Digestion of Fats, vits, mins Flashcards
How is the majority of water absorbed in the GIT?
Passive diffusion through the tight junction following the osmotic Na gdt
What does lipase act on?
The outside of a lipid droplet
How can lipase be made more efficient?
Reducing the size of lipid droplets
What is the effect of pancreatic lipase on TAGs?
TAG -> monoglyceride + 2 FAs
Is lipase water or fat soluble?
Water soluble
would be useless if soluble in fat
What is emulsification?
Large water droplets divided into smaller droplets (1mm) increasing its surface area
What are the requirements of emulsification?
Mechanical disruption
Emulsifying agent
How does mechanical disruption occur for gastric emulsification?
Smooth muscle contraction grinding/mixing lumenal contents
What are the emulsifying agents present in the gastric secretions?
Bile Salts
Phospholipids
What is the charge of emulsifying agents?
Amphiphatic (polar and non-polar portions)
What is the orientation of amphiphatic poles in fat droplets?
Non-polar side in the fat phase, polar in the water phase (makes it soluble)
What is the function of micelles?
Speed up the fat digestion process moreso that small droplets of fat
Carry FAs to the brush border membrane
How is the reformation of large fat droplets prevented?
Polar portions of the amphiphatic molecules repel the polar portions on others
Is the micelle absorbed?
No - the micelle is just a transportER
What are the components of a micelle?
Bile Salt
Phospholipids
Monoglycerides
Fatty acids
What is the effect of the acidic microclimate on micelles?
The FAs become proteinated, destabilising the micelle causing it to release them for diffusion across the membrane
Are all FAs/MGs released at once?
No, some stored to contantly replenish free molecules
Where do FAs/MGs go after entering the cell?
Smooth Endoplasmic Reticulum
What does the sER do with FAs/MGs?
Reform into Triacylglycerols, then covered in an amphiphatic protein (emulsified)
What happens with the TAG droplets?
Packaged into vesicles on sER membrane, processed by Golgi and exocytosed
Where are TAG vesicles exocytosed into the extracellular fluid?
Serosal membrane
What are extracellular fat droplets called?
Chylomicrons
What do Chylomicrons contain? How large are they?
TAGs PPLs Cholesterol Fat-soluble vitamins 1um diameter
Where are Chylomicrons sent?
Passed into lacteals
What are lacteals?
Small lymphatic branches between endothelial cells
What are the fat soluble vitamins?
A
D
E
K
What are the water soluble vitamins?
B group
C
Folic acid
How are water soluble vitamins absorbed?
Passive diffusion
Carrier mediated transport
Why is Vit B12 not passively absorbed?
Large charged molecule
How is B12 absorbed?
Binds to Intrinsic Factor in stomach
Absorbed by transport mechanism in Ileum
What is the name given to B12 deficiency?
Pernicious anaemia (RBC don't mature)
How much iron is absorbed in the intestine?
10%
What protein is used to transport iron across the brush border membrane?
DMT1
Protein coupled
Where is iron transported to?
Duodenal enterocytes
How is iron bound in the cell?
Ferritin
What happens to unbound iron?
Transported across the serosal membrane
Stored as transferrin in the blood
What is the ferritin expression in Hyperaemia?
Increased ferritin levels, more iron bound in the cells
What is the ferritin expression in anaemia?
Decreased ferritin levels, less iron bound in cells, more in blood
What is the risk of having free iron in the cell/blood?
Formation of oxygen free radicals
