Ions Minerals And Vitamins

Question 1

What 4 ways does Na+ enter enterocytes?

Answer 1

Proximal bowel = against h+
Jejunum = with amino acids
Ileum = with cl-
Colon = facilitated diffusion

Question 2

How does Na+ enter the blood?

Answer 2

Na+/k+ ATPase

Question 3

How is calcium reabsorbed?

Answer 3

Ca2+ binds to IMcal
Enters cell
Binds to calbindin
Either leaves by:
- pmca 
- Na+/ca2+ exchanger high capacity but low affinity

Question 4

Where is calcium most absorbed?

Answer 4

Ileum and duodenum

Question 5

How is iron absorbed?

Answer 5

As haem
Binds to hcp1 
Endocytosis 
Binds to haemoxygenase 
Releases fe2+

Duodenal cytochrome b convert fe3+ to fe2+
Enters by divalent metal transporter against h+

Question 6

How is fe2+ released into the blood?

Answer 6

Fe2+ forms ferric
Enters blood by ferroportin 
Hephaestin converts fe2+ to fe3+
Fe3+ binds to apotransferrin 
Travel in blood as transferrin 

WHEN THER IS TOO MUCH
Binds to apoferrin to form ferritin
Fe2+ to fe3+ and crystallises

Question 7

How is vit b12 released?

Answer 7

Stomach acid releases it from proteins
Binds to R protein as b12 can be broken down by stomach acid as well
R protein broken down in duodenum

Question 8

How is b12 absorbed?

Answer 8

Binds to intrinsic factors 
Then binds to cubulin in ileum 
Endocytosis
Complex broken down by mitochondria 
B12 binds to trans cobalamin 
Goes to liver