11 The Male Reproductive System

Page 1: Introduction to Male Reproductive System

• Lecturer: Dr. Elita Partosoedarso

• Recording Availability: Can be accessed on YouTube.

• GoogleSlides & GoogleDocs Notes:

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  • Do not request edit access.

• Lecture Approach: Watch complete recording without pauses; a 40-minute video should take 40 minutes to view.

Page 2: General Function and Structure of the Male Reproductive System

Function

• Gamete Production:

  • Produces sperm (male gametes) for sexual reproduction.

  • Unites with female gamete (oocyte) to create an offspring, enhancing genetic variation.

• Transport:

  • Moves sperm to the female reproductive tract for fertilization.

General Structure

• Essential Organs (Gonads):

  • Testes: Produce sperm and androgens (mainly testosterone).

• Accessory Organs and Ducts:

  • Facilitate sperm maturation and transport through ducts to the penis.

Page 3: Overview of Male Reproductive Organs

Essential Organs

• Testes: Produce male gametes (sperm).

• Accessory Organs:

  • Genital Ducts:

    • Epididymis (2), Vas deferens (2), Ejaculatory ducts (2), Urethra.

  • Reproductive Glands:

    • Seminal vesicles (2), Prostate, Bulbourethral glands (2).

  • Other Structures:

    • Scrotum, Penis, Spermatic cords (2).

Page 4: Homeostasis and Scrotum Function

Homeostasis

• Scrotum:

  • Structure: Skin-covered pouch divided into two sacs, each with a testis and epidermis.

  • Location: Extends from body behind penis; aids in keeping testes at 2-4°C below body temp for effective sperm production.

  • Dartos & Cremaster Muscles:

    • Dartos: Helps in contraction and heat conservation.

    • Cremaster: Elevates testes, allowing temperature regulation.

Response to Temperature Changes

• Cold Environment: Muscles contract; testes move closer to the body to retain heat.

• Warm Environment: Muscles relax; testes move away for heat loss.

Page 5: Testes Structure and Function

• Functions:

  • Produce sperm and androgens, active throughout male reproductive lifespan.

• Structure:

  • Paired within the scrotum, surrounded by:

    1. Tunica Vaginalis: Outer serous membrane.

    2. Tunica Albuginea: Dense connective tissue, divides testes into lobules containing interstitial cells and Sertoli cells.

Page 6: Seminiferous Tubules

Structure

• Tightly coiled hollow tubules, comprise majority of the testis.

Function

• Site of sperm cell formation; cells develop from the basement membrane to the lumen.

Cell Types

1. Sustentacular (Sertoli) Cells:

• Support and protect developing sperm.

• Secrete inhibin to inhibit GnRH and FSH; produce ABP to maintain testosterone solubility.

2. Interstitial (Leydig) Cells:

• Secrete testosterone; located between tubules.

• Blood-Testis Barrier (BTB):

  • Formed by tight junctions, protects developing sperm from immune response.

Page 7: Structure and Function of the Penis

• Function:

  • Male copulatory organ; adapts to both flaccid (urination) and turgid (sexual arousal) states.

Structure

1. Penile Shaft:

• Contains erectile tissues:

  • Corpus Cavernosum: 2 larger lateral chambers.

  • Corpus Spongiosum: Smaller chamber surrounding the urethra.

2. Glans Penis:

• Highly innervated for sexual sensitivity.

Erection Mechanism

• Increased pressure fills erectile chambers; venous return is constrained to maintain erection.

Page 8: Structure of Mature Sperm

• Size: Smaller than most cells, sperm volume is much less than oocyte volume.

Parts of Mature Sperm

1. Head:

• Compact haploid nucleus covered by acrosome containing enzymes for fertilization.

2. Middle Piece:

• Contains mitochondria for ATP production.

3. Tail:

• Comprises flagellum and end-piece for motility.

Page 9: Spermatogenesis

Overview

• Begins at puberty; production cycles take ~64 days.

• Production Rate: 100-300 million sperm daily.

• Chromosomal Counts:

  1. Spermatogonia: Diploid (2n), 46 chromosomes.

  2. Mature Sperm: Haploid (1n), 23 chromosomes.

Stages of Development

• Spermatogenesis Process:

  • Progresses through stages from spermatogonia to spermatozoa; involves cytoplasm reduction and organelle formation.

Page 10: Pathway of Sperm

Movement Through Reproductive Tract

1. Epididymis:

• Length: 6 m when straightened.

2. Ductus Deferens:

• Joins with seminal vesicle at ampulla.

3. Prostate Gland:

• Secretes alkaline fluid for coagulation of sperm.

4. Ejaculatory Duct:

• Transports sperm into prostatic urethra.

5. Seminal Vesicles:

• Contribute fluids containing fructose.

Page 11: Fertilization Process

Definition

• Fertilization: Sperm uniting with oocyte.

Mechanism

• Interaction leading to a diploid zygote formation.

  1. Sperm binds to oocyte receptors.

  2. Acrosomal enzymes facilitate penetration.

  3. Timeframe: Journey can take 30 minutes to 2 hours.

  4. Sperm viability: 3-5 days in uterine tubes.

Page 12: Mechanisms to Prevent Polyspermy

Definition

• Polyspermy: More than one sperm entering an oocyte.

Prevention Mechanism

1. Fast Block:

• Change in sodium ion permeability of the oocyte membrane.

2. Slow Block (Cortical Reaction):

• Release of proteins to prevent further sperm penetration.

Page 13: Functions of Testosterone

• Promotes spermatogenesis.

• Development of secondary sexual characteristics.

• Regulates metabolism and protein synthesis.

• Impacts growth and skeletal development.

Page 14: Control of Testosterone Production

Mechanism

• Negative feedback loop involving:

  • Gonadotropin-releasing hormone (GnRH): from hypothalamus.

  • Luteinizing hormone (LH): produced by anterior pituitary, stimulates Leydig cells.

  • Follicle-stimulating hormone (FSH): promotes spermatogenesis, stimulates Sertoli cells.

  • Inhibin: inhibits FSH release.

Page 15: Comparison of Gametogenesis

• Female vs Male Gametogenesis:

  • Differences in timing, duration, and quantity of gamete production.

Page 16: Sexual Differentiation

Overview

• Begins weeks 9-12 of fetal development.

• Requires SRY gene on Y chromosome to develop male characteristics.

• Suppression of female developmental genes and differentiation into spermatogonia.

Page 17: Further Sexual Development at Puberty

Changes During Puberty

• Become less sensitive to negative feedback; gonads mature with increased hormone production leading to spermatogenesis.

Page 18: Signs of Puberty

Male Characteristics

• Growth of testes, scrotum, penis, voice deepening, muscular development, hair growth.

Page 19: Hormone Production in Females

Estrogen Levels

1. Low until puberty.

2. Increase during reproductive years, falls at menopause.

Page 20: Hormone Production in Males

Testosterone Levels

• Rise during fetal development, peak at puberty, taper off with age.