Human Reproduction

Humans are sexually reproducing and viviparous organisms. The key reproductive events include:

• Gametogenesis: Formation of gametes (sperms in males and ovum in females).
• Insemination: Transfer of sperms into the female genital tract.
• Fertilisation: Fusion of male and female gametes leading to zygote formation.
• Implantation: Development and attachment of blastocyst to the uterine wall.
• Gestation: Embryonic development.
• Parturition: Delivery of the baby.

The reproductive events begin post-puberty and show distinct differences between males and females, such as continuous sperm production in males and cessation of ovum formation in females around fifty years.

The Male Reproductive System

• Location: Pelvis region.
• Components:
  • Testes: Located in the scrotum, maintain a temperature 2-2.5°C lower than body temperature, essential for spermatogenesis. Each testis has:
    • Testicular lobules: About 250 per testis, containing seminiferous tubules where sperm production occurs.
    • Cells: Male germ cells (spermatogonia), undergo meiotic divisions for sperm formation; Sertoli cells provide nutrition.
    • Leydig cells: Located outside seminiferous tubules, secrete androgens.
  • Accessory Ducts: Include rete testis, vasa efferentia, epididymis, and vas deferens. They store and transport sperms.
  • Penis: Male external genitalia, facilitates insemination.
  • Accessory Glands: Seminal vesicles, prostate, bulbourethral glands; secretions form seminal plasma.

The Female Reproductive System

• Components:
  • Ovaries: Produce ovum and hormones, located in lower abdomen, connected by ligaments.
  • Accessory Ducts: Oviducts (fallopian tubes), uterus, cervix, vagina.
  • External Genitalia: Include mons pubis, labia majora, labia minora, hymen, clitoris.
  • Mammary Glands: Produce milk post-pregnancy.

Gametogenesis

• Spermatogenesis: Occurs in testes, starts at puberty. Spermatogonia undergo mitotic and meiotic divisions to form spermatids, which develop into spermatozoa.
• Oogenesis: Begins during embryonic development; oogonia form primary oocytes which eventually develop into ovum.

Menstrual Cycle

• Phases:
  • Menstrual Phase: Shedding of endometrial lining.
  • Follicular Phase: Development of Graafian follicle, endometrial regeneration.
  • Ovulation: Release of ovum.
  • Luteal Phase: Corpus luteum formation, secretion of progesterone.
• Hormonal Regulation: Involves gonadotropins (LH, FSH), estrogens, and progesterone.

Fertilisation and Implantation

• Fertilisation: Sperm fuses with ovum in the ampullary region of the fallopian tube.
• Zygote Formation: Fusion of haploid sperm and ovum nuclei.
• Implantation: Blastocyst embeds in the uterine wall, leading to pregnancy.

Pregnancy and Embryonic Development

• Placenta Formation: Chorionic villi and uterine tissue form the placenta, facilitating nutrient and waste exchange.
• Fetal Development: Heart formation by one month, limb and organ development by the first trimester. Fully developed by the ninth month.

Parturition and Lactation

• Parturition: Childbirth induced by hormonal and uterine signals.
• Lactation: Milk production and feeding of newborn, initial milk (colostrum) rich in antibodies.

Summary

• Human reproduction involves complex physiological processes and hormonal regulation.
• The male and female reproductive systems are anatomically and functionally distinct.
• The menstrual cycle reflects reproductive health and hormonal balance.
• Pregnancy involves careful coordination between mother and fetus via the placenta.
• Parturition and lactation are critical for newborn health and maternal recovery.

Exercises: Cover questions on reproductive anatomy, physiology, and processes to reinforce understanding.