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