Nutrient Digestion 2 (Fats, Vitamins and Minerals) Flashcards
What is the function of Lipase?
Conversion of ingested fat (in the form of triacylglycerol) to Monoglyceride and 2 FAs
Why does Lipase digest fats very slowly?
Because it is a water-soluble enzyme and therefore can only digest at the surface of the molecule
What is the purpose of Emulsification of fats?
▷Divides large lipid droplets into smaller droplets
▷This increases the surface area and allows the water-soluble Lipase to effectively break down lipid molecules quicker
How are fats emulsified?
▷Via Bile salts and Phospholipids secreted in Bile
▷Amphipathic molecules -> non-polar portion dissolves inside the lipid molecule and the polar heads exposed at the water surface -> polar heads repel the polar heads of other emulsified lipid droplets -> prevent reformation into large lipid droplets
What is the function of Micelles?
▷Smaller emulsion droplets formed from the breakdown products of lipid digestion (bile salts + phospholipids + monoglycerides + FAs)
▷Amphipathic molecules (polar + non-polar portions)
▷Responsible for retaining the products of Lipid digestion in solution, while constantly replenishing supply of free molecules for absorption -> Dynamic equilibrium between FFAs and Monoglycerides in solution and in Micelles
How are Monoglycerides + FFAs released from Enterocytes into the Lymphatic System?
▷After entering Enterocytes: reformed into Triacylglycerols in the sER
▷In sER: coated with amphipathic protein, and packaged into vesicles made from sER membrane -> cholesterol and fat-soluble vitamins added to form Chylomicrons
▷In Golgi apparatus: Chylomycrons are processed into secretory vesicles and exocytosed into ECF from basolateral membrane
▷From ECF: Chylomicrons pass into Lacteals
(NB. too big to pass through capillary BM)
What are the fat-soluble vitamins, and how are they absorbed?
▷Vitamins A, D, E and K
▷Absorbed via the same Absorptive pathway as Fat
What are the water-soluble vitamins?
▷B- Group
▷C
▷Folic Acid
How is Vitamin B12 absorbed?
▷Requires Intrinsic Factor which is secreted by Parietal cells in the Stomach
▷Vit B12 forms a complex with IF and they are both absorbed at the Distal/Terminal Ileum
What is Pernicious Anaemia and why is it “pernicious”?
▷Failure of maturation of RBCs due to Vit B12 deficiency
▷It is “pernicious” bc it takes a while to develop as your Liver contains a large store of Vit B12 (about 3 years worth), so symptoms develop gradually over time
Where and how is Iron absorbed into enterocytes?
▷Via DMT1 into the Duodenum
NB. Iron is a MINERAL not a vitamin!
What is the difference between Ferritin and Transferrin?
▷Ferritin: intracellular store of iron
▷Transferrin: main iron transporting protein in the bloodstream -> binds unbound iron which has been released from ferritin inside cells
What would happen to Transferrin and Ferritin levels during Iron-deficiency Anaemia?
▷Ferritin: levels would decrease -> bc ferritin is expressed depending on the body’s iron status (iron deficiency = low ferritin, hyperaemia = increased ferritin)
▷Transferrin: levels would increase -> bc in iron-deficiency, ferritin would release more iron into the bloodstream (ie. more “unbound” iron), necessitating increased transferrin levels!
