Note:   You should also use the multimedia web program for this lesson.  Go back to Histology Part 2 Index and choose Male Reproductive System under "Multimedia Lessons, Reproductive System".


The primary function of the male reproductive system is reproduction, which includes the production of spermatozoa, the transportation of spermatozoa from the testes out of the male body, the secretion by glands, and the placement of spermatozoa in the female reproductive tract. Spermatozoa are produced in the testes then transported from the testes by a series of ducts which become gradually larger and connect with the urethra of the penis.  Various accessory glands in the male system secrete materials which together with the spermatozoa constitutes the semen. A secondary function of the male reproductive system is the production of the male hormones which are responsible for the secondary sex characteristics of the male animal.

The male reproductive system is composed of several distinct organs. These include the testes, epididymis, deferent ducts, accessory glands, and the penis. The testis (plural, testes) is both an exocrine organ (compound, coiled, tubular gland) producing cells, i.e., spermatozoa, and an endocrine organ, secreting hormones, i.e., testosterone. Accessory glands (not all are present in all species) include the ampullary glands, vesicular glands, prostate gland, bulbourethral gland and urethral glands.


The testes are paired organs, and each one is enclosed in a fibrous white capsule of dense connective tissue(tunica albuginea) containing blood vessels (the stratum vasculare). A layer of peritoneum is tightly adhered to the tunica albuginea of each testis. The stallion has obvious smooth muscle fibers in the capsule. The connective tissue of the capsule continues into the testis on the posterior aspect as the mediastinum testis.

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Micrographs of cat testis (Lab slide 89B). 

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The dense connective tissue of the tunica albuginea is continuous with the loose areolar connective tissue of the septuli testis (septa) which extend through the parenchyma of the testis and divide it into lobules.    Each lobule is composed of several seminiferous tubules (tubuli contorti) and the surrounding connective tissue.  Spermatogenesis (formation of spermatozoa) occurs in the epithelial lining of the seminiferous tubules.  The interstitium is composed of loose connective tissue containing fibroblasts and Leydig cells (interstitial cells)Spermatozoa produced in the seminiferous epithelium move through the lumen of the tubules to the tubuli recti (straight tubes) which extend to a network of spaces in the mediastinum, the rete testis (except in the stallion).  Efferent ductules (ductuli efferentes) carry the spermatozoa from the rete testis, then converge to form the ductus epididymis, a convoluted duct. The ductus epididymis straightens and becomes the ductus deferens.  In domestic mammals, testes are not in a major body cavity, but are enclosed in the scrotum. Each testis is suspended at the end of a tissue called the spermatic cord which contains the ductus deferens, the blood vessels, and the nerves supplying the testis.

Each testis is composed of an exocrine part (seminiferous tubules) and an endocrine part (interstitial or Leydig cells).  The testis is divided into lobules by septa consisting of loose areolar connective tissue.  Several seminiferous tubules are found in each lobule, and interstitial cells are found in the connective tissue septa surrounding the seminiferous tubules.  The seminiferous tubules are the exocrine portion of the testis producing and "excreting" spermatozoa.   These tubules are lined by a stratified epithelium that consists of the developing spermatozoa and supporting cells (Sertoli cells). 

Seminiferous tubules.

The stratified epithelium of the seminiferous tubules is composed of different stages of developing sperm cells. Spermatogonia are stem cells located near the basement membrane of the tubule which proliferate by mitosis.  Some of the progeny cells differentiate into sperm and move away from the basement membrane toward the lumen of the tubule.  These differentiating cells first undergo meiosis then undergo a morphological change to become spermatozoa.  Some of the progeny cells undergo mitosis again to produce more progeny cells providing a continuous source of stem cells for the production of spermatozoa.


Spermatogenesis: the process by which stem cells develop into mature spermatozoa. There are three phases: (1) Spermatocytogenesis (Mitosis), (2) Meiosis, and (3) Spermiogenesis.


Spermatocytogenesis:(also called Mitosis): Stem cells (Type A spermatogonia; singular = spermatogonium) divide mitotically to replace themselves and to produce cells that begin differentiation (Type B spermatogonia).  Spermatogonia have spherical or oval nuclei, and rest on the basement membrane. (You are not responsible for distinguishing between Type A and Type B spermatogonia in lab.) 


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Micrograph of seminiferous tubules of rat testis (Lab slide 213)




Meiosis:  Cells in prophase of the first meiotic division are primary spermatocytes.  They are characterized by highly condensed chromosomes giving the nucleus a coarse chromatin pattern and an intermediate position in the seminiferous epithelium. This is a long stage, so many primary spermatocytes can be seen.  Primary spermatocytes go through the first meiotic division and become secondary spermatocytes.  The cells quickly proceed through this stage and complete the second meiotic division. Because this stage is short there are few secondary spermatocytes to be seen in sections. You are not responsible for identifying secondary spermatocytes in lab.  Meiosis is the process by which the diploid number of chromosomes present in spermatogonia (the stem cells) is reduced to the haploid number present in mature spermatozoa.



