Human Reproduction Anatomy and Spermatogenesis

Introduction

• Human reproduction involves both male and female participation
• Males produce gametes and assist in transporting them through the female reproductive tract

Anatomical Components

• Gonads: Testes
• Ducts: Epididymis, vas deferens, ejaculatory ducts, urethra
• Glands: Seminal vesicles, prostate, bulbourethral glands
• Penis

Testicle Anatomy and Histology

• Oval-shaped; adult size ~4.5 cm x 2.5 cm, volume ~18 mL
• Located within the scrotum
• Surrounded by a fibrous capsule (tunica albuginea)
• Divided into lobules (250-300) containing seminiferous tubules

Seminiferous Tubules

• Each lobule contains 2-4 seminiferous tubules (~165µm diameter, 30-80 cm long)
• Seminiferous tubules converge into the rete testis
• Connect to efferent ductules, then to the epididymis

Spermatogenesis

• Process: Production of sperm from spermatogonia
• Stages:
  • Multiplication phase: spermatogonia multiply
  • Meiotic division phase: spermatocytes divide, forming spermatids
  • Spermiogenesis phase: spermatids mature into sperm
• Takes ~74 days in males
• Production: ~50-150 million sperm/day at age 20, declining to about 3.8 million at 90

Hormonal Control of Spermatogenesis

• Hormones Involved: FSH (Follicle-Stimulating Hormone) and testosterone. Both have both direct and indirect effects on Sertoli cells.
• Hormonal Action:
  • FSH stimulates Sertoli cells
  • Testosterone potentiates this action by increasing gene expression levels for proteins and enzymes.
• Local Control: Feedback mechanisms involving factors exchanged between Sertoli cells and germ cells.

Testicle Endocrine Function

• Hormone Production: Primarily testosterone by Leydig cells (95%), with some androgens produced by other tissues.
• Testosterone Metabolism: primarily in the liver and other tissues. Some testosterone is converted into dihydrotestosterone (DHT), while some is converted to estrogen.

Testosterone Effects

• Internal & External Gender Development: Involves significant internal and external differences in development of the male reproductive system both at fetal/placental stages and during puberty.
• Secondary Sexual Characteristics: Development of male secondary sexual characteristics, such as deepening of the voice, body hair, and muscular development.
• Anabolic Effects: Increased protein synthesis and muscle mass.

Function of the Penis

• Erection: A physiological mechanism involved in sexual intercourse and involves vascular changes to the penis.
  • Requires activation of parasympathetic nerves and subsequent release of nitric oxide (NO)
  • Blood flow into the corpora cavernosa causes an erection.
  • Sympathetic impulses reduce blood flow to the corpora cavernosa and cause the return to the flaccid state.
  • The degree of relaxation and contraction of the muscles of the corpora cavernosa is involved.
• Ejaculation: expulsion of semen involves muscular contractions in the epididymis, seminal vesicles, prostate and urethra.

Hormonal Regulation of Male Reproductive Function

• Hypothalamus & Pituitary Gland: Crucial roles in initiating and controlling the release of reproductive hormones.
• Feedback Mechanisms: Regulation involves negative feedback loops to maintain hormonal homeostasis.

Life Span Changes in Testicular Function

• Fetal Period: Significant testosterone production and development of male reproductive tract.
• Adulthood: Relatively stable hormone levels, but decreased sperm production is gradual after 20-30 years of age.
• Aging: Gradual decline in testicular function and hormone production.

Epididymis, Seminal Vesicles and Prostate Functions

• Epididymis: Maturation and storage of sperm, and facilitating the movement and transport of spermatozoa to the vas deferens.
• Seminal Vesicles: Contribute fluid to the ejaculate, rich in fructose for sperm energy.
• Prostate: Secretion contributes to the seminal fluid, and it contains various components vital to sperm viability.

This quiz explores the anatomical components and histology of male reproductive structures, including the testes and seminiferous tubules. Delve into the process of spermatogenesis, examining the stages involved in sperm production. Perfect for students studying human biology or anatomy.