Digestion Absorption + Metabolism

Question 1

What does the small intestine do?

Answer 1

Digestion of food, absorption of water, nutrients and electrolytes

Question 2

What is peristalsis?

Answer 2

Where adjacent segments of the GI tract contract in sequence resulting in the propulsion of food along the GI tract

Question 3

What are some functions of the stomach?

Answer 3

• stores large quantities of food until it can be accommodated in the intestine
• mixing of food with gastric sections to form chyme
• regulates emptying chyme into duodenum
• secretion of intrinsic factor (for B12 absorption)
• secretion of HCL and proteases

Question 4

What does HCL do within the stomach?

Answer 4

Activates pepsin (pepsinogen-pepsin)

Kills pathogenic organisms

Denatures and breaks down food proteins

Increases absorption of iron/calcium

Question 5

How does the small intestine fulfill its roll of increasing surface area

Answer 5

Does this by the folds of kerckring, villi and microvilli (3,10,20X) SA increase

Question 6

Describe the structure of villi?

Answer 6

Large SA for absorption due to fold in the mucosal layer, microvilli and the brush border membrane of mucosal epithelial cells

Question 7

What does the large colony of bacteria in the large intestine do?

Answer 7

It can metabolize fiber to short chain fatty acids which is then absorbed by passive diffusion.

These bacteria also produce vitamin K

Question 8

How is starch broken down in they GI tract and what enzymes are used?

Answer 8

Starch goes to dextrins and maltose via salivary amylase

Then this goes to maltose via pancreatic amylase

Finally maltose to glucose via maltase

Question 9

How are glucose and galactose absorbed?

Answer 9

They get into the epithelial cell via a sodium-dependent glut transporter (SGLT-1)

Glut 2 helps facilitate them out the cell (actively transported out via Na+/k+
Pump)

Question 10

How is fructose transported out of cell into blood?

Answer 10

Glut2 transporter

Question 11

In terms of protein digestion in GI tract, explain the full process

Answer 11

Starting at stomach, HCL activates pepsin which breaks down proteins to large peptides

Then specific pancreatic enzymes break down larger peptides into smaller peptides
Then at BB more enzymes break down the small peptides to di-peptides or amino acids

Question 12

How is pepsinogen converted to Pepsin in the stomach?

Answer 12

HCL is released from the parietal cells which will convert inactive pepsinogen to active pepsin

Question 13

How are the pancreatic proteases in the duodenum activated?

Answer 13

They remain inactive until food arrives at small intestine to active mate membrane-bound enterokinase which will in turn convert trypsinogen-trypsin, chymotrypsinogen-chymotrypsin and procarboxypeptidase to carboxypeptidase

Question 14

How is protein absorbed in the small intestine? (Not di-peptides)

Answer 14

Active transporters will take Na+ and amino acids across the brush border and into the capillary

Question 15

How are di-peptides absorbed in the small intestine?

Answer 15

They can get into the intestinal membrane through active transport using a hydrogen co-transporter
Cytoplasmic peptidases then split di-peptide into amino acids to allow them to go into the hepatic portal vein

Question 16

Where do the amino acids go after absorption

Answer 16

They Go to the liver, can be used to make pyruvate or can go to muscles to stimulate protein synthesis

Question 17

Where does lipid digestion originate?

Answer 17

In the mouth (saliva contains small amounts of lipase)

In the stomach the acid-stable lipase will continue to hydrolyse triglycerides (slow process as TG not water soluble)

Question 18

What does pancreatic lipase do?

Answer 18

It is secreted into the duodenum and will further continue hydrolysing the triglycerides

Question 19

Describe the process of lipid digestion in GI tract

Answer 19

Bile salts from the gall bladder will break down large lipid droplets to emulsion droplets, then panc. Lipase breaks the emulsion droplets to FFA’s and monoglycerides, these then go to micelles

Question 20

What are micelles and what is their structure

Answer 20

Tiny lipid that is free to move in a water medium

Consists of a hydrophobic core (monoglycerides and FFAs) and bile salts on the outside (hydrophilic side outwards)

Question 21

How are medium chain FFA absorbed in the small intestine?

Answer 21

They travel from the lumen to the capillary via passive diffusion and carrier mediated transport and are water soluble (albumin coated with FFA in capillary)

Question 22

Triglycerides are synthesized in the endoplasmic reticulum, how does this occur?

Answer 22

TG synthesis occurs from FFA (typically long chain) and monoglycerides crossing the brush border

Question 23

How are chylomicrons formed?

Answer 23

Following TG synthesis in ER, chylomicrons are formed from TG, phospholipid, protein and cholesterol and are essentially the carrier lipoprotein for getting dietary TG in the body. They are water soluble and get transported to the lymphatic system

Question 24

Where does vitamin absorption typically occur?

Answer 24

In the jejunum and ileum (via passive diffusion)

Question 25

How are the fat soluble vitamins (ADEK) absorbed?

Answer 25

They are absorbed along with FFA (particularly LCFA, eg. Chylomicrons - lymphatic system)

Question 26

Where are the water soluble vitamins absorbed?

Answer 26

C - distal part of small intestine
B6 - mainly in jejunum
B12 - mainly in ileum

Question 27

What happens to water-soluble vitamins at high concentrations?

Answer 27

They will diffuse into epithelial cells of small intestine

Question 28

What happens to the water soluble vitamins at low concentrations?

Answer 28

Active processes are now involved in absorbing water soluble vitamins in small intestine

Question 29

What type of active process is required for absorption of vitamin B1 and vitamin C?

Answer 29

An Na+ dependent active process

Question 30

How is vitamin B12 absorbed?

Answer 30

It requires the formation of a complex with an intrinsic factor (released by parietal cells).

B12 is then absorbed in the ileum by binding a B12 intrinsic-factor complex to a receptor to then be engulfed by epithelial cells

Question 31

What happens if there is a deficiency of a vitamin?

Answer 31

Active transport will occur (apart from vitamin D)

Water soluble rarely become deficient

Question 32

Where does absorption of minerals occur?

Answer 32

In the small intestine, in general they aren’t absorbed very well

Question 33

How is sodium absorbed?

Answer 33

Via an active transport process, produces a osmotic gradient which then allows water to enter cell and be absorbed by osmosis

Question 34

What things are required in an energy drink?

Answer 34

Carbohydrate (energy)

Sodium - 40mg/100ml as this increases water and carb absorption