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Male Reproductive System

Dr. Muna Zuhair

The male reproductive system is responsible for:

1-Production, nourishment & temporary storage of haploid male gamates (spermatozoa).
2-Introduction of suspension of spermatozoa (semen) into the genital system.
3-Production of male sex hormone (Androgen).
Male Reproductive System


The male genital system consists of:Testis: produce spermatozoa & synthesize & release androgen.Epididymis, vas deferens, ejaculatory duct &part of male urethra – which form the ductal system carrying spermatozoa to the exterior.Seminal vesicle, prostate & bulbourethral gland (of Cowpers) which are secretory glands provide fluid & nourishment to the spermatozoa & form the bulk of semen.Penis. The testis, epididymis, & vas deferens are located in the scrotal sac which is a skin-covered pouch enclosing a mesothelium lined cavity continuous with peritoneal cavity of the inguinal ring.

Scrotom:

It is covered by:
Skin: containing hair follicles &numerous eccrine sweat glands.
Deeper to the skin there is smooth muscle fibers arranged in a rather haphazard manner forming "Dartos muscle", contraction of which produces wrinkling of the scrotal skin.
Beneath Dartos muscle lies a fibrocollagenous fascia called "Colle's fascia".
Deepest layer of the Colle's fascia compacted to form a dense parietal layer of "Tunica Vaginalis" which is lined by flattened mesothelial cells; this layer forms the inner layer of scrotal sac & separated from the external surface of the testis by a potential space containing a watery fluid which acts as a lubricant allowing testis to move freely without friction.


These are paired organs located outside the body cavity in the scrotum means that they are maintained in a temperature approximately 2-3 oc below the body temperature, this lower temperture is important for spermatogenesis.
the testis developed in a high position on the posterior abdominal wall & migrate to the scrotum, usually arrived at the 7th month of the intrauterine life, when the testis fail to migrate to the scrotum a condition called (Cryptochidism), they fail to produce sperm.
Each mature testis is a solid organ, ovoid 4-5 cm length, 3 cm depth, 2-3 cm width & weight 11-17 gm , the right testis is larger & heavier than the left one.
Each testis has an epididymis attached to its posterior surface &it is suspended in the scrotal sac by the "spermatic cord" containing vas deferens, venous plexus &lymphatic vessels.
Testis:


The testis covered by a thick collagenous capsule (the visceral layer of the tunica vaginalis or called tunica albuginea), it's outer surface is coated with flattened mesothelial cells, beneath the tunica albuginea lies a narrow variable layer of loosely arranged collagen fibers containing blood vessels internal to this located the "Seminiferous tubules". The tunica albuginea is thickened to form the "mediastinum", fibrous septa from this mediastinum divide the body of testis into 250-350 lobules, and each lobule contains 1-4 seminiferous tubules.

Seminiferous tubules:

It is a coiled non-branching closed loop both ends of which open into the "rete testis" which is a system of channels located at the posterior hilum of the testis closed to the mediastinum. Each seminiferous tubule is approximately 150Mm in diameter &80 cm long, it has been calculated that the total length of all seminiferous tubule in each testis is (300-900 meter) in sexually mature adult, each S.T has a central lumen lined by an actively replicating epithelium called "germinal epithelium" mixed with a population of supporting (sustentacular )cells called the "Sertoli cells".


The lining cells sited on mesothelial basement membrane lying within a collagenous layer containing fibroblasts &other spindle-shaped cells which are contractile "Myoid cells" containing intermediate filaments & desmin (like smooth muscle cells) in human testis, the myoid cells form a less distinct layer ¬ a continuous layer, the outer wall of the tubule consisting of basal lamina together with the collagen layer& myoid cells layer, all are sometime called "Tunica Propria", blood vessels &clusters of hormone-producing interstitial cells "Leydig cells" are found between the adjacent S.T.

