Nutrient Digestion and Absorption 2 Flashcards
What is the form of almost all the ingested fat?
Triacylglycerol
Where does all fat digestion take place?
In the small intestine
Which enzyme is involved with fat digestion in the small intestine?
Pancreatic lipase
What does lipase break triacylglycerol down into?
Monoglyceride + 2 fatty acids
Are triacylglycerol’s insoluble or soluble in water?
Insoluble
Is lipase a water soluble or insoluble enzyme?
Water soluble enzyme
How do triacylglycerol’s present?
As large lipid droplets
Why is it hard for lipase to completely degrade triacylglycerol?
Because it’s a water soluble enzyme and triacylglycerol is insoluble.
Why is the digestion of fat a slow process?
Lipase can only act on the surface of a lipid droplet as it’s lipid insoluble and water soluble
What helps to turn a large fat globule into smaller fat globules to make it easier to be broken down?
Bile salts
Where is bile synthesised?
In hepatocytes in the liver
Why do bile salts act as an emulsifier?
They have a hydrophilic and a hydrophobic part
Describe the orientation of bile slats and their hydrophobic and hydrophilic parts when they are attached to a fat globule.
Hydrophobic part of bile slat will be facing inward and the hydrophilic part will be facing outwards
What does emulsification mean?
Dividing large fat droplets into smaller droplets
What is the benefit of emulsification?
Increases the surface area which increases accessibility for lipase action
How can mechanical disruption occur?
By contraction of the muscles in the stomach or the intestine
Why is an emulsifying agent required?
Prevents the small droplets from gathering back into a larger droplet
Give some examples of emulsifying agents
Bile salts
Phospholipids
RECAP- what does amphipathic mean?
A molecule has a hydrophobic and hydrophilic part (or polar and non-polar)
Are hydrophilic substances polar or non-polar?
Polar
Are hydrophobic substances polar or non-polar?
Non-polar
How do emulsifying agents prevent smaller droplets from joining together?
The polar or hydrophilic outer layer is not attracted to the other small lipid droplets
Absorption can be enhanced by the formation of what?
Micelles
Are micelles smaller or larger than emulsion droplets?
Smaller
What are micelles composed of?
Bile salts + phospholipids + monoglycerides + fatty acids
In a micelle, which part of the molecule would be facing outwards?
Polar/hydrophilic portion
How do micelles cross the intestinal epithelial cells?
By diffusion
Name to the forms of fat in the blood.
Low density lipoprotein
High density lipoprotein
After entering epithelial cells, where do fatty acids and monoglycerides go?
Smooth endoplasmic reticulum
What happens when fatty acids and monoglycerides are in the SER?
They reformed into triacylglycerol by enzymes
What are extracellular fat droplets known as?
Chylomicrons
Chylomicrons cannot get through the capillary basement membrane so how do they get through the cells?
Go through lacteals found between endothelial cells
What is the function of lacteal?
They absorb fat and fat soluble vitamin cholesterol
What are the fat soluble vitamins?
K, E, D, A
What are the water soluble vitmains?
B, C and folic acid
How are water soluble vitamins absorbed?
By passive diffusion or carrier-mediated transport
What are fat soluble vitamins absrobed by?
Chylomicrons
Is Vitamin B12 hydrophobic or hydrophilic?
Hydrophilic
How can vitamin B12 be absorbed?
Can only be absorbed when bound to an intrinsic factor
Where are intrinsic factors synthesised?
The stomach
Where will the intrinsic factor bind to the vitamin B12?
The small intestine
Where will the vitamin B12 intrinsic factor complex be absorbed?
Distal ileum of small intestine
What will a vitamin B12 deficiency cause?
Pernicious anaemia.
How long can it take to present with symptoms of pernicious anemia?
3 years
What happens in pernicious anemia?
Failure of red blood cell maturation
Where is most of the vitamin B12 stored?
Liver
How much of the daily iron ingested is absorbed across the intestine and goes into the blood?
10%
Where does the rest of the ingested iron go?
Into faeces
How is iron transported across the brush border membrane?
Via DMT1
Where does the iron go into after getting across the brush border membrane?
Duodenal enterocytes
What are the iron ions incorporated into?
Ferritin
Why can iron not be released as a free ion and must only be released as part of a complex?
It’s highly reactive and corrosive and can damage enterocytes and the intestine
What does the iron in blood bind to?
Transferrin
What is meant by hyperaemia?
Increased ferritin levels meaning more iron is bound in enterocytes
What is meant by anaemia?
(not the condition exactly so don’t get too excited x).
Decreased ferritin levels meaning more iron is released into the blood.
What is transferrin?
A carrier of iron when it’s in the blood
