Reproductive Systems and Function

The Reproductive System Overview

• Sexual Reproduction

  • Produces new individuals via gametes (sperm and oocyte).
  • Fertilization results in a diploid zygote.
  • Gonads (testes in males, ovaries in females) produce gametes and secrete sex hormones.

• Reproductive Systems Structure

  • Includes gonads, ducts, glands, and supporting structures.
  • Gynecology: Study of the female reproductive system.
  • Urology: Study of the urinary and male reproductive systems.

The Essence of Sex

• Key Property of Life: Reproduction ensures genetic diversity and species evolution.
• Sexual Reproduction: Offspring inherit genetic material from both parents.

The Two Sexes

• Male Gametes:

  • Sperm has motility.
  • XY chromosomes (Y chromosome indicates male).

• Female Gametes:

  • Eggs provide nutrients for developing zygotes.
  • XX chromosomes.

• Parental Roles:

  • Males produce sperm, while females provide shelter and nutrients for embryos (uterus and placenta).

Anatomy of the Reproductive System

• Primary Sex Organs:

  • Gonads: Testes (males) and ovaries (females).

• Secondary Sex Organs:

  • Males: Ducts, glands, penis.
  • Females: Uterine tubes, uterus, vagina.

• Secondary Sex Characteristics:

  • Develop at puberty to attract mates (e.g., body hair, voice pitch).

Chromosomes and Genetics

• Human Cells:

  • Contain 23 pairs of chromosomes (22 pairs autosomes, 1 pair sex chromosomes).
  • Males: 50% Y sperm, 50% X sperm; females: all eggs carry X.

• Offspring Sex Determination:

  • Dependent on whether the fertilizing sperm carries X or Y chromosome.

Hormones and Sex Differentiation

• Gonadal Development:

  • Begins at 6 weeks gestation with the formation of gonadal ridges.
  • Two duct systems:
  • Mesonephric ducts develop into male reproductive system (supported by SRY gene).
  • Paramesonephric ducts develop into female reproductive system (degenerate in males).

• SRY Gene: Codes for the development of testes, testosterone secretion, and müllerian-inhibiting factor (inhibits female tract development).

Spermatogenesis and Sperm Structure

• Spermatogenesis:

  • Formation of sperm from spermatogonia.
  • Stages include primary spermatocyte → secondary spermatocytes → spermatids → spermatozoa.
  • Each sperm cell undergoes meiosis, creating genetic diversity.

• Sperm Structure:

  • Head with acrosome and nucleus; tail divided into midpiece (with mitochondria), principal piece, and endpiece.

Hormones regulating Reproduction

• Hormonal Control:

  • Gonadotropin Release Hormone (GnRH) triggers FSH and LH secretion.
  • Testosterone: Stimulates secondary sexual characteristics and spermatogenesis.

• Feedback Mechanisms:

  • Increased testosterone leads to decreased GnRH, FSH, and LH, maintaining homeostasis.

Male Duct System and Semen Production

• Ducts:

  • Pathway for sperm includes seminiferous tubules → rete testes → efferent ducts → epididymis → ductus deferens → ejaculatory duct → urethra.

• Seminal Fluid:

  • Mixture of sperm, secretions from seminal vesicles, prostate, and bulbourethral glands.
  • Typical ejaculate: 2.5 to 5 ml, containing nutrients and enzymes necessary for sperm function.

Sexual Response and Ejaculation

• Phases of Sexual Response:

  • Excitement (vasocongestion, erection), plateau (maintaining erection), orgasm (ejaculation), resolution (detumescence).
  • Distinction between emission (sperm moved into urethra) and expulsion (ejaculation).

• Erectile Dysfunction:

  • Inability to maintain erection; causes include psychological factors and physical health conditions.
  • Viagra: Enhances erection by increasing blood flow to the erectile tissue via vasodilation.