Digestion & Absorption

Question 1

What are the three major food categories?

Answer 1

• Carbohydrates
• Proteins
• Fats

Question 2

What is the purpose of digestion? Where does it take place?

Answer 2

Serves to convert complex foodstuffs into manageable units for absorption

-Some digestion takes place in the mouth (salivary amylase) and stomach (pepsin) but most takes place in the small intestine

Question 3

What is the purpose of absorption? Where does it take place?

Answer 3

Serves to extract useful substances from the intestinal contents

Occurs in small intestines where microvilli provide large surface area

Question 4

What is the pancreas role in digestion?

Answer 4

Produces an enzyme rich secretion and an aqueous alkaline solution

-Involves HCO3- exchange with Cl- (the Cl- ion channel is absent in cystic fibrosis)

Question 5

What is the function of bicarbonate? Why is it necessary?

Answer 5

neutralise acid chyme

chyme = food

Necessary for:

• Digestive enzyme activity
• micelle formation
• Protecting duodenal mucosa (epithelial cells)

Question 6

What form are carbohydrates digested as?

Answer 6

Ingested as complex carbs (starch in plants and glycogen in meat)

Digestion begins in mouth through salivary alhpa-amylase

Most carbohydrate digestion occurs in the small intestine by the action of pancreatic alhpa-amylase

Question 7

How does the pancreatic alhpa-amylase work?

Answer 7

digests complex carbohydrates acting on alpha-1/4 glycosidic bonds on chains larger than disaccharides

Question 8

Where do the subsequent reactions occur?

Answer 8

Brush barrier

-closely associated with sodium co-transport which transfers monosaccharides from gut lumen to vascular system

Question 9

How does protein digestion occur?

Answer 9

Begins in the stomach (pepsin)

two major pancreatic enzymes responsible:

1) Endopeptidases - cleave interior peptide bonds
2) Exopeptidases - cleave external peptide bonds

Question 10

What is the role of trypsin on protein digestion?

Answer 10

Involved in the breakdown of molecules to form proteins by activating other peptidases to digest. Present in an inactive form secreted from the pancreas called trypsinogen

Question 11

How are proteins absorbed?

Answer 11

Occurs by either passive or facilitated diffusion

Question 12

How are fats digested?

Answer 12

Pancreatic lipase is water soluble so has the access to lipid site required to emulsify lipid droplets to increase surface area of lipid water layer.

Emulsification involves bile acids derived from the liver and released from stores in the gall bladder

Question 13

What are the products produced by pancreatic lipase?

Answer 13

monoglycerides and free fatty acids (and some glycerol)

-these products are still not soluble so so are absorbed by forming a micelle

Question 14

How are the control on pancreatic secretions altered?

Answer 14

1) Vagus nerve (presence of food in the stomach)
2) Secretin (released in response to acid in duodenum)
3) Cholycystokinin (CCK) (released in response to presence of fat and protein in duodenum)

Somatostatin inhibits pancreatic secretions

Question 15

What are some abnormalities of digestion and absorption?

Answer 15

Lactase insufficiency - Intolerance to lactose produces osmotic diarrhoea and flatulance

Gluten Enteropathy - gluten in diet causes mucosal damage - decreases villi surface area for absorption. Increased delivery of nutrients to large intestine produces diarrhoea and flatulance

Question 16

What are the types of pancreatitis? symptoms

Answer 16

Acute - autodigestion of pancreas by secreted enzymes

Chronic - normally associated with alcohol abuse

Symptoms:

• fatty stools
• diabetes
• no major effect on carbohydrate and protein digestion due to presence of additional digestive enzymes in small intestine