised
3. inside the axon sodium ions diffuse along inside the axon to the neighbouring part that is still polarised
4. outside the axon the sodium ions diffuse from the polarised part back to the part that has just depolarised
153
state the effect of local currents
reduce the concentration gradient in the part of the neuron that has not yet depolarised. this makes the membrane potential rise from the resting potential of -70mV to about -50mV. sodium channels in the axon membrane are voltage-gated and open when a membrane potential of -50mV is reached (known as threshold potential). this causes depolarisation
154
draw a diagram for local current
pg 323
155
draw and describe an action potential peak
pg 324
156
define a synapse
a junction between neurons and between neurone and receptor or effector cells
157
when pre-synaptic neurons are depolarised, they release
a neurotransmitter into the synapse
158
describe synaptic transmission
1. a nerve impulse is propagated along the pre-synaptic neuron until it reaches the end of the neuron and the pre-synaptic membrane
2. depolarization of the pre-synaptic membrane causes calcium ions (Ca2+) to diffuse through channels in the membrane into the neuron
3. influx of calcium causes vesicles containing neurotransmitter to move to the pre-synaptic membrane and fuse with it
4. neurotransmitter is released into the synaptic cleft by exocytosis
5. the neurotransmitter diffuses across the synaptic cleft and binds to receptors on the post-synaptic membrane
6. the binding of the neurotransmitter to the receptors causes adjacent sodium ion channels to open
7. sodium ions diffuse down their concentration gradient into the post-synaptic neuron, causing the post-synaptic membrane to reach the threshold potential
8. an action potential is triggered in the post-synaptic membrane and is propagated on along the neuron
9. the neurotransmitter is rapidly broken down and removed from the synaptic cleft
159
function of acetylcholine
used as the neurotransmitter in many synapses
160
how is acetylcholine produced
in the presynaptic neuron by combining choline, absorbed from the diet, with an acetyl group produced during aerobic respiration
161
describe the use of acetylcholine as a neurotransmitter
- loaded into vesicles and then released into the synaptic cleft during synaptic transmission
- receptors for acetylcholine in the post-synaptic membrane have a binding site to which acetylcholine will bind
- acetylcholine only remains bound to receptor for a short time, during which only one action potential is initiated in the post-synaptic neuron
- enzyme acetylcholinesterase is present in the cleft and rapidly breaks down acetylcholine down into choline and acetate
- choline reabsorbed into pre-synaptic neuron, where it is converted back into active neurotransmitter by recombining it with an acetyl group
162
what do neonicotinoids do?
insecticides:
- they bind to the acetylcholine receptor in cholinergic synapses in the CNS of insects
- acetylcholinesterase does not break them down, so binding is irreversible
- receptors blocked so acetylcholine is unable to bind and synaptic transmission is prevented
- results in insect paralysis and death
163
give an advantage and disadvantage of neonicotinoid use
+ not highly toxic to humans and other mammals: greater proportion of synapses in CNS are cholinergic in insects than in mammals and neonicotinoids bind less strongly to acetylcholine receptors in mammals than insects
- effects on honeybees and other beneficial insects
164
a nerve impulse is only initiated if...
the threshold potential is reached
165
nerve impulses follow an ---- why?
all or nothing principle; only at the threshold potential do voltage-gated sodium channels start to open, causing depolarisation
166
what determines whether a nerve impulse travels to the neighbouring neuron? explain
the amount of neurotransmitter secreted following depolarisation of the pre-synaptic membrane may not be enough to cause the threshold potential to be reached in the post-synaptic membrane, which then does not depolarise.
167
what happens when the post-synaptic membrane does not depolarise?
sodium ions that have entered the post-synaptic neuron are pumped out by sodium-potassium pumps and the post-synaptic membrane returns to the resting potential
168
what mechanism can be used to process information from different sources in the body to help in decision-making?
