Notes: Autocrine and Paracrine Hormones and MCQ for GPAT, NEET, CUET, NURSING EXAM
1. Autocrine Hormones
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Definition: Hormones or chemical messengers that act on the same cell that secreted them.
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Mechanism:
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The cell releases a substance.
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The substance binds to receptors on its own membrane.
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Function:
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Local regulation of cell growth, immunity, and feedback.
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Examples:
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Interleukin-2 (IL-2) in activated T cells.
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Prostaglandins (in some tissues).
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Tumor growth factors (e.g., TGF-β in cancers).
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🔹 2. Paracrine Hormones
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Definition: Hormones that act on neighboring or adjacent cells within the same tissue.
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Mechanism:
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Secreted by one cell.
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Diffuses through interstitial fluid to affect nearby target cells.
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Function:
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Local signaling and coordination of function within tissues.
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Examples:
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Nitric oxide (NO) from endothelial cells → causes vasodilation in nearby smooth muscle.
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Somatostatin → inhibits insulin/glucagon secretion in pancreas.
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Histamine → released by mast cells, acts on nearby blood vessels.
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🔹 Comparison Table
| Feature | Autocrine | Paracrine |
|---|---|---|
| Acts on | Same cell | Nearby cells |
| Range | Intracellular/local | Local (short-distance) |
| Examples | IL-2, prostaglandins | NO, histamine, somatostatin |
| Role | Self-regulation, feedback | Local coordination |
📝 MCQs: Autocrine vs Paracrine Hormones
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1. Autocrine signaling refers to hormones that:
A. Act on distant organs
B. Are stored in vesicles
C. Act on the same cell that secretes them
D. Require secondary messengers
✅ Answer: C
2. Which of the following is an example of paracrine signaling?
A. Insulin acting on liver cells
B. Histamine acting on nearby blood vessels
C. Growth hormone acting on bone
D. Thyroxine affecting metabolic rate
✅ Answer: B
3. Interleukin-2 (IL-2) secreted by activated T cells acts on the same cell to stimulate proliferation. This is an example of:
A. Paracrine action
B. Endocrine action
C. Autocrine action
D. Neurocrine action
✅ Answer: C
4. Paracrine hormones differ from endocrine hormones in that they:
A. Act on receptors inside the cell nucleus
B. Travel via bloodstream to distant targets
C. Affect neighboring cells within the same tissue
D. Are not involved in feedback mechanisms
✅ Answer: C
5. Which hormone acts via both autocrine and paracrine mechanisms in various tissues?
A. Oxytocin
B. Prostaglandins
C. Thyroxine
D. Insulin
✅ Answer: B