Question

Intrinsic mechanism of blood coagulation refers to the sequence of enzymatic reactions which is due to
A. Damage to a vessel
B. Exposure to air
C. Foreign surface
D. Sufficiently traumatic blood vessel
Choose the correct answer from the options given below

• A. A only
• B. A and B only
• C. A, B and C only
• D. All A, B, C and D

Hint:

Coagulation Pathways:
Intrinsic Pathway = Triggered by Contact Activation (Factor XII) with subendothelial collagen Foreign surface Damaged vessel.
Extrinsic Pathway = Triggered by Tissue Factor (Factor III).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Hemostasis and the contact activation cascade: the intrinsic pathway of blood coagulation is triggered when factor XII (Hageman factor) contacts negatively charged subendothelial collagen, foreign surfaces, damaged vessel walls, or glass in vitro.
Key Formula or Approach:
\[ \text{Factor XII (Hageman)} \xrightarrow{\text{Contact with Subendothelial Collagen / Foreign Surface / Damaged Vessel}} \text{Factor XIIa} \longrightarrow \text{Intrinsic Cascade} \]

Step 2: Detailed Explanation:
In hemostasis and hematology:
- The Intrinsic Pathway of Blood Coagulation (Contact Activation Pathway) is initiated endogenously without requiring external tissue factor (thromboplastin):
1. Triggered when blood contacts damaged vessel walls (A, D), subendothelial collagen, or negatively charged foreign surfaces (C) (e.g., glass tube, prosthetic valves), or during exposure to air (B) and traumatic surface contact.
2. This activates Factor XII (Hageman Factor) to XIIa in the presence of high-molecular-weight kininogen (HMWK) and prekallikrein, which sequentially activates Factor XI $\rightarrow$ Factor IX $\rightarrow$ Factor X (Tenase complex with Factor VIIIa).
Thus, all listed trauma/surface factors trigger the intrinsic clotting cascade.

Step 3: Final Answer:
Therefore, the intrinsic mechanism is due to All A, B, C and D, corresponding to option (D).