Human Reproduction

NEET 2026 - Human Reproduction in One Shot

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Overview of Human Reproduction

  • Human Characteristics: Humans are sexually reproducing and viviparous organisms.
    • Major reproductive events include:
    1. Gametogenesis
    2. Insemination
    3. Fertilization
    4. Implantation
    5. Gestation
    6. Parturition

Male Reproductive System

Primary and Secondary Sex Organs
  • Primary Sex Organ: Testis
  • Secondary Sex Organs Include:
    • Epididymis
    • Vas deferens
    • Seminal vesicles
    • Prostate gland
    • Bulbourethral gland
    • Penis
Testis Structure and Function
  • Spermatogenesis: The process of forming sperm through meiotic division.
  • Internal Temperature Regulation: Testes located in the scrotum maintain a temperature of 2-2.5°C lower than body temperature, essential for normal spermatogenesis.
  • Testes Composition:
    • Sertoli Cells: Provide nourishment to spermatogonia.
    • Leydig Cells: Synthesize and secrete androgens, specifically testosterone.
  • Anatomy:
    • Oval shape, size: 1-3 cm in length, 2-3 cm in width, surrounded by tunica albuginea, comprising 250 lobules with seminiferous tubules.
Anatomical Pathway of Sperm Maturation
  • Components:
    • Seminiferous Tubules: Where sperm are formed.
    • Vasa Efferentia: Connect seminiferous tubules to the epididymis.
    • Epididymis: Stores and matures sperm, consisting of a head (caput), body (corpus), and tail.
    • Vas Deferens: Transports sperm to the ejaculatory duct.
    • Ejaculatory Duct: Stores and transports sperm to urethra.
Accessory Glands Function
  • Seminal Vesicles, Prostate, Bulbourethral glands:
    • Secretions consist of seminal plasma rich in fructose, calcium, and various enzymes that aid in sperm motility and lubrication of the penis.

Female Reproductive System

Primary Sex Organs and Functions
  • Primary Sex Organ: Ovaries
    • Responsibilities include:
    • Receiving sperm
    • Development of the fetus
    • Hormonal production
  • Accessory Glands: Bartholin's glands, mammary glands
  • Accessory Ducts: Oviducts (Fallopian tubes), Uterus, Vagina
  • External Genitalia: Mons pubis, labia majora, labia minora, hymen, clitoris
Ovary Anatomy
  • Ovaries measure 2-4 cm in length, consist of ovarian stroma (cortex and medulla), and are the site of female gamete (ovum) production.
  • Each ovary is connected to the pelvic wall and uterus by ligaments.
Oviducts (Fallopian Tubes)
  • Length: 10-12 cm
  • Function: Collect ova with fimbriae and transport them to the uterus.
Uterus Structure
  • Described as an inverted pear shape with various layers:
    • Perimetrium: Outer layer
    • Myometrium: Middle layer of smooth muscle
    • Endometrium: Inner glandular layer responsible for implantation and expansion during pregnancy.
External Female Genitalia
  • Mons Pubis: Fatty tissue covered by pubic hair.
  • Labia Majora: Paired folds of tissue surrounding the vaginal opening.
  • Hymen: Membrane that can be torn during physical activities such as sports or vaginal intercourse.
Mammary Glands
  • Comprise glandular tissue and fat; each breast contains 15-20 lobes of alveolar cells for milk production during lactation.

Gametogenesis

Spermatogenesis
  • Location: Sertoli cells in seminiferous tubules during puberty.
  • Process Includes:
    • Mitosis and differentiation of spermatogonia (46 chromosomes).
    • First meiotic division producing secondary spermatocytes (23 chromosomes).
    • Second meiotic division creating haploid spermatids.
    • Final differentiation into spermatozoa (sperms).
  • Normal sperm count: Approximately 300 million per ejaculation including motility dynamics.
Oogenesis
  • Initiated in embryonic development; no new oogonia form after birth.
  • Each primary oocyte gets surrounded by granulosa cells forming primary follicles.
  • Only 60,000-80,000 primary follicles remain at puberty, each containing an oocyte.
  • Oogenesis involves a first meiotic division during puberty (producing secondary oocyte and polar body).
  • Completion of Oogenesis occurs upon fertilization, resulting in a diploid zygote.

Menstrual Cycle

Phases
  • Cycle typically lasts 28-29 days, begins with menarche during puberty.
  • Phases Include:
    • Follicular Phase: Development of primary follicles to Graafian follicle.
    • Ovulation: Mid-cycle release of ovum triggered by LH surge.
    • Luteal Phase: Maintenance of endometrium by progesterone for possible implantation.
  • Changes in ovarian hormone levels direct changes in the uterine lining and follicular development.
Pregnancy
  • Upon fertilization, the menstrual cycle halts, and hormonal changes prevent menstruation.
  • Gestational Changes: Include formation of the placenta to support fetal development and nutrient exchange.
  • Trimesters cover different developmental milestones and fetal growth.

Parturition and Lactation

Parturition Process
  • Occurs after 9 months of gestation, involving uterine contractions and expulsion of the fetus.
  • Oxytocin plays a crucial role in inducing contractions and birth canal opening during childbirth.
Lactation Process
  • Initiated by prolactin for milk formation and oxytocin for milk ejection.
  • Colostrum, the first milk, is rich in antibodies providing passive immunity to the newborn.