Male Reproductive System Lab

Learning Objectives

  • Describe the histological organization of the testis and the process of spermatogenesis in the germinal epithelium of the seminiferous tubule.
  • Contrast spermatogenesis from spermiogenesis.
  • Draw a sperm cell and label its major parts.
  • Explain the importance of each portion of the duct system and accessory glands of the male reproductive tract.
  • Explain the structural and functional significance of the blood-testis barrier.
  • Describe the structure and function of the prostate gland.
  • Recognize some key pathological examples related to the tubes and glands of the male reproductive system.

Keywords

  • testis
  • excretory duct system
  • accessory gland
  • semen
  • tunica albuginea
  • tunica vascularis
  • septa
  • seminiferous tubule
  • germinal epithelium
  • Sertoli cell
  • blood-testis barrier
  • adluminal compartment
  • spermatogenic cell
  • Leydig (interstitial) cell
  • crystal of Reinke
  • spermatogenesis
  • spermatogonium
  • primary spermatocyte
  • secondary spermatocyte
  • spermatid
  • spermiogenesis
  • spermatozoan
  • acrosome
  • flagellum
  • residual body
  • capacitation
  • tubulus rectus
  • rete testis
  • ductus efferentes
  • ductus epididymis
  • epididymis
  • stereocilia
  • basal cell
  • ductus deferens
  • ampulla
  • ejaculatory duct
  • urethra
  • seminal vesicle
  • prostate
  • prostatic concretion
  • bulbourethral gland
  • Cowper’s gland
  • penis
  • corpus cavernosa
  • corpus spongiosum
  • glans penis
  • helicine artery

Pre-Lab Reading

Overview of the Male Reproductive System

The male reproductive system, like the internet, can be thought of as a series of tubes. These tubes deliver the male gametes from their site of production in the testes to their destination outside the body. The system itself is divided into two distinct units:

  • The testes , located outside the major body cavity and housed in the scrotum.
  • The excretory duct system , which transports the sperm from the testes and whose accessory glands produce and modify the contents of semen .

Testes

Like the ovaries, the testes are a source of gametes and steroid sex hormones. Each testis is a compound tubular gland contained within the tunica albuginea , a thick connective tissue coat that contains myofibroblasts that rhythmically contract, and the tunica vascularis , a highly vascular region. The gland is divided into lobules by thin septa that radiate outwards from the dorsal portion of the tunica albuginea. Each of these lobules contains between one and four seminiferous tubules , which are the site of sperm production.

The testes contain several important cell types that are important to understand. The first two of these are found in the germinal epithelium , the layer of the seminiferous tubule in which gamete production and development occurs:

  • Sertoli cells extend from the basement membrane of the germinal epithelium to the lumen of the tubule. These cells envelope the developing sperm cells. They are joined to one another by junctional complexes and form the blood-testis barrier . This barrier separates the germinal epithelium into a basal compartment , containing Sertoli cells and diploid germ cell precursors, and an adluminal compartment , which contains the products of meiosis.
  • Spermatogenic cells include each of the stages between the spermatogonium and the mature spermatozoan. These cells appear in layers that represent advancing stages in their differentiation, with the least mature cells near the basal layer of the epithelium and the most mature cells near the luminal layer.
  • Leydig (interstitial) cells are located within the loose connective tissue surrounding the seminiferous tubules. They appear pale due to their high cholesterol content and often contain crystals of Reinke , which have an unknown function. Leydig cells produce testosterone in response to leutinizing hormone released by the pituitary gland. Testosterone is responsible for male secondary sexual characteristics and the maintenance of the germinal epithelium.

Spermatogenesis

The development of a mature sperm cell takes place in two steps, spermatogenesis and spermiogenesis.

