The Male Reproductive System

The Male Reproductive System

Reproduction

  • Definition: Creation of a new organism by combining the genetic material of two parent organisms.

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Reproductive System

  • Purpose: Designed to produce offspring and perpetuate the species.

    • Male gametes: Sperm cells.

    • Female gametes: Ova.

    • Fertilization: The joining of a sperm cell and an ovum.

    • Zygote: Formed as a result of fertilization.

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Components of the Reproductive System

  • Primary Sex Organs (Gonads):

    • Testes: Produce gametes (sex cells) and secrete steroid sex hormones.

    • Ovaries: Also produce gametes and secrete hormones.

  • Accessory Reproductive Organs:

    • Ducts, glands, external/internal genitalia.

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Role of Sex Hormones

  • Functions:

    • Development and function of reproductive organs.

    • Influence sexual behavior and drives.

    • Growth and development of various other organs and tissues.

  • Types of Hormones:

    • Androgens (in males).

    • Estrogens and progesterone (in females).

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Male Reproductive System Overview

  • Functions: Produces, nourishes, stores, and transports gametes (sperm cells).

  • Reproductive Structures:

    • Testis: Gonads responsible for sperm production.

    • Penis: Copulatory organ.

    • Epididymis: Site for sperm maturation.

    • Ductus deferens: Transports sperm.

    • Ejaculatory duct: Conveys sperm into the urethra.

    • Urethra: Final passage for urine and semen.

    • Seminal gland: Produces seminal fluid.

    • Prostate gland: Adds fluid to semen.

    • Bulbo-urethral gland: Produces pre-ejaculate fluid.

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Anatomical Components of Male Reproductive System

  • Illustration Includes: Peritoneum, seminal gland (vesicle), ampulla of ductus deferens, ejaculatory duct, rectum, prostate, bulbo-urethral gland, anus, bulb of penis, ductus deferens, epididymis, testis, scrotum, ureter, urinary bladder, prostatic urethra, etc.

Testes

  • Definition: The male gonads responsible for sperm production.

  • Location: Hang outside of the body in a pouch called the scrotum.

  • Functions of Scrotum:

    • Rodent skin pouch that helps maintain a temperature 3ºC lower than core body temperature, which is necessary for sperm production.

  • Muscular Structures Involved:

    • Dartos muscle: Pulls the scrotum close to the body.

    • Cremaster muscles: Elevate and lower the testes.

  • Development: Testes are formed near the kidneys in the abdominal cavity and descend into the scrotum during development through inguinal canals.

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Testis Structure

  • Each testis is surrounded by two tunics:

    • Tunica vaginalis: Outer serous membrane.

    • Tunica albuginea: Inner tough fibrous lining, also forms septa inside the testis which separates the testes into lobules containing seminiferous tubules.

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Clinical Aspects of Testes

  • Testicular Cancer:

    • Rare but most common cancer in men aged 15–35.

    • Risk Factor: Cryptorchidism (undescended testis).

    • Sign: Painless solid mass in the testis.

    • Treatment: 90% cured by surgical removal of the testis with possible use of radiation or chemotherapy.

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Seminiferous Tubules

  • Function: Site of sperm production contained in lobules of the testes.

  • Structure: Thick, stratified epithelium surrounding a central fluid-containing lumen.

  • Leydig Cells: Interstitial endocrine cells that produce testosterone and secrete it into the interstitial fluid.

  • Pathway:

    • Seminiferous tubules uncoil and lead to the straight tubules, which interconnect to form the rete testis, leading to efferent ductules that connect to the epididymis.

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Function of Testes

  • Primary Functions:

    • Produce sperm.

    • Sperm pathway: Seminiferous tubules → straight tubule → rete testis → efferent ductules → epididymis → ductus deferens → ejaculatory duct → urethra.

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Male Reproductive Tract

  • Definition: A system of ducts that carry sperm from the testes to the body exterior.

