The Male Reproductive System Study Notes

The Male Reproductive System

Lecture Outline

  • Anatomy Overview

  • Testis

  • Epididymis

  • Ductus deferens

  • Scrotum

  • Inguinal canal

  • Accessory sex glands

    • Ampullae

    • Vesicular glands

    • Prostate gland

    • Bulbourethral glands

  • Penis

  • Prepuce

  • Physiology Overview

  • Seminiferous tubules and spermatogenesis

  • Epididymis

  • Semen and semen technology

  • Hormones of the male reproductive system

Learning Objectives

  • Describe the process of spermatogenesis from an anatomy standpoint.

  • Trace the path of spermatozoa from development in the seminiferous tubules of the testes to ejaculation from the penile urethra.

  • Compare and contrast the unique penile structures among domesticated animal species.

  • Be able to identify and describe the male accessory reproductive glands.

  • Illustrate the mitotic and meiotic divisions that result in haploid spermatozoa.

  • Describe how and where a round spermatid cell becomes an elongated, fully formed spermatozoa (differentiate between the role of the testis versus epididymis).

  • Differentiate the role of interstitial cells versus sustentacular cells for spermatogenesis (location, gonadotropin binding, hormones produced).

  • Explain the endocrine regulation of testicular function and important gonadotropin releasing factors.

  • Describe the exocrine glandular secretions and cellular components present in an ejaculate.

  • Discuss how characteristics of semen can affect fertility.

Background

  • Urology: The branch of medicine focusing on surgical and medical diseases of the male and female urinary-tract system and male reproductive organs.

  • Andrology: The medical study of the male reproductive system.

  • Endocrinology: The scientific study dealing with the endocrine system, its diseases, and its secretions known as hormones.

Overview of Male Reproductive System

  • The male reproductive tract manufactures the male gamete (spermatozoa) and delivers it to the female reproductive tract.

  • Embryologically, the reproductive system is related to the urinary system; both develop interdependently.

  • In adult males, the urethra serves as a passage for both urinary and reproductive functions.

  • Consists of two testes (testicles) in the scrotum, accessory organs including ducts and glands, and the penis.

Anatomy – Testis

  • Variability: Testes vary in shape, size, and location/attachment between species; however, their essential structure remains largely consistent.

  • Spermatic Cord: Contains blood vessels, nerves, lymphatics, and the ductus deferens, suspending each testis within the scrotum.

  • Peritoneal Investment: The spermatic cord and testis are doubly invested with peritoneum, forming the vaginal tunic/sheath, reflecting their abdominal origin and migration into the scrotal position.

Testicular Structure

  • Each testis is composed of coiled seminiferous tubules encased by the tunica albuginea, a fibrous capsule.

  • Fibrous septa (trabeculae) pass inward, dividing the testis into lobules and supporting the seminiferous tubules and interstitial tissue that produces testosterone.

  • Spermatogenesis: Takes place in seminiferous tubules where spermatozoa are formed.

Transport of Spermatozoa

  • The seminiferous tubules deliver sperm to the rete testis, which drains into the efferent ductules that coalesce into a single epididymal duct.

  • Cell Types in Seminal Tubules:

    • Leydig Cells: Interstitial cells in connective tissue secrete testosterone.

    • Sertoli Cells: Surround and support developing sperm.

Cells of the seminiferous tubule

Anatomy – Epididymis

  • Composed of a long, convoluted duct connecting the testis to the ductus deferens.

  • Houses spermatozoa during maturation (10-15 days) post-testis until ejected during ejaculation.

Anatomy – Ductus Deferens

  • Function: Muscular tube that facilitates peristaltic contractions during ejaculation, transporting sperm from the epididymis to the urethra.

  • Passages: Leaves the epididymis and traverses the inguinal canal, then routes back within the abdomen.

Anatomy – Scrotum

  • Defined as a cutaneous sac that adapts in size and shape to enclose the testes, maintaining an optimal cooler temperature for spermatogenesis.

Descent of the Testis

  • In male fetal development, the gonads begin caudal to the kidneys. Testes descend to the scrotum guided by the gubernaculum through the inguinal canal.

  • Cryptorchidism: A condition where one or both testes fail to descend, potentially leading to sterility due to higher abdominal temperatures inhibiting spermatogenesis.

Castration

  • Castration generally refers to the removal of the testes to prevent reproduction of inferior quality animals, with benefits including improved meat quality in early castration.

  • Vasectomy: Transections of the ductus deferens; prevents sperm release without affecting testosterone production.

Anatomy – Accessory Sex Glands

  • Produce the bulk of the ejaculate, providing a medium for sperm transport. Key glands include:

    • Ampulla: Enlargements at the terminal ends of the ductus deferens, especially developed in stallions, bulls, and rams, contributing to semen volume.

    • Vesicular Glands: Paired glands merging with the ductus deferens in most domesticated species, forming the ejaculatory duct.

    • Prostate Gland: Surrounds the pelvic urethra, producing alkaline secretions that influence semen odor.

    • Bulbourethral Glands: Paired glands near the pelvic urethra, notably large in boars.

Anatomy – Penis

  • Divided into three areas: glans, body, and crura (roots).

  • Composed mainly of paired erectile tissues, the corpora cavernosa, supported by connective tissue and the tunica albuginea.

  • Erection Types: Fibroelastic (ruminants and swine) versus musculocavernous (stallions) penises, affecting how reliance on blood filling influences firmness and adaptability of erection.

Unique Variations in Penile Structure

  • Varies among animal species:

    • Horses have an extended urethral process.

    • Bulls ram have helmet-shaped glans.

    • Boars possess a twisted cranial extremity with a smaller glans.

Anatomy – Prepuce

  • An external fold of skin surrounding the penis, varying in complexity among species, with notable features such as the diverticulum in pigs that accumulates secretions contributing to odor.

Anatomy – Muscles of Male Genitalia

  • Urethral Muscle: Forms the voluntary sphincter for ejaculation assistance.

  • Bulbospongiosus Muscle: Striated muscle involved in furthering peristaltic contractions for semen expulsion.

  • Ischiocavernosus Muscles: Assist in erection by compressing the venous drainage.

Physiology – Seminiferous Tubules and Spermatogenesis

  • Composed of sustentacular cells and developing sperm cells that secrete fluid aiding transport of sperm from tubules to rete testis.

  • Leydig Cells: Secreting testosterone are pivotal for male reproductive development.

Rates and Timing of Spermatogenesis

  • Varies among species from weeks to months; generally takes around 2 months in farm animals.

  • Daily production ranges from $4.4 imes 10^9$ sperm in rams to $2.0 imes 10^9$ in bulls.

Ejaculation Characteristics

  • Semen volume and sperm count decrease after multiple ejaculations; maintaining sexual rest may recoup lower sperm counts.

Physiology – Epididymis

  • Storage and Maturation: The epididymis serves as the primary storage site for sperm, transitioning them from immotile status to readiness for fertilization as they mature.

Physiology – Semen and Semen Technology

  • Composed of sperm suspended in fluid from male accessory glands.

  • Characteristics evaluated for fertility predictions include: motility, morphology, and concentration of spermatozoa.

Physiology – Hormones of the Male Reproductive System

  • Gonadotropins: FSH and LH from the anterior pituitary are essential for stimulating testicular function and spermatogenesis.

  • Testosterone: Functions beyond supporting sperm maturation, influencing secondary sex characteristics and libido.

Conclusion

  • Understanding the structure and physiology of the male reproductive system is essential in veterinary science for effective reproduction management and treatment of reproductive issues.