Male Reproductive SystemThe 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 female genital system.3-Production of male sex hormones (Androgens).
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 which carries the 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.
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.
Testis: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 temperature 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.
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 outer layer of the scrotal sac which is a potential space containing a watery fluid acts as a lubricant allowing testis to move freely without friction.
The testis covered by a thick collagenous capsule or called (the visceral layer of the tunica vaginalis) or called (tunica albuginea), it's outer surface is coated with flattened mesothelial cell layer forming the inner layer of the scrotal sac, 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 Tubule: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 close 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 tubules in each testis is (300-900 meter) in sexually mature adult male, 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 called "Myoid cells" containing intermediate filaments & desmin (like smooth muscle cells), in the human testis the myoid cells form a less distinct layer or discontinuous 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 spermatogonia 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 which further replicate by mitosis to form clusters of daughter cells linked