Which one of the following is NOT true about chemical mediators:
First, the core concept here is about chemical mediators in the body. They are substances released during immune or inflammatory responses, like histamine, cytokines, prostaglandins. Their roles include vasodilation, increasing vascular permeability, recruiting immune cells, etc.
Now, possible incorrect statements could be about their mechanisms. For example, maybe an option says they are stored in the nucleus, but actually, they're stored in granules. Or perhaps an option claims they are synthesized on demand, but some are preformed. Another wrong option might confuse their role, like saying they cause vasoconstriction instead of vasodilation.
Wait, the correct answer is the one that's not true. So if one of the options states that chemical mediators are primarily stored in the cytoplasm, that's incorrect because they're stored in granules. Another could be about their release mechanism. Let me structure this properly.
Core Concept: Chemical mediators are preformed or synthesized molecules released during immune/inflammatory responses. They act via specific receptors to modulate vascular permeability, smooth muscle contraction, and immune cell recruitment.
Why correct answer is right: For example, if the correct answer is that they are stored in the nucleus, that's wrong because they're stored in granules. If the correct answer is that they are all synthesized on demand, that's incorrect because some are preformed.
For the wrong options, each should be explained. Let's say the correct answer is option C: "They are all synthesized in the cytoplasm." That's incorrect because some are preformed in granules. Option A might say they are released from mast cells, which is true, so that's not the correct answer. Option B could state they cause bronchoconstriction, which is true for some mediators. Option D might say they are inactivated by enzymatic degradation, which is true. So the correct answer is the one that's false.
Clinical pearl: Remember that chemical mediators like histamine and leukotrienes are stored in mast cell granules, not the cytoplasm. Enzymatic inactivation is a key regulatory mechanism.
Putting it all together, the correct answer would be the one that incorrectly states they are stored in the cytoplasm. So the correct answer is C. They are all synthesized in the cytoplasm.
**Core Concept:** Chemical mediators are preformed or synthesized molecules released during immune/inflammatory responses. They act via specific receptors to modulate vascular permeability, smooth muscle contraction, and immune cell recruitment. Key mediators include histamine, cytokines, and prostaglandins.
**Why the Correct Answer is Right:** The correct answer states that all chemical mediators are stored in the cytoplasm. This is false because **many are stored in granules** (e.g., histamine in mast cell granules) or synthesized *de novo* (e.g., arachidonic acid metabolites). Preformed mediators are stored in secretory granules, while others are produced on demand via enzymatic pathways like COX or LOX.
**Why Each Wrong Option