Nutrient digestion and absorption 2 Flashcards
in what form is almost all fat ingested
triacylglycerol
where does all fat digestion take place
small intestine
what enzyme is responsible for digestion of fats in the small intestine
pancreatic lipase
what do triacylglycerols present as
large lipid droplets which are insoluble
what is a water soluble enzyme
lipase
where is the only place digestion can take place for a droplet
on the surface
slow process
when triacylglycerol is digested by lipase what is formed
monoglyceride and 2 fatty acids
what do bile salts act as
emulsifiers or surfactants
emulsification
ividing large lipid droplets into smaller droplets (~1 mm diameter) ⇒ increased surface area and accessibility to lipase action.
what does emulsification require
Mechanical disruption of large lipid droplets into small droplets.
Emulsifying agent - prevents small droplets reforming into large droplets.
mechanical disruptor
Smooth muscle contraction grinds and mixes lumen contents.
Emulsifying agent
Amphiphatic molecules (ie polar (charged) and non-polar portions)
where is bile released
duodenum
what prevents fats reforming into large droplets
Polar portions repel other small lipid droplets (also coated with bile salts/phospholipids) ⇒ prevent reforming into large droplets
what can enhance absorption of lipid digestion
formation of micelles
what are micelles
similar to emulsion droplets but much smaller
Micelle = bile salt + monoglycerides + fatty acids + phospholipids
what makes up a micelle surface
polar portions (bile salts)
what makes up a micelle core
non polar portions
Micelle breakdown
release of small amounts of free fatty acids (FFA) and monoglycerides into solution
then diffuse acriss plasma membrane of absorbing cells
Dynamic equilibrium
between fatty acids and monoglycerides in solution and in micelles - retains most of fat digestion products in solution while constantly replenishing supply of free molecules for absorption.
what does the ER contain
triacylglycerol synthetic enzymes
what is released from basolateral membrane of epithelial cells
chylomicron
chylomicron
Chylomicrons are composed of a main central lipid core that consists primarily of triglycerides, however like other lipoproteins, they carry esterified cholesterol and phospholipids
doesnt absorb through blood, to move in blood they must go in certain forms eg low density lipoprotein or HDL
what happens after entering epithelial cells
fatty acids and monoglycerides enter smooth endoplasmic reticulum (sER) where they are reformed into triacylglycerols (by enzymes located within the sER)
what happens inside the epithelial cell
Triacylglycerol droplets coated with amphiphatic protein (inside the cells) ⇒ emulsification
how are Triacylglycerol droplets transported through cell
in vesicles formed from sER membrane
what happens after Triacylglycerol droplets are transported through vesciles
processed through Golgi apparatus and exocytosed into extracellular fluid at serosal membrane (basolateral membrane)
how are chylomicrons transported
pass into lacteals between endothelial cells (cannot pass through capillary basement membrane)
what are the two classes of vitamins
Fat-soluble vitamins: A, D, E, K
Water-soluble vitamins: B group, C and folic acid
how are fat soluble vitamins absorbed
Follow same absorptive path as fat
how are water soluble vitamins absorbed
Either absorbed by passive diffusion or carrier-mediated transport.
how is vitamin B12 absorbed
Binds to intrinsic factor in stomach to form complex which is absorbed via specific transport mechanism in distal ileum.
what is vitamin B12 deficiency known as
pernicious anaemia
pernicious anaemia
(failure of red blood cell maturation)
Pernicious
delayed / harmful effect / comes over different stages / happens over time - can take 3 years to have symptoms - failure of red blood cell to mature hard for blood cells to carry O2
how much of daily ingested iron is absorbed
10% the rest in faeces
how is iron transported
across brush border membrane (via DMT1) into duodenal enterocytes
what are iron ions incorporated into
ferritin (protein-iron complex ⇒ intracellular iron store)
what does unbound iron after transporting across serosal membrane bind to
transferrin
hyperaemia
too much iron in blood
increased ferritin levels ⇒ more iron stored and bound in enterocytes
anaemia
⇒ decreased ferritin levels ⇒ more iron released to blood
why is unbound iron harmful
Free iron is iron that is not bound; it is the most dangerous kind of iron because free iron can cause oxidative damage to organs, nourish harmful bacteria, change DNA or help to spread cancer.