Germinal epithelium & Spermatogenesis:

The epithelium lining the S.T produce spermatozoa by series of steps called "Spermatogenesis", in spermatogenesis there is mitotic divisions to produce more spermatozoa& cells that differentiated into primary spermatocytes called "spermatogonia".
1-The spermatogenia in human can be divided into 3 groups according to their nuclear appearance:
Type A-dark cells (Ad).
Type A-pale cells (AP).
Type B cells.


It is thought that type(Ad) spermatogonia are the stem cells of the system, their mitotic division produces (more Ad) cells and some(AP) cells with further replicate by mitosis to form clusters of daughter cells linked together by cytoplasmic bridges, type AP spermatogonia mature into type B-cells which divides by mitosis to produce further type B-cells. These cells then mature in a cluster to produce (1ry spermatocytes).
2-1ry spermatocytes replicate their DNA shortly after their formation (i.e. they are 4N). 1ry spermatocytes formation is the end step of spermatogenesis, meiotic division occurs at the spermatocytes stage.


3-the 1ry spermatocytes pass through long prophase lasting about 22 days, during which changing patters of nuclear chromatin enable [preliptotane liptotane, zygotane, pachyten and diplotene] stages to be identified.
The first meiotic division occurs after the late [pachytene-diplotene] stages leading to formation of diploid secondary spermatocytes which rapidly within few hours undergo the 2nd meiotic division to produce spermatids.
{1ry spermatocyte 1st meiotic 2ndry spermatocyte 2nd meiotic spermatids}

Spermiogenesis:-

Is the process by which haploid spermatids are transformed into spermatozoa, spermiogenesis can be divided into 4 stages all of which occurs while the spermatids are embedded in a small hollows in the free luminal surface of the Sertoli cells, these stages are:
Golgi phase
Cap phase
Acrosome phase
Maturation phase
The mature spermatozoon is formed from (head, tail, the later being composed of neck, middle piece, principle piece and end piece).

1-The head of mature spermatozoon is composed of nucleus covered by acrosomal cap. The head is flattened and pointed, the chromatin of the nucleus is condensed and broken only by occasional clear nuclear vacuoles.The acrosomal cap cover the anterior 2/3 to 3/4 of the nucleus, it is a glycoprotein containing numerous enzymes including (protease, acid phosphatase and neuraminidase and hyaluronidase), it can be regarded as specialized giant lysosomes.The acrosomal cap enzymes are released when the spermatozoon contacts the ovum, they facilitate penetration of the corona radita and zona pellucida of the ovum by the spermatozoon nuclear head.


2-The tail region: The axoneme runs through the tail & it is responsible for the spermatozoon motility. It is a long specialized cilium with 9 outer douplets tubules around a central pair of tubule consists of:
Neck: forms the proximal portion of the tail as a short narrow segment consists of pair of centrioles & connecting piece are nine fibrous rings surrounding the axoneme surrounded by outer zone of highly packed elongated mitochondria.
Middle piece: through which runs the axoneme surrounded by 9 coarse longitudinal fibers, the lower limit of the middle piece is marked by a sudden narrowing, sometime associated with an annular thickening of the cell membrane (annulus).


Principle piece: Is the longest part of the tail & comprises the axoneme surrounded by the 9 coarse longitudinal fibers which in turn enclosed by numerou external sheath fibers oriented as circumferential fibers, the remaining 7 fibers are distributed a symmetrically, 4 in one lateral compartments & 3 in the other.
End piece: is composed of axoneme onlybecause at the junction between the principle piece & the short end piece, the longitudinal & circumferential fibers disappear.

The acrosomal cap cover the anterior2/3 to 3/4 of the nucleus, it is a glycoprotein containing numerous enzymes including (protease, acid phosphatase and neuraminidase and hyaluronidase). And can be regarded as specialized giant lysosomes.
The acrosomal cap enzymes are released when the spermatozoon contacts the ovum, they facilitate penetrate ion of the corona radita and zona pellucida of the ovum by the spermatozoon nuclear head.
The tail region:
running through the tail is axoneme which is responsible for spermatozoon motility. It is a long specialized cilium with 9 outer douplets tubules around a central tubular pair, the proximal of the tail is the neck, this is also a short narrow segment containing the pair of centrioles &connecting piece which form the 9 fibrous rings surrounding the axoneme.


