Male Reproductive System

Dr. Sangeeta Gourh

Introduction

The male reproductive system consists of specialized organs that are responsible for the production, maturation, and transport of male gametes and hormones.

It includes the following structures:

  • Testes

    • A pair of testes act as the primary male sex glands and are located in the scrotum.

    • They produce male gametes called spermatozoa.

    • They also secrete the male sex hormone testosterone.

  • Genital ducts

    • These include the epididymis, vas deferens, and ejaculatory duct.

    • Their function is to conduct sperms to the urethra.

    • During passage through the duct system, especially the epididymis, sperms mature and become motile.

    • Smooth muscle in the duct walls contracts during ejaculation to expel sperms.

  • Accessory sex glands

    • These include a pair of seminal vesicles, a single prostate gland, and a pair of bulbourethral glands.

    • They secrete seminal fluid, which acts as a transport medium and provides nourishment to sperms.

    • The structure and function of these glands depend on testosterone.

  • Penis

    • The penis functions as the organ of copulation.

Testis

General architecture of the testis

  • Unlike the ovary, the testes are located outside the body in the scrotum.

  • The scrotal temperature is about 2–3°C lower than body temperature, which is essential for normal spermatogenesis.

  • Each testis is oval in shape and measures approximately 5 cm in length and 2.5 cm in width.

  • The weight of each testis ranges from 10 to 15 g.

  • Tunica vaginalis

    • Each testis is surrounded, except at the posterior border, by a serous sac called the tunica vaginalis.

    • It is derived from the peritoneum during the descent of the testis.

  • Tunica albuginea

    • Deep to the tunica vaginalis is a thick white fibrous connective tissue capsule called the tunica albuginea.

    • It completely encloses the testis.

    • Along the posterior border, it thickens and projects inward to form the mediastinum testis.

  • Lobules of testis

    • Thin fibrous septa extend from the mediastinum testis to the tunica albuginea.

    • These septa divide the testis into several compartments called lobules.

    • Each lobule contains one to four highly coiled seminiferous tubules.

  • Tunica vasculosa

    • Internal to the tunica albuginea lies a layer of vascular loose connective tissue known as the tunica vasculosa.

    • It extends into the interior as interstitial connective tissue surrounding the seminiferous tubules.

    • This connective tissue contains clusters of interstitial cells of leydig, which secrete testosterone.

  • Rete testis and straight tubules

    • The mediastinum testis contains a network of irregular channels called the rete testis.

    • Seminiferous tubules connect to the rete testis through short straight tubules.

    • Straight tubules are lined by cuboidal or low columnar epithelium.

    • Rete testis is lined by simple squamous or cuboidal epithelium.

  • Efferent ductules

    • The rete testis connects to the epididymis through 10–15 efferent ductules.

    • These ductules emerge from the upper part of the testis.

    • They are lined by epithelium composed of cells of different heights, giving the lumen an uneven contour.

    • Tall columnar cells possess cilia, while short cuboidal cells contain microvilli.

Seminiferous tubules

  • Seminiferous tubules are highly coiled and tightly packed tubules present within the testis.

  • Each seminiferous tubule measures approximately 50–80 cm in length and 150–250 μm in diameter.

  • These tubules are the sites of spermatozoa production through the process known as spermatogenesis.

  • Seminiferous tubules are lined by a specialized stratified germinal epithelium, also called the seminiferous epithelium.

  • Seminiferous epithelium

    • The epithelium consists of two distinct populations of cells.

    • Spermatogenic cells, which are directly involved in spermatogenesis.

    • Sertoli cells, which provide structural support and nourishment to developing spermatozoa.

    • This specialized epithelium rests on a basement membrane.

    • Beneath the basement membrane are slender contractile smooth muscle–like cells called myoid cells.

Spermatogenic cells

  • Spermatogenic cells are arranged in an orderly developmental sequence from the basement membrane toward the lumen.

  • The stages include spermatogonia, spermatocytes, spermatids, and finally spermatozoa.

  • The process by which spermatogonia divide, differentiate, and mature into spermatozoa is termed spermatogenesis.

  • Spermatogenesis occurs in waves along the length of the seminiferous tubules.

  • In humans, the complete process takes approximately 64 ± 4 days.

  • Spermatogonia

    • Spermatogonia are immature spermatogenic cells located on the basement membrane of the seminiferous tubules.

    • They undergo mitotic division to form two types of cells.

    • Type A sper spermatogonia have darkly stained nuclei and function as stem cells of the germinal epithelium.

