The Male Reproductive System: Structure, Function, and Hormonal Regulation

Male and Female Reproductive System Overview

Introduction

The reproductive system ensures the continuation of species through the production of gametes and the secretion of sex hormones. Both male and female systems have primary sex organs (gonads) and accessory structures that support reproductive function.

• Gonads: Primary sex organs (testes in males, ovaries in females) responsible for hormone secretion and gamete production.

• Hormones: Testes secrete testosterone; ovaries secrete estrogens.

• Gametes: Produced via meiosis—sperm in males, ova in females.

• Accessory reproductive organs: Additional structures aiding in gamete transport, fertilization, and support.

Chromosome Sets

Diploid and Haploid Cells

Human cells contain chromosomes in sets, which are crucial for genetic inheritance and sexual reproduction.

• Diploid (2n): Most body cells have two sets of chromosomes.

• Haploid (n): Gametes (sperm and egg) have one set of chromosomes, ensuring genetic diversity upon fertilization.

Male Reproductive System

Overview of Structures

• Gonads (Testes): Produce sperm and secrete testosterone.

• Ducts: Mature, store, and transport sperm (epididymis, ductus deferens, ejaculatory duct, urethra).

• Accessory Sex Glands: Add secretions to semen (seminal vesicles, prostate, bulbourethral glands).

• Support Structures: Penis and scrotum.

Scrotum and Testes

• Scrotum: External sac, divided by a vertical septum, housing the testes. The cremaster muscle regulates testis position for temperature control.

• Testes: Descend during fetal development; contain seminiferous tubules where sperm are produced.

Testes: Internal Anatomy

• Tunica vaginalis: Outer covering formed during testicular descent.

• Tunica albuginea: Fibrous capsule beneath tunica vaginalis; extends inward to divide testis into 200–300 lobules.

• Each lobule contains 1–3 seminiferous tubules, the site of spermatogenesis.

Testes: Histology

• Interstitial (Leydig) cells: Located between seminiferous tubules; secrete testosterone.

• Sustentacular (Sertoli) cells: Support sperm development; form the blood-testis barrier.

Reproductive Ducts

• Epididymis: Site of sperm maturation and storage.

• Ductus (vas) deferens: Transports sperm to the urethra.

• Ejaculatory duct: Formed by the union of the ductus deferens and seminal vesicle duct.

• Urethra: Shared passage for urine and semen; divided into three sections (prostatic, membranous, spongy).

Penis

• Functions as a conduit for urine and semen.

• Composed of root, body, and glans penis.

• Body contains three erectile cylinders: two corpora cavernosa and one corpus spongiosum (surrounds urethra).

• Glans penis is covered by the prepuce (foreskin).

Reproductive Accessory Glands

Gland	Number	Main Secretions	Function
Seminal Vesicles	2	Viscous, alkaline fluid; fructose; prostaglandins; clotting proteins	Nourishes sperm, enhances motility, forms semen clot
Prostate Gland	1	Whitish, alkaline fluid; citrate; PSA; antimicrobial chemicals	Activates sperm, protects against infection
Bulbourethral Glands	2	Mucus; alkaline secretions	Lubricates urethra, neutralizes acidic urine

Spermatogenesis

Process and Cellular Changes

• Spermatogenic cells: Include spermatogonia (stem cells) and developing sperm cells.

• Blood-testis barrier: Formed by tight junctions between Sertoli cells; prevents immune attack on sperm.

• Duration: Takes 65–75 days to complete.

• Stages:

  • Spermatogonia and primary spermatocytes are diploid (2n).

  • Meiosis I: Produces two haploid (n) secondary spermatocytes.

  • Meiosis II: Produces four haploid (n) spermatids.

  • Spermiogenesis: Maturation of spermatids into spermatozoa.

Structure of Sperm

• Approximately 300 million sperm produced daily.

• Sperm can survive 2–5 days in the female reproductive tract.

• Head: Contains nucleus with 23 chromosomes; acrosomal cap with enzymes for oocyte penetration.

• Midpiece: Packed with mitochondria for energy.

• Tail: Flagellum for motility.

Hormonal Control of the Testes

Endocrine Regulation

• GnRH (Gonadotropin-Releasing Hormone): Released from the hypothalamus; increases at puberty.

• Stimulates the anterior pituitary to secrete:

  • FSH (Follicle-Stimulating Hormone): Promotes spermatogenesis.

  • LH (Luteinizing Hormone): Stimulates testosterone secretion from Leydig cells.

Example: If GnRH secretion increases at puberty, this triggers a rise in LH and FSH, leading to increased testosterone production and the onset of sperm production.