Human reproduction

• Humans

  • Sexually reproducing
  • Viviparous
• Reproductive events in humans

  1. Formation of gametes (gametogenesis)

  2. Transfer of sperms into the female genital tract (insemination)

  3. Fusion of male and female gametes (fertilisation)

  4. Formation and development of blastocyst and its attachment to the uterine wall (implantation)

  5. Embryonic development (gestation)

  6. Delivery of the baby (parturition)
• Reproductive events occur after puberty
• There are remarkable differences between the reproductive events in the male and in the female
• Sperm formation


  • Continues even in old men
• Formation of ovum


  • Ceases in women around the age of fifty years
• Male reproductive system


  Located in the pelvis region
• Components of male reproductive system

  • Testes
  • Accessory ducts
  • Glands
  • External genitalia
• Testes

  • Situated outside the abdominal cavity within a pouch called scrotum
  • Scrotum helps in maintaining the low temperature of the testes (2–2.5o C lower than the normal internal body temperature) necessary for spermatogenesis
  • In adults, each testis is oval in shape, with a length of about 4 to 5 cm and a width of about 2 to 3 cm
  • Testis is covered by a dense covering
  • Each testis has about 250 compartments called testicular lobules
• Seminiferous tubules


  • One to three highly coiled seminiferous tubules in each lobule
  • Lined on its inside by two types of cells called male germ cells (spermatogonia) and Sertoli cells
• Spermatogenesis

  1. Male germ cells (spermatogonia) undergo meiotic divisions finally leading to sperm formation

  2. Sertoli cells provide nutrition to the germ cells
• Interstitial spaces

  • Contain small blood vessels and interstitial cells or Leydig cells
  • Leydig cells synthesise and secrete testicular hormones called androgens
• Male sex accessory ducts

  • Rete testis
  • Vasa efferentia
  • Epididymis
  • Vas deferens
• Sperm transport

  1. Seminiferous tubules of the testis open into the vasa efferentia through rete testis

  2. Vasa efferentia leave the testis and open into epididymis

  3. Epididymis leads to vas deferens that ascends to the abdomen and loops over the urinary bladder

  4. Vas deferens receives a duct from seminal vesicle and opens into urethra as the ejaculatory duct

  5. Urethra originates from the urinary bladder and extends through the penis to its external opening called urethral meatus
• Penis

  • Male external genitalia
  • Made up of special tissue that helps in erection of the penis to facilitate insemination
  • Enlarged end of penis called the glans penis is covered by a loose fold of skin called foreskin
• Male accessory glands

  • Seminal vesicles
  • Prostate
  • Bulbourethral glands
• Seminal plasma

  • Secretions of male accessory glands
  • Rich in fructose, calcium and certain enzymes
  • Secretions of bulbourethral glands also helps in the lubrication of the penis
• Female reproductive system

  • Consists of a pair of ovaries, a pair of oviducts, uterus, cervix, vagina and the external genitalia located in pelvic region
  • Integrated structurally and functionally to support the processes of ovulation, fertilisation, pregnancy, birth and child care
  • Alongwith a pair of the mammary glands
• Ovaries

  • Primary female sex organs
  • Produce the female gamete (ovum) and several steroid hormones (ovarian hormones)
  • Located one on each side of the lower abdomen
  • Each ovary is about 2 to 4 cm in length and is connected to the pelvic wall and uterus by ligaments
  • Covered by a thin epithelium which encloses the ovarian stroma
  • Stroma is divided into two zones – a peripheral cortex and an inner medulla
• Female accessory ducts

  • Oviducts (fallopian tubes)
  • Uterus
  • Vagina
• Oviducts (fallopian tubes)


  • Each fallopian tube is about 10-12 cm long and extends from the periphery of each ovary to the uterus
  • Part closer to the ovary is the funnel-shaped infundibulum
  • Edges of the infundibulum possess finger-like projections called fimbriae, which help in collection of the ovum after ovulation
  • Infundibulum leads to a wider part of the oviduct called ampulla
  • Last part of the oviduct, isthmus has a narrow lumen and it joins the uterus
• Uterus

