Ions, vitamins and minerals Flashcards
What are some examples of primary active transporters?
Na/K ATPase
H/K ATPase
What are some examples of secondary active transporters?
SGLT-1 - uses Na gradient to take up glucose
HCO3-/Cl- counter-transport
Na+/H+ counter transport
What are some examples of facilitated transport/diffusion?
GLUT-5 -
GLUT-2
Where does the greatest amount of water get absorbed?
Jejunum Small intestine absorbs 8 lirtes - saliva - gastric secretions - pancreas - bile - water - intestine
how is water abosrobed?
Standing gradient osmosis
the absorption of water is powered by absorption of ions
Na+ —-
It is then pumped out of the cells that it is in in exchange for K+ and this creates a high conc of Na+ near basement membrane. electrochem grad changes so Cl- and HCO3- move out as well, drives H2O absorption via both para and transcellular paths
How is Na+ absorbed?
- counter transport with H+ bowel
- cotransport with monosac - jej Cl- - ileum
- ion channel colon
How are K+ and Cl- absorbed?
K+ diffuses via paracellular pathways - small intestine transcellular in colon Cl- cotransport with na+ in the ileum Exchanged for HCO3 in the colon
Where is calcium absorbed? What increases it?
In the duodenum and ileum
deficiency increases ability to absorb
PTH and Vit D increase absorption
How is calcium absorbed?
Intestinal calcium-binding protein
- fac diff
Ion channel
Why is ca2+ low in the cell? how is Ca2+ brought in while maintaining this low conc? how is it then pumped into the blood?
Acts as a signalling molecule
- Constant intake might cause loops of secondary messenger
calcium is bound to CALBINDIN to prevent action as intracellular signal and then moved into blood
Has to be pumped as against concentration gradient
- plasma membrane Ca ATPase
- High affinity but sklow but lowers conc in cell
- Na/Ca exchanger
- Low affinity, needs lots of Ca but v fast
Why is Vit D needed for Ca uptake?
Enhances transport of Ca2+ thru cytosol
Increases calbindin levels
Increases rate of extrusion on BM - increases levels of PMCA
Why is iron absorbed??
Needed as is e- donor, acceptor
Ox transport
Ox phos
but, is toxic in excess and no active excretion mechanism
- so, mediate it
How is iron present in the diet?
inorganic iron, haem group - Hb etc
Why must Ffe2+ be absorbed?
Fe3+ has to be reduced to Fe2+ because body can’t absorb Fe3+
This is done by Vit C
What does Fe3+ form
Insoluble salts with OH, Po4 and HCO3
How is haem absorbed?
Absorbed through haem carrier protein and endocytosis
Kept intact
Fe2+ is then liberated by haem oxygenase
how can Fe3+ be utilised by ce;l;
Duodenal cytochrome b catalyses formation of Fe2+ from Fe3+
Fe2+ is then transported by divalent metal transporter 1 -DMT-1, a H+ co transporter
Fe2+ binds to factors, moves to BM and moves into blood via FERROPORTIN channel
How is iron carried in the blood?
Reforms Fe3+ via Hephaestin
Fe3+ binds to apotransferrin, now in blood as transferrin
Regulated by hepcidin
- suppresses ability to pump fe2+ out into blood by ferroportin
What might occur if iron is not required in the blood?
immobilised in cytosol by binding to apoferritin
Fe2+ gets oxidised, and then this complex is ferritin - forms crystallised micelle
this prevents too much absorption which would be toxic
- irreversible
- iron not available for blood
- then gets lost in the lumen, excreted as faeces
stimulated by increased cytosolic iron concentration
What is a vitamin?
ORGANIC MOLECULE THAT CANNOT BE MADE BY BODY
How are vitamins taken up?
Passive diffusion
ADEK - brush border micelle - fat soluble
K - active transport
C, folic acid, B1, B12 by specific mechanisms
Where is B12 stored andwhat are the problems if low
Liver, retards blood cell maturation
When is it released? Describe its journey
Low pH and digestion of proteins but gets denatured by HCl - Prevented by binding to R protein - haptocorrin - released by parietal cells - broken down in duodenum
- B12 is then bound to intrinsic factor, recognised by Cubilin and stopped from being digested
- Then taken up into ileum after binding to cubilin receptor
- endocytosis
- This complex is then broken down inside and B12 binds to TRANSCOBALAMIN II, crosses BM
- Then it travels to liver in blood where it is taken up after binding to TCII receptor
- Proteolysis breaks TCII down in liver