    • Type B spermatogonia have lightly stained nuclei and undergo further maturation.

    • Type B spermatogonia differentiate to form primary spermatocytes.

 

Genital ducts

  • Genital ducts are responsible for conducting sperms to the urethra.

  • The genital duct system includes the epididymis, ductus deferens, and ejaculatory duct.

Epididymis

  • The epididymis is a comma-shaped structure located on the posterolateral aspect of the testis.

  • It is composed of a highly coiled tube called the ductus epididymis.

  • The ductus epididymis measures approximately 6 m in length.

  • It is supported by vascular connective tissue.

  • The epididymis is divided into three parts: head, body, and tail.

  • Histological features

    • The ductus epididymis is lined by pseudostratified columnar epithelium.

    • This epithelium consists of two types of cells.

    • Tall columnar principal cells.

    • Small basal cells.

    • The tall columnar principal cells bear long microvilli known as stereocilia.

    • These cells are involved in both secretion and absorption.

  • Muscle layer

    • Beneath the epithelium lies a layer of circularly arranged smooth muscle fibers.

    • The thickness of this muscle layer gradually increases from the head to the tail.

    • In the tail region, the muscle may be organized into inner circular and outer longitudinal layers.

    • The smooth muscle is richly innervated by sympathetic fibers.

    • Intense rhythmic contractions of this muscle help in the expulsion of sperms during ejaculation.

  • Functions of epididymis

    • Storage of spermatozoa, mainly in the tail of the epididymis.

    • Maturation of spermatozoa, during which they acquire motility.

    • Absorption of testicular fluid, with approximately 90% of the fluid being absorbed.

 

Vas deferens (ductus deferens)

  • The ductus deferens is a thick, muscular tube extending from the tail of the epididymis to the prostatic urethra.

  • The distal end of the ductus deferens is dilated to form the ampulla.

  • The ampulla joins with the duct of the seminal vesicle to form the ejaculatory duct.

  • The ejaculatory duct from each side passes through the prostate gland.

  • It opens into the prostatic urethra.

  • Structure of the wall

    • The wall of the ductus deferens is composed of three distinct coats.

  • Mucosa

    • The mucosa consists of a pseudostratified columnar epithelial lining.

    • It is supported by an underlying lamina propria.

    • The epithelial cells possess stereocilia.

    • The mucosa is thrown into longitudinal folds.

    • These folds allow expansion of the duct during ejaculation.

  • Muscle layer

    • The muscle layer is composed of smooth muscle fibers.

    • The fibers are arranged into three layers.

      • Inner longitudinal layer.

      • Middle circular layer, which is the thickest.

      • Outer longitudinal layer.

  • Adventitia

    • The outermost layer is the adventitia.

    • It is composed of fibroelastic connective tissue.

    • It contains blood vessels and nerves.

Ejaculatory duct

  • Ejaculatory ducts are two in number.

  • Each ejaculatory duct measures approximately 2 cm in length.

  • Each duct is formed by the union of the duct of the seminal vesicle and the ampulla of the vas deferens.

  • After formation, the ejaculatory duct passes through the substance of the prostate gland.

  • It runs lateral to the prostatic utricle.

  • The ejaculatory duct opens into the prostatic urethra.

  • It is lined by simple columnar epithelium.

 

Seminal vesicle

  • Seminal vesicles are paired accessory sex glands located at the base of the urinary bladder.

  • Each seminal vesicle is an elongated blind tube measuring about 12–15 cm in length.

  • The tube is highly coiled upon itself, reducing its overall size to approximately 5 cm.

  • In histological sections, the same tube is seen cut at different orientations due to its coiled nature.

  • Secretions

    • Seminal vesicles secrete a thick, yellow, viscous, alkaline fluid.

    • The secretion is rich in fructose, which serves as a major energy source for sperms.

    • It also contains ascorbic acid and prostaglandins.

  • Structure of the wall

    • The wall of the seminal vesicle is composed of three coats.

  • Mucosa

    • The mucosa is thrown into complex folds.

    • These folds branch and anastomose to form crypts and cavities.

    • This arrangement gives a characteristic honeycomb appearance to the lumen.

    • The mucosal epithelium is secretory in nature.

    • It is predominantly pseudostratified low columnar epithelium.

    • In some regions, the epithelium may appear simple columnar or cuboidal, depending on the level of secretory activity.

    • The lamina propria is rich in elastic fibers.

    • It extends into and supports the mucosal folds.

