1.4 digestion and absorption Flashcards
define digestion
Digestion - mechanical, chemical and microbial breakdown of large insoluble food molecules into smaller absorbable molecules
define absorption
process by which these small molecules are taken across the intestinal membranes into the blood stream
what does salivary glands digest
lipids (lingual lipase)
carbs (amylase)
what does stomach digest
proteins
what does pancreas digest
carbs, fats, proteins
what does liver digest
it emulsifies fat into small fat droplets
two types of a-amylases
salivary a-amylase, pancreatic a-amylase
function of a-amylase
it attacks the 1,4-glycosidic links only, they are called endoglycosidase
what are the functional unit of the digestive tract (intestines)
enterocyte
enterocyte life cycle
- 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
the 4 absorption mechanism by brush border
- Passive diffusion
- Facilitated diffusion
- Active transport
- Endocytosis
where are nutrients first directed to after absorption and by what vessels
to the liver by hepatic portal vein
what would inhibit the absorption of glucose (6)
- 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
process of glucose transport (3)
- 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
what are inactive proteases called
zymogens
two types of GIT proteases and how they work
- Endopeptidases
a. Attack and cleavage in the middle of the amino acid chain
b. Secreted by: stomach and pancreas
- Exopeptidases
a. Split off amino acids from the end of the chain
b. Secreted by: pancreas and small intestinal glands
what protein is in mucus
mucin (it cannot be digested by proteases)
secretion of HCl by parietal cells
- 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
how does pepsinogen become pepsin
- 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
the 3 types of zymogens and active enzymes produced by the pancreas (only talking bout proteases)
zymogens: trysinogen, chymotrypsinogen, pro-elastase
active enzymes: trypsin, chymotrypsin, elastase
2 types of exopeptidases
aminopeptidases, carboxypeptidases
where do aminopeptidases, carboxypeptidases split the amino acids
carboxypeptidases: split at the carboxy terminal
aminopeptidases: split the amino acid at the N-terminal
where are aminopeptidases and carboxypeptidases secreted from
carboxypeptidases: pancreas
aminopeptidases: small intestinal glands found on the intestinal cell membrane
two main type of lipase
lingual lipase, pancreatic lipase
what does pancreatic lipase need to be activated
bile acids
two main use of bile
- Bile acids aid in the digestion and absorption of fat
- Bile also excretes cholesterol and the toxic breakdown products of haem (bile pigment)
explain emulsification
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
how are micelles formed
- 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
how are chylomicrons formed
The fatty acids, 1-monoacylglycerol and 2-monoacyglycerol then forms triacylglycerol with a protein cholesterol coat, they are now called chylomicrons
what happens to chylomicron
- 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
what happens to the chylomicron remnant
- 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)
