male reproductive system. i. general layout of the male reproductive tract

MALE REPRODUCTIVE SYSTEM

I. General layout of the male reproductive tract.

A. Each testis is surrounded by a thick capsule of collagenous connective tissue called the tunica albuginea.

1. This capsule is thin on the anterior side and thick on the posterior.

2. The thickened area is a region called the mediastinum testis or rete testis.

3. Septa extend from the thin anterior side of the tunica albuginea and from the mediastinum testis dividing the interior of the testis into incomplete compartments called testicular lobules.

4. Within each lobule are 1 - 4 seminiferous tubules that are enmeshed in loose connective tissue.

a. The connective tissue of the lobules is rich in nerves and lymph and blood vessels.

6. The seminiferous tubules are the sites of production of spermatozoa.

B. Ducts associated with the male reproductive tract in the order that a spermatozoon would pass through them on it's way to urethral opening at the tip of the penis.

1. Ducts in the testis

a. Seminiferous tubules (see below for more detailed description).

b. Tubuli recti

* Lined by a simple cuboidal epithelium that is composed of Sertoli cells.

http://www.finchcms.edu/anatomy/histology/organology/male/o_m_3.htmlhttp://www.finchcms.edu/anatomy/histology/organology/male/o_m_4.html

c. Rete testis* An anastomosing network of channels in the mediastinum testis.

* Lined by a combination of simple cuboidal and simple columnar epithelia.

d. Ductuli efferentes (also called efferent ductules) - connect between the testis and the ducts outside this organ

* 10 - 15 twisted ducts that extend from the rete testis to the epididymis.

• Lined by a combination of cuboidal cells and columnar ciliated cells. Columnar cells are ciliated.

* Epithelium may appear to be a pseudostratified columnar epithelium

*Ducts are surrounded by a layer of smooth muscle.

* This is the only part of the male reproductive tract where cells with motile cilia are found.

http://www.finchcms.edu/anatomy/histology/organology/male/o_m_4.htmlhttp://www.finchcms.edu/anatomy/histology/organology/male/o_m_5.html

2. Ducts outside the testisa. Epididymis

* A single, highly convoluted tube that sperm enter via the ductuli efferentes.

* Lined by pseudostratified columnar epithelium.

* Surface of these cells covered with stereocilia which are large branched microvilli, NOT cilia.

*Epididymis tubule is surrounded by layer of smooth muscle.

* Final maturation of the sperm occurs in the epidydimis.

b. Vas deferens (also called the ductus deferens)

* A straight tube with thick walls.

* Consists of narrow lumen surrounded by thick wall of smooth muscle (3 layers, inner longitudinal, middle circular, outer longitudinal).

* Mucosa of tube is in longitudinal folds.

* Lined with pseudostratified columnar epithelium with stereocilia on surface.

http://www.lab.anhb.uwa.edu.au/mb140/

* Two sub-components in the last portion of the vas deferens near the urethra.

** Ampulla - a widening near the connection of the vas deferens to the urethra

** Ejaculatory duct - short portion of the vas deferens between the ampulla and the urethra

* Empties into the urethra in the region of the prostate gland.

b. Vas deferens (also called the ductus deferens)

c. Urethra* Consists of 3 parts - prostatic urethra, membranous urethra, and the penile, (= cavernous or pendulous urethra).

* prostatic urethra** lined with transitional epithelium

** ejaculatory ducts of vas deferens empty into this portion of urethra.

* membranous urethra** Short, about 1 cm. long

** Lined with pseudostratified or stratified columnar epithelium.

** Striated muscle sphincter surrounds this portion of urethra - called the external sphincter.

http://www.finchcms.edu/anatomy/histology/organology/

male/o_m_10.html

** Lined by mostly pseudostratified or stratified columnar epithelium, near the end it is lined with stratified, non-keratinized, squamous epithelium.

** Mucous glands called the glands of Littre are found along the entire length of this portion of the urethra.

* penile or pendulous urethra

http://www.finchcms.edu/anatomy/histology/organology/

male/o_m_10.html

http://www.medsch.wisc.edu/anatomy/histo/htm/tmalebas.htm

http://www.finchcms.edu/anatomy/histology/organology/male/o_m_13.html

** The bulbourethral glands (Cowper's glands) empty their contents into the membranous urethra. These glands provide the first fluids of ejaculation that act to lubricate the urethra for the passage of the semen that follows.

