Ions, vitamins and minerals

Question 1

What are some examples of primary active transporters?

Answer 1

Na/K ATPase

H/K ATPase

Question 2

What are some examples of secondary active transporters?

Answer 2

SGLT-1 - uses Na gradient to take up glucose
HCO3-/Cl- counter-transport
Na+/H+ counter transport

Question 3

What are some examples of facilitated transport/diffusion?

Answer 3

GLUT-5 -

GLUT-2

Question 4

Where does the greatest amount of water get absorbed?

Answer 4

Jejunum
Small intestine absorbs 8 lirtes
- saliva
- gastric secretions
- pancreas
- bile
- water
- intestine

Question 5

how is water abosrobed?

Answer 5

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

Question 6

How is Na+ absorbed?

Answer 6

• counter transport with H+ bowel
• cotransport with monosac - jej Cl- - ileum
• ion channel colon

Question 7

How are K+ and Cl- absorbed?

Answer 7

K+
diffuses via paracellular pathways - small intestine
transcellular in colon
Cl-
cotransport with na+ in the ileum
Exchanged for HCO3 in the colon

Question 8

Where is calcium absorbed? What increases it?

Answer 8

In the duodenum and ileum
deficiency increases ability to absorb
PTH and Vit D increase absorption

Question 9

How is calcium absorbed?

Answer 9

Intestinal calcium-binding protein
- fac diff

Ion channel

Question 10

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?

Answer 10

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

Question 11

Why is Vit D needed for Ca uptake?

Answer 11

Enhances transport of Ca2+ thru cytosol
Increases calbindin levels
Increases rate of extrusion on BM - increases levels of PMCA

Question 12

Why is iron absorbed??

Answer 12

Needed as is e- donor, acceptor
Ox transport
Ox phos

but, is toxic in excess and no active excretion mechanism
- so, mediate it

Question 13

How is iron present in the diet?

Answer 13

inorganic iron, haem group - Hb etc

Question 14

Why must Ffe2+ be absorbed?

Answer 14

Fe3+ has to be reduced to Fe2+ because body can’t absorb Fe3+

This is done by Vit C

Question 15

What does Fe3+ form

Answer 15

Insoluble salts with OH, Po4 and HCO3

Question 16

How is haem absorbed?

Answer 16

Absorbed through haem carrier protein and endocytosis
Kept intact

Fe2+ is then liberated by haem oxygenase

Question 17

how can Fe3+ be utilised by ce;l;

Answer 17

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

Question 18

How is iron carried in the blood?

Answer 18

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

Question 19

What might occur if iron is not required in the blood?

Answer 19

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

Question 20

What is a vitamin?

Answer 20

ORGANIC MOLECULE THAT CANNOT BE MADE BY BODY

Question 21

How are vitamins taken up?

Answer 21

Passive diffusion
ADEK - brush border micelle - fat soluble
K - active transport

C, folic acid, B1, B12 by specific mechanisms

Question 22

Where is B12 stored andwhat are the problems if low

Answer 22

Liver, retards blood cell maturation

Question 23

When is it released? Describe its journey

Answer 23

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