HISTOLOGY - BIOL 4000 - LECTURE NOTES 15
REPRODUCTIVE SYSTEM - MALE
MALE REPRODUCTIVE SYSTEM TEXT - POWERPOINT
Web sites concerned with the male reproductive system
Male reproductive system
Male reproductive system histology
Male reproductive system histology - good site, images and text
Possible benefits of circumcision
Male genital pathology
I. Embrological origin of the male reproductive tract and germ cells
A. The germ cells are derived from extraembryonic yolk sac endoderm in mammals.
1. The primordial germ cells are first found in this area at about the 4th week of development in humans.
2. Between 4 and 6 weeks of development, they migrate through the circulatory system into the embryo and eventually lodge in intermediate mesoderm adjacent to the dorsal portion of the peritoneal cavity.
3. This intermediate mesoderm will form the testes (or in the female, the ovaries).
B. The primordial germ cells induce the intermediate mesoderm that surrounds them to form the testes (or in the female, the ovaries).
C. The testes, and the seminiferous tubules and other ducts within them, form from intermediate mesoderm during the 6th - 8th weeks of human development. The remaining ducts and associated glands of the human male reproductive system develop between the 8th and 12th weeks of gestation.
D. The ductuli efferentes are derived from components of the embryonic mesonephric kidney called mesonephric tubules.
E. The epididymis and vas deferens are formed from the mesonephric duct, a tube that drains urine from the mesonephric kidney to the cloaca of the embryo.
F. The urethra forms from a short portion of the allantoic stalk and a new tube that is created as the penis develops.
II. General layout of the male reproductive tract.
A. The general layout of the male reproductive system is as shown above.
1. The testes (not shown in the figure above) lie within the scrotal sac
B. Each testis is surrounded by a thick capsule of collagenous connective tissue called the tunica albuginia.
1. This capsule is thin on the anterior side and thick on the posterior.
2. The thickened area is called the mediastinum testis.
3. Septa extend 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.
C. 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
See figures above
a. Seminiferous tubules (see below for more detailed description)
b. Tubuli recti
* Lined by a simple cuboidal epithelium that is composed of Sertoli cells.
c. Rete testis
* An anastomosing network of channels in the mediastinum testis.
* Lined by a combination of simple squamous and simple cuboidal 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 secretory cells and columnar ciliated cells.
* This is the only part of the male reproductive tract where cells with motile cilia are found.
2. Ducts outside the testis
a. Epididymis
* A single, highly convoluted tube that sperm enter through the ductuli efferentes.
* Lined by pseudostratified columnar epithelium.
* Surface of these cells covered with stereocilia which are essentially branched microvilli, NOT cilia.
* 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.
* Mucosa of tube is in longitudinal folds.
* Lined with pseudostratified columnar epithelium with stereocilia on surface.
* 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 area of prostate.
c. Urethra
* Consists of 4 parts - prostatic urethra, membranous urethra, bulbous urethra, and 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 columnar epithelium.
** Striated muscle sphincter surrounds this portion of urethra - called the external sphincter.
* bulbous and pendulous urethra
** Lined by mostly pseudostratified cloumnar epithelium, but there are some areas lined with stratified squamous epithelium.
** The bulbourethral glands (Cowper's glands) empty their contents into the base of the pendulus urethra. These glands provide the first fluids of ejaculation that act to lubricate the urethra for the passage of the semen that follows.
** Mucous glands called the glands of Littre are found along the entire length of these portions of the urethra.
3. Structures below the level of the urethra are paired on left and right sides.
B. Glands associated with the male reproductive tract
See figure of male reproductive system above.
See pp. 443 - 446 in text
1. Seminal vesicles - produce a fluid secretion that forms part of the semen, 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 - produce a fluid secretion that forms part of the semen, multiple glans located along the length of the urethra
III. Structure of the ducts of the male reproductive tract.
A. The seminiferous tubules within testis consist of:
1. A wall or capsule of fibrous connective tissue called the tunica propria 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 conrtraction.
