Nutrient Digestion and Absorption of Fats and Vitamins Flashcards
What form does almost all ingested fat take?
- triacylglycerol
Which enzyme breaks down fats in the small intestine?
- pancreatic lipase
What is triacylglycerol initially broken down into?
- monoglyceride
- two fatty acids
True or False.
Lipase can only act on the polar end of the triacylglycerol molecule.
True.
- this is because lipase is also a polar molecule.
How does the body overcome the very slow process of digestion with lipase?
- the addition of emulsifiers
What does action by emulsifiers require?
- mechanical disruption
- emulsifying agents
Why is mechanical disruption important?
- breaks down large lipid droplets into smaller droplets
- this increases the surface area available for reaction
How is mechanical disruption achieved?
- smooth muscle contracts to grind and mix the luminal contents
Why is the addition of emulsifying agents important?
- prevents the smaller droplets from reforming larger droplets
- they are amphipathic, allowing fat and water to mix, and repelling other lipid molecules
What is the function of micelles?
- they act as a ‘fat-taxi’, transporting fat
- they are smaller and therefore can get closer to the microvilli
How do the micelles come into contact with the microvilli?
- they undergo a randomised introduction process
- they eventually reach the acid microclimate which pulls them closer
What happens when the micelles meet the microvilli?
- they break down, releasing small amounts of free fatty acids and monoglycerides into solution
- these then diffuse across the plasma membrane into absorbing cells
True or False.
Micelles themselves are absorbed.
False.
Micelles themselves are NOT absorbed.
What happens to fatty acids and monoglycerides upon entering the cell?
- they enter the sER
- here, they are reformed into triacylglycerols by enzymes, also located in the sER
What happens to triacylglycerols after they are reformed in the sER?
- they are emulsified by coating them with an amphipathic protein
- they are then transported through the cell in vesicles
- they are processed through the Golgi apparatus
- they are then exocytosed into the extracellular fluid at the serosal membrane
- the droplets are now termed chylomicrons
What happens to chylomicrons?
- they pass into lacteals between endothelial cells
Name some fat-soluble vitamins.
Vitamins A, D, E, K
The follow the same absorptive path as fats.
Name some water-soluble vitamins.
Vitamin B group, vitamin C and folic acid
How are water-soluble vitamins absorbed?
Either via passive diffusion or carrier-mediated transport.
Describe vitamin B12.
It is a large, charged molecule.
How is vitamin B12 absorbed?
- it binds to intrinsic factor, which is secreted by the stomach
- together they form a complex
- the complex is then absorbed via specific transport mechanism found in the distal ileum
How much B12 does the liver store?
- around three years worth
What can a B12 deficiency lead to?
- pernicious anaemia (the failure of red blood cell maturation)
True or False.
Around 10% of daily ingested iron is absorbed from the intestines into the blood.
True.
Why is it important for the body to store iron effectively?
- it is highly reactive
- it may rust within the body creating free radicals
How does the body deal with iron?
- iron is absorbed in the duodenum
- it is transported across the brush border membrane by divalent metal transporter 1 (DMT1)
- iron ions are then lead into cage-type structures called ferritin
- the ferritin will eventually be sent out in the faeces.
How often does the entire surface of the small intestine replenish?
- every five days
What happens to iron present in the blood?
- it binds to transferrin
If someone is anaemic, what happens to their ferritin?
- the body will stop releasing ferritin, therefore more iron will be present in the blood
If someone is hyperanaemic, what happens to their ferritin?
- the body will release increased levels of ferritin, therefore there will be less iron present in the blood