The axoneme runs through the center of the middle piece &it is surrounded by the 9 coarse longitudinal fibers, from the connecting piece in the neck &outer zone of highly packed elongated mitochondria, the lower limit of the middle piece is marked by a sudden narrowing, sometime associated with an annular thickening of the cell membrane (annulus).
The principle piece: Is the longest part of the tail &comprises the axoneme surrounded by the 9 coarse longitudinal fibers which in turn enclosed by numerous external sheath fibers oriented circumferential fibers, the remaining 7 fibers are distributed a symmetrically, 4 in one lateral compartments & 3 in the other. At the junction between the principle piece &the short end piece, a longitudinal &circumferential fibers disappear, thus the end piece is composed of axoneme only.

Sertoli cells:

Sertoli cells are sited on the basement membrane of the S.T.
They are tall, columnar cells representing the main cell type until puberty, after which they comprise only about 10% of the cells lining the S.T, in elderly men the decrease in number of the germinal epithelial cells is common, sertoli cells are not affected by any of the factors that injure the sensitive germinal epithelium (e.g. they do not degenerate when they are exposed to the normal body temperature & can therefore survive in the undescended testis.
Microscopically the sertoli cells have an irregular apex extending into the lumen of the S.T, their nuclei are irregular in shape but tend to be oval with long axis at right angle to the basement membrane, the nuclei have vesicular chromatin pattern & prominent nucleolus.


The sertoli cells are characterized by irregular outline with many cytoplasmic extensions which make with those from nearby cells form a meshwork of cytoplasm, this meshwork encloses the developing cells of the germinal epithelium &forms tight junctions which roughly divide the S.T lining epithelium into basal &luminal compartments, the spermatogonia & preleptotene spermatocytes occupy the basal & adluminal compartment while the remaining primary & secondary spermatocytes & spermatids are located in the adluminal compartment.
Other forms of intercellular junctions between the sertoli cells including gap junction&desmosomeshave been seen.

Sertoli cells cytoplasm is eosinophilic &finely granular, it may contain lipid vacuoles.

By E/M abundant endoplasmic reticulum usually found in the cytoplasmic processes interdigitating between the developing germ cells + ribosomes, lipid vacuoles, microfilaments µtubules are common in the area of cytoplasm close to the developing spermatids.

Functions of sertoli cells:

Sertoli cells have supportive, phagocytic & secretory functions:
Supportive function includes provision of nutrients to the developing germinal epithelium by their cytoplasmic processes &transport of waste products from spermiogenesis to the blood &lymphatic vascular systems surrounding the S.T.
Sertoli cells phagocytoze any residual cytoplasm produced by maturating cells during spermatogenesis.
Secretory function varies with sexual maturation stage, in the prepubertal stage they secrete substances preventing meotic division of the germinal epithelial cells while in mature testis they secrete androgen-binding protein (ABP) which binds to the testosterone hormone produced outside the S.T, this hormone is required for normal germ cell maturation.


Testicular Interstitium:It contains hormone – secreting cells (Leydig cells, interstitial cells)The interstitial tissue lying between the S.T is a loose network of fibrocollagenous tissue composed of:Fibroblasts.Collagen fibers associated with macrophage &mast cells.Blood &lymphatic vessels.Clumps of interstitial or "Leydig cells".

