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Question 321
Physiology → Haematology
Classification
Question
SSBAQuestion Header
A circulating platelet remains metabolically active and can release substances already stored within its granules. Which limitation follows most directly from its structure?
Question Stem
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Options
A
It cannot adhere to exposed collagen
B
It cannot participate in clot retraction
C
It cannot release stored granule contents
D
It cannot synthesise new proteins because it lacks a nucleus
E
It cannot contain mitochondria
Explanation
Platelets are non-nucleated fragments of megakaryocytes. Although metabolically active and capable of releasing stored substances, states that they cannot synthesise new proteins because they lack a nucleus.
Option Validity
A) describes platelet adhesion after exposure to collagen, accompanied by pseudopodia formation. Lack of a nucleus does not prevent this function.
B) Clot retraction is a platelet function. The relevant structural limitation is the inability to synthesise new proteins.
C) Platelets contain alpha and dense granules and can release stored substances. Their inability to synthesise new proteins does not prevent release of pre-existing granule contents.
E) platelet cytoplasm contains mitochondria as well as granules and lysosomes. The absent organelle relevant to new protein synthesis in is the nucleus.
Further Reading
Saxena. Textbook for MRCOG-1. Physiology - Haematology - Platelets, p.70.