Nutrient Digestion 2 - fats, vitamins and minerals Flashcards
What is the enzyme responsible for breaking down fat in humans?
Pancreatic lipase
Triacylglycerol - monoglyceride + 2 fatty acids
Almost all ingested fat is in the form of triacylglycerols which present as large fat globules in water, why is it important these are emulsified for digestion?
Because pancreatic lipase is a water soluble enzyme, and fats are not water soluble - so unless large globules are separated into smaller ones, digestion will be very slow as it can only occur at the surface of the fat globule
What is required for emulsification to occur?
Mechanical disruption of large lipids to small droplets (smooth m. contraction)
Emulsifying agent - prevents small droplets reforming into large globule (bile)
Why are bile salts and phospholipids good emulsifying agents?
Because they are amphipathic molecules
How do bile salts and phospholipids emulsify lipid droplets?
Their non-polar portions associate with the lipid droplets, leaving the polar portions exposed. Polar portions repel other small lipid droplets
What is a micelle? how does it function to increase speed of fat absorption?
A micelle is an association of:
Bile salt + monoglyceride + fatty acid + phospholipid. Polar portions at the surface, non-polar at the core
Micelles increase absorption rate by transporting lipids to cell surface away from water, and then breaking down at the surface and releasing lipids
Why do micelles break down at the epithelial cell surface? And are micelles themselves absorbed?
Because the acid microclimate destabilizes them
Micelles are not absorbed - transport
What happens once fatty acids first enter the epithelial cell?
They enter the smooth ER to be reformed into triacylglycerols, which are then coated by amphipathic proteins synthesized in the sER
After processing in the sER what happens to fats?
They are transported to the golgi in vesicles made from the sER membrane
They are then exocytosed into the ECF at the serosal membrane
What happens when the fats pass into the ECF?
They associate with phospholipids, cholesterol and fat soluble vitamins to form chylomicrons
Chylomicrons then enter into lacteals - the lymphatic vessels of the small intestine that absorb fats
How are fat soluble vitamins absorbed? Which vitamins are they?
Follow the same path of absorption as fat
ADEK
How are non fat soluble vitamins absorbed?
Via carrier-mediated transport in the gut lumen, or passive diffusion
How is vitamin B12 absorbed? (large, charged molecule)
It binds to intrinsic factor in the stomach and then gets absorbed by specific transporter in the distal ileum of the gut
What is B12 deficiency called? How does it manifest?
Pernicious anaemia
Vitamin B12 is usually stored in the liver, carry about a 3 year supply - therefore effects of pernicious anaemia only felt about 3 years after onset.
B12 deficiency causes red blood cells to form the wrong shape - can’t carry oxygen - become fatigued
How is iron absorption regulated?
It is regulated by the gut itself, only about 10% ingested iron absorbed
Iron is absorbed in duodenum by DMT1 , gets incorporated into ferritin - intracellular iron storage
