Human Physiology Flashcards
list the digestive system components
- mouth
- esophagus
- stomach
- small intestine
- pancreas
- liver
- gallbladder
- large intestine
function of mouth
- voluntary control of eating and swallowing
- mechanical digestion by chewing and mixing with saliva
- saliva contains lubricants and enzymes that start starch digestion
function of esophagus
movement of food by peristalsis from mouth to stomach
function of stomach
- churning and mixing with secreted water and acid to kill pathogens in food
- initial stages of protein digestion
function of small intestine
- final stages of digestion of lipids, carbohydrates, proteins, and nucleic acids
- neutralising stomach acid
- absorption of nutrients
function of pancreas
secretion of lipase, amylase, and protease
function of liver
secretion of surfactants in bile to break up lipid droplets
function of gallbladder
storage and regulated release of bile
function of large intestine
- reabsorption of water
- further digestion (especially of carbohydrates by symbiotic bacteria)
- formation and storage of feces
define peristalsis
- the contraction of circular and longitudinal muscle layers of the small intestine
- which mixes food with enzymes and moves it along the gut
structure of the small intestine’s wall
from outer to inner layer
- serosa: outer coat
- muscle layers: longitudinal muscle, and inside it, circular muscle
- sub-mucosa: tissue layer containing blood and lymph vessels
- mucosa: lining of small intestine with epithelium that absorbs nutrients on its inner surface
types of gland tissue in pancreas
- one type secretes insulin and glucagon into the blood
- the other type synthesises and secretes digestive hormones into the gut in response to eating a meal (mediated by hormones synthesised and secreted in the stomach)
digestive enzymes in pancreatic juice
- amylase: to digest starch
- lipase: to digest triglycerides and phospholipids
- protease: to digest proteins and peptides
function of amylase
starch -> maltose
function of lipase
triglycerides -> fatty acids and glycerol
function of phospholipase
phospholipids -> fatty acids, glycerol, and phosphate
function of protease
proteins/polypeptides -> shorter peptides
enzymes produced by small intestine
- nuclease
- maltase
- lactase
- sucrose
- exopeptidase
- dipeptidase
characteristics of small intestine enzymes
- some are secreted into intestinal juice
- but most are immobilised in the plasma membrane of epithelium cells
function of nuclease
DNA/RNA -> nucleotides
function of maltase
maltose -> glucose
function of lactase
lactose -> glucose & galactose
function of sucrase
sucrose -> glucose and fructose
what is exopeptidase
- proteases that digest peptides
- by removing single amino acids either from the carboxy or amino terminal of the chain
- until only a dipeptide is left
dipeptidase
dipeptide -> amino acid
substances absorbed by villus cells
- monosaccharides: glucose, fructose, galactose…
- any of the 20 amino acids used to make proteins
- fatty acids, monoglycerides, glycerol
- bases from digestion of nucleotides
- mineral ions: calcium, potassium, sodium…
- vitamins
what if harmful substances are absorbed by villus cells?
- sometimes harmful substances pass through the epithelium
- but they are subsequently removed from the blood and detoxified by the liver
- other absorbed unwanted (but harmless) substances pass out as urine
- some pathogens may be absorbed but are quickly removed by phagocytes in the liver
methods of absorption: triglyceride example
- triglycerides are digested into fatty acids and monoglycerides, which can be absorbed into villus epithelium cells via simple diffusion (they can pass through phospholipids in the membrane)
- fatty acids can also be absorbed via facilitated diffusion through fatty acid transporter proteins in microvilli membrane
- inside epithelium cells, fatty acids + monoglycerides -> triglycerides again, and cannot diffuse back out into the lumen
- triglycerides coalesce with cholesterol to form droplets of 0.2 microns in diameter, which become coated in phospholipids and protein
- these lipoprotein particles are release via exocytosis on the inner side of villus epithelium cells
- they either enter the lacteal to be carried away in the lymph, or they enter the blood capillaries in the villi
methods of absorption: glucose example
- glucose can’t pass through the membrane via simple diffusion as it’s polar (hydrophilic)
- sodium-potassium pumps in the inward-facing part of the plasma membrane pump sodium ions via active transport from cytoplasm to spaces inside the villus, and potassium in the opposite direction
- creating low conc of sodium in the villus epithelium cells
- sodium-glucose co-transporter proteins in the microvilli transfer a sodium ion and glucose molecule together from the intestinal lumen to the cytoplasm of the epithelium cells via a passive facilitated diffusion
- glucose channels allow the glucose to move via facilitated diffusion from cytoplasm to spaces inside the villus and into blood capillaries in the villus
