Vitamin D - Calciferol

Question 1

uptake of what form in the intestines

Answer 1

all forms: vitD2+3 and provit.D2+3 - tp. in chylomicrons to the liver

Question 2

source of the different forms

Answer 2

provit.D2: ergosterol - plants, fungi provit.D3: 7-dehydrocholesterol - liver, then tp. to skin D2: ergocalciferol - sundried skin D3: cholecalciferol - milk, egg, liver, meat

Question 3

how are the provit.’s converted to vitamins

Answer 3

UV light in the skin, then (D3) is transported to the liver to be converted: –25-alpha-hydroxylase–> 3, 25-OH-cholecalciferol, which is tp. to the kidney (vit.D binding protein) to be converted: –1-alpha-hydroxylase–> 1,3,25-OH-cholecalciferol = vit D3

Question 4

storage of Vit D

Answer 4

liver and adipose tissue as 3, 25-OH-calciferol + palmitic acid

Question 5

excretion of vit D

Answer 5

bound to glucoronic acid - same as vit. A (bile->faeces)

Question 6

biochemical role of vit D is found where

Answer 6

small intestines kidney bone

Question 7

biochemical role: small intestines

Answer 7

absorbing Ca²⁺ binding protein is induced by vit. D (CBP=calbindine) - increases absorption of calcium and phosphorus in small intestines to basolateral side, then chylomicron to blood to incr. its conc of Ca and P

Question 8

biochemical role: kidney

Answer 8

CBP increase reabsorption of Ca²⁺ and Pin -> incr. conc in the blood

Question 9

biochemical role: bone

Answer 9

• *young animals**
• promote synth of newly formed bones and incr. mineralization of bones: Ca and Pin is built into the bone
• *elder animals**
• promote maintinance of pre-existing bone
• demineralization, due to PTH-like activity of vit. D, to elevate Ca²⁺/Pin in the blood

Question 10

reason of incr/decr Ca²⁺/Pin caused by calciferol

Answer 10

hypo: alkaline phosphatase increase -> incr. osteoblast activity -> bone formation -> decr. Ca²⁺/Pin
hyper: no alkaline phosphatase activity-> no bone formation, incr. Ca²⁺/Pin

Question 11

hypovitaminosis

Answer 11

• *young animals:** decr/incomplete mineralization due to decr. Ca and Pin → soft bone formation → rickets
• *adult animals:** incr. PTH lead to demineralization → fragile bone formation → osteomalatia

→treatment = vit. D injection, cod-liver oil, suncured hay

Question 12

hypervitaminosis

Answer 12

→ too high Ca²⁺ and Pin

• calciferol with PTH-like act. → demineraliz., fragile bone
• high Pin/Ca²⁺ → calcification in organs, tissue, membrane
• incr. reabs of Pin/Ca²⁺ in kidney → ppt. in lumen → kidney failure
• GI problems
• slow growth