  • Components Include:

    • Epididymis: Where sperm mature.

    • Ductus deferens: Transports sperm.

    • Ejaculatory duct: Joins with sperm and seminal fluid.

    • Urethra: Final pathway for semen.

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Epididymis

  • Function: Sperm maturation.

    • Sperm cells travel from seminiferous tubules to epididymis to mature, taking about 20 days.

    • Can store sperm for several months.

    • During ejaculation, the epididymis contracts and expels sperm into the ductus deferens.

  • Structure:

    • Parts of Epididymis:

    • Head: Receives immature sperm via efferent ducts.

    • Body: Contains coiled tubes.

    • Tail: Tubes begin to uncoil into the ductus deferens.

    • Microvilli: Absorb testicular fluid and provide nutrients to stored sperm.

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Spermatic Cord

  • Definition: Cord-like structures that run from the deep inguinal ring to each testicle.

  • Contents of Spermatic Cord: Encloses nerve fibers, blood vessels, lymphatics that supply testes.

  • Includes ductus deferens, blood vessels, lymphatics, and nerves.

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Ductus (Vas) Deferens

  • Measurement: Approximately 45 cm long.

  • Pathway:

    • Begins at the tail of the epididymis, travels through spermatic cord, ascends into abdominal cavity through inguinal canal, curves around urinary bladder, descends towards the prostate gland, and joins the duct of seminal vesicle to form the ejaculatory duct.

  • Function: Smooth muscle in walls propels sperm from epididymis to urethra.

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Urethra

  • Function: Conveys both urine and semen but at different times.

  • Regions:

    • Prostatic urethra: Surrounded by prostate gland.

    • Membranous urethra: Intermediate part of urethra.

    • Penile (spongy) urethra: Runs through penis and opens at external urethral orifice.

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Accessory Reproductive Organs

  • Components:

    • Seminal Vesicles (Glands): Produce alkaline seminal fluid, joins ductus deferens to form ejaculatory duct; accounts for 70% of semen volume.

    • Prostate: Encircles prostatic urethra, secretes milky fluid contributing 30% of semen volume, plays a role in sperm activation.

    • Bulbo-urethral Glands: Also known as Cowper’s glands, produce pre-ejaculate that lubricates the glans penis and neutralizes acidic urine in urethra, constitutes 5% of semen volume.

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Seminal Vesicles

  • Location: On the posterior surface of the bladder.

  • Secretion: Produces viscous alkaline seminal fluid containing fructose, citric acid, coagulating enzyme (vesiculase), and prostaglandins; yellow pigment fluoresces with UV light.

  • Function: Provides primary nutrient source for sperm and contributes significantly to semen volume.

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Prostate Gland

  • Location: Encircles prostatic urethra, inferior to bladder.

  • Secretion: Milky, slightly acidic fluid containing citrate, enzymes, and prostate-specific antigen (PSA), which plays a role in sperm activation.

  • Function: 30% of semen volume.

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Clinical Aspects of Prostate

  • Prostate Cancer: Second leading cause of cancer death in males; detected through digital exam and PSA levels; can be treated with drugs, surgery, and occasionally radiation.

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Bulbo-Urethral Glands

  • Definition: Also called Cowper's glands, pea-sized glands located inferior to prostate.

  • Secretion: Produces pre-ejaculate, a thick clear mucus serving to lubricate glans penis and neutralize remnants of acidic urine in the urethra.

  • Volume Contribution: 5% of semen volume.

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Penis Structure

  • Components:

    • Root: Anchors penis proximally to pubic arch.

    • Body (Shaft): Composed of erectile tissue.

    • Glans penis: Forms the distal end surrounding the external urethral orifice.

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Internal Anatomy of the Penis

  • Structure: Spongy urethra surrounded by three cylindrical bodies of erectile tissue:

    • Corpus spongiosum: Surrounds the urethra and expands to form glans penis.

    • Corpora cavernosa: Paired dorsal erectile bodies.