- a typical post-synaptic neuron in the brain or spinal cord has synapses with many pre-synaptic neurone
- it may be necessary for several of these to release neurotransmitter at the same time for the threshold potential to be reached and nerve impulse to be initiated
169
function of cells in the pancreas
to respond to changes in blood glucose levels
170
set point of blood glucose concentration
5 mmol/L
171
what region of the pancreas secretes hormones directly into the bloodstream?
small regions of endocrine tissue islets of Langerhans
172
alpha cells
synthesise and secrete glucagon if blood glucose levels fall below set point.
173
function of glucagon
stimulates breakdown of glycogen into glucose in liver cells and its release into the blood, increasing the concentration
174
beta cells
synthesise insulin and secrete it when the blood glucose concentration rises above the set point
175
function of insulin
stimulates uptake of glucose by various tissues, particularly skeletal muscle and liver, in which it also stimulates conversion of glucose to glycogen, reducing blood glucose concentration
176
why must secretion of insulin be ongoing?
it is broken down by the cells it acts upon
177
define diabetes
a condition where a person has consistently elevated blood glucose levels
178
effects of continuously elevated glucose
- damages tissues, particularly their proteins
- impairs water reabsorption from urine while it is forming in the kidney, resulting in an increase in the volume of urine and body dehydration
179
symptoms of diabetes
- urinate more frequently
- constantly thirsty
- feels tired
- cares sugary drinks
180
type 1 diabetes (early onset diabetes)
- characterised by an inability to produce sufficient quantities of insulin
- autoimmune disease arising from the destruction of beta cells in the islets of Langerhans by the body's own immune system
181
type 2 diabetes (late onset diabetes)
- characterised by an inability to process or respond to insulin because of a deficiency of insulin receptors or glucose transporters on target cells
182
main risk factors of type 2 diabetes
- sugary, fatty diets
- prolonged obesity due to habitual obesity and lack of exercise
- genetic factors that affect energy metabolism
183
treatment of type 1 diabetes
- testing blood glucose concentration regularly and injecting insulin when it is too high or likely to become too high
- injections often done before a meal to prevent peak of blood glucose as the food is digested/absorbed
184
treatment of type 2 diabetes
- adjusting diet to reduce peaks and troughs of blood glucose.
- small amounts of food eaten frequently rather than infrequent large meals
- foods with high sugar content avoided; starchy foods only allowed if low glycemic index (digested slowly); high-fibre foods included to slow digestion of other foods
- strenuous exercise and weight loss
185
what is thyroxin secreted by
thyroid gland (in neck) §
186
why is thyroxin unusual?
- chemical structure - contains four atoms of iodine
- almost all cells in body are targets
187
what prevents synthesis of thyroxin?
prolonged deficiency of iodine in the diet
188
function of thyroxin
- regulates body's metabolic rate, so all cells need to respond
- main targets are most metabolically active such as liver, muscle and brain
- control of body temperature
189
higher metabolic rate ->
more protein synthesis and growth and increases the generation of body heat
190
in a person with normal physiology, cooling triggers...
increased thyroxin secretion by the thyroid gland, which stimulates heat production so body temperature rises
191
effects of hypothyroidism
thyroxin deficiency:
- lack of energy/persistent tiredness
- forgetfulness and depression
- weight gain
- persistent feeling cold
- constipation
- impaired brain development
192
explain weight gain despite of loss of appetite in hypothyroidism
less glucose and fat are being broken down to release energy by cell respiration
193
explain constipation in hypothyroidism
contractions of muscle in the wall of the gut slow down
194
define leptin
a protein hormone secreted by adipose cells (fat storage cells)
195
what controls the concentration of leptin in the blood?
food intake and amount of adipose tissue in the body
196
target of leptin
group of cells in the hypothalamus of the brain that contribute to the control of appetite - leptin binds to receptors in the membrane of these cells.
