Nutrition and Digestion (FATS + VITAMINS + MINERALS) Flashcards
what form does dietary fat usually take
triglycerides (triacylglycerol)
What form do triglycerides have
glycerol backbone with 3 stearic (fatty) acid chains
what digests fat in the small intestine
pancreatic lipase
how do triglycerols present in water
large lipid droplets - insoluble in water
what kind of enzyme of lipase
water soluble - digestion can only take place at the surface of the lipid droplet so very slow
emulsification definition
dividing large lipid droplets into smaller droplets
how does emulsification help with digestion of lipids
by making the droplets smaller the surface area on which lipase can act is increased
three steps to emulsification
- mechanical disruption - large droplets to small droplets
- smooth muscle contraction grinds and mixes lumens content
- emulsifying agents present - prevent small droplets reforming large droplets
how do emulsifying agents work
they are amphipathic molecules (i.e. have polar and non-polar portions)
- Polar (charged) surfaces so repel each other and stop reaggregation
- non-polar portions associate with non-polar interior interior
emulsifying agents
bile salts and phospholipids secreted in bile
Aside from emulsification, what else helps speed up absorption of lipids
micelles - similar to emulsion droplets but smaller
what makes up a micelle
bile salt + monoglycerides + fatty acids + phospholipids
where are the polar and non-polar portions of micelles
polar - at micelle surface
non-polar - form micelle core
*Micelles never enter cells
How do micelles breakdown
- in low pH layer there is an acid microclimate at cell surface
- causes them to take on H ions - become uncharged
- small amounts of free fatty acids (FFA) and monoglycerides released into solution
- FFA diffuse across the the membrane into the cells
where do fatty acids and monoglycerides go when they enter epithelial cells and what happens there
go to the smooth ER
reformed into triacylglycerols (by enzymes in sER)
what happens during emulsification of triacylglyceril
triacylglycerol coated with amphiphatic proteins
what happens after the triacylglycerol droplets have been emulsified
transported through cell in vesicles formed from sER membrane - processed through Golgi apparatus and exocytosed into extracellular fluid at serosal membrane
what are the extracellular fat droplets known as
chylomicrons (also contain phospholipids, cholesterol and fat soluble vitamins)
where do chylomicrons pass through
pass into lacteals between endothelial cells (cannot pass through capillary basement membrane)
what are the 2 classes of vitamins
fat soluble
water soluble
what are fat soluble vitamins and how are they absorbed
A, D, E, K - follow the same absorptive path as fat
what are water soluble vitamins and how are they absorbed
B group, C, folic acid - either absorbed by passive diffusion or carrier-mediated transport.
how is B12 (a large charged molecule) absorbed
Binds to intrinsic factor in stomach to form complex which is absorbed via specific transport mechanism in distal ileum
what can B12 deficiency lead to
pernicious anaemia
failure of red blood cell maturation
where and how is iron absorbed into the blood
across the intestine - transported across brush border membrane into duodenal enterocytes via DMT1 (divalent metal transporter 1)
what happens to iron ions once in the duodenal enterocytes
incorporated into ferritin (protein-iron complex intracellular iron store) - becomes BOUND
what happens to unbound iron
transported across serosal membrane into blood - here it binds to transferrin
what regulates ferritin expression in the body
the body’s iron status
what does hyperaemia cause
increased ferritin levels - more iron bound in enterocytes
what does anaemia cause
decreased ferritin levels - more iron released to blood
when iron reacts with oxygen what is formed
free radicals which are bad for the body
how does the body get around the formation of free radicals
reduces them from Fe3+ to Fe2+
Fe2+ is held in ferritin - prevents it from reacting with oxygen - once in it cannot get out
what happens to faeces if there is more iron in them
get much darker
