Nutrient digestion Flashcards
In what form is most ingested fat in?
Triacylglycerol
How and where is fat digested?
It is broken down in the small intestine by pancreatic lipases.
Emulsion from the smooth muscle within muscularis externa grinds up larger lipid droplets into smaller ones.
Bile salts act as an amphiphatic molecule and keeps molecules smaller to increase surface area and allow TAG to be broken down to monoglycerol and 2 free fatty acids.
These then form micelles with bile salts.
When micelle enters acidic microclimate in apical part on cell, the fatty acids take on H ion and depolarise, allowing them to be absorbed across the cell membrane.
Why is fat needed to become emulsified?
Because otherwise it forms massive droplets and it would take too long for the water soluble lipases to break it down into the fatty acids as they can only break down from the outer surface.
Emulsification increases the surface area and allows it to be broken down faster.
How big are the emulsification droplets?
around 1mm
How does emulsification occcur?
Jostling of the contents by the muscularis externa breaks down into smaller droplets.
Then bile salts and phsospholipids act as amphiphatic molecules and keep droplets away (non-polar end inside lipid, polar end outside).
What is a micelle?
Much smaller emulsion droplets (4-7 micro meters, size of rbc) that contain free fatty acids and mono glycerides and are surrounded by bile salts and phospholipids
How are micelles broken down and diffuse across apical membrane?
They reach the acidic microclimate surrounding the apical membrane of the epthelial cells in the small intesting, the free fatty acids get a proton and so lose their charge, so they can then be easily absorbed.
What happens to fatty acids when they enter the epithelial cells?
Converted back into TAG through the smooth endoplasmic reticulum and coated with an amphipathic protein. Then exocytosed.
What is a chylomicron?
Extracellular fat droplets, also contain phospholipids, cholesterol & fat-soluble vitamins) ~1 µm diameter
How does fat travel through and out of the intestinal cells?
Protein surrounded TAG and exocytosed out of golgi apperatus.
Triacylglycerol droplets transported through cell in vesicles formed from sER membrane - processed through Golgi apparatus and exocytosed into extracellular fluid at serosal membrane
how do chlymicrons end up in blood?
Through the lymph system… Too big and can’t cross into blood vessels, so pass into LACTEALS between endothelial cells and ends p in thoracic duct and emptied into the venous system
What are the fat soluble vitamins?
ADEK
(if you just lie on A DEK you will get fat)
How do fat sol vitamins get processed?
just the same was as fats
Water soluble vitanins
B C and Folic acid
How do water soluble vitamins get into the intestinal cells?
Passive diffusion or carrier mediated transport
