Digestion and Absorption

Question 1

Functional organisation of a villus in the small intestine

Answer 1

Central lacteal, entering artery, capillaries, exiting vein.
Basement membrane, absorptive epithelial cells (enterocytes), brush border cells.

Question 2

Sphlanic circulation

Answer 2

Blood enters GI organs via branches of the abdominal aorta, first to the liver via the portal vein, through the sinusoids, then to the hepatic veins to the vena cava.

Question 3

Hepatocytes functions

Answer 3

Detoxify substances such as bacteria

Question 4

Sources of carbohydrates

Answer 4

Sucrose - glucose and fructose disaccharide
Lactose - glucose and galactose disaccharide
Starches - non-animal foods
Glycogen - animal starch
Cellulose - dietary fiber

Question 5

Salivary and pancreatic amylase functions

Answer 5

Initiate the breakdown of starches
α-amylases target the α1,4 bonds in amylose and amylopectin.
This produces maltose, maltriose and glucose dimers that must be further broken down.

Question 6

Brush border enzymes function

Answer 6

Finalise the breakdown of starches
1. Maltose and multriose into glucose
2. α-limit dextrin is broken down ONLY by isomaltose

Question 7

Sucrase-isomaltose

Answer 7

Cleaves sucrose into glucose and fructose, absorbed by SGLT1 and GLUT5

Question 8

Lactase

Answer 8

Hydrolyses lactose into glucose and galactose, absorbed by SGLT1 transporter.

Question 9

__________ are the only forms in which carbohydrates are absorbed

Answer 9

Monosaccharides!!

Question 10

GLUT5

Answer 10

Facilitated diffusion. Transports fructose out of intestinal lumen and then again transports into portal vein

Question 11

GLUT2

Answer 11

Facilitated diffusion. Transports glucose and galactose from the epithelial cell into the portal blood.

Question 12

SGLT1

Answer 12

Secondary active. Uses Na+ to cotransport glucose and galactose into the epithelial cell from the intestinal lumen.

Question 13

Malabsorption of carbohydrates (2)

Answer 13

Issues pertaining to the SGLT1 transporter lead to the malabsorption of glucose and galactose. This causes severe diarrhea.
Excessive fructose intake can overwhelm the GLUT5 transporter and impede the metabolism of fructose into glucose -> metabolised by colonic bacteria, leads to bloating, flatulence, diarrhea

Question 14

Pepsin

Answer 14

Initiates protein digestion in the stomach, into polypeptides and amino acids

Question 15

Trypsinogen activation

Answer 15

Enteropeptidase secreted by the brush border cells of the duodenum and jejunum.
Creates trypsin.

Question 16

Trypsin

Answer 16

Acts or activate even more enzyme precursors
- Tryspinogen (autocatalysis)
- Chymotrypsinogen
- Proelastase
- Procarboxypeptidase A and B

Question 17

Pancreatic enzyme functions

Answer 17

Cleave polypeptides into oligopeptides and amino acids.

Question 18

Brush border peptidase function

Answer 18

Breaks oligopeptides into tripeptides and dipeptides.

Question 19

Absorption of small and neutral amino acids

Answer 19

through specialised transporters using secondary active cotransport with Na+

Question 20

Absorption of large and neutral amino acids

Answer 20

Using Na+ independent transporters.

Question 21

Absorption of small peptides

Answer 21

Secondary cotransport with Na+ independent transporters (PEPT1)

Question 22

PEPT1

Answer 22

Cotransport of Na+ and small peptides, also responsible for transporting numerous peptidomimetic drugs, such as various antibiotics.

Question 23

Cytosolic peptidase

Answer 23

Absorbed peptides undergo further digestion into single amino acids within the epithelial cell.

Question 24

Important dietary lipids

Answer 24

Neutral fats, phospholipids, plant sterols, cholesterol.

Question 25

Lipase enzymes mechanism

Answer 25

Only act on the surface of the droplet, so work best following emulsion. Lingual and gastric lipases have minimal significance compared to pancreatic lipases. Hydrolyse lipids to produce FFAs, MGs, and some glycerol.

Question 26

Cholesterol esterase

Answer 26

Degrades cholesterol esters, and the esters of vitamins A, D, E. Produces cholesterol and fatty acids.

Question 27

Phospholipase E2

Answer 27

Main enzyme in digesting phospholipids into lysolecithins and fatty acids.

Question 28

Mixing micelles and bile salts

Answer 28

Micelles without are too hydrophobic to cross unstirred water layer to reach brush border cells. Mixed micelles have a hydrophobic fatty acid core surrounded by a hydrophilic exterior of bile acids, cholesterol, and lysolecithin.

Question 29

Within enterocytes, ______ of FAs determines their destination in either the _____ blood or the ________

Answer 29

length; portal; lacteal

Question 30

Destination of re-esterified lipids in enterocytes

Answer 30

Chylomicrons -> the lacteal

Question 31

Destination of short add medium chain fatty acids in the enterocytes

Answer 31

to the capillary of the portal blood where they bind albumin

Question 32

Chylomicrons

Answer 32

Lipoproteins with a triglyceride core, surrounded by phospholipids, cholesterols, cholesterol esters, and apolipoproteins.

Question 33

Absorption of fat soluble vitamins (ADEK)

Answer 33

Incorporated into micelles and absorbed with lipids.

Question 34

Absorption of water soluble vitamins

Answer 34

(B1/2/6, biotin, nicotinic acid, pantothenic acid) absorbed by sodium dependent cotransport.

Question 35

Sodium is cotransported with nutrients in the SI

Answer 35

Low intracellular sodium levels are maintained via the atpase facilitating passive transport from the cumin that is thencoupled to other molecule transport has SGLT1, or for small/neutral amino acids.

Question 36

Sodium absorption in the SI and colon via exchangers

Answer 36

NHE 3, passive transport of Nat into epithelial cells in exchange for protons. The DRA chloride/bicarbonate exchanger is connected to this via the KCCI,

Question 37

Colon sodium rebsorption

Answer 37

Primarily relies on enac to facilitate the diffusion of Nat into the cell where it is thin pumped out across the basolateral membrane. Also provides for the movement of the kt into blood via increase in there electrochemical gradient

Question 38

Secretory (water diarrhea)

Answer 38

Caused by inactivation of apical sodium channel (water reabsorption inhibited) and the stimulation of CACC via calcium, and CFTR via Camp

Question 39

CACC

Answer 39

Chloride channel that is regulated by calcium • increased calcium increases chloride efflux, secretory diarrhea

Question 40

Cystic fibrosis transmembrane regulator

Answer 40

Channel for chloride secretion that increases activity in the presence of increased Camp, caused by bacteria, medications or serotonin via VIP and prostaglandins, secretory diarhnca