GI Week 8 - The Intestines

Question 1

What is starch made up of?

Answer 1

1-4 Amylase

1-6 Amylopectin

Question 2

What enzymes break down the linkages in carbohydrates?

Answer 2

Amylase (Salivary and Pancreatic)
Isomaltase

Then also Maltase, Lactase, Sucrase, Alpha Dextrinase

Question 3

How is Glucose absorbed?

Answer 3

SGLT2 on apical which is a Na+ cotransporter
The GLUT2 on basolateral membrane
Gradient for low Na in the cell is by NaKATPase

Question 4

How is Fructose absorbed?

Answer 4

GLUT5 on the apical membrane, facilitated diffusion then GLUT2 on basolateral membrane

Question 5

How does ORS work?

Answer 5

ORS have a mixture of salt and sugar as water uses the Na gradient to be absorbed in the intestines
Na can be transported with glucose so having both in the ORS creates a better gradient for Na+ uptake and therefore H2O

Question 6

In what form are Proteins absorbed?

Answer 6

Amino Acids

Di and Tripeptides

Question 7

What changes proteins into absorbable forms?

Answer 7

Pepsinogen/Pepsin act on proteins to produce amino acids and oligopeptides
Zymogens, Trypsin and others are proteases

Question 8

What are the two types of proteases and give examples

Answer 8

Exopeptidases- hydrolyse from C ends, carboxypeptidase A and B

Endopeptidases- hydrolyse internal peptide bonds, trypsin & elastase

Question 9

How are proteins absorbed?

Answer 9

Via Na Amino Acid cotransporters

Di/Tripeptides are transported by H+ cotransporters and are converted intracellularly

Question 10

What are the things absorbed in the Intestines?

Answer 10

Carbohydrates 
Lipids
Protein
Water
Electrolytes (Na+ Ca2+)
Vitamins
Iron

Question 11

How is water absorbed?

Answer 11

Follows osmotic gradient made by Na+

Makes the fluid being absorbed isosmotic

Question 12

How is Na+ absorbed?

Answer 12

NaKATPase on basolateral drives the gradient
On apical:
Small - Na cotransporters
Large- Na+ channels which can be induced by aldosterone

Question 13

How is Calcium absorbed in the intestines?

Answer 13

Actively- Transcellular
Requires PTH to stimulate Vitamin D
Enters Cell via facilitative diffusion then leave via Ca2+ATPase

Distal Intestines:
Passively - Paracellular

Question 14

How is iron absorbed?

Answer 14

Mostly will be in haem or Fe2+ form

Iron absorbed across apical membrane, then goes across via apoferritin and is bound to transferrin in the circulation

Question 15

How are vitamins absorbed?

Answer 15

Water soluble can be absorbed via Na+ cotransporters e.g. B and C

B12 absorbed in terminal ileum along with intrinsic factor

Question 16

Describe intestinal motility: small intestine

Answer 16

There are pacemaker cells which drive slow progression of contents
There is a higher frequency of them proximally

Segmentation - mixes contents
Peristalsis - contractions move contents

Question 17

Describe intestinal motility: Large Intestine

Answer 17

Segmentation - Haustral Shuttling, mixes and allows H2O absorption
Mass Movements - move rapidly towards rectum, often triggered by food

Question 18

How do we defaecate?

Answer 18

We get impulse to at 25% full rectum
The internal sphincter (smooth muscle) relaxes via parasympathetic control
Voluntary control of external sphincter (striated)

Intra-abdominal pressure also rise to aid expulsion

Question 19

In what form are carbohydrates absorbed?

Answer 19

Only monosaccharides can be absorbed