Human Physiology Flashcards
Digestion (chemical & mechanical)
The biochemical breakdown of large, insoluble molecules into smaller ones.
Starch broken down to glucose
Chemical Digestion - is breaking down of food with chemical agents. Includes enzymes, acids, and bile.
Mechanical Digestion - Is physically digesting food through chewing, churning, and segmentation
Structure of the small intestine
- Has an inner layer of longitudinal muscle and an outer layer of circular
muscle. - The surface of intestinal cells have villi, each have a network of capillaries and a lacteal (a
branch of the lymphatic system that enables lipid absorption) that connect to larger
blood vessels and the lymphatic system. - Each cell that lines the intestinal wall have micro-villi that further increase surface area for absorption
Digestion in the small intestine
- Circular muscles contract behind the food to prevent backflow, whereas the
longitudinal muscles contract to move the food along the intestine. - When both muscle contract , food is mixed with enzymes from the gall bladder and pancreas
- Enzymes digest most macromolecules in food into monomers in the small intestine
Digestion of starch
- Starch consists of amylose and amylopectin linked by alpha-glucose 1,4 link.
- Amylopectin contains a few alpha-glucose 1,6 bonds. Amylose the chains are unbranched
- Amylase breaks 1,4 bonds of 4 or more glucose monomers ,
digesting amylose into maltose molecules. - Amylopectin molecules have fragments containing 1,6 bond, dextrin’s which amylase cannot breakdown
- Digestion is completed when maltase and dextrinase in the small intestine convert the remaining molecules into glucose, which are absorbed by the villus through protein
pumps (active transport). - Blood carrying products of digestion flows through villus capillaries to venules in the submucosa of the wall of the small intestine
- The blood is carried via the hepatic portal vain to the liver, excess glucose is absorbed by liver cells and converted to glycogen for storage
Digestive enzymes
Enzyme- Amylase Example- Salivary amylase Source - Salivary glands Substrate - Starch Products- Maltose Optimal pH- 7
Enzyme - Amylase Example - Alpha amylase Source - Pancreas Substrate - Starch Products - Maltose Optimal pH - 7
Enzyme - Maltase Example - Intestinal maltase Source - Intestinal wall Substrate - Maltose Products - Glucose Optimal pH- 7
Enzyme- Protease Example- Pepsin Source - Stomach wall Substrate - Proteins Products - Small polypeptides / amino acids Optimal pH - 2–3
Enzyme - Endopeptidase Example - Trypsin Source - Pancreas Substrate - Proteins Products - Small polypeptides Optimal pH - 7
Enzyme - Lipase Example - Pancreatic lipase Source - Pancreas Substrate - Triglycerides Products - Fatty acids + glycerol Optimal pH - 7
Absorption
The process of taking substances into cells and the blood
- In the human digestive system nutrients are absorbed by epithelium, single layer of cell forming the inner lining of mucosa
- Rate of absorption depends on the surface area of the epithelium
- Small intestine is 7m long, 25-30mm wide & has folds on its inner surface- large SA of epithelium
Villi
- Finger-like projections of mucosa, on the intestine wall
- 0.5 to 1.5 mm long
- Have a large surface area to volume ration.
- One-cell thick structures, good for the products of digestion to cross from the lumen to the network of capillaries and lacteals
- Cell in the mucosa have microvilli that further increase
SA for absorption of nutrients. - Contain specific protein pumps and channels that facilitate the movement of molecules from intestine to capillaries/lacteals
Methods of diffusion
Facilitated diffusion- Nutrients pass down the concentration gradient through specific channel proteins in the membrane - e.g., hydrophilic nutrients like fructose
Simple diffusion - Nutrients pass down the concentration gradient between phospholipids in the membrane. e.g., hydrophobic nutrients like fatty acids
Endocytosis (pinocytosis) - small droplets of fluid are passed trough the membrane by vesicles - e.g. cholesterol and triglycerides in lipoproteins particles
Active transport - nutrients are pumped trough the membrane against the concertation gradients by specific pump proteins - e.g., charged ions like calcium and sodium
Absorption of glucose
- Glucose is absorbed by sodium co-transporter proteins which move a molecule of glucose with a sodium ion across the membrane into the epithelium cells.
- Glucose can be moved against its concentration gradient because the sodium
ion is moving down its concentration gradient. - The sodium gradient is generated by active transport of sodium out of the epithelium cell by a pump protein.
Modelling absorption
- Dialysis tubing can be used
to model absorption by the
epithelium of the intestine.
- Cola drink contains a mixture of substances which can be used to model digested and undigested foods in the intestine.
