vitamin K

Question 1

Mention the sources, the RDA and different chemical forms of Vitamin K

Answer 1

Sources and forms:
1. Phylloquinone (K1)
- Rich in leaf vegetables especially cabbage, kale, spinach
2. Menaquinone (K2)
- Animal sources, especially egg yolk and liver
- Synthesized by intestinal bacteria
3. Menadione (K3)
- Synthetic form and able to be converted to K2. Used for therapy (IM injection to newborns with hemmorhagic disease)

RDA of Vit K:
1. 120ug/day for adult males and 90ug/day for females

Question 2

Explain the functions of Vitamin K

Answer 2

1. Formation of the funtional clotting factors
   → Vitamin K (hydroquinone) acts as a coenzyme for the carboxylation of glutamic acid residues. It involves the conversion of glutamate (Q) to gamma-carboxyglutamate
   → SYnthesised in the liver as an inactive zymogen after undergoing post translational modification.
   → Formation of gamma-carboxyglutamate helps products Factor II (prothrombin), Factor VII (SPCA), Factor IX (Christmas Factor), Factor X (Stuart Prower factor).
2. Activation of osteocalcin
   → Vitamin K is also required forthe carboxylation of glutamic acid residues of osteocalcin, a calcium binding protein present in bone

Question 3

Explain the causes, effects, clinical presentation and treatments of Vitamin K deficiency. Specifically the cause of Vit K deficiency in newborns.

Answer 3

Causes of Vitamin K deficiency:
1. Actual deficiencies are rare since it is synthesized by the intestinal bacteria, therefore malabsorption of lipids leads to vitamin K deficiency.
2. Destruction of intestinal bacteria due to prolonged antibiotic therapy and GIT infections with diarrhea can destroy it
3. New-borns have sterile intestine so they lack the bacteria that synthesize vitamin K. Human milk cannot provide enough vit K

Effects of Vitamin K deficiency:
1. Hypoprothrombinemia → increase in blood coagulation time, hences slower coagulating.
2. Affects bone growth and mineralization.

Clinical features:
1. Haemorrhagic disease of the new born
2. Bruising tendency, ecchymosis, mucosal bleeding
3. Internal bleeding
4. Prolongation of Prothrombin Time.

Treatmet of Vitamin K deficiency.
1. Supplements are given by single IM injection of Vitamin K (menadione) to protect against haemorrhagic diseaes.

Question 4

Explain the causes and effetcs of excessive Vitamin K. Name the antagonists of Vitamin K

Answer 4

Excessive Vitamin K ⇒ Hypervitaminosis K

Cause:
1. Administer large doses of menadione (K3) → toxicity

Effects:
1. Haemolyic anemia
2. Jaundice (in infant, due to toxic effects on the RBC membrane)

Antagonist ⇒ Warfarin and Dicumarol
→ Competitively inhibit the Vitamin K epoxide reductase (VKOR), due to structural similarity with Vitamin K
→ Inhibition of VKOR results in interfering with the regeneration of vitamin K hydroquinone required for carboxylation
→ Results in a block of formation of Gla residues