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Flashcards in Human Physiology Deck (29)
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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



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