The acrosome reaction is essential for fertilisation. It is triggered by:

• A Capacitation-induced hyperpolarisation of the sperm plasma membrane
• B Progesterone secreted by granulosa cells binding to nuclear receptors in the sperm head
• C Hyaluronidase pre-digesting the cumulus oophorus before zona contact
• D Zona pellucida glycoprotein ZP3 binding to sperm surface receptors, triggering Ca2+ influx and exocytosis of acrosomal enzymes ✓

Explanation

Following capacitation (which removes cholesterol from the sperm plasma membrane and enables Ca2+ hyperactivation), the acrosome reaction is initiated when sperm contact the zona pellucida. ZP3 (zona pellucida glycoprotein 3) binds to complementary receptors on the capacitated sperm head, triggering Ca2+ influx via T-type and CatSper channels, activating phospholipase C-delta and PKC. This causes exocytosis of the acrosomal membrane, releasing acrosin (protease) and hyaluronidase that digest the zona pellucida, allowing sperm penetration. Progesterone also stimulates CatSper Ca2+ channels during chemotaxis.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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