2. A well defined (thick) basement membrane
3. 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 epithelium under two major catagories.
a. Reproductive or germinal cells. These cells constitute the spermatogenic cell linage.
* spermatogonia - diploid cells in terms of genetic content
* primary spermatocytes - diploid cells in terms of genetic content
* secondary spermatocytes - haploid cells in terms of genetic content
* spermatids - immature spermatozoa - haploid cells in terms of genetic content
* mature spermatozoa - haploid cells in terms of genetic content
b. Supportive cells called Sertoli cells (see below)
5. The reproductive cells that make up the majority of the germinal epithelium are all derived from the same group of stem cells, the spermatogonia.
6. 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.
7. Spermatogenesis can be divided into three stages
Good link for seminiferous tubule and spermatogenesis
See figure below and pp. 433 - 438 in text.
a. Mitotic division of the spermatogonia that form various sub-types of spermatogonia and eventually many primary spermatocytes
b. Meiosis that involves the first meiotic division of the primary spermatocytes and the second meiotic division of the secondary spermatocytes.
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:
See figures above and pp. 433 - 438 in text.
* 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
* 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
* 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 th sperm.
** The residual bodies are phagocytosed by Sertoli cells.
* 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
* 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.
d. 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.
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.
Image showing different seminiferous tubules with different spermatogenic sequences
a. This is the result of the spermatogonial cells dividing cyclically rather than continuously.
b. The cycle in humans is 16 +1 days.
9. In addition, in a given histological section, not all portions of the wall of the seminiferous tubules are in the same part of a given cycle.
Image of seminiferous tubule showing different spermatogenic sequences in same seminiferous tubule
a. Thus different parts of a given tubule will contain different asociations 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.
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.
Image of sertoli cells and surrounding gamete stages
a. This is a somatic cell (i.e. not part of the germ cell lineage).
b. These cells provide nutrients to 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 bodies immune system and the effects of certain hormones.
IV. Interstitial tissue (tissue between the seminiferous tubules) of the testis
See pp. 441 - 442 in text.
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 found in the interstitial tissue
1. fibroblasts
2. mast cells
3. macrophages
4. interstitial cells of Leydig
Image 1 of interstitial cells of Leydig
Image 2 of interstitial cells of Leydig
a. Generally these cells are found as clusters of ovoid cells between the seminiferous tubules.
b. During embryonic life and particulalrly starting at puberty, these cells secrete testosterone.
c. This hormone is important in the development and maintenance of primary male sex characteristics, i.e. the penis and scrotum, and secondary male sex characteristics such as pubic hair growth and muscle mass. It also is involved in the control of spermatogenesis.
* In the embryo, testosterone is important in the formation of components of the internal and external male reproductive system.
* The development of the external male genetalia is completely dependent on the production of testosterone and its conversion to 5 alpha dihydrotestosterone (DHT).
* DHT provides the signal that tells the tissues that form the penis and scrotum to actually differentiate into these organs.
* If DHT is absent in an XY male, or if it is not produced in sufficient quantities, or if the receptors that bind this hormone are defective, the XY male embryo will develop a female phenotype, complete with labial lips and vagina. At the age of puberty large breasts will develop.
* This person is, for all intents and purposes, female. She does not, however, have ovaries, oviducts, or a uterus and cannot conceive children.
The following links have information that concerned with such "intersex" conditions.
Androgen Insensitivity syndrome
Intersexed people
V. Structue of the penis
See p. 446 in text.
A. Contains three masses of spongy erectile tissue plus the urethra.
1. The two dorsal cylinders of erectile tissue are called the corpora caverosa.
a. The dorsal corpora cavernosa are surrounded by a layer of dense connective tissue called the tunica albuginea.
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.
2. The ventral cylinder of erectile tissue surrounds the urethra and is called the corpus cavernosum of the urethra or the corpus spongiosum.
3. This corpus spongiosum is dialated at its end to form the glans penis or head of the penis.
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.
Information on circumcision