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Flashcards in Human Physiology Deck (29)
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1

list the digestive system components

- mouth
- esophagus
- stomach
- small intestine
- pancreas
- liver
- gallbladder
- large intestine

2

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

3

function of esophagus

movement of food by peristalsis from mouth to stomach

4

function of stomach

- churning and mixing with secreted water and acid to kill pathogens in food
- initial stages of protein digestion

5

function of small intestine

- final stages of digestion of lipids, carbohydrates, proteins, and nucleic acids
- neutralising stomach acid
- absorption of nutrients

6

function of pancreas

secretion of lipase, amylase, and protease

7

function of liver

secretion of surfactants in bile to break up lipid droplets

8

function of gallbladder

storage and regulated release of bile

9

function of large intestine

- reabsorption of water
- further digestion (especially of carbohydrates by symbiotic bacteria)
- formation and storage of feces

10

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

11

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

12

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)

13

digestive enzymes in pancreatic juice

- amylase: to digest starch
- lipase: to digest triglycerides and phospholipids
- protease: to digest proteins and peptides

14

function of amylase

starch -> maltose

15

function of lipase

triglycerides -> fatty acids and glycerol

16

function of phospholipase

phospholipids -> fatty acids, glycerol, and phosphate

17

function of protease

proteins/polypeptides -> shorter peptides

18

enzymes produced by small intestine

- nuclease
- maltase
- lactase
- sucrose
- exopeptidase
- dipeptidase

19

characteristics of small intestine enzymes

- some are secreted into intestinal juice
- but most are immobilised in the plasma membrane of epithelium cells

20

function of nuclease

DNA/RNA -> nucleotides

21

function of maltase

maltose -> glucose

22

function of lactase

lactose -> glucose & galactose

23

function of sucrase

sucrose -> glucose and fructose

24

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

25

dipeptidase

dipeptide -> amino acid

26

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

27

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

28

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

29

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