  • Muscle layer

    • The muscle layer is composed of smooth muscle fibers.

    • These fibers are arranged into two layers.

      • Inner circular layer.

      • Outer longitudinal layer.

    • Contraction of the muscle layer helps in expressing the glandular secretion into the urethra through the ejaculatory duct.

  • Adventitia

    • The outermost layer is the adventitia.

    • It is made of loose connective tissue.

    • It contains blood vessels and nerves.

 

Prostate

  • The prostate is the largest accessory sex gland in males.

  • It surrounds the beginning of the male urethra.

  • In an adult male, it is approximately the size of a chestnut.

  • It weighs about 20 g.

  • General structure

    • The prostate is composed of 30–50 branched tubuloalveolar glands.

    • These glands are embedded in a fibromuscular stroma.

    • The ducts of the glands open into the prostatic urethra.

  • Capsules of prostate

    • The prostate is enclosed by two capsules.

    • The true capsule is formed by condensation of the fibromuscular stroma at the periphery.

    • The false capsule is formed by the pelvic fascia.

    • A rich venous plexus is present between the true and false capsules.

  • Secretions

    • The prostate secretes a thin, milky fluid.

    • The secretion is rich in citric acid, acid phosphatase, amylase, and fibrinolysin.

    • Fibrinolysin helps in liquefaction of coagulated semen after ejaculation.

    • Prostatic secretion forms approximately 75% of the seminal fluid.

    • Serum prostate specific antigen (psa) levels are increased in patients with prostatic tumors.

  • Arrangement of prostatic glands

    • Prostatic glands are arranged concentrically around the urethra.

    • They are divided into three groups.

      • Mucosal glands.

      • Submucosal glands.

      • Main glands.

    • Mucosal glands are small tubular glands located in the inner zone.

    • They open directly into the urethra.

    • Submucosal glands are tubuloalveolar glands located in the intermediate zone.

    • Main glands are tubuloalveolar glands present in the outer zone.

    • Submucosal and main glands open into the prostatic sinus of the urethra through long ducts.

  • Histological features

    • Histologically, the prostate consists of parenchyma and fibromuscular stroma.

    • The parenchyma is formed by large irregular prostatic alveoli with wide lumina.

    • The secretory epithelium lining the alveoli varies from cuboidal to columnar depending on secretory activity.

    • The lumen may contain spherical prostatic concretions known as corpora amylacea.

    • These concretions are formed by condensation of prostatic secretions.

    • The number of prostatic concretions increases with age and may undergo calcification.

  • Fibromuscular stroma

    • The fibromuscular stroma provides support to the parenchyma.

    • It is composed of smooth muscle fibers mixed with connective tissue fibers.

    • The fibers run in different directions.

    • The stroma also contains blood vessels, lymphatics, and nerves.

  • Prostatic urethra

    • The prostatic urethra within the prostate is crescent-shaped.

    • It shows multiple diverticula or outpocketings.

    • The upper part is lined by transitional epithelium.

    • The lower part is lined by stratified columnar epithelium.

 

Penis

Gross features

  • The penis is an erectile male organ of copulation.

  • It is cylindrical in shape.

  • During erection, it becomes enlarged, elongated, and turgid.

  • Erectile bodies

    • The penis is composed of three cylindrical masses of spongy cavernous tissue.

    • A pair of corpora cavernosa.

    • A single corpus spongiosum.

    • The corpora cavernosa are positioned side by side on the dorsal aspect of the penis.

    • Each corpus cavernosum is traversed by the deep artery of the penis.

  • Corpus spongiosum and glans

    • The corpus spongiosum is located ventrally.

    • It is traversed by the penile urethra.

    • Distally, the corpora cavernosa end blindly beneath the glans penis.

    • The glans penis is the enlarged cap-like terminal part of the corpus spongiosum.

    • The glans penis forms the tip of the penis.

    • It is covered by a retractable fold of skin called the prepuce.

    • The fossa navicularis of the urethra passes through the glans penis and opens at the external urethral meatus.

Microscopic structure

  • The erectile cavernous tissue of the corpora cavernosa and corpus spongiosum consists of endothelium-lined cavernous spaces.

  • These spaces are separated by trabeculae.

  • The trabeculae contain collagen fibers, elastic fibers, and smooth muscle fibers.

  • Blood supply and erection

    • The cavernous spaces receive blood from the dorsal and deep arteries of the penis.

    • Additional blood supply comes from the bulbourethral artery.