The products of the second meiotic division are called spermatids. They are spherical cells with interphase nuclei, positioned high in the epithelium.  Since spermatids go through a metamorphosis into spermatozoa, they occur in early through late stages.  You are not responsible for distinguishing the different stages of spermatids, but you are required to identify a spermatid.




All of these progeny cells remain attached to each other by cytoplasmic bridges. The bridges remain until sperm are fully differentiated.

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Micrograph of seminiferous tubules of rat testis (Lab slide 213).  Note that the primary spermatocytes are closer to the lumen than the spermatogonia which rest on the basement membrane of the seminiferous tubule.

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Micrograph of seminiferous tubules of rat testis (Lab slide 213).  Note the presence of early spermatids in one tubule and late spermatids in the other tubule.

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Micrograph of seminiferous tubule of rat testis (Lab slide 213).  High magnification to show the close relationship between the spermatids and the cytoplasm of the Sertoli cell.



After production in the testes, spermatozoa pass through a series of ducts in their journey out of the male system. 



The ductus epididymis is lined with a pseudostratified stereociliated columnar epithelium. Stereocilia are actually nonmotile, long microvilli which serve to increase the absorptive and/or secretory surface of this epithelium. With its associated connective tissue and muscle, the ductus epididymis coils to form the head, body and tail of the epididymis which then continues into the ductus deferens.  Spermatozoa are stored within the epididymis while they undergo maturation to become mature sperm.






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Micrographs of cat epididymis
 (Lab slide 89B).


The products of these glands serve to nourish and activate the spermatozoa, to clear the urethral tract prior to ejaculation, serve as the vehicle of transport of the spermatozoa in the female tract, and to plug the female tract after placement of spermatozoa to help ensure fertilization.  Although the glands are ususally described as being branched tubular or branched tubuloalveolar, they vary in their organization and in their distribution in different species.


Prostate gland

Grossly the prostate gland can be divided into two parts: the body and the disseminate part.  Low cuboidal to low columnar epithelium provides the lining for this compound, tubuloalveolar gland which consists primarily of serous secretory end pieces.  The secretion of this gland is more serous in dogs and more mucous in bulls.   It serves to promote the movement of spermatozoa and to form a vaginal plug.  Additionally, in bulls, the secretion contains high amounts of fructose and citric acid.  Concretions may be present in the secretory end pieces as well as parts of the duct system.


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Micrograph of prostate gland of dog 
(Lab slide 92).

Bulbourethral glands.  

The lining of these paired, compound, tubuloalveloar glands is simple columnar epithelium.  A capsule of dense connective tissue contains some smooth muscle as well as skeletal muscle of the bulbocavernous and urethral muscles.  All domestic species have these glands except the dog, and their mucous secretion serves to clear the urethra of urine and to lubricate it and the vagina.  The product may also serve as an energy source for the spermatozoa.



The male urethra consists of two portions; the pelvic urethra and the penile urethra. Both portions are lined with transitional epithelium, both contain erectile tissue, and both contain (species variable) branched tubular mucous glands, the urethral glands.  In the pelvic urethra, the three layers of smooth muscle in the tunica muscularis near the bladder are replaced (or joined in some species) by the striated urethral muscle. The tunica adventitia is present and typical. 

The tunica muscularis is smooth muscle, and cavernous (corpus cavernosum urethra) tissue is present in the connective tissue beneath the epithelium. In the penile urethra, the corpus cavernosum penis is also present.



The penis provides an outlet for both urine and the copulatory ejaculate (spermatozoa and semen). The histology and gross anatomy of the penis varies dramatically from species to species and from region to region within the same species. In general, the body of the penis consists of the urethra, erectile tissue (corpora cavernosa penis and corpora cavernosum urethra), smooth and skeletal muscle, touch and pressure receptors (Pacinian corpuscles) and a dense connective tissue capsule (tunica albuginea). 






























Erectile tissue and the erectile mechanism. The erectile tissue is composed of dense irregular connective tissue which contains numerous elastic fibers and sinuses. Under stimulation, the primary blood supply of the penis is directed through helicine arteries which open into the venous sinuses.   During erection, these vessels and the sinuses become engorged with blood, and the thin-walled veins beneath the tunica albuginea are effectively closed, further increasing the rigidity of the organ. Because the capsule around the erectile tissue of the corpus cavernosum urethra is not as thick as that around the corpus cavernosum penis, the urethra is not occluded during erection.  After ejaculation, the helicine arteries contract and regain their normal tone resulting in a relaxing of the pressure around the veins which leads to the restoration of normal blood flow to the region. 


Micrographs of primate penis (Lab slide 91A).

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Copyright 2002 Charlotte L. Ownby
Histology Part 2 Index