197
if adipose tissue increases,
blood leptin concentrations rise, causing long-term appetite inhibition and reduced food intake
198
describe experiments done on obese mice
- they had two copies of recessive allele, ob, causing their adipose cells to be unable to produce leptin
- feed ravenously, become inactive and gain body weight, mainly through increased adipose tissue
- when these mice were injected with leptin their appetite declined, energy expenditure increased, and body mass dropped
199
why did leptin injections not work as a weight loss method?
- in contrast to ob/ob mice, most obese humans have exceptionally high blood leptin concentrations
- target cells in hypothalamus have become resistant to leptin so fail to respond to it, even at high concentrations
- appetite not inhibited and food intake is excessive
- more adipose tissue develops, causing a rise in blood leptin concentration but leptin resistance prevents inhibition of appetite
200
a very small proportion of cases of obesity in humans are due to
mutations in the genes for leptin synthesis or its various receptors on target cells
201
trials in people with such obesity have shown
significant weight loss while the leptin injections are continuing; however, leptin is a short lived protein and has to be injected several times a day. also affects the development and functioning of the reproductive system, so is not suitable to children and YAs
202
circadian rhythms
humans are adapted to live in a 24-hour cycle and have rhythms in behaviour that fit this cycle
203
what do circadian rhythms depend on?
two groups of cells in the hypothalamus - suprachiasmatic nuclei (SCN).
204
function of SCN
control secretion of melatonin (hormone) by pineal gland.
205
describe melatonin secretion
increases in the evening and drops to a low level at dawn
206
why do blood concentrations of melatonin rise and fall rapidly in response to changes in secretion?
the hormone is rapidly removed from the blood by the liver
207
state three effects of melatonin
- the sleep-wake cycle: high levels of melatonin cause drowsiness and promote sleep through the night. falling levels encourage waking at the end of the night
- night-time drop in core body temperature
- decreased urine production at night: melatonin receptors have been discovered in the kidney
208
describe how melatonin secretion is regulated
a special type of ganglion cell in the retina of the eye detects light of wavelength 460-480nm and passes impulses to cells in the SCN. This indicates to the SCN the timing of dusk and dawn and allows it to adjust melatonin secretion so that it corresponds to the day-night cycle.
209
how does jet lag come about?
the SCN and pineal gland are continuing to set a circadian rhythm to suit the timing of day and night at the point of departure rather than destination.
210
initially, the development of the embryo is
the same in all embryos and embryonic gonads develop that could either become ovaries or testes
211
what does the developmental pathway of the embryonic gonads and thereby the whole baby depend on?
the presence or absence of one gene
212
if the gene SRY is present
the embryonic gonads develop into testes.
213
what does SRY do?
it codes for a DNA binding protein called TDF (testis determining factor(, which stimulates the expression of other genes that cause testis development
214
where is SRY located?
on the Y chromosome
215
when would embryonic gonads develop as ovaries?
when embryos have 2 X chromosomes and so do not have a copy of the SRY gene. TDF is not produced and the embryonic gonads develop as ovaries
216
when do the testes develop from the embryonic gonads?
in about the eighth week of pregnancy
217
the testes develop 1, 2, 3, at an early stage and these produce 4 which causes male genitalia to develop
testosterone-secreting cells
testosterone
218
what happens at puberty in males?
