Lecture Notes: Physiology of the Male Reproductive System

Overview

Focus on spermatogenesis (sperm production) and hormones regulating male reproductive functions.

Somatic Cell Division (Mitosis):
- Produces two genetically identical cells.
- Used for replacing dead/injured cells and tissue growth.
Reproductive Cell Division (Meiosis):
- Produces gametes (sperm and eggs).
- Reduces chromosome number by half.

Takes 65-75 days.
Spermatogonia:
- Stem cells with 46 chromosomes (2n).
- Some remain as a reservoir for future sperm production.
Primary Spermatocytes:
- Also have 46 chromosomes.
- Undergo DNA replication before meiosis.
Meiosis Stages:
- First Phase: Formation of secondary spermatocytes each with 23 chromosomes (1n).
- Second Phase: Formation of spermatids, each with 23 chromosomes.
Spermiogenesis:
- Transformation of spermatids into sperm.
- Development of acrosome, flagellum, and mitochondria.
- Sperm released into lumen of seminiferous tubules.

Gonadotropin-Releasing Hormone (GnRH):
- Secreted by hypothalamus.
- Stimulates anterior pituitary to secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

Luteinizing Hormone (LH):
- Stimulates secretion of testosterone from interstitial cells.
Follicle-Stimulating Hormone (FSH):
- Indirectly stimulates spermatogenesis.
- Works with testosterone on sustentacular cells to secrete androgen-binding protein.
Testosterone:
- Produced by testes (interstitial cells).
- Stimulates spermatogenesis, development of male reproductive system, secondary sexual characteristics, and sexual behavior.
Androgen-Binding Protein:
- Keeps testosterone concentration high in blood for spermatogenesis.
Inhibin:
- Released when sufficient spermatogenesis occurs.
- Inhibits secretion of FSH.

Before birth: Development of male reproductive ducts and testes descent.
At puberty: Enlargement of male sex organs and development of masculine characteristics (e.g., muscle growth, voice deepening).
Adulthood: Influences sexual behavior and libido.