- The water outside the bag is tested at intervals to see if substances in the cola have diffused through the dialysis tubing.
The expected result is that
glucose and phosphoricacid,
with small-sized particles, diffuse through the tubing but
caramel, which consists of larger polymers of sugar, does not.
Harvey & the circulation of blood
- In the 17th century, doctrines of Galen about blood were accepted with little questioning for doctors
- Galen taught that blood
is produced by the liver, pumped out by the heart and
consumed in the other organs. - William Harvey demonstrated that the 4-chambered heart was the central “pumping mechanism” that caused blood to circulate the body at high pressures in arteries, and returned to the heart through veins.
He also found that these two types of blood vessels are connected by small, hardly visible vessels now known as capillaries.
- Blood flow through vessels is unidirectional with valves that
prevent the backflow of blood and high levels of blood to be consumed - Heart pumps blood out in the arteries and returns in veins
Pulmonary circulation
Carries deoxygenated blood from the heart to the lungs,
where it becomes oxygenated and returns to the heart.
Systemic circulation
Carries newly oxygenated blood to the rest of the body, and
returns deoxygenated blood back to the heart to enter pulmonary circulation.
Double circulation
Harvey discovered circulation in humans is double
Circulations for the lungs- pulmonary circulation
Circulations for other organs- systemic circulation
The right & left sides of the heart
- The right side of the heart pumps deoxygenated blood to the lungs via pulmonary artery
- Oxygenated blood returns to the left side of the heart in the pulmonary vein
- The left side pumps blood via the aorta to all organs of the body apart from the lungs.
- Deoxygenated blood is carried back the right side of the heart in the vena cava.
Arteries
- Blood is pumped out at high pressure by the ventricles of the heart. Cary blood to tissues of the body
Structure
- Tough outer coat
- Thick wall to withstand the high pressures
- Narrow lumen to help maintain high pressures
- Thick layers containing elastic fibres that maintain high pressure between pumping cycles & muscles that contracts or relaxes to adjust the diameter of lumen
Capillaries
- Carry blood trough tissues. Have permeable walls that allow exchange of materials between cell of tissues and blood in the capillary
Structure
- Wall consists of a single layer of thin cells so the distance for diffusion is small
- Pore between cells in the wall, allow some plasma to leak out & form tissue fluid. Phagocytes can also squeeze out
- Very narrow lumen- so capillaries fit into small spaces. Large SA
Veins
- Collect blood at low pressure from the tissues of the body and return it to the atria of the heart
Structure
- Thin layers of tissue with few/no elastic fibers or muscles, blood flow is not pulsatile
- Wide lumen needed for low pressure, slow flowing blood
- Valves are present at intervals in veins to prevent back-flow
- Thin walls allow veins to be pressed flat by adjacent muscles, helps move blood
- Outer coat is thin, no risk of veins bursting
Cardiac muscle
Heart walls are made of cardiac muscle.
- They can contract on its own without being stimulated by a nerve , myogenic contraction
- Many capillaries in the muscular wall of the heart.
-The blood running
through these capillaries is supplied by the coronary arteries, which branch of the
aorta, close to the semilunar valve.
- Blood brought by the coronary arteries
brings nutrients & oxygen for
aerobic cell respiration, provides energy for cardiac muscle contraction. - Valves in the heart ensure circulation of blood by preventing back-flow.
The atria are collecting chambers and the ventricles
are pumping chambers
Pulmonary circulation
Go trough this with a diagram of a heart
- Deoxygenated blood from the superior & inferior vena cava collects in the right atrium.
- The walls of the right atrium contract, pushing blood from the atrium into the right ventricle through the
atrioventricular valve
3 Once blood has accumulated in the right ventricle, it contracts powerfully causing:
1. right atrioventricular valve to close to prevent backflow;
2. increase of pressure in the right ventricle, leading to the
opening of the right semilunar valve, pulmonary valve, pumping blood into the pulmonary artery. an artery that carries deoxygenated blood.
4 Blood is carried by arteries, arterioles and capillaries toward the lung alveoli, where it is oxygenated
5 Pulmonary veins return oxygenated blood to the left atrium. Note that these are veins that carry oxygenated blood.
Systemic circulation
Go trough this with a diagram of a heart
- Blood from the pulmonary veins collects in the left atrium.
- The walls of the left atrium contract, pushing blood from the atrium into the left ventricle through the left atrioventricular valve.
- Once blood has accumulated in the left ventricle, it contracts powerfully causing:
- left atrioventricular valve to close to prevent backflow;
- increase of pressure in the left ventricle, leading to the opening of the left semilunar valve, aortic valve, pumping blood into the aorta.