the secretion of testosterone increases
219
effects of increased testosterone secretion
- sperm production in the testes (primary sexual characteristic of males)
- secondary sexual characteristics: enlargement of the penis, growth of pubic hair, deepening of voice due to growth of the larynx
220
describe female hormone secretion
- estrogen and progesterone are always present in pregnancy
- at first they are secreted by the mother's ovaries and later by the placenta
- in the absence of fetal testosterone and the presence of maternal oestrogen and progesterone, female reproductive organs develop
221
effects of increased oestrogen and progesterone secretion during puberty
- female secondary secondary sexual characteristics: enlargement of the breasts, growth of pubic and underarm hair
222
draw a labelled diagram of the female and male reproductive systems
223
testis
produce sperm and testosterone
224
scrotum
hold testes at lower than core body temperature
225
epididymis
store sperm until ejaculation
226
seminal vesicle and prostate gland
secrete fluid containing alkali, proteins and fructose that is added to sperm to make semen
227
urethra
transfer seen during ejaculation and urine during urination
228
penis
penetrates the vagina for ejaculation of semen near the cervix
229
ovary
produce eggs, oestrogen, and progesterone
230
oviduct
collect eggs at ovulation, provide a site for fertilisation then move the embryo to the uterus
231
uterus
provide the needs of the embryo and then foetus during pregnancy
232
cervix
protect the foetus during pregnancy and then dilate to provide a birth canal
233
vagina
stimulate the penis to cause ejaculation and provide a birth canal
234
vulva
protect internal parts of the female reproductive system
235
what is the menstrual cycle controlled by?
negative and positive feedback mechanisms involving ovarian and pituitary hormones
236
state the two phases of the menstrual cycle
follicular phase
luteal phase
237
follicular phase
- a group of follicles is developing in the ovary
- in each follicle an egg is stimulated to grow
- at the same time the lining of the uterus (endometrium) is repaired and starts to thicken
- the most developed follicle breaks open, releasing its eggs into the oviduct
- the other follicles degenerate
238
luteal phase
- the wall of the follicle that released an egg becomes the corpus luteum
- continued development of the endometrium prepares it for the implantation of an embryo
- if fertilisation does not occur the corpus lute in the ovary breaks down
- the thickening of the endometrium in the uterus also breaks down and is shed during menstruation
239
FSH and LH
protein hormones produced by the pituitary gland that bind to FSH and LH receptors in the membranes of follicle cells
240
estrogen and progesterone
ovarian hormones produced by the wall of the follicle and corpus lute. they are absorbed by many cells in the female body, where they influence gene expression and therefore development
241
FSH function
rises to a peak towards the end of the menstrual cycle
- stimulates the development of follicles, each containing an oocyte and follicular fluid
- stimulates the secretion of oestrogen by the follicle wall
242
Estrogen function
rises to a peak towards the end of the follicular phase
- stimulates repair and thickening of the endometrium after menstruation and an increase in FSH receptors that make the follicles more receptive to FSH, boosting oestrogen production (positive feedback)
- at high levels, oestrogen inhibits FSH secretion (negative feedback) and stimulates LH secretion
243
LH function
rises to a sudden and sharp peak towards the end of the follicular phase
- stimulates the completion of meiosis in the oocyte and partial digestion of the follicle wall allowing it to burst open at ovulation
- LH promotes development of wall of follicle after ovulation into corpus luteum, which secretes oestrogen (positive feedback) and progesterone
244
progesterone function
rise at the start of the luteal phase, reach a peak and then drop back to a low level by the end of this phase
- promotes thickening and maintenance of endometrium
- inhibits FSH and LH secretion by pituitary gland
245
draw a diagram showing the various stages of the menstrual cycle and hormones
p337
246
describe ivf
1. down-regulation: woman takes a drug each day (usually nasal spray) to stop her pituitary gland secreting FSH or LH. secretion of oestrogen and progesterone therefore also stops. menstrual cycle suspended and doctors can control timing and amount of egg production in woman's ovaries
2. superovulation- intramuscular injections of FSH and LH given daily for ~10 days, to stimulate follicles to develop. FSH injections are of higher concentration than usual so far more follicles develop than usual.
3. injection of HCG- stimulates follicles to mature
4. micropipette mounted on an ultrasound scanner is passed through uterus wall to wash eggs out of the follicles
5. each egg is mixed with 50-100,000 sperm cells in sterile conditions in a shallow dish, which is then incubated at 37'C until the next day
6. if fertilisation occurs then one or more embryos are placed in the uterus when they are ~48 hours old
7. extra progesterone usually given as a tablet placed inside vagina, to ensure uterus lining is maintained
