6.10- ABSORPTION OF THE PRODUCTS OF DIGESTION Flashcards
What function is the ileum adapted for?
absorbing products of digestion
What is done to the wall of the ileum?
wall of ileum folded
What does the walls of the ileum possess?
finger-like projections, about 1mm long, called villi
What are the walls of the ileum like?
thin walls, lined with epithelial cells on outer side of which is rich network of blood capillaries
What do the villi do?
considerably increase SA of ileum + so accelerate rate of absorption
Where are the villi situated?
at interface between lumen of intestines + blood and other tissues inside body
What are the villi part of?
specialised exchange surface adapted for absorption of products of digestion
What properties does the villi have to increase efficiency of absorption? (5)
increase SA for diffusion very thin walled contain muscle so able to move well supplied with blood vessels epithelial cells lining villi possess microvilli
How does the villi being thin walled increase efficiency of absorption?
reduce distance over which diffusion happens
How does the villi containing muscle + so able to move increase efficiency of absorption?
helps maintain diffusion gradients as their movement mixes contents of ileum
this ensures that, as products of digestion absorbed from food adjacent to villi, new material rich in products of digestion replace it
How does the villi being well supplied with blood vessels increase efficiency of absorption?
so blood carry away absorbed molecules + hence maintain diffusion gradient
How does the epithelial cells lining the villi possessing microvilli increase efficiency of absorption?
further increase SA for absorption
What does the digestion of proteins produce?
amino acids
What does the digestion of carbohydrates produce?
monosaccharides i.e. glucose, fructose + galactose
What are the methods of absorbing amino acids + monosaccharides?
diffusion + co-transport
What do monoglycerides and fatty acids remaining doing after being formed in digestion?
remain in association with bile salts that initially emulsified the lipid droplets
What are the structures of the monoglycerides and fatty in association with the bile salts called?
micelles
What is the size of a micelle?
tiny, being around 4-7nm in diameter
How do the micelles come into contact with the epithelial cells lining the villi of the ileum? (absorption of triglycerides)
through movement of material within lumen of ileum
What happens to the micelles when in contact with the epithelial cells lining the villi of the ileum? (absorption of triglycerides)
micelles break down, releasing monoglycerides + fatty acids
Why do the monoglycerides + fatty acids easily diffuse across the cell-surface membrane into the epithelial cells? (absorption of triglycerides)
non-polar molecules
What happens to the monoglycerides + fatty acids once inside the epithelial cells? (absorption of triglycerides)
monoglycerides + fatty acids transported to ER where they’re recombined to form triglycerides
Where do the triglycerides go to from the ER and what do they do? (absorption of triglycerides)
continue into Golgi apparatus, triglycerides associate with cholesterol + lipoproteins
What is it called when the triglycerides associate with cholesterol + lipoproteins in the Golgi apparatus? (absorption of triglycerides)
chylomicrons
What are chylomicrons? (absorption of triglycerides)
special particles adapted for transport of lipids
How do chylomicrons move out of the epithelial cells? (absorption of triglycerides)
by exocytosis
Where do the chylomicrons enter from the epithelial cells? (absorption of triglycerides)
lymphatic capillaries called lacteals found at the centre of each villus
Where do the chylomicrons pass to from the lacteals? (absorption of triglycerides)
pass via lymphatic vessels + into blood system
What happens to the triglycerides in the chylomicrons? (absorption of triglycerides)
hydrolysed by enzyme in endothelial cells of blood capillaries from where they diffuse into cells
