2- Spermatogenesis 3

Male Genital System Overview

  • Composed of the following structures:

    • Testicles

    • Ducts

    • Accessory glands

    • Scrotum

    • Penis

    • Pubic bone

    • Urethra

Gametogenesis

  • Refers to the process of forming male and female gametes from germ cells.

Germ Cell Migration

  • In early mammalian development, primordial sex cells migrate to embryonic gonads (testicles and ovaries).

  • They reproduce to form gametes (spermatozoon and ovum).

Germ Cells vs. Soma Cells

  • Germ cells are involved in gamete formation.

  • Soma cells, or somatoplasm, do not directly influence gametogenesis.

Gametogenesis Stages

  1. Origin and Migration: Germ cells originate and migrate to gonads.

  2. Mitosis: Germ cells reproduce through mitosis.

  3. Meiosis: Chromosome number is halved to produce gametes.

  4. Maturation: Gametes undergo final maturation, developing into sperm or ova.

Mitosis in Germ Cells

  • Mitosis occurs in different patterns between males and females:

    • In females, high mitotic activity occurs during 2nd to 5th month of pregnancy, resulting in numerous ovogonium.

    • In contrast, males maintain continuous mitotic activity throughout life, producing spermatogonia.

Meiosis in Gametogenesis

  • Meiosis is a type of cell division that reduces genetic material.

  • Results in the formation of haploid gametes (1n).

  • Involves two nuclear divisions with only one DNA replication.

Meiosis I and II

  • Meiosis I includes phases: Prophase I, Metaphase I, Anaphase I, Telophase I, Interphase.

  • Meiosis II leads to formation of spermatids or ova and polar bodies.

Testes Structure

  • Testicles are located in the scrotum, which maintains lower temperatures necessary for spermatogenesis.

  • Anatomical Layers:

    • Tunica Vaginalis: Surrounds and supports the testes.

    • Tunica Albuginea: A durable capsule composed of fibrous connective tissue.

Lobular Structure

  • Testes contain approximately 300 lobules housing seminiferous tubules (tubulus seminiferus contourus).

    • Around 1-4 seminiferous tubules per lobule.

Leydig and Sertoli Cells

  • Leydig Cells: Found in interstitial tissue, secrete hormones (e.g., testosterone).

  • Sertoli Cells: Support and nourish spermatogenic cells; play a crucial role in forming the blood-testis barrier and regulating spermatogenesis.

Sperm Morphogenesis

  • Spermiogenesis: Involves development of spermatozoa from spermatids; includes:

    • Formation of acrosome

    • Condensation of chromatin

    • Development of a tail

Sperm Structure

  1. Head: Contains the nucleus and acrosomal cap for fertilization.

  2. Neck: Junction between the head and tail, houses centrioles.

  3. Middle Piece: Contains the mitochondria for energy.

  4. Principal Piece: Longest part of the tail with spiral filaments.

  5. End Piece: Concludes the sperm's structure.

Epididymis and Ductus Deferens

  • Structures for transferring and maturing spermatozoa:

    • Consists of convoluted duct leading to the ductus deferens.

    • Takes around 10-15 days for sperm to mature from production to storage.

Accessory Glands

  • Glandula Vesiculosa: Enriches ejaculate with nutrients for sperm.

  • Prostate Gland: Contributes to seminal fluid and aids in sperm motility.

  • Bulbourethral Gland: Pre-ejaculatory function, lubricates and neutralizes urethra.

Urethra Structure

  • Comprises three distinct segments: prostatic, membranous, and spongy urethra.

  • Functions in expulsion of urine and seminal fluid during ejaculation.