Leydig cells:

They are most common in the tubular interstitium, they can be found occasionally in the mediastinum of testis, epididymis or even in the spermatic cord.
Leydig cells synthesize testosterone, these cells have round vesicular nuclei with one or two nucleoli.
Most of leydig cells are round or polygonal in shape but some are small &spindle- shaped & those are thought to be immature form.
They have eosinophilic cytoplasm containing lipase &oxidative enzymes& number of steroid- dehydrogenase.
Characteristic feature of these cells is "Reik's crystalloid" which is intracytoplasmic eosinophilic masses which are not seen before puberty but increase in number during years of sexual maturity.

The Rete Testis:

Is a complex arrangement of interconnecting channels located at the mediastinum of testis. The spermatozoon formed in the S.T loops, pass to the terminal portions & then via few short straight tubules, they reach to the rete testis, both straight tubules & rete testis are lined by simple cuboidal or low columnar epithelium bearing microvilli on their luminal surface .

Efferent ductules:

Channels of the rete testis fused to form efferent ductules which emerges from the upper end of the mediastinum penetrating the tunica albuginea 7entering the head of the epididymis, here they are gradually emerge to become a single tube called (epididymal duct). The efferent ductules are lined by a mixed epithelium of tall ciliated columnar cells & non ciliated cuboidal or low columnar cells with microvilli on their luminal surface, the cilia beats towards the epididymis & propel the spermatozoa onward while the non ciliated cells absorb some of the testicular fluid which is the transport medium for the immature spermatozoa, the efferent ductules are highly convoluted & have a narrow sheath of smooth muscle fibers +elastic fibers, contraction of this muscle fibers enhance the progression of the spermatozoa.

Epididymis:

The epididymal duct is formed by the fusion of the efferent ductules, this duct is a single highly convoluted tube about 5 meter long embedded in a loose vascular supporting stroma consisting of fibroblasts, collagen fibers & glycosaminoglycan matrix, it is surrounded by dense capsule to form a comma- shaped body called "epididymis" (i.e. duct + stroma + capsule).
Epididymis is divided into (head, body, &tail regions), the efferent ductules enter the head while the distal end of the epididymis emerges at the tail region to become the vas deferens, the epididymal duct is highly convoluted &it is all contained within the epididymis.


The epididymal duct is lined by a tall columnar epithelium bearing very long a typical microvilli which are immotile, so they are called "stereocilia" because they do not contain the microtubules & not function like the cilia.
The cells also posses lysosomes, RER &prominent Golgi.
The cells have absorptive, phagocytic & secretory functions:

Absorption of testicular fluid.

Phagocytosis of degenerated spermatozoa.
Secretion of glycoproteins which play a role in the maturation of the spermatozoa.
The entire epididymal duct is surrounded by a narrow sheath of circular SMF, but in the tail region there is longitudinal layer internal to the circular layer &other outer longitudinal layer, all of the muscle layers are thickened at the tail where the epididymal duct emerges to become the vas deferens.

Vas deferens:

Is a straight tube running vertically upward behind the epididymis within the spermatic cord, the vas deferens has a thick muscular wall composed of middle circular layer with outer & inner longitudinal layers.
internal to the inner layer there is fibroelastic lamina propria covered by columnar epithelium similar to that of the epididymis but thrown into longitudinal folds, this produce small stellaite lumen, contraction of thick muscular wall move the spermatozoa forward.

each vas deferens has a dilatation called "ampulla" where the muscle layer become thinner &the folds are branched & taller at distal end of the ampulla, the vas deferens joined the short duct from the seminal vesicle.

Seminal vesicle:

Each S.V is highly convoluted &unbranched tubular diverticulum of the vas deferens, the S.V is a coiled tube &surrounded by an inner circular &outer longitudinal smooth muscle fibers.
The mucosa is composed of fibroelastic lamina propria covered by epithelial cells, the mucosa is thrown into tall narrow complicated folds covered by non- ciliated tall columnar epithelium & some few basal rounded cells lie at the basement membrane , the tall cells have a characteristic secretory vacuoles near their luminal surface +RER.
the complex mucosal folds increase the surface area for secretion, 70% to 80% of the ejaculate is a thick creamy secretion produced by the S.V, contraction of smooth muscle fibers propels the accumulated secretions into the ejaculatory ducts

Ejaculatory duct:

It is 1 cm long & it is lined by tall columnar epithelium & small rounded cells, there is no SMF in its wall, the Rt. & Lt. ducts run through the prostatic gland &open in the prostatic urethra.

