Physiology Absorption

Question 1

Define absorption.

Answer 1

Net passage of substances from the lumen across the epithelium to the interstitial fluid.

Question 2

List the factors affecting absorption.

Answer 2

SA 
Motility 
Adequate digestion 
Penetration 
Removal of substances from interstitial space

Question 3

Explain how the SA is maximized for absorption.

Answer 3

Circular folds, villi and microvilli present to increase SA.

Question 4

Describe how motility is involved in absorption.

Answer 4

Segmentation - squeeze and squish for churning
Absorption is only possible if the molecule can come into contact with the epithelium.
Also need adequate contact time - cannot have too much motility.
Needs to be a balance between fast and slow movement.
Issues with motility result in diarrhoea or vomiting.

Question 5

Explain why adequate digestion is needed for absorption.

Answer 5

Small pieces of food are needed for absorption
Brush border enzymes are needed
Breakdown of food is to create molecular units (small enough for absorption)

Question 6

Explain the information regarding penetration involved in absorption.

Answer 6

Solubility/size
Transporters (in membrane)
Pathways (into and out of cells)

Question 7

How do we move substances from the intersitial space?

Answer 7

We need gradients.

Question 8

List some absorption mechanisms.

Answer 8

Diffusion/carrier/passive or active

Question 9

What is key for absorption?

Answer 9

Na permeability and transport is key

Question 10

What is key for secretion?

Answer 10

Cl ions

Question 11

How is water absorbed?

Answer 11

Via an osmotic gradient

Question 12

How are lipids absorbed?

Answer 12

Via diffusion

Question 13

What is the key driver for absorption and secretion respectively?

Answer 13

Cl is key for secretion

Na is key for absorption

Question 14

What structure is present for secretion and absorption respectively?

Answer 14

Villus is present for absorption

Crypt is present for secretion

Question 15

Describe absorption in the mouth.

Answer 15

Minimal
Some drugs e.g. GTN under tongue due to good blood supply
Recreational drugs e.g. ketamine, tobacco chewing

Question 16

What is absorbed in the stomach?

Answer 16

Aspirin

Ethanol

Question 17

What are the main functions of the mouth and stomach?

Answer 17

Preparation for absorption

Question 18

Where does the most absorption take place?

Answer 18

Small intestine (90%)

Question 19

What is absorbed in the colon?

Answer 19

Water and sodium - swap water and sodium for K secretion.
Decreases faecal volume
Neuronal and hormonal control
Bacterial products - SCFA/vitamins
Drugs - rectal mucosa has good blood supply e.g. suppositories

Question 20

Describe the absorption of sodium.

Answer 20

1000mmol/day - mostly from secretions
90% small intestine, solute co-transport
10% colon, K exchange?SCFA/ENaC

Question 21

How much sodium is excreted in the faeces?

Answer 21

5-10mmol/day

Question 22

Describe the absorption of water.

Answer 22

10L/day - mostly from secretions
90% SI, solute co-transport
1L in colon 
0.1L in faeces 
Moves down osmotic gradient from Na absorption

Question 23

Describe the absorption of carbohydrates.

Answer 23

Duodenum/jejunum = proximal absorption
Amylase –> disaccharides
Brush border enzymes for further breakdown –> monosaccharides
Absorbed as disaccharides and monosaccharides
Absorption by Na co-transport (GLUT 5 or SLGT1)

Question 24

Describe how proteins are absorbed.

Answer 24

Come from our diet, sloughed cells, secretions
Pepsin, pancreatic proteases digest them into amino acids
Brush border peptidases
Amino acids with Na
Di/tri peptides also absorbed

Question 25

Describe the absorption of minerals/vitamins.

Answer 25

Proximal duodenum

Question 26

Where is calcium and Vit D absorbed?

Answer 26

Duodenum

Question 27

Where is iron absorbed?

Answer 27

Proximal duodenum

Absorption and storage depend on iron status and ferritin levels

Question 28

What are the fat soluble vitamins?

Answer 28

A, D E and K

Question 29

Where are the fat soluble vitamins absorbed?

Answer 29

Micelles and bile salts

Question 30

Where is vitamin B12 absorbed?

Answer 30

Distal ileum

Needs IF

Question 31

What produces IF?

Answer 31

Gastric mucosa in stomach

Question 32

How are lipids absorbed?

Answer 32

Bile salts emulsify lipids
Pancreatic lipase hydrolyzes them
Micelles - contact with epithelium
Chylomicrons –> lymph

Question 33

Why is absorption so important?

Answer 33

Most of what we absorb came from us

Ensures we do not lose excessive amounts of substances