L30 - Digestion 3

Question 1

What is the net result of the gastric phase?

Answer 1

digestion of proteins by pepsin, formation of chyme by action of pepsin, acid & peristaltic contractions and controlled entry of chyme to small intestine

Question 2

When does the intestinal phase begin?

Answer 2

begins once chyme enters small intestine

most digestion and absorption occurs here

Question 3

Intestinal phase triggers reflexes that…

Answer 3

feed back - regulate delivery of chyme from stomach

feed forward - promote digestion, motility and utilisation of nutrients

Question 4

Chemical digestion of which nutrients will have begun by the time chyme reaches the small intestine?

Answer 4

starch/carbohydrates, fats and proteins

Question 5

How is acid neutralised in the small intestine?

Answer 5

secretin is released which is a hormone that mediates the release of bicarbonate from the pancreas

Question 6

Which hormone is released upon entry of fats and proteins into the small intestine?

Answer 6

CCK which mediates the release of pancreatic enzymes that break down fats and proteins
also triggers contraction of the gallbladder which releases bile salts

Question 7

Which compounds are released upon entry of carbohydrates into the small intestine?

Answer 7

GIP and GLP-1 which both trigger insulin signalling

Question 8

Which hormone inhibits gastric motility and acid secretion?

Answer 8

CCK which is released when fats and proteins move into the small intestine

Question 9

What is the role of intestinal motility?

Answer 9

mix chyme with enzymes for digestion, expose digested nutrients to mucosa for absorption, slowly propel food forward (stimulated by PNS and inhibited by SNS)

Question 10

What are characteristics of the microbiome?

Answer 10

includes bacteria and fungi, 10 times more cells than host, 100 times more genes than human genome, dynamic ecosystem which reflects diet, sometimes symbiotic, often parasitic and detrimental

Question 11

What does bile contain?

Answer 11

bile salts and drugs cleared from the body

Question 12

What is the hepatic portal system?

Answer 12

everything absorbed from the GIT is delivered directly to the liver e.g. glucose and toxins
recirculates bile salts (twice for typical meal)

Question 13

What is the role of the pancreas?

Answer 13

has endocrine and exocrine functions

endocrine: insulin in fed state and glucagon in fasted state
exocrine: pancreatic enzymes and alkaline solution

Question 14

What is the role of the exocrine function in the pancreas?

Answer 14

proteolytic enzymes (inactive enzymes) digest protein
pancreatic amylase (active) converts polysaccharides into disaccharides
pancreatic lipase (active) digests fat

Question 15

How are pancreatic enzymes activated?

Answer 15

inactive enzymes are released into the small intestine e.g. trypsin -> enteropeptidase in the wall of the SI converts trypsinogen into trypsin which activates other proenzymes

Question 16

Where does does digestion occur in the GI tract?

Answer 16

some amylase in saliva: carbohydrate
some protein digestion in stomach
but most digestion occurs in small intestine

Question 17

Into which system are fats absorbed?

Answer 17

the lymphatic system

Question 18

What is the role of amylase?

Answer 18

breaks polysaccharides down into disaccharides maltose, sucrose and lactose

Question 19

Which enzymes break down disaccharides?

Answer 19

disaccharidases which are found on the intestinal brush-border
include maltase, sucrase and lactase

Question 20

What is carbohydrate absorption in the small intestine driven by?

Answer 20

Na+-K+ ATPase on the basolateral membrane and transporters on the apical membrane
e.g. glucose enters the cell with Na+ on the SGLT symporter and exits on GLUT 2

Question 21

What is protein absorption in the small intestine driven by?

Answer 21

proteins are broken down into peptides -> di- and tripeptides cotransport with H+, amino acids cotransport with Na+ and small peptides are carried intact across the cell by transcytosis

Question 22

A decrease in luminal [Na+] will decrease intestinal reabsorption of which compounds?

Answer 22

glucose, galactose and amino acids

Question 23

Which fats are digested by the body?

Answer 23

triglycerides, cholesterol, phospholipids and fat soluble vitamins

Question 24

What is the role of bile salts and colipase in fat digestion?

Answer 24

since fats are not water soluble bile salts emulsify fat and colipase facilitates lipase access

Question 25

What are chylomicrons?

Answer 25

combination of triglycerides, cholesterol and protein which are absorbed into the lymphatic system

Question 26

Of the 8-10 L of fluid entering the GI tract daily…

Answer 26

only 100-200 mL are excreted in the stool

Question 27

How is fluid balance in the digestive system maintained?

Answer 27

water absorbed by osmosis: gradient created by absorption of ions and nutrients into interstitial fluid

Question 28

What is osmotic diarrhoea?

Answer 28

unabsorbed osmotically active solutes hold water in the lumen e.g. lactose, sorbitol

Question 29

What is secretory diarrhoea?

Answer 29

bacterial toxins enhance colonic secretion of Cl-

intestinal infection e.g. cholera toxin, E. coli