    • Blood drains from the cavernous spaces through the dorsal veins.

    • During erection, parasympathetic stimulation causes vasodilatation of arteries.

    • This results in filling and engorgement of cavernous spaces.

    • Engorgement compresses peripheral veins, reducing venous outflow and maintaining erection.

  • Penile urethra

    • The penile urethra has an irregular outline.

    • This is due to deep outpocketings known as sinuses of morgagni.

    • It is lined by stratified columnar epithelium.

    • The urethra is lubricated by mucous secretion from the paraurethral glands of littre.

    • These glands open into the outpocketings of the penile urethra.

  • Epithelial lining

    • The glans penis, external urethral meatus, and navicular fossa are lined by stratified squamous epithelium.

  • Tunica albuginea

    • The erectile bodies are enclosed by a fibrous sheath called the tunica albuginea.

    • The tunica albuginea consists of two layers.

    • An outer layer.

    • An inner layer.

    • The outer layer is composed of longitudinal collagen fibers.

    • It forms a common covering for all three erectile bodies.

 

MCQs

1. Seminiferous tubules are lined by:

A. Simple squamous epithelium
B. Simple columnar epithelium
C. Stratified germinal epithelium
D. Pseudostratified epithelium

Answer: C

2. Which cell forms the blood–testis barrier?

A. Spermatogonia
B. Myoid cells
C. Leydig cells
D. Sertoli cells

Answer: D

3. Interstitial cells of leydig are located in:

A. Lumen of seminiferous tubules
B. Tunica albuginea
C. Interstitial tissue between tubules
D. Rete testis

Answer: C

4. Hormone secreted by leydig cells is:

A. Estrogen
B. Progesterone
C. Testosterone
D. Inhibin

Answer: C

5. Myoid cells are present:

A. Inside seminiferous tubules
B. Beneath basement membrane
C. Inside rete testis
D. In epididymal lumen

Answer: B

6. Stereocilia are characteristically seen in:

A. Vas deferens
B. Seminiferous tubules
C. Epididymis
D. Ejaculatory duct

Answer: C

7. Epithelium of epididymis is:

A. Simple columnar
B. Stratified squamous
C. Pseudostratified columnar
D. Transitional

Answer: C

8. Principal cells of epididymis are involved in:

A. Phagocytosis
B. Spermatogenesis
C. Secretion and absorption
D. Hormone synthesis

Answer: C

9. Irregular lumen of epididymis is due to:

A. Mucosal folds
B. Stereocilia
C. Variable cell height
D. Muscular contraction

Answer: C

10. Which duct shows the thickest smooth muscle coat?

A. Epididymis
B. Vas deferens
C. Ejaculatory duct
D. Urethra

Answer: B

11. Muscle layers of vas deferens are:

A. One
B. Two
C. Three
D. Four

Answer: C

12. Thickest muscle layer of vas deferens is:

A. Inner longitudinal
B. Middle circular
C. Outer longitudinal
D. Adventitia

Answer: B

13. Epithelium of vas deferens is:

A. Simple columnar
B. Pseudostratified columnar with stereocilia
C. Stratified squamous
D. Transitional

Answer: B

14. Ejaculatory duct is formed by:

A. Epididymis and urethra
B. Vas deferens and prostate
C. Ampulla of vas deferens and seminal vesicle duct
D. Seminal vesicle and urethra

