Gastrointestinal: Digestion and absoprtion

Question 1

What are the 2 composites of food?

Answer 1

Macro and micro constituents

Question 2

What are the macro-constituents? (3)

Answer 2

• Carbohydrate
• Protein
• Lipids

Question 3

What are the micro-constituents? (3)

Answer 3

• Vitamins
• Minerals
• Water

Question 4

How much carb should we get a day and what is it consumed as?

Answer 4

250-800g a day

Disaccharides or polysaccharides

Question 5

What are examples of carbs? (6)

Answer 5

Sucrose
Lactose
Maltose
Starch
Glycogen
Cellulose

Question 6

What is the carbohydrate problem and what enzymes are used to solve it? (2)

Answer 6

Can only be absorbed as monosaccharides

• Salivary amylase
• pancreatic amylase

Question 7

What are the 5 other digestion enzymes and where are they located?

Answer 7

Dectrinase 
Glucoamylase
Sucrase
Lactase
Maltase
Located in the brush border of small intestine

Question 8

How are monosaccharides such as glucose (2) and fructose absorbed?

Answer 8

Glucose: Secondary active transport across apical membrane
Glucose: Facilitated diffusion across basolateral membrane
Fructose: facilitated diffusion across both membranes

Question 9

How much protein a day should we get and where do we get it from? (3)

Answer 9

125g/day, only need 40-50g though

• consumed in diet
• secreted into lumen of intestinal tract
• sloughed off with cells lining intestinal tract

Question 10

What are examples of protein digestion products? (3)

Answer 10

• amino acids
• dipeptides
• tripeptides

Question 11

What are the 3 types of proteases?

Answer 11

Endopeptidases
Zymogens
Exopeptidases

Question 12

What does a exopeptidase do? (2)

Answer 12

Cleave off A.A. from one end of polypeptide

Product = A.A.

Question 13

What does an endopeptidase do? (2)

Answer 13

Split polypeptide at interior peptide bonds

Product = small peptide fragment

Question 14

What do zymogens do? (4)

Answer 14

• inactive storage form of proteases
• Stored im zymogen granules
• Secreted by exocytosis
• Activated by proteolytic activation

Question 15

How is protein digested in the stomach? (2)

Answer 15

Pepsin is secreted: pepsinogen

Activated by acid

Question 16

How is pepsin activated and what does it do? (3)

Answer 16

Chief cell secrete pepsinogen
HCl cleaves pepsinogen to pepsin
Parietal cells secrete HCl

Question 17

List the proteases in the pancreas (3) and the brush border (2):

Answer 17

Pancreas: trypsin, chymotrypsin, carboxypeptidase

Brush border: aminopeptidase, enterokinase

Question 18

How are amino acids absorbed?

Answer 18

1. Cross apical membrane - active transport
2. Broken down inside cell to A.A.
3. Amino acids cross basolateral membrane - facilitated diffusion

Question 19

How much lipid should we intake a day?

Answer 19

25-160g/day - 90% triglyceride

Question 20

Why are lipids hard to digest and absorb? (3)

Answer 20

• Not water soluble
• Do not mix with stomach/intestinal contents
• Form fat droplets

Question 21

What is the enzyme of lipid digestion called?

Answer 21

Lipase

Question 22

Where is lipase secreted from and how does it work?

Answer 22

Secreted from the pancreas

Bind to the edge of the fat droplets

Question 23

What are bile salts and where are they secreted from?

Answer 23

Bile salts break lipids into smaller droplets

Synthesised in the liver from cholesterol

Question 24

What do triglycerides turn into?

Answer 24

Monoglyceride + 2 fatty acids

Question 25

How are monoglycerides and fatty acids absorbed? (3)

Answer 25

Simple diffusion across epithelium - due to equilibrium
Enter smooth ER - reform triglycerides
Lipids enter Golgi - packaged into chylomicrons

Question 26

What happens to chylomicrons? (2)

Answer 26

Secreted by exocytosis into interstitial fluid

Enter lymphatic system via lacteal

Question 27

What is the route of enterohepatic circulation? (8)

Answer 27

1. Liver
2. Gallbladder
3. Common bile duct
4. Duodenum
5. Bile salts
6. Ileum
7. Capillaries
8. Hepatic portal vein

Question 28

How do we absorb vitamins? (3)

Answer 28

Absorbed with lipids (A, D, E, K)
Dissolve in droplets, micelles, chylomicrons
Some require special transport systems (B12)

Question 29

How do we absorb minerals? (3)

Answer 29

Solvent drag with water reabsorption (Na+)
Passively follows sodium absorption (Cl-)
Passively absorbed (K+)

Question 30

How do we absorb calcium? (4)

Answer 30

• Actively absorbed in duodenum and jejunum
• Binds to brush border protein
• Transported to epithelial cell
• Transported across basolateral membrane by Ca2+ pump

Question 31

How do we absorb iron? (5)

Answer 31

• Transferrin secreted by enterocytes in small intestine
• Transferrin binds iron
• Taken into cell by endocytosis
• Some stored as ferritin in enterocytes
• Some transported into blood

Question 32

How do we absorb and secrete bicarbonate? (2)

Answer 32

Jejunum - bicarbonate ions passively absorbed

Ileum and colon - bicarbonate secreted in exchange for chloride ions

Question 33

How do we absorb water? (4)

Answer 33

• 7L of secretions
• 2L intake
• Passive absorption
• Follows solutes by osmosis

Question 34

What are the 3 absorbing abnormalities?

Answer 34

• Failiure of substances to reach absorbing epithelium
• Absorbing substances unavailable
• Loss of absorptive surface