Spermatogenesis is the process by which a spermatogonium develops into a spermatid. During this process, the number of chromosomes is halved through meiosis. It involves the following stages:

  • Spermatogonia rest on the basement membrane of the seminiferous tubule and divide mitotically to produce more spermatogonia and primary spermatocytes. The spermatogonia remain in the basal compartment while the spermatocytes are located in the adluminal compartment.
  • Primary spermatocytes are located in the middle region of the seminiferous tubule, within the adluminal compartment. These cells have a prolonged prophase that gives rise to the first meiotic division.
  • Secondary spermatocytes are the product of the first meiotic division. They have 23 pairs of chromatids. This stage is short-lived and ends with the second meiotic division.
  • Spermatids are the haploid products of meiosis. They remain connected to one another by cytoplasmic bridges. These bridges result from incomplete cytokinesis and allow for synchronous maturation.

Spermiogenesis is the process by which a spermatid matures into a spermatozoan . This process involves several steps:

  • The acrosome , containing hydrolytic enzymes, develops and comes to overlie the dense, elongated nucleus.
  • A flagellum grows out of the pole opposite the acrosome, facing the tubular lumen. This flagellum is a modified cilium that develops from the centrioles of the spermatid.
  • Mitochondria become arranged around the flagellum.
  • The bulk of the cytoplasm is cast off as a residual body , leaving only a thin rim of cytoplasm around the nucleus. Sertoli cells consume the residual body.

The final maturation of sperm occurs in the epididymis, where the cells gain the ability to move. They gain the ability to fertilize the egg through the process of capacitation , which occurs in the female reproductive tract.

Testicular Duct System

Each seiminiferous tubule has a short terminal segment lined by Sertoli cells that transitions to the tubulus rectus and rete testis . These tubes are lined by cuboidal epithelial cells that bear cilia. They turn into the ductus efferentes , which emerge from the dorsal portion of each testis and fuse to form the ductus epididymis . The epithelium of this tube is lined by alternating columnar and cuboidal cells, which give it a scalloped appearance.

Extra-Testicular Duct System

These extra-testicular duct system brings the spermatozoa from the testes to the outside of the body. This system is composed of several distinct tubes:

  • The epididymis is a muscular, convoluted tubule that stores spermatozoa and is the site at which they acquire their motility. It is lined by a pseudostratified epithelium whose cells contain non-motile stereocilia . These stereocilia absorb much of the excess fluid containing the spermatozoa. The epithelium of the epididymis also contains mitotic basal cells .
  • The ductus deferens is another muscular tubule that carries sperm downstream from the epididymis. Its wall is thicker than that of the epididymis and contains three muscular layers: inner longitudinal, middle circular, and outer longitudinal. The epithelium of the ductus deferens is similar to that of the epididymis, with pseudostratified cells bearing stereocilia. The ampulla of the ductus deferens receives secretions from the seminal veiscles.
  • The ejaculatory duct extends from the ampulla of the epididymis to the urethra. The initial portion of the duct has the same pseudostratified columnar epithelium as the previous tubes. Near its termination, it is lined by transitional epithelium.
  • The urethra is lined primarily by stratified or psueodstratified columnar epithelial cells, but its opening displays a stratified squamous epithelium.

Accessory Glands of the Male Reproductive System

The male reproductive system contains several accessory glands that contribute to the composition of semen:

  • The seminal vesicles are glandular sacs that empty into the ampulla of the ductus deferens. They produce a secretion that makes up over 80% of the seminal fluid and contains fructose, fibrinogen, and prostaglandins. The pseudostratified epithelial cells appear foamy because of the lipid droplets they contain, and the muscular wall of the vesicles contains inner circular and outer longitudinal layers that contract in response to sympathetic stimulation during ejaculation.
  • The prostate is a walnut-sized conglomeration of tubulo-acinar glands that surrounds the initial segment of the urethra. This gland produces a secretory product containing citric acid and proteolytic enzymes that prevent coagulation of semen. The prostate often contains prostatic concretions in the acinar lumina.
  • The bulbourethral glands , or Cowper’s glands , empty into the urethra and secrete a lubricating fluid. Their secretory cells and duct contain small mucoid droplets.