Answer: C

15. Epithelium of ejaculatory duct is:

A. Pseudostratified columnar
B. Stratified squamous
C. Simple columnar
D. Transitional

Answer: C

16. Seminal vesicle secretion is rich in:

A. Citric acid
B. Fructose
C. Testosterone
D. Urea

Answer: B

17. Lumen of seminal vesicle shows:

A. Smooth outline
B. Honeycomb appearance
C. Narrow lumen
D. Villi

Answer: B

18. Epithelium of seminal vesicle is:

A. Stratified squamous
B. Pseudostratified low columnar
C. Transitional
D. Simple squamous

Answer: B

19. Muscle layer of seminal vesicle consists of:

A. Only circular layer
B. Only longitudinal layer
C. Inner circular and outer longitudinal
D. Skeletal muscle

Answer: C

20. Largest accessory sex gland is:

A. Seminal vesicle
B. Bulbourethral gland
C. Prostate
D. Epididymis

Answer: C

21. Prostatic glands are:

A. Simple tubular
B. Alveolar
C. Tubuloalveolar
D. Compound tubular

Answer: C

22. Which substance liquefies coagulated semen?

A. Fructose
B. Citric acid
C. Fibrinolysin
D. Amylase

Answer: C

23. Corpora amylacea are seen in:

A. Seminal vesicle
B. Epididymis
C. Prostate
D. Testis

Answer: C

24. Corpora amylacea increase with:

A. Puberty
B. Infection
C. Age
D. Ejaculation

Answer: C

25. Fibromuscular stroma of prostate contains:

A. Skeletal muscle
B. Smooth muscle and connective tissue
C. Elastic cartilage
D. Adipose tissue

Answer: B

26. Upper part of prostatic urethra is lined by:

A. Stratified squamous epithelium
B. Transitional epithelium
C. Simple columnar epithelium
D. Pseudostratified epithelium

Answer: B

27. Penis contains how many erectile bodies?

A. One
B. Two
C. Three
D. Four

Answer: C

28. Corpora cavernosa are located on:

A. Ventral aspect
B. Dorsal aspect
C. Lateral aspect
D. Central region

Answer: B

29. Penile urethra passes through:

A. Corpora cavernosa
B. Corpus spongiosum
C. Tunica albuginea
D. Glans only

Answer: B

30. Erectile tissue is composed of:

A. Solid muscle mass
B. Cavernous spaces
C. Glandular tissue
D. Fat cells

Answer: B

31. Cavernous spaces are lined by:

A. Cuboidal epithelium
B. Columnar epithelium
C. Endothelium
D. Stratified epithelium

Answer: C

32. Erection of penis is mediated mainly by:

A. Sympathetic nerves
B. Parasympathetic nerves
C. Somatic nerves
D. Endocrine reflex

Answer: B

33. Tunica albuginea of penis is:

A. Muscular layer
B. Epithelial covering
C. Fibrous sheath
D. Serous membrane

Answer: C

34. Sinuses of morgagni are present in:

A. Prostatic urethra
B. Penile urethra
C. Membranous urethra
D. Bladder

Answer: B

35. Glands of littre secrete:

A. Enzymes
B. Testosterone
C. Mucus
D. Fructose

Answer: C

36. Glans penis is lined by:

A. Simple columnar epithelium
B. Pseudostratified epithelium
C. Stratified squamous epithelium
D. Transitional epithelium

Answer: C

37. Seminiferous tubules open into:

A. Epididymis directly
B. Efferent ductules
C. Rete testis via straight tubules
D. Vas deferens

Answer: C

38. Rete testis is lined by:

A. Stratified epithelium
B. Simple squamous or cuboidal epithelium
C. Pseudostratified epithelium
D. Transitional epithelium

Answer: B

39. Efferent ductules show:

A. Smooth lumen
B. Scalloped lumen
C. Collapsed lumen
D. Narrow lumen

Answer: B

40. Cilia in efferent ductules are present on:

A. Cuboidal cells
B. Basal cells
C. Columnar cells
D. Myoid cells

Answer: C

41. Primary function of epididymis is:

A. Hormone secretion
B. Spermatogenesis
C. Sperm maturation and storage
D. Ejaculation

Answer: C

42. Basement membrane of seminiferous tubules supports:

A. Leydig cells
B. Sertoli cells and spermatogonia
C. Spermatozoa
D. Rete testis

Answer: B

43. Spermatogenesis occurs in:

A. Epididymis
B. Seminiferous tubules
C. Rete testis
D. Vas deferens

Answer: B

44. Duration of spermatogenesis in humans is:

A. 30 days
B. 45 days
C. 64 days
D. 90 days

Answer: C

45. Tunica vaginalis is derived from:

A. Mesentery
B. Pelvic fascia
C. Peritoneum
D. Endoderm

Answer: C

46. Mediastinum testis contains:

A. Seminiferous tubules
B. Rete testis
C. Leydig cells
D. Vas deferens

Answer: B

47. Efferent ductules connect:

A. Seminiferous tubules to vas deferens
B. Rete testis to epididymis
C. Epididymis to vas deferens
D. Prostate to urethra

Answer: B

48. Predominant muscle type in male reproductive ducts is:

A. Skeletal muscle
B. Cardiac muscle
C. Smooth muscle
D. Elastic tissue

Answer: C

49. Sympathetic stimulation is important for:

A. Erection
B. Ejaculation
C. Spermatogenesis
D. Hormone secretion

Answer: B

50. Prostate specific antigen is produced by:

A. Seminal vesicle
B. Sertoli cells
C. Prostate
D. Leydig cells

Answer: C