B. Glands associated with the male reproductive tract

1. Seminal vesicles - produce a fluid secretion that forms about 70% of the semen’s fluid volume, one associated with each vas deferens

2. Prostate - produces a fluid secretion that forms part of the semen - surrounds the points where the vas deferens connects to the urethra

3. Bulbourethral glands/ Cowper’s glands - produce a fluid secretion that lubricates the urethra and forms part of the semen, multiple glands located at base of penile urethra.

4. Glands of Littre - small, individual mucous producing glands that connect along length of penile urethra

III. Structure of the seminiferous tubules.

A. The seminiferous tubules within testis consist of:

1. A wall or capsule of fibrous connective tissue called the tunica propria (sometimes just referred to as the capsule) that is composed of:

a. several layers of fibroblasts

b. an innermost layer of myoid cells (muscle-like cells) that contain actin filaments and are capable of contraction.

http://www.medsch.wisc.edu/anatomy/histo/htm/tmalebas.htm

2. The seminiferous tubules are lined with what might be called a deciduous complex stratified epithelium (my own terminology) that is called the germinal epithelium. Can catagorize cells of epithelium under two major catagories.a. Reproductive or germinal cells. These cells constitute the

spermatogenic cell linage.b. Somatic cells - Sertoli cells

http://www.uoguelph.ca/zoology/devobio/210labs/testes1.html

http://www.medsch.wisc.edu/anatomy/histo/htm/tmalebas.htm

d. Meiosis involves the first meiotic division of the primary spermatocytes and the second meiotic division of the secondary spermatocytes.

4. The reproductive cells that make up the majority of the germinal epithelium are all derived from the same group of stem cells, the spermatogonia.

5. The spermatogonia and the cell types derived from them undergo a cycle of mitosis and meiosis called spermatogenesis. This is the entire process of production and maturation of sperm from the divisions of the spermatogonial stem cells, through meiosis, through the maturation of spermatids into mature sperm.

http://www.uoguelph.ca/zoology/devobio/210labs/testes1.html

a. spermatogonia - diploid cells in terms of genetic content and chromosome number - divide by mitosis.

b. primary spermatocytes - diploid cells in terms of genetic content and (prior to chromosome replication in preparation for division) chromosome number - divide during first meiotic division.

c. secondary spermatocytes - haploid cells in terms of genetic content, but diploid in terms of chromosome number - divide during second meiotic division.

d. spermatids - immature spermatozoa - haploid cells in terms of genetic content and chromosome number.

http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab27/Lab27.htm

6. Stages and cell types of spermatogenesis

e. Nearly mature spermatozoa - fully formed spermatozoa, haploid cells in terms of genetic content and chromo-some number.

Additional cells in seminiferous tubules:

* Supportive cells called Sertoli cells (see below)

http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab27/Lab27.htm

7. Spermiogenesis (also called spermateleosis or spermatozoan metamorphosis) - cellular differentiation of the spermatids into mature spermatozoa. A number of events occur during this process:

3. Spermatogenesis can be divided into three stages

a. Mitotic division of the spermatogonia that form various sub-types of spermatogonia and eventually many primary spermatocytes

b. Meiosis - two divisions

* Meiosis I

* Meiosis II

c. Spermiogenesis (also called spermateleosis or spermatozoan metamorphosis) - cellular differentiation of the spermatids that are formed by the second meiotic division into mature spermatozoa. A number of events occur during this process:

a. The Golgi apparatus forms a membrane bound vesicle called the acrosomal granule that eventually covers the anterior part of nucleus to form the acrosome.

* The acrosome contains enzymes that help the sperm penetrate an acellular layer surrounding the ovum that is called the zona pellucida

b. The centrioles of the spermatid migrate to the posterior end of this cell and give rise to the flagellar axoneme that consist of a 9 + 2 structure of microtubules

http://www.ansci.cornell.edu/courses/as300/img0026b.jpg

c. The majority of the spermatid cytoplasm shifts to posterior region of the maturing sperm.

* This cytoplasm will eventually be shed as the residual body, a process that helps streamline the body of the sperm.

* The residual bodies are phagocytosed by Sertoli cells.

http://www.ansci.cornell.edu/courses/as300/img0026b.jpg

d. The mitochondria of the spermatid organize around forming flagellum.

* In humans these mitochondria fuse to form a spirally wound supermitochondrion

* This super mitochondrion produces ATP to power the sperms flagellum

http://www.ansci.cornell.edu/courses/as300/img0026b.jpg

e. The spermatid nucleus condenses to small size.

