1.4 digestion and absorption

Question 1

define digestion

Answer 1

Digestion - mechanical, chemical and microbial breakdown of large insoluble food molecules into smaller absorbable molecules

Question 2

define absorption

Answer 2

process by which these small molecules are taken across the intestinal membranes into the blood stream

Question 3

what does salivary glands digest

Answer 3

lipids (lingual lipase)
carbs (amylase)

Question 4

what does stomach digest

Answer 4

proteins

Question 5

what does pancreas digest

Answer 5

carbs, fats, proteins

Question 6

what does liver digest

Answer 6

it emulsifies fat into small fat droplets

Question 7

two types of a-amylases

Answer 7

salivary a-amylase, pancreatic a-amylase

Question 8

function of a-amylase

Answer 8

it attacks the 1,4-glycosidic links only, they are called endoglycosidase

Question 9

what are the functional unit of the digestive tract (intestines)

Answer 9

enterocyte

Question 10

enterocyte life cycle

Answer 10

• The lumen is toxic
• Instead of repairing every damaged and old enterocyte, they die by apoptosis
• Removed from the epithelial layer, and continuously replaced by new ones
• The new ones migrates towards the apex
  Pathological = diarrhoea

Question 11

the 4 absorption mechanism by brush border

Answer 11

• Passive diffusion
• Facilitated diffusion
• Active transport
• Endocytosis

Question 12

where are nutrients first directed to after absorption and by what vessels

Answer 12

to the liver by hepatic portal vein

Question 13

what would inhibit the absorption of glucose (6)

Answer 13

• Saturable

○ Too much glucose in cell will inhibit absorption into the cell

• Competitively inhibit the absorption of glucose by galactose
• Inhibited by glucose analogues (competitively inhibit since its structures are similar to glucose)
• Sodium dependent
• Inhibited by sodium/potassium ATPase inhibitor
• Requires energy

Question 14

process of glucose transport (3)

Answer 14

• Sodium glucose co-transporter-1 (SGLT-1)

○ It transport glucose from lumen to intestinal cell

• Inside the cell, there is a lot of glucose and sodium
• Sodium potassium pump allows the sodium to leave the cell and potassium to enter the cell
• Carrier mediated diffusion (GLUT-2)

○ It transport glucose from intestinal cell to the bloodstream

Both process by SGLT-1 and GLUT-2 requires energy

Question 15

what are inactive proteases called

Answer 15

zymogens

Question 16

two types of GIT proteases and how they work

Answer 16

1. Endopeptidases

a. Attack and cleavage in the middle of the amino acid chain

b. Secreted by: stomach and pancreas

2. Exopeptidases

a. Split off amino acids from the end of the chain

b. Secreted by: pancreas and small intestinal glands

Question 17

what protein is in mucus

Answer 17

mucin (it cannot be digested by proteases)

Question 18

secretion of HCl by parietal cells

Answer 18

• CO2 binds to water to form carbonic acid by carbonic anhydrase, it then dissociates to form hydrogen ions and hydrogen carbonate ions
• Hydrogen carbonate ions goes to the blood while Cl- ions move into the parietal cell by carrier mediated transport
• Cl- and H+ ions then move into the lumen of the intestines by carrier-mediated active transport

Question 19

how does pepsinogen become pepsin

Answer 19

• Pepsinogen in acidic environment becomes activated
• Then loses an amino acid, forming pepsin
• Pepsin (endopeptidases) can then cleave the middle of the amino acid chain
• Pepsin can also further more causes more activated pepsinogen to lose an amino acid, forming more pepsin

Question 20

the 3 types of zymogens and active enzymes produced by the pancreas (only talking bout proteases)

Answer 20

zymogens: trysinogen, chymotrypsinogen, pro-elastase

active enzymes: trypsin, chymotrypsin, elastase

Question 21

2 types of exopeptidases

Answer 21

aminopeptidases, carboxypeptidases

Question 22

where do aminopeptidases, carboxypeptidases split the amino acids

Answer 22

carboxypeptidases: split at the carboxy terminal

aminopeptidases: split the amino acid at the N-terminal

Question 23

where are aminopeptidases and carboxypeptidases secreted from

Answer 23

carboxypeptidases: pancreas

aminopeptidases: small intestinal glands found on the intestinal cell membrane

Question 24

two main type of lipase

Answer 24

lingual lipase, pancreatic lipase

Question 25

what does pancreatic lipase need to be activated

Answer 25

bile acids

Question 26

two main use of bile

Answer 26

• Bile acids aid in the digestion and absorption of fat
• Bile also excretes cholesterol and the toxic breakdown products of haem (bile pigment)

Question 27

explain emulsification

Answer 27

Emulsification

• Forcing the stomach’s content through te pyloric sphincter into duodenum
• Bile salts coat the lipid droplets and prevent them from coalescing (sticking back together)
• Peristalsis help stabilise the emulsion droplets and keep them in suspension

Question 28

how are micelles formed

Answer 28

• The fat droplets needs to solubilized for absorption to occur
• Bile acids and phospholipid from bile breaks the lipids down to small particles called Micelles

Question 29

how are chylomicrons formed

Answer 29

The fatty acids, 1-monoacylglycerol and 2-monoacyglycerol then forms triacylglycerol with a protein cholesterol coat, they are now called chylomicrons

Question 30

what happens to chylomicron

Answer 30

• Chylomicrons forms fatty acids in the presence of lipoprotein and lipase
• This leaves a chylomicron remnant
  The fatty acids are released to tissues as energy

Question 31

what happens to the chylomicron remnant

Answer 31

• Chylomicron remnants are taken up by the liver and metabolized into other lipid particles
  e.g. HDL (high density lipids), LDL, VLDL (very low density lipids)