Digestion and absorption of food

Question 1

Digestion in the stomach

Answer 1

• Kills ingested bacteria
• Denatures proteins - particle breakdown
• Facilitates action of pepsin
• Converts pepsinogen to pepsin - initiates protein digestion

Question 2

Gastrin

Answer 2

Released from G cells in pyloric glands - stimulates acid secretion

Question 3

What does somatosensin do?

Answer 3

Inhibit acid secretion

Question 4

How is pepsin formed?

Answer 4

H+ from parietal cells cleaves pepsinogen

Question 5

How are zymogens activated?

Answer 5

Hydrolysis

Question 6

How is trypsin activated

Answer 6

Enetropeptidases activate trypsinogen

Question 7

Digestion and absorption of proteins

Answer 7

Brush border amino peptidases finish job
Amino acids and small peptides transported across epithelium by secondary active transport with sodium/hydrogwn
Basal NA/K+ pump establishes electrochemical gradient for Na+ transport
Luminal Na+ symporters transport amino acids
Luminal H+ symporters transport small peptides

Question 8

How do chylomicrons enter capillaries?

Answer 8

Chylomicrons too big to get into capillaries so enter lacteals (capillaries of lymphatic system) which enters subclavian vein

Mainly happens in duodenum

Question 9

How do the products of digestion reach the liver?

Answer 9

Hepatic portal vein

Question 10

Digestion and absorption of carbohydrates

Answer 10

Brush border disaccharidases convert disaccharides to monosaccharides
Monosaccharides transported across epithelium by secondary active transport
Brush border enzymes = lactase, maltase and sucrase
SGLT = sodium glucose transporter
GLUT = glucose transporter
Basal NA+/K+ pump establishes gradient for Na_ transport

Question 11

Digestion and absorption of fats

Answer 11

Monoglycerides and fatty acids pass across epithelium by diffusion
Lipases (cholesterol ester hydrolase, phospholipase A2) turn fat into monoglycerides, fatty acids, cholesterol which are transported by micelles

Question 12

Function of micelles

Answer 12

Digestion products re-esterifies back into original forms and packaged into chylomicrons which enter lymphatic system

Question 13

Bile

Answer 13

• Made from bile salts derived from cholesterol
• 8 types of bile salts - depends on acid derived from
• Phospholipids and cholesterol and components made from bilirubin
• Bicarbonate neutralises acidic chyme
• Bile salts emulsify fats and form micelles
• Micelles transport pancreatic enzymes to enterocyte surface
• Bile salts are antipathic - water and loving and water hating regions - negatively charges OH groups on outer surface are hydrophilic and hydrophobic region derived from cholesterol
• Bile salts encircle lipids - forms micelle for transport through lumen