Flashcards in Intestinal Absorption and Secretion Deck (65):
how many litres is the dietary intake?
what is the internal secretion formed of and the proportions?
saliva - 1.5L
gastric juice - 3L
pancreatic juice - 2L
bile - 0.5L
how many litres is the internal secretion in total?
how many litres is the faecal loss?
how many grams of NaCl have to be retrieved?
7L x 9g/L = 63 g of NaCl
are there villi in the colon?
no - just deep pits
500mL presented and 300mL recovered
what do crypt cells produce?
cells that migrate along villi in 48 hours
when can cells absorb?
when they mature
are tip cells mature?
yes - they can absorb
what do individual cells on villus have?
brush border with enzymes
what is present in the enterocytes
lateral spaces and tight junctions
how are the tight junctions at the top of the small intestine (jejunum)
how are the tight junctions at the bottom end of the small intestine (ileum)
what do tight junctions allow?
permeability - fluid can enter the cell
how much does the surface area expands from simple cylinder
how much do the folds of kerckring increase the surface area?
how much do the villi increase the surface area?
how much do the microvilli increase the surface area?
how does this influence absorption
it is assumed to enhance absorption - it may be more for a surface for brush border enzymes
what does hydrostatic pressure do?
aid or prevent fluid absorption
is there net absorption when pressure is zero?
how does the luminal pressure affect the blood pressure
if the luminal pressure increases so does the blood pressure
how does the luminal suction pressure affect the fluid absorption
it decreases the absorption rate
what does the "standing gradient" explain?
the absorption at zero net pressure - NaCl is pumped into the lateral spaces
how many stages are there in the standing gradient
how does the first stage of the standing gradient work
an increase in the osmotic pressure in the lateral spaces pulls fluid in through paracellular and transcellular routes
what happens in the second stage of the standing gradient
an increase in the lateral space hydrostatic pressure pushes fluid into the interstitial space and from there into the capillaries
what does the biochemical engine for sodium ion transport consist of?
a serial membrane sited Na/K ATPase pump that pumps sodium ion out of the cell and takes K ion in
how is the concentration of sodium within the cell
it is lowered
why does the sodium ion diffuses in
because of a diffusion gradient for sodium ion
what makes the absorbate close to plasma values
water dilution and lateral space hypertonicity
where does some leakage of Na+ into lumen happen
in tight junctions
where is the sodium ion from the sodium leakages recycled?
in the jejunum
how effective is the absorption of the recycled sodium in the jejunum?
what makes the water absorption more effective in the ileum
the tight junctions are tight
what is linked to the sodium ion gradient
the time it takes the solutes to be absorbed
what does a sodium ion-glucose transporter (SGLT1) pulls in the brush border membrane?
a glucose molecule actively into the cell
how does the glucose exits the cell?
passively via GLUT2
what can glucose force sodium to do?
it can force sodium ion entry
what is also absorbed by the route
many amino acids
what makes the transporter PEPT pull peptides into the cell?
the proton gradient - pH outside the cell is pH6 through Na/H but inside is pH7.4
what kind of ions also facilitate fatty acid absorption?
hydrogen ions - sp3 main foodstuffs absorbed by gradients in ions
what does sodium ion gradient energises?
sugar and some amino acid absorption
what does hydrogen ion gradient energises
peptides and some amino acid absorption
how do fats converted to fatty acids enter the cell?
by associating with H+ ions - protonating
what type of transport do some essential minerals undergo
what type of transport do most essential vitamins undergo if they are nor fat soluble
undergo active transport
how much liquid can be secreted in an hour by a person infected with cholera?
1L per hour
what type of infection is cholera
what occurs in cholera?
intestinal secretion form the villus cells (enyerocytes) enhanced by enterotoxins
what is the normal secretion value per day accepted after 1971
1500mls per day -- without proof
what is the fluid circuit hypothesis
separation of secretion and absorption
which is the new requirement for new biochemical apparatus
chloride to be transported towards the lumen with Na+ passively following
what does NKCC1 do
it is a co-transporter and powers Cl- entry into the cell down the sodium ion gradient
what does CTFR protein do?
allows Cl- out into the lumen
what is the net effect
Cl- is propelled towards the lumen
what does the cholera toxin do?
enhance the propulsion of Cl- towards the lumen and heat stable STa enterotoxin
what attaches to intestinal receptors?
STa and cholera toxin (CT)
how does STa cause Cl secretion
via cGMP guanylate cyclase
how does CT cause Cl secretion
via cAMP adenylate cyclase
how does STa influence fluid absorption
it reduces it
what should the chloride channel blockers do if the secretion by Cl- channel blockers is ocurring
the chloride blockers should restore fluid absorption - but they don't
what does vibrio cholera promote?
the production of large amounts of VIP, a neurotransmitter vasoactive intestinal polypeptide), and Bona Occludens Toxin (ZOT)
what is the function of ZOT
keep lateral spaces open