The left ventricle has a much thicker musculature, as the aorta distributes blood to the entire body, so a more powerful contraction is necessary - The aorta branches towards the entire body, one of the first branches directs blood to the coronary arteries (which supply the heart muscle with oxygenated blood for efficient muscle contraction). The rest of the blood is carried by arteries,
arterioles and capillaries to the whole body to provide nutrients and oxygen. - Venules, veins and the inferior and superior vena cava return deoxygenated blood to the right atrium
Cardiac cycle
- The walls of the atria contract, pushing blood from the
atria into the ventricles through the atria-ventricular valves, which are open. The semilunar valves are closed, so the ventricles fill with blood. - The walls of the ventricles contract powerfully and the blood pressure rapidly rises inside them. This causes the
atria-ventricular valves to close, preventing back-flow and then causes the semilunar valves to open, allowing blood to be pumped out into the arteries. At the same time the atria start to refill by collecting blood from the veins. - The ventricles stop contracting so pressure falls
inside them. The semilunar valves close, preventing
back-flow. When the
ventricular pressure drops below the atrial pressure, the
atria-ventricular valves open. Blood entering the atrium
from the veins then flows on to start filling the ventricles.
The next cardiac cycle begins when the walls of the atria
contract again
Control of heartbeat
- Cardiac muscle cells in the wall of the right atrium acts as a pacemaker of the heart by initiating each contraction, sinoatrial node(SA)
- The SA node sets the basic pace of the heart, the initial impulse that causes both atria to contract at the beginning of each heartbeat.
- The SA node sends electrical signals that spreads between cells of the heart to create a coordinated contraction.
- First through the walls of the atria and then trough the walls of the ventricles to cause coordinated ventricular contraction.
- The atrioventricular (AV) node is located at the bottom of the right atrium. This has a pacemaker cells, with a slower pace than the SA node.
- The SA node reaches the AV node and sets the pace of the heart beat.
- If there were to be any dysfunction of the SA node, the
AV node could then take over and set a survival pace of the heart. - The natural rhythm of the pacemaker is modulated by the nervous system, signals from
the medulla and hormones, adrenalin. - Signals to speed up heart rate pass along the sympathetic nerve, and those to slow down
heart rate pass through the parasympathetic to slow down heart rate. - Emotions such as stress and increase in activity level cause the adrenal glands to release the hormone adrenalin/epinephrine , stimulates the pacemaker to increase heart rate.
Coronary artery disease/ occlusion
- Caused by fatty plaques
building up in the inner lining of coronary arteries, which become occluded (narrow) - Bloods flow to the cardiac muscle is restricted.
- This can cause chest pain and potential cardiac failure.
Potential causes :
- Hypertension
- Smoking
- High blood glucose levels,
usually due to diabetes - High cholesterol levels
- Genetic factors
Blood clot
A semi-solid lump from liquid blood that is used to seal the cut
in the blood vessels and prevent further entry of pathogens into the
blood stream.
Platelets
Cell fragments present in blood that help create a blood clot
upon injury
Clotting factors
Molecules produced by damaged tissues and platelets
which set off a cascade of events that lead to the formation of a blood
clot
Blood clotting
- When the skin is cut the blood escapes from blood vessels, platelets and damaged cells release clotting factors.
- These clotting factors are released and cause the reactions of inactive protein prothrombin into an
an active form called thrombin. - Thrombin further catalyzes the conversion of soluble fibrinogen to insoluble fibrin, which
is a long protein that forms a fibrous mesh that catches surrounding blood cells and
forms a lump of blood called the blood clot.
If the clot is exposed to air, it dries and protects the
blood vessels from further entry of pathogens and blood loss.
Blood clotting in coronary arteries
- In case of serious plaque deposits in coronary arteries (atherosclerosis), there is a high
chance of the plaque rupturing and spilling into the bloodstream. - The rupture, and the contact of blood with the plaque causes a clotting cascade to begin, leading to the formation of a blood clot.
- Coronary arteries are narrow, a clot often blocks the blood supply through, and therefore the heart tissue stops receiving oxygen and nutrients.
- If a blood clot breaks, it releases a thrombus that move through circulation until it gets stuck in smaller arterioles or near capillary beds, cutting off blood supply.
- If the supply is blocked for long periods of time the heart tissue gets damaged, heart attack, or to uncontrolled contractions of the heart called fibrillation.
- Some heart attacks are less serious, and the heart can partially recover and start beating again, while serious artery blocks lead to complete loss of heart function and death.
Pathogen
An organism that causes disease, for example, a virus, bacterium
or a fungus.
