Nutrient Digestion

Question 1

Four Functions of the Gut

Answer 1

Digestion
Absorption
Secretion
Motility

Question 2

Monosaccharides Examples

Answer 2

Hexose Sugars (6C)
Glucose, Fructose, Galactose

Question 3

Disaccharides and their monomer constiuents)

Answer 3

2 hexose sugars linked together by a glycosidic bond

```
Lactose
glucose and galactose
Sucrose
(glucose and fructose)
Maltose
(glucose and glucose)
~~~

Question 4

Polysaccarides

Answer 4

Complex Carbohydrates

Starch ( plant storage of glucose)
Cellulose (plant cell walls)
Glycogen (animal storage of glucose)

Question 5

What breaks down Starch

Answer 5

Amylases

Question 6

Where is amylase produced and what is it’s action

Answer 6

The pancreas and the salivary glands. They hydrolyse α-1,4 glycosidic bonds, to break starch into it’s monomer constituents

Question 7

How is cellulose broken down?

Answer 7

Mammals do not produce the necessary enzymes but some of our gut bacteria does.

Indigestible cellulose = fibre.

Question 8

Where are carbs absorbed ?

Answer 8

Carbohydrates are absorbed by the columnar epithelial of the small intestine.

They travel via transcellular transport

Question 9

How do carbs pass the apical layer of the columnar epithelial

Answer 9

SGLT - Utilises the Na+ gradient to passively transport glucose (&galactose, GLUT-5 transports fructose by the same mechanism)

Question 10

How do carbs pass the basal-lateral layer of the columnar epithelial

Answer 10

Two Components
A) Na/K ATpase - (active transport) maintains the osmotic gradient between the lumen and the ICF

B) GLUT-2 - facilitated diffusion across the basal lateral membrane (fructose, glucose and galactose)

Question 11

Define ParaCellular Transport

Answer 11

Transfer of substances between cells. Water in carbohydrate absorption travels through the tight junction between cells,. The Na+ gradient means water moves across the intestinal lumen into circulation

Question 12

Name the enzymes groups that break down proteins

Answer 12

Proteases (endopeptidases)

Peptidases

Question 13

Action of Proteases

Answer 13

Proteases hydrolyses internal peptide bonds to break larger chains into smaller fragments.

Question 14

Metabolism of Proteases

Answer 14

Proteases are secreted as proenzymes called Zymogens by epithelial cells in the head of the pancreas, stomach and intestine.

They are activated in the GI tract.

Question 15

Common Proteases

Answer 15

Pepsin (stomach)
Trypsin
Chymotrypsin (pancreas)

Question 16

Action of Peptidases

Answer 16

Peptide hydrolyses of terminal amino acids.

Question 17

Absorption of Amino Acids through the apical surface and basal lateral surface

Answer 17

Apical: SAAT1 (sodium, amino acid transporter)

Basal/Lateral: Facilitated diffusion through a transport protein.

Na/K+ maintains Na+ gradient.

Question 18

Absorption of Dipeptides through the apical and basal/lateral membrance

Answer 18

Apical: PepT1 (paired hydrogen/dipeptide transporter)

NHE3: The hydrogen ion is returned to the lumen via a Na/H transporter.

Unknown how dipeptide crosses basal/lateral membrance

Question 19

Structure of Triglycerides

Answer 19

Condensation reaction between glycerol and three long-chain fatty acids.

Question 20

Location of fat digestion

Answer 20

Fat digestion takes place in the small intestine via pancreatic lipase.

Question 21

Describe Lipid Digestion

Answer 21

1. Fatty Droplets suspended in water due to insolubility in water. Lipase can only act on the external surface.
2. Emulsification breaks down the fatty droplets into smaller globules. Increasing surface area for the action of lipase
3. Micelle Formation (smaller)

Question 22

Describe Lipase

Answer 22

Water soluble enzyme. Secreted by the pancreas. Breakdowns fat into constituents.

Question 23

Requirements of Emulsification

Answer 23

1) Mechanical Disruption - Smooth muscle contraction of the intestine mix the luminal contents
2) Emulsifying agent - bile salts and phospholipids amiphatic molecules, secreted by the gallbladder

Question 24

Lipid Absorption

Answer 24

Micelles breakdown at the cell membrane and lipids diffuse across the cell membrane.

Question 25

Journey of lipids inside the cell

Answer 25

1. FFA & Monoglycerides, diffuse across the cell membrane.
2. In the sER, the absorbed constituents are reformed to triglycerides and emulsified.
3. The emulsified triglycerides travel trough the vesicles of the sER to the golgi apparatus.
4. The golgi apparatus exocytoses into the ECF at the serosal membrane as chylomicrons.
5. Chylomicrons pass into the lacteals, which drain into the thoracic duct before going into the IVC

Question 26

Define Chylomicrons

Answer 26

Extracellular fat droplets, also containing phosolipids, cholesterol and fat soluble vitamins ~1um.

Question 27

What are lacteals

Answer 27

Lymphatic capillary beds of the epithelia.

Question 28

Absorption of Fat Soluble Vitamins

Answer 28

Absorbed in the same way as fats - A D E K

Question 29

Absorption of Water Soluble vitamins ex

Answer 29

B12 - binds to intrinsic factor (secreted by the stomach) and is absorbed by a transport protein in the ileum

Question 30

Iron Absorption

Answer 30

Transported across the ‘brush border membrane’ via DMT1.

Question 31

Fate of Iron

Answer 31

1. Stored with Ferritin as a intracellular iron store

2. Transferred to the blood, and binds to transferrin.

Question 32

Hyperaemia

Answer 32

Increased Ferritin levels cause more iron to be bound to the entreocytes

Question 33

Anaemia

Answer 33

Decreased ferritin levels cause more iron to be released into the blood

Question 34

Pernicious Anaemia

Answer 34

B12 deficiency resulting in failure of red blood cell maturation