* This small nucleus is surrounded by a linear arrangement of microtubules called the manchette.

* The manchette may play a role in the elongation and flattening of the nucleus.

f. The mature spermatozoan has lost the majority of its cytoplasm and has become specialized for locomotion, penetration of the ovum, and transmission of genetic material to the next generation. In humans, the entire process from the first mitotic division of spermatogonial cell to fully formed spermatozoa takes about 64 days.

http://www.ansci.cornell.edu/courses/as300/img0026b.jpg

8. As you examine the seminiferous tubules on your testes slide you'll note that the same combination of gamete stages is not present in every tubule section.

a. This is the result of the spermatogonial cells dividing cyclically rather than continuously and at different times in different portions of the seminiferous tubules.

b. The division cycle of a given spermatogonial cell in human males is every 16 +1 days.

http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab27/EXAMPLES/EXSEMTUB.HTM

9. In addition, in a given histological section (in humans), not all portions of the wall of the seminiferous tubules are in the same part of a given cycle.

a. Thus different parts of a given tubule will contain different associations of the various gamete stages.

b. Some regions may appear to contain mostly mature spermatozoa, while other regions will contain a mixture of primary and secondary spermatocytes and early spermatid stages.

c. Other combinations possible.

d. In humans there are 6 recognizable combinations of gamete stages, while in rodents, for example, there are 12.

http://dml.georgetown.edu/educ/hist/lab12/4.htm

10. Finally, as sperm become fully mature, they are shed. That's why I term this a complex deciduous stratified epithelium.

11. The other cell type found in the epithelium lining the seminiferous tubules is the sertoli cell.

a. This is a diploid somatic cell (i.e. not part of the germ cell lineage).

b. These cells provide nutrients to and remove wastes from the developing gametes.

c. They also phagocytose and digest cytoplasm that is shed by the developing spermatids, thus recycling nutrients.

d. They secrete fluid to carry mature sperm out of seminiferous tubules.

e. They secrete hormones such as anti-mullarian hormone and inhibin.

f. They act to compartmentalize the developing gametes, separating them from the body’s immune system and the effects of certain hormones.

http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab27/EXAMPLES/EXSERTOL.HTM

IV. Interstitial tissue (tissue between the seminiferous tubules) of the testis

A. Consists of connective tissue, specialized hormone secreting cells, nerves, and blood and lymphatic vessels.

1. Nerves, blood vessels, and lymphatic vessels enter and leave the testis through the connective tissue of the mediastinum testis.

B. Cell types commonly found in the interstitial tissue

1. fibroblasts

2. mast cells

3. macrophages

http://www.kumc.edu/instruction/medicine/anatomy/histoweb/male/male06.htm

4. Interstitial cells of Leydig

a. Generally these cells are found as clusters of ovoid cells between the seminiferous tubules.

b. Starting at puberty, these cells secrete testosterone.

c. This hormone is important in the development and maintenance of primary (penis) and secondary male sex characteristics such as pubic hair and muscle mass, and it is also involved in the control of spermatogenesis.

http://dml.georgetown.edu/educ/hist/lab12/8.htmhttp://www.kumc.edu/instruction/medicine/anatomy/histoweb/male/male06.htm

http://www.medsch.wisc.edu/anatomy/histo/htm/tmalebas.htm

V. Structue of the penis

A. Contains three masses of spongy erectile tissue plus the urethra.

1. The two dorsal cylinders of erectile tissue are called the corpora caverosa.

http://www.histology.anatomy.wisc.edu/htm/tmalebas.htm

a. The dorsal corpora cavernosa are surrounded by a thick layer of dense connective tissue called the tunica albuginea. This C.T. also surrounds the corpus spongiosum, but it’s not as well defined in this region.

b. Internally they consist of an endothelium lined, anastomosing network of blood sinuses that receive blood from the coiled helicene arteries that are also located in the corpora cavernosa.

* Engorgement of the blood sinuses by blood from the helicene arteries is what causes the male erection.

http://www.histology.anatomy.wisc.edu/htm/tmalebas.htm

2. The ventral cylinder of erectile tissue surrounds the urethra and is called the corpus cavernosum of the urethra or the corpus spongiosum - also surrounded by tunica albuginea.

3. This corpus spongiosum is dialated at its end to form the glans penis or head of the penis.

http://www.histology.anatomy.wisc.edu/htm/tmalebas.htm

B. A flap of skin called the prepuce (foreskin) covers the glans penis. This is the skin that is cut away when a circumcision is done.