Penis

The penis is composed of two types of erectile tissue:

  • The corpus cavernosa are two columns of erectile tissue located on the dorsal side of the penis.
  • The corpus spongiosum is a single column of erectile tissue located on the ventral side of the penis. It contains the penile urethra and expands distally into the glans penis.

The erectile tissue of the penis appears as a vast sponge-like system of irregular vascular spaces intercalated between the arteries and veins. These sinuses receive blood from the helicine arteries , which dilate during erection to engorge the sinuses with blood. This, in turn, restricts venous outflow.

The skin covering the penis is thin and contains an abundant subcutaneous layer with smooth muscle but no adipose tissue. The glans penis lacks hair follicles and contains only small sweat glands.

Pre-Lab Quiz

  1. In a slide showing the development of sperm in the germinal epithelium, which stage would you not expect to see and why?
    2. Answer:
  2. Contrast spermatogenesis from spermiogenesis. At what stage do sperm cells finally become fully mature?
    3. Answer:
  3. What function do Leydig and Sertoli cells play in the development of sperm?
    4. Answer:
  4. What is the blood-testis barrier, what two compartments does it create, and what are the cellular contents of each compartment?
    5. Answer:

Slides

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Study Mode
Quiz Mode
  1. Testis
  2. Seminiferous Tubules
  3. Spermatogenesis
  4. Leydig Cells
  5. Sertoli Cells
  6. Sertoli Cells EM
  7. Rete Testis
  8. Ductuli Efferentes
  9. Epididymis
  10. Ductus Deferens
  11. Urethra
  12. Seminal Vesicle
  13. Prostate Gland
  14. Penis

Virtual Microscope Slides

  1. Testis
    2. Begin by identifying the seminiferous tubules.
  2. Epididymis
    3. This is a cross section of the epididymis.
  3. Prostate
    4. Note the heterogeneous epithelium of the prostate and the abundant stroma consisting of smooth muscle and connective tissue.

Pathology

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Study Mode
Quiz Mode
  1. Atrophic Testis
  2. Nodular Hyperplasia of the Prostate
  3. Adenocarcinoma Prostate

Quiz

  1. Is this cell on the blood or lumenal side of the testis blood-barrier?
    2. Answer: It is on the lumenal side of the barrier. Note the acrosome adjacent to the nucleus which indicates this is a spermatid.
  2. What organ is this?
    3. Answer: Prostate. Note the concretion in the lumen.
  3. What is a function of thee cells?
    4. Answer: Resorption of fluid, note stereocilia on surface of epithelial cells.
  4. What is the stage of the large cells with pale cytoplasm?
    5. Answer: Primary spermocytes
  5. Where in the male reproductive tract is this?
    6. Answer: Epididymis
  6. Name this structure.
    7. Answer: Ductus deferens
  7. What is the red structure and of what is it made?
    8. Answer: Prostatic concretions: lamellated and calcified glycoprotein
  8. Identify A, B, C, and D in this image of the germinal epithelium.
    9. Answer: A = Leydig cell, B = spermatozoa, C = primary spermatocyte, D = spermatogonium
  9. Damage to the testes as a result of torsion can lead to the destruction of the blood-testis barrier. What cells are affected structurally (ie - what cells make up this barrier) and why would you expect the body to mount an immune response to its own spermatozoa?
    10. Answer: The Sertoli cells create the blood-testis barrier because of the tight occluding junctions that connect them. Normally, blood is exposed only to the 2N spermatogonia, which have the typical “self” genome. Spermatozoa are haploid and express sperm-specific antigens not normally recognized as “self” by the body. Antibodies can bind to these antigens.
  10. A patient is sterile because of a breach in his blood-testis barrier. Upon histological observation with immunostaining, you observe that there are antibodies attached to the head of his sperm. How would the reason for this patient's sterility differ from that of another patient, who has antibodies attached to his sperm's flagella?
    11. Answer: The first patient’s antibodies are attacking the sperm head, which could compromise the activity of the acrosome by altering the ability of the sperm to bind to the zona pellucida of the female ovum. The second patient’s sperm are likely unable to move properly due to the antibodies bound to their flagella.