Deficiency of which specific vitamin in the human body leads to defective blood clotting and an increased tendency to bleed due to impaired synthesis of clotting factors?

Introduction / Context:
Blood clotting is a vital protective mechanism that prevents excessive bleeding after injury. Several proteins in the clotting cascade must be activated in the correct sequence, and their proper synthesis depends on specific vitamins and minerals. Among the fat soluble vitamins, vitamin K plays a central role in the synthesis of certain clotting factors in the liver. This question tests whether you can correctly link a deficiency in blood clotting with the corresponding vitamin deficiency.

Given Data / Assumptions:

• The question asks about non clotting or impaired clotting of blood.
• We are to choose which vitamin deficiency leads to this condition.
• Options include several vitamins with different functions: C, K, E, B12, and A.
• We assume standard knowledge that blood clotting involves vitamin K dependent clotting factors.

Concept / Approach:
Vitamin K is essential for the post translational modification of certain clotting factors, including prothrombin and factors VII, IX, and X. In the liver, vitamin K acts as a cofactor for enzymes that add carboxyl groups to specific glutamic acid residues in these proteins. This modification allows them to bind calcium ions and function properly in the clotting cascade. When vitamin K is lacking, these clotting factors are produced in an inactive form, resulting in prolonged bleeding time and an increased tendency to bleed even after minor injuries. Other vitamins in the options are important for different processes but are not directly responsible for blood clotting.

Step-by-Step Solution:
Step 1: Identify that the problem described is non clotting or poor clotting of blood. Step 2: Recall that vitamin K is the key vitamin associated with the synthesis of certain clotting factors in the liver. Step 3: Recognize that deficiency of vitamin K results in hypoprothrombinaemia, which leads to bleeding tendencies. Step 4: Compare this with the roles of vitamins C, E, B12, and A, none of which is primarily associated with the clotting mechanism. Step 5: Select the option that links vitamin K deficiency with impaired blood clotting.

Verification / Alternative check:
A practical reminder is that newborn babies are often given vitamin K injections shortly after birth to prevent haemorrhagic disease of the newborn, which is caused by low levels of vitamin K dependent clotting factors. Patients on certain anticoagulant medications such as warfarin are monitored for their vitamin K interaction because these drugs work by inhibiting vitamin K recycling. This real world association between vitamin K and clotting provides strong confirmation that vitamin K deficiency leads to non clotting of blood.

Why Other Options Are Wrong:
Vitamin C, important for collagen synthesis and wound healing: Deficiency leads to scurvy with weak connective tissue and bleeding gums, but the clotting cascade itself is not primarily vitamin C dependent. Vitamin E, an antioxidant that protects cell membranes: Deficiency can cause neurological problems, but it is not directly linked to clotting factor synthesis. Vitamin B12, important for red blood cell formation: Deficiency causes megaloblastic anaemia and neurological symptoms, not direct non clotting of blood. Vitamin A, essential for vision in dim light: Deficiency mainly affects vision and epithelial tissues, not the coagulation pathway.

Common Pitfalls:
Students sometimes confuse bleeding due to fragile blood vessels or poor wound healing with defects in clotting factor synthesis. Vitamin C deficiency can cause bleeding gums, which may lead to the wrong impression that it is the clotting vitamin. However, vitamin C acts on collagen and connective tissue, whereas vitamin K specifically affects the clotting factors. Understanding that clotting factors are made in the liver and require vitamin K for activation helps avoid this confusion and leads to the correct answer in examination questions.

Final Answer:
Therefore, non clotting of blood due to failure of clotting factor synthesis is caused by deficiency of Vitamin K, required for synthesis of clotting factors.