Nutrient digestion and absorption 2 Flashcards
(27 cards)
What form is almost all ingested fat in?
Triacyglycerol
What is fat digestion in the small intestine carried out by?
Pancreatic lipases
What is triacyglycerol broken down into?
Monoglyceride + 2 fatty acid
What is emulsification?
Dividing large lipid droplets into smaller droplets
This increases surface area and accessibility to lipase action
What does emulsification require?
Mechanical distruption of large lipid droplets into small droplets
Emulsifying agent
Smooth muscle contraction grinds and mixes lumenal contents
Bile salts + phospholipids
Amphipathic molecules
What does an emulsifying agent do?
It prevents small droplets reforming into large droplets
What does polar portions repelling other small lipid droplets do?
Prevents reforming into large droplets
How is absorption of lipase digestion products enhanced?
By formation of micelles
What is a micelle composed of?
Micelle = bile salt + monoglycerides + fatty acids + phospholipids
What parts of the micelle are polar and non-polar?
Polar portions of molecules at micelle surface
Non-polar portions of molecules form micelle core
What does micelle breakdown cause?
Release of small amounts of free fatty acids and monoglycerides into solution
- causing diffusion across plasma membrane of absorbing cells
Are micelles themselves absorbed?
NO
Where do fatty acids and monoglycerides go after entering epithelial cells?
They enter smooth endoplasmic reticulum (sER) where they are reformed into triacylglycerols
What do chylomicrons pass into between endothelial cells?
They pass into lacteals between endothelial cells
- They cannot pass through capillary basement membrane
What is used to break down fat droplets?
Bile salts
Phospholipids
Pancreatic lipases
What happens to free molecules of fatty acids and monoglycerides?
They diffuse across the epithelial cell
Then triacylglycerol synthetic enzymes in ER form droplets of triacylglycerol enclosed by membrane from the ER
Then it forms a chylomicron
What are the 2 classes of vitamins?
Fat-soluble vitamins
Water-soluble vitamins
What are the fat-soluble vitamins?
A D E K
- Follow same absorptive path as fat
What are the water-soluble vitamins?
B group, C and folic acid
- They are absorbed by passive diffusion or carrier-mediated transport
What is vitamin B12?
Large charged molecule
Binds to intrinsic factor in stomach to form complex which is absorbed via specific transport mechanism in distal ileum
What does vitamin B12 deficiency result in?
Pernicious anaemia
failure of red blood cell maturation
What percentage of daily ingested iron is absorbed across intestine into the blood?
10%
How does iron transport across brush border membrane into duodenal enterocytes?
Via DMT1
What are iron ions incorporated into?
Ferritin