  • Single, shaped like an inverted pear
  • Supported by ligaments attached to the pelvic wall
  • Opens into vagina through a narrow cervix
  • Cavity of the cervix is called cervical canal which alongwith vagina forms the birth canal
  • Wall of the uterus has three layers of tissue - external thin membranous perimetrium, middle thick layer of smooth muscle, myometrium and inner glandular layer called endometrium that lines the uterine cavity
  • Endometrium undergoes cyclical changes during menstrual cycle
  • Myometrium exhibits strong contraction during delivery of the baby
• Female external genitalia

  • Mons pubis
  • Labia majora
  • Labia minora
  • Hymen
  • Clitoris
• Mons pubis


  A cushion of fatty tissue covered by skin and pubic hair
• Labia majora

  Fleshy folds of tissue, which extend down from the mons pubis and surround the vaginal opening
• Labia minora


  Paired folds of tissue under the labia majora
• Hymen


  • A membrane that partially covers the opening of the vagina
  • Often torn during the first coitus (intercourse)
  • Can also be broken by a sudden fall or jolt, insertion of a vaginal tampon, active participation in some sports like horseback riding, cycling, etc.
  • Presence or absence of hymen is not a reliable indicator of virginity or sexual experience
• Clitoris


  A tiny finger-like structure which lies at the upper junction of the two labia minora above the urethral opening
• Mammary gland

  • Characteristic of all female mammals
  • Paired structures (breasts) that contain glandular tissue and variable amount of fat
  • Glandular tissue of each breast is divided into 15-20 mammary lobes containing clusters of cells called alveoli
  • Cells of alveoli secrete milk, which is stored in the cavities (lumens) of alveoli
  • Alveoli open into mammary tubules
  • Tubules of each lobe join to form a mammary duct
  • Several mammary ducts join to form a wider mammary ampulla which is connected to lactiferous duct through which milk is sucked out
• Gametogenesis

  1. Testis produces sperms by spermatogenesis

  2. Ovaries produce ova
• Spermatogenesis

  1. Immature male germ cells (spermatogonia) multiply by mitotic division and increase in numbers

  2. Some spermatogonia called primary spermatocytes undergo meiosis

  3. Primary spermatocyte completes the first meiotic division leading to formation of two equal, haploid cells called secondary spermatocytes

  4. Secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids

  5. Spermatids are transformed into spermatozoa (sperms) by the process called spermiogenesis

  6. Sperm heads become embedded in the Sertoli cells, and are finally released from the seminiferous tubules by the process called spermiation
• Spermatogenesis starts at the age of puberty due to significant increase in the secretion of gonadotropin releasing hormone (GnRH)
• GnRH


  A hypothalamic hormone
• Gonadotropins

  Luteinising hormone (LH) and follicle stimulating hormone (FSH)
• LH


  Acts at the Leydig cells and stimulates synthesis and secretion of androgens
• FSH


  Acts on the Sertoli cells and stimulates secretion of some factors which help in the process of spermiogenesis
• Sperm

  • Microscopic structure composed of a head, neck, a middle piece and a tail
  • Plasma membrane envelops the whole body of sperm
  • Sperm head contains an elongated haploid nucleus, the anterior portion of which is covered by a cap-like structure, acrosome
  • Acrosome is filled with enzymes that help fertilisation of the ovum
  • Middle piece possesses numerous mitochondria, which produce energy for the movement of tail that facilitate sperm motility essential for fertilisation
• Human male ejaculates about 200 to 300 million sperms during a coitus
• For normal fertility, at least 60 per cent sperms must have normal shape and size and at least 40 per cent of them must show vigorous motility
• Secretions of epididymis, vas deferens, seminal vesicle and prostate are essential for maturation and motility of sperms