Lipid soluble vitamins: ADEK

Question 1

Metabolically active form of vitamin D

Answer 1

1, 25 - dihydroxycholecalciferol / 1, 25-OHD

Question 2

Dehydrocholesterol is another name for

Answer 2

Pro-vitamin D

Question 3

Vit D is formed in which layer of the skin?

Answer 3

Epidermis stratum basale

Question 4

Vit D precursor is

Answer 4

cholesterol

Question 5

Mechanism of Vit D regulation by PTH, calcitonin and Calcium levels in blood

Answer 5

When calcium levels low –> PTH secreted –> causes increased synthesis of 1, 25-OHD –> causes increase calcium absorption from intestines + high vit D levels cause bone resorption = levels of calcium in plasma rise = secretion of calcitonin –> causes uptake by bones(calcification) and lowers amount absorbed by intestines –> calcium levels go back to normal

Question 6

Vit D deficiencies

Answer 6

1. Rickets (in children, seen by large joints, bow legs, bossing chest, knock knees)
2. Osteomalacia (in adults, bone is demineralized, can lead to arthritis and osteoporosis)
3. Hypocalcemic tetany (as low levels of calcium lead to increased permeability to sodium ions)

Question 7

Enumerate the two forms of rickets

Answer 7

Classical rickets - caused by Vit D deficiency and can be treated by administering Vit D supplements

Vit D resistant rickets/Refractory rickets - caused by defect in enzymes that convert cholecalciferol or other precursors to 1, 25-OHD so administering vit D does not help at all. Can be due to kidney dysfunction due to long term use of convulsion drugs and corticosteroids

Question 8

Is there Vit D excess toxicity? Explain.

Answer 8

Yes. Symptoms include

1. Nausea
2. Excess calcium deposited in soft tissues leading to their calcification and eventual malfunction
3. Lethargy and weakness due to difficulty in eliciting action potentials as high calcium levels make cells less permeable to sodium
4. Kidney stones

Question 9

Explain synthesis of 1, 25-OHD

Answer 9

1. In skin; ProvitD –> PrevitD –> Liver
2. In liver; PrevitD –> 25-hydroxycholecalciferol –> kidneys
3. In kidneys; 25-hydroxycholecalciferol –> 1, 25-dihydroxycholecalciferol

Question 10

Functions of Vit D

Answer 10

Bone mineralization at low levels
Bone resoprtion at high levels
Improves absorption of Calcium and Phosphate from intestine

Question 11

Conditions for Vit E absoprtion

Answer 11

1. Emulsification
2. Solubilization within the micelles
3. Uptake into enterocytes
4. Secretion into circulation

Question 12

Vit E is also called

Answer 12

Tocotrienol/Tocopherol

Question 13

Factors affecting intestinal absorption of Vit E

Answer 13

Micelle formation
Bile secretion
Pancreas functioning properly

Question 14

Mode of transportation of Vit E into enterocytes

Answer 14

Passive diffusion

Question 15

vit E is transported through plasma in which form?

Answer 15

in cholymicrons

Question 16

The forms of tocopherol/tocotrienol

Answer 16

alpha, gamma, beta, and delta

Question 17

Which form of Vit E is actually used by human body to meet metabolic needs?

Answer 17

alpha form –> alpha -tocopherol

Question 18

Importance of alpha-TTP in vit E transportation.

Answer 18

alpha-tocopherol transfer protein is the liver protein alpha tocopherol binds to so it can be incorporated into cholymicrons

Question 19

Symptoms of Vitamin E deficiency

Answer 19

Infertility (inhibits spermatogenesis and leads to testicular atrophy)
Miscarriage (placenta not getting enough blood due to hemolytic anemia, resulting in not enough oxygen getting to fetus leading to death)
Hemolytic anemia (RBCs poly saturated fatty acids attacked by oxygen producing peroxides which are toxic to cell leading to cell death)
Demyelination of spinocerebellar tract

Acanthocytosis (spikes on RBCs = diarrhea, nausea, vomiting, foul smelling stool)

*Neurologic effects similar to those of Vit B12 deficiency

Question 20

Functions of Vit E.

Answer 20

Enhances cellular respiration by stabilizing co-enzyme Q in electron transport chain

Involved in Heme synthesis for proper functioning of RBCs

Anti-inflammatory by inhibiting synthesis of some prostaglandins involved in immune response

Question 21

Why does Glucose-6-phosphate dehydrogenase deficiency lead to hemolytic anemia?

Answer 21

NADPH is produced when the glucose-6-PDH enzyme converts glucose6P into phosphogluconates.

NADPH is required to convert glutathione disulfide into glutathione which is an antioxidant. Without NADPH, glutathione can’t be regenerated by glutathione reductase, causing accumulation of radicals in RBCs

Question 22

In which phase of blood clotting is Vit K needed?

Answer 22

When prothrombin is being converted to thrombin

Question 23

Function of Vit K

Answer 23

Promote formation of clots

Question 24

Name an antagonist of Vit K

Answer 24

Warfarin because it’s an anticoagulant but vit K is a coagulant

Question 25

Sources of Vit K

Answer 25

plants

intestinal flora

Question 26

vit K deficiency

Answer 26

Neonatal hemorrhagic disease

Impaired blood clotting in adults

Question 27

Suggest 2 methods of determining Vit K Deficiency in a blood sample.

Answer 27

Add thromboplastin and shake. It takes longer for blood to clot in deficient individuals than in normal individuals sample.

Add thromboplastin and excess Calcium. Normal blood clots in 10-15 seconds, while it takes much longer for Vit K deficient blood to do so