GI physiology

Question 1

what makes up the upper GI system (5)

Answer 1

• mouth - saliva - pharynx - oesophagus - stomach

Question 2

lower GI system

Answer 2

• liver - gallbladder - pancreas - small intestine - large intestine

Question 3

role of the mouth

Answer 3

• lips: speech - palate: roof of oral cavity, uvula seals nasal cavity - tongue: skeletal muscle - teeth: digestion

Question 4

role of saliva

Answer 4

contains amylase, used for lubrication, antibacterial, controlled by pressure/chemo receptors in the mouth and smell/thought of food

Question 5

role of pharynx

Answer 5

swallowing is an all or nothing reflex, pharynx prevents bolus from re-entering mouth

Question 6

role of oesophagus

Answer 6

straight muscular tube with sphincters on each end, peristaltic waves pass through to push food

Question 7

role of the stomach

Answer 7

stores food, secretes enzymes and mixes

Question 8

three sections of stomach

Answer 8

fundus - air body - food antrum - mixing

Question 9

3 secretory cells in stomach

Answer 9

• mucus – thin watery - chief – pepsinogen - parietal – HCL and intrinsic factor

Question 10

three parts of gastric juice

Answer 10

pepsinogen - HCL -> pepsin which digests peptides mucus - protection intrinsic factor - B12 absorption

Question 11

three gastric phases

Answer 11

cephalic - increase secretion in response to stimuli gastric - food reaches the stomach intestinal - acid/fat/hypertonicity inhibits secretion

Question 12

gastric emptying

Answer 12

controlled by duodenum (neural or hormonal)

Question 13

factors affecting gastric emptying

Answer 13

• chyme in the gut (increases) - fat in duodenum decreases - acid in duodenum decrease - high osmolality in duodenum decreases

Question 14

role of the liver

Answer 14

metabolic processing of carbs/proteins/fats and production of plasma proteins, stores fats/iron vitamins and produces hormones

Question 15

role of gallbladder

Answer 15

stores bile made in liver

Question 16

make up of bile

Answer 16

• aqueous fluid, bile salts, cholesterol, lethicin, bilirubin

Question 17

role of pancreas

Answer 17

• exocrine and endocrine tissues, release juices

Question 18

role of small intestine

Answer 18

absorption by enzymes in brush border and digestion (3 sections - duodenum, jejunum and ileum)

Question 19

role of large intestine

Answer 19

• drying and storage (colon, cecum, appendix, rectum

Question 20

exocrine pancreatic enzymes

Answer 20

• secretin: stimulates NaHCO3 from duct bells - CCK: stimulates enzyme release from acinar cells- trypsinogen/chymotrypsinogen and procarboxypeptidase: protein digestion once activated by HCL

Question 21

endocrine function of pancreas

Answer 21

insulin and glucagon release

Question 22

motility in small intestine

Answer 22

• segmentation: ring like contractions along length of SI initiated by pacemaker cells - response depends on distension, gastrin and extrinsic activity

Question 23

protein absorption

Answer 23

1. hydrolysed to amino acids by pepsin and proteolytic enzymes 2. Na+ co transporters move them into cells 3. exit cell via passive carriers 4. enters the blood via diffusion

Question 24

carbohydrate absorption

Answer 24

1. maltose produced by amylase 2. transformed to monomers by disaccharidases 3. monosaccharides absorbed by SGLT receptor (Na out) - fructose can passively diffuse via GLUT 5 4. monosaccharides move into blood via GLUT 2

Question 25

fat absorption

Answer 25

1. emulsified by bile 2. lipase hydrolyse to monosaccharides 3. carried into cell via water soluble micelles 4. leave micelle and passively diffuse across membrane 5. reform triglycerides 6. aggregate with lipoprotein to form chylomicrons 7. exocytosis to lymph

Question 26

motility in large intestine

Answer 26

haustral contractions: main motility - autonomous rhythmicity of smooth musclemass movements: big contractions to move contents

Question 27

taeniae coli

Answer 27

longitudinal bands of muscle

Question 28

haustra

Answer 28

sacs that change location during contraction

Question 29

defecation reflex

Answer 29

initiated when stretch receptors in rectum are activated, causes sphincter relaxation and rectal contraction

Question 30

what does gastrin cause

Answer 30

increases HCL secretion and pepsinogen to increase mass movements

Question 31

what does secretin do

Answer 31

inhibits gastric emptying and acid secretion until acid in duodenum is neutralised also stimulates NaOH release from duct cells

Question 32

role of CCK

Answer 32

inhibits gastric motility and secretion and increases pancreatic enzymes

Question 33

role of glp

Answer 33

stimulates insulin release by pancreas

Question 34

how is acid secretion caused in the parietal cells

Answer 34

1. ACh/histamine or gastrin activates causing Ca influx 2. H+K+ ATPase pumps H out of the cell and K in 3. Cl- and K+ also being pumped out of cell