Lecture 12

Question 1

what is the definition of chyme ?

Answer 1

mixture of food and secretions from salivary glands, liver, gallbladder and pancreas

Question 2

what are the 4 processes of the digestive system ?

Answer 2

1) secretion : from cells into lumen or ECF

2) digestion : chemical and mechanical breakdown of food

3) absorption : from GI lumen to ECF

4) motility : movement through GIT (result of muscle contraction)

Question 3

how does mass balance work in the digestive system ?

Answer 3

volume of fluid entering the GI tract by intake or secretion must equal the volume leaving the lumen

Question 4

content of saliva, how much per day ?

Answer 4

water, ions, mucus, proteins (enzymes)

3 pairs of glands -> 1.5 L/day

Question 5

what 2 purposes does motility serve ? Names of the 2 types of movement ?

Answer 5

1) moving food from mouth to anus
2) mechanically mix food to break it down + maximise exposure to enzymes

1) peristalsis : progressive waves of contraction (circular muscles)
2) segmental contractions : segments that alternately contract (no net movement, but mixing)

Question 6

sections of the stomach and roles

Answer 6

1) upper fundus : reservoir for food

2) central body

3) lower antrum : busy with digestion, push food towards pylorus and mix with gastric juice

4) pylorus / polyric valve

Question 7

cross-section through the stomach : layers, name 2 secreting cells

Answer 7

mucosa - muscularis mucosae - submucosa - muscularis externa

mucosa : opening of gastric glands
- mucus cells
- parietal cells (HCl)

Question 8

4 substances secreted in the stomach and role

Answer 8

• mucus : physical barrier between lumen and epithelium
• bicarbonate : buffer
• gastric acid HCl : activated pepsin, kills bacteria
• intrinsic factor : B12 absorption

Question 9

what is mainly digested in the stomach ? and in the small intestine ?

Answer 9

stomach -> proteins

small intestine -> peptides, carbohydrates, fats

Question 10

anatomy of the small intestine : 3 sections

Answer 10

1) duodenum : enzymes break down proteins and bile emulsifies fats into micelles

2) jejunum : circular folds and villi, absorption of nutrients

3) ileum : also villi, absorbs mainly B12 and bile acids

Question 11

main thing that happens at villi and crypts

Answer 11

villi -> absorption
crypt -> fluid secretion

Question 12

2 main roles of the pancreas

Answer 12

exocrine -> digestive enzymes and bicarbonate

endocrine -> insulin and glucagon secretion

Question 13

role of bile for fat digestion

Answer 13

bile salts cover fat droplets -> enzymes break the m down into monoglycerides and fatty acids -> those move out of the micelles and enter cells -> they combine with cholesterol and are removed by the lymphatic system

Question 14

what circulates through the hepatic portal system ?

Answer 14

most nutrients absorbed by the intestine pass through the liver -> filter that can remove potentially harmful xenobiotics before they enter systemic circulation

Question 15

what is the hormone secreted in the stomach ? and primary target

Answer 15

gastrin -> ECL cells and parietal cells (gastric acid secretion and mucosal growth)

Question 16

name 4 hormones released by the intestine and main target / effect

Answer 16

1) CCK : gallbladder, pancreas (enzyme secretion), stomach -> promotes satiety

2) secretin : pancreas, stomach -> stimulates bicarbonate secretion

3) motilin : gastric and intestinal smooth muscle -> migrating motor complex

4) gastric inhibitory peptide GIP : beta cells of pancreas -> insulin release

Question 17

3 hormones that decrease food intake and one that increases food intake

Answer 17

decrease :
- peptide YY : quantity increases after eating
- obestatin : opposes ghrelin
- OXM : suppression of ghrelin

increase :
- ghrelin : stimulates appetite