Prostate:

The prostate composed of secretory glands "or alveoli" open in the prostatic urethra which runs through its body, these prostatic alveoli & their ducts are embedded in a supporting stroma consisting of fibroblasts, collagen fibers, & smooth muscle fibers, the entire gland is surrounded by a fibrocollagenous capsule, from which septa extended into it's body dividing it into ill-defined lobes (i.e. gland, stroma, capsule).
The prostatic gland becomes larger in elderly.

The prostatic glands arranged in 3 concentric groups:

Small group of mucosal glands open directly into the urethra.
Larger group of submucosal glands open into the urethra by short ducts.
Outer group called main prostatic glands open into the urethra by long ducts.
The ducts of submucosal & main prostatic glands open directly into the urethral sinuses on either sides of a long ridge called "urethral crest"
The epithelium lining of the prostatic is thrown into complex folds accompanied by a narrow supporting lamina propria.

There are 2 types of the epithelial cells:

1-tall columnar or cuboidal cells with pale foamy cytoplasm + basal pale staining nucleus.
2- Scanty flat basal cells with small dark staining nuclei lie in contact with the basement membrane.
The tall columnar cells have prominent Golgi, lysosomes, secretory granules& RER (the secretory products are acid phosphatase, citric acid, amylase, and fibrinolysin).

The ducts of the prostate are lined by tall columnar epithelium but as they reach the urethra, they become gradually lined by cuboidal &even transitional epithelium likes that of the urethra.
The prostatic epithelium depends adequate testosterone level to maintain its function & structure.

The lumen of the prostatic glands contains some stored secretions in elderly form small spherical “corpora amylacea" which are condensed glycoproteine &often calcified.

Bulbourethral glands:

Seminal fluid enters the prostatic urethra from the Rt. & Lt. ejaculatory ducts passing through short membranous urethra & penile urethra befor entering the vagina.
Bulbourethral gland are paired small glands, their ducts open into the membranous urethra, the gland lined with tall mucous secretory epithelium, they produce a watery slightly mucoid fluid containing galactase & siliac acid, this fluid provides a lubricating function, run before the thick semen along the penile urethra.


Penis:
Is composed of erectile tissue & contains part of the urethra, the erectile tissue arranged into 2 dorsal cylinders (corpora cavernosa) + smaller central ventral cylinder (corporus spongiosum) through which the penile urethra runs. The cylinders are each surrounded by a dense fibrocollagenous sheath, the (tunica albuginea) which also holds them together.
The erectile tissues are interconnecting vascular spaces which are empty when the penis is flaccid, but filled with blood during erection.

The blood supply is provided by "dorsal artery", "deep artery" &"helicine artery " which supply the erectile tissue, the helicine arteries are so named because they are spiral in the flaccid condition, but during erection, they straighten & dilated filling the corpora with blood, this filling effect is partly due to closure of arteriovenous shunts present between the helicine arteries & deep vein.

The erectile component of the penis is surrounded by skin & loose subcutaneous tissue, at the distal end of the penis, the corporus spongiosum terminates into the (glans penis) which is covered by non- keratinized squamous epithelium containing sebaceous glands.
The penile urethra opens at the (meatus) which lies at the center of the glans penis.


Most of the penile urethra is lined by non- secretory columnar epithelium into which small mucous glands embedded.
The urethra dilates to form "navicular fossa" within the glans penis lined by non- keratinized squamous epithelium (like the glans).
The end of the penis is covered by an overlap of the penile skin called "propuce" which is rich in elastic fibers to permit it to retract over the glans penis



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