Barriers to infection- Skin
- The skin and mucous membranes is the primary defense against pathogens
- Outer layers of the skin is tough and form a physical barrier. Sebaceous glands in the skin secrete lactic acid and fatty acids, which make the surface of the skin acidic, prevent growth of most pathogenic bacteria
- Mucous membranes are soft areas of skin that are kepts moist with mucus
- arts of the skin covered in a secretion called mucous, that keeps the skin moist and prevents the growth of bacteria by killing them with lysozyme enzymes, an enzyme in mucus
Mucous membranes can be found in the nose, throat, vagina, and urethra.
- In the trachea pathogens tends to get caught in the sticky mucus cilia then push the mucus and bacteria up and out of the trachea
Barriers to infection- Phagocytes
- Phagocytes are white blood cells that ingest pathogens through a process called
phagocytosis. - Once ingested, pathogens are killed by the enzymes in cellular vesicles called lysosomes.
- Phagocytes ingest pathogens in the blood & other tissues, by leaving the capillaries and infiltrating the sites of infections.
- Phagocytes are a form of non-specific immunity.
Barriers to infection- lymphocytes
- White blood cells that are involved in specific immunity.
- Upon encounter with antigens,
lymphocytes can either activate
other lymphocytes, or produce
antibodies. - Specific immunity is triggered by lymphocytes
- Produces a response when in contact with a specific type of pathogen
Specific immunity
- When pathogens are encountered, phagocytic cells engulf and break down
pathogens. These cells attack anything encountered as
“non-self”. - After engulfment, these cells will display fragments of the
broken down pathogens on their surface, and migrate to the lymph nodes to alert the immune system of a threat. - Certain lymphocytes called “T-cells” will get activated by this warning and release cytokines to activate particular B lymphocytes.
- The activated B lymphocytes are capable of producing the specific antigens for the antigen that was presented by the initial phagocytes.
- These activated B lymphocytes will rapidly divide into high numbers of short-lived
plasma cells that release large numbers of antibodies into the bloodstream to target
the pathogens for destruction. - A small proportion of the activated B and T cells will become memory cells, providing long-lasting immunity to the pathogen. In a case of subsequent infection, these cells can react to produce large numbers of antibodies much faster
Antigen
Any sort of molecule that is recognised by our body as foreign
Antibody
A protein produced by lymphocytes in response to the
recognition of antigens.
HIV – Human Immunodeficiency Virus
- HIV is a virus that reduces the effectiveness of the immune system by reducing the
the number of active lymphocytes. - HIV penetrates the lymphocytes and integrating their RNA into the cell’s
- DNA with the enzyme reverse transcriptase, This viral DNA does not allow the virus to replicate with the cell’s machinery, leads to a imparied ability to produce antibodies.
- The infected person has a
lowered immunity and is more susceptible to infections. - Once the body has lost the majority of its lymphocytes, the condition is termed
AIDS, acquired immunodeficiency syndrome, since the body lacks the immunity formed
by antibody production. - AIDS can culminate in death, as the body cannot fight even the most common infections
such as the common cold. - HIV is a virus, it cannot survive long outside the body, it is transmitted through bodily fluids:
• Through blood in hypodermic needles (often in drug abusers).
• Through unprotected vaginal, oral or anal sexual intercourse.
• Through the placenta or breast milk.
• Through blood transfusions.
Antibiotics
Chemicals produced by certain microorganisms to kill or control the growth of other bacteria
Penicillin
- Penicillin is an antibiotic obtained from a Penicillium fungus which is uses to kill
bacteria that might potentially invade it. - Antibiotics kill prokaryotic organisms (bacteria), and not eukaryotic, as they target metabolic processes specific for prokaryotes.
- Antibiotics can kill bacteria in our body, without harming our own cells.
- Viruses cannot be killed by antibiotics because they use the metabolism of the host cell,
and therefore, to kill a virus, the cell containing it would also have to be killed. - With different types of antibiotics, most bacterial diseases can be contained, but antibiotic resistance, some strains of bacteria cannot be so easily killed.
Florey and Chain
- Florey and Chain tested penicillin on 8 mice that were infected with a pneumonia
causing bacterium. - The treated mice recovered, while the untreated ones died.
- Florey and Chain then treated the same antibiotic on patients dying from bacterial infections, and these patients recovered.
- Today, drugs have to go through much rigorous testing, before they are given to humans.
- Safety is thoroughly tested on animals.
- Then, healthy humans are given the drug to assess if it is tolerated well.
- If all of this goes well, a small number of very sick patients are given the drug, and if
this is successful too, only then, a large scale study can be performed