  • Function: Erection occurs when erectile tissue engorges with blood.

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Male Sexual Response

  • Erection Mechanism:

    • Parasympathetic nerves activate, causing smooth muscles in arterial walls to relax.

    • Arterial vessels dilate and engorge with blood, leading to erection.

  • Semen Release and Ejaculation:

    • Sympathetic nerves induce peristaltic action in the ductus deferens, seminal glands, prostate, and bulbo-urethral glands to facilitate ejaculation.

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Clinical Aspects of Sexual Health

  • Erectile Dysfunction:

    • Occurs when parasympathetic nerves release insufficient nitric oxide (NO).

    • Causes include alcohol, drugs, hormonal changes, blood vessel issues, and nervous system problems.

    • Treatment options include drugs like Viagra and Cialis that enhance NO effects.

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Semen Composition

  • Volume: Contains 20–150 million sperm/ml with accessory gland secretions.

  • Components:

    • Fructose for ATP production.

    • Alkaline pH to neutralize acidity of male urethra and female vagina, enhancing motility.

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Functions of Semen

  • Mechanisms:

    • Prostaglandins decrease cervical mucus viscosity and stimulate reverse peristalsis in the uterus.

    • Hormone relaxin and enzymes facilitate sperm motility while ATP provides energy.

    • Semen suppresses the female immune response and has antibacterial properties.

    • Contains clotting factors that initially coagulate semen to prevent loss, followed by liquefaction due to fibrinolysin.

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Sperm Development Processes

  • Spermatogenesis: Formation of sperm cells initiated by mitosis of spermatogonia (stem cells).

  • Meiosis Process: Involves two rounds of cell division producing haploid cells.

  • Spermiogenesis: Physical transformation of spermatids into mature spermatozoa.

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Detailed Mechanism of Spermatogenesis

  • Mitosis of Spermatogonia: Stem cells divide to form primary spermatocytes.

    • Type A cells maintain germ cell line; Type B cells become primary spermatocytes.

  • Meiotic Stages:

    • Primary spermatocyte undergoes Meiosis I (2n) yielding secondary spermatocytes (n).

    • Secondary spermatocytes undergo Meiosis II producing haploid spermatids (n).

    • Eventually maturing into sperm cells.

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Role of Sustentocytes (Sertoli Cells)

  • Functions:

    • Extend through the wall of tubule surrounding developing sperm cells.

    • Provide nutrients and signals for division, move cells along to lumen, and secrete testicular fluid for transport.

    • Phagocytize faulty germ cells and excess cytoplasm.

    • Produce mediators to regulate spermatogenesis, including inhibin to control sperm formation rate and androgen-binding protein (ABP) to bind testosterone within seminiferous tubules.

    • Maintain the blood-testis barrier, supporting gamete development.

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Final Stages of Sperm Development

  • Spermiogenesis: Nonmotile spermatids become motile spermatozoa through elongation, loss of excess cytoplasm, and tail formation.

  • Major Regions in Sperm:

    • Head: Contains genetic material and acrosome, which enables penetration of the egg.

    • Midpiece: Contains mitochondria for energy.

    • Tail (Flagellum): Responsible for motility.

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Male Sex Hormones

  • Testosterone: Main male hormone synthesized from cholesterol influencing spermatogenesis and secondary sex characteristics.

    • Acts on accessory organs, promotes growth, and has anabolic effects.

    • Deficiency leads to atrophy and impaired erectile function; treatable with testosterone replacement.

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Male Secondary Sex Characteristics

  • Features induced by male hormones (mainly testosterone):

    • Masculinization of the embryonic brain.

    • Growth of pubic, axillary, and facial hair.

    • Enhanced growth of chest hair and deepening voice.

    • Increase in skin thickness and oiliness.

    • Bone growth and increased density.

    • Muscle growth and mass increase.

    • Boosts basal metabolic rate and influences sex drive (libido) in both genders.

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