Nutrient Digestion and Absorption Flashcards
what does lactose break down into?
glucose and galactose
what does sucrose break down into?
glucose and fructose
what does maltose break down into?
2 glucose monomers
what bonds link monomers in starch and glycogen?
alpha-1,4 glycosidic bonds
what enzyme breaks down polysaccharides into disaccharides?
amylase
how does glucose enter cells in the brush border of the gut?
through sodium coupled transporter SGLT1
how does glucose leave the cell in the gut and enter the blood?
glucose accumulates in the cell, increasing the concentration to above 5mm at which point it leaves the cell down the conc. gradient through a facilitated transporter GLUT 2.
what sugar enters the blood the same way as glucose?
galactose
how does fructose enter the blood stream?
it enters the cell through GLUT-5 then leaves via GLUT-2 by facilitated transport.
how do amino acids enter the blood stream?
they enter the cell through a sodium coupled amino acid transporter. they then leave the cell through a specific amino acid transporter.
describe how peptides are taken into the bloodstream
the acid microclimate at the brush border means peptides are transported into the cell at a hydrogen ion coupled transporter. the peptides the enter the blood through facilitated transport while the h ion returns to the lumen via a sodium coupled hydrogen transporter
what enzyme breaks down triacylglycerol?
lipase
what is triacylglycerol broken down into?
monoglyceride and 2 fatty acids
define emulsification
dividing larger droplets into smaller droplets
name emulsifying agents
> bile salts
> phospholipids
what two things emulsify fats in the stomach?
> mechanical disruption
> emulsifying agents
how do the emulsifying agents prevent the small droplets of fat from reforming?
they are amphipathic, non-polar facing inwards and polar facing outwards. the polar charge repels other droplets (as they have the same charge) preventing them from reforming.
what makes up a micelle?
> bile salts
monoglyceride
fatty acid
phospholipid
what size are micelles?
> 4-7 um
describe the process of fats in micelles getting in the epithelial cells
the micelle breaks down at the membrane due to the acid microclimate which makes it uncharged so unstable. this releases small amounts of fatty acids and monoglyceride into solution which diffuses across the membrane into absorbing cells.
what happens to the fatty acids/monoglycerides when they enter the cell?
they enter the smooth endoplasmic reticulum where they are reformed into triacylglycerol by enzymes.
what is triacylglycerol coated with in the smooth endoplasmic reticulum inside the cell?
an amphipathic protein (emulsification)
what happens to the triacylglycerol after it has been emulsified in the cell?
it is transported through vesicles, processed in the Golgi apparatus and exocytosed to extracellular fluid
what are chylomicrons?
extra cellular fat droplets containing phospholipids, cholesterol and fat soluble vitamins
what do chylomicrons pass into between endothelial cells?
lacteals
what two classes of vitamins?
> fat soluble vitamins
> water soluble vitamins
how do fat soluble vitamins enter the cell?
follow the same absorption pathway as fat
how do water soluble vitamins enter the cell?
through carrier mediated diffusion
what problems occur in vitamin b12 deficiency?
pernicious anaemia: blood cells fail to mature, symptoms have a slow onset due to large stores in the liver.
how are iron ion transported into duodenal enterocytes?
via DMTI
what is ferritin?
a protein iron complex that binds iron in the cell to stop the production of harmful free radicals
what happens to unbound iron?
it is transported across the serosal membrane and binds to transferrin in the blood
what happens to ferritin?
it is shed with the intestinal cells and passed out in faeces
what does ferritin expression depend on?
the body’s iron status
does hyper anaemia have increased or decreased ferritin levels?
increased, more iron is bound in enterocytes
