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Uploaded byAnil Khade
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Detailed Overview of Gamete Approximation and Sperm Capacitation Processes in Human Reproduction

This presentation provides a comprehensive overview of the approximation and capacitation of gametes, two important events preceding fertilization in mammals. It explains how the sperm and ovum come into close proximity and how sperm undergoes physiological and biochemical changes that enable it to fertilize the egg. The presentation covers the transport and approximation of sperm and ovum, sperm capacitation, biochemical and structural changes during capacitation, hyperactivation of sperm motility, removal of surface proteins and glycoproteins, changes in the sperm plasma membrane, and preparation for the acrosome reaction. The role of the female reproductive tract in sperm capacitation and the importance of these processes in successful fertilization are also discussed. Key Topics Covered: Approximation of male and female gametes Transport of sperm through the female reproductive tract Movement and positioning of the ovum Sperm–egg interaction Definition and significance of sperm capacitation Physiological changes during capacitation Changes in sperm plasma membrane Increased sperm motility and hyperactivation Calcium influx and intracellular signaling Preparation of sperm for the acrosome reaction Importance of capacitation in fertilization

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Approximation of Gametes And Capacitation of sperm Approximation refers to the process that brings the sperm and ovum close enough for fertilization. By Prof. Anil N. Khade Department of Zoology
A. Transport of Sperm • During ejaculation, about 200–300 million sperms are deposited in the vagina. • After the entry of sperm, mixed with seminal fluid. • It act as buffering component, helps to survive in acidic environment of vagina. • Some proteins bind with sperm which mediate the binding with oviduct. • Sperms move through: • Vagina • Cervix • Uterus • Fallopian tube (oviduct) • Their movement is aided by: • Flagellar movement • Uterine contractions • Ciliary action of the oviduct
Sperm chemotaxis in humans • Sperm chemotaxis in humans is a process where mature spermatozoa are guided toward an oocyte (egg) by following a chemical concentration gradient. • Cumulus cells: Secrete factors such as the steroid progesterone, which attracts capacitated sperm at very low concentrations. • The oocyte: Secretes potent, non-peptide hydrophobic molecules bound to carrier proteins, providing a continuous chemical beacon. • Other molecules: Compounds like β-defensin (DEFB119) and specific odorant or microbial ligands (such as methional via olfactory receptors like OR2H1) have also been shown to influence human sperm motility and orientation.
Thermotaxis in Female Reproductive Tract. • Thermotaxis is the directed movement of sperm toward a warmer temperature. It is one of the mechanisms that helps sperm locate the egg during fertilization. • Temperature Gradient • The isthmus of the fallopian tube is slightly cooler. • The ampulla (the usual site of fertilization) is approximately 1–2°C warmer. • Capacitated sperm sense this small temperature difference and swim toward the warmer ampulla where the oocyte is present.
B. Transport of Ovum • After ovulation, the secondary oocyte is released from the ovary. • It is picked up by the fimbriae of the fallopian tube. • Ciliary movement and muscular contractions transport the ovum toward the ampulla. • Fertilization usually occurs in the ampullary-isthmic junction of the fallopian tube.
Capacitation of Gametes • Capacitation is the physiological maturation process that sperm undergo in the female reproductive tract before they become capable of fertilizing the ovum. • Duration: Approximately 5–7 hours in humans.
Where Does Capacitation Occur? • Uterus • Fallopian tube (oviduct)
Changes During Capacitation • Removal of glycoprotein and cholesterol coating from the sperm plasma membrane. • Increased membrane permeability to calcium ions (Ca²⁺). • Increased motility (hyperactivation). • Increased metabolic activity. • Preparation of the acrosome for the acrosome reaction.
Hyperactivation • After capacitation: • Sperm swim faster. • Tail movement becomes vigorous. • Helps sperm penetrate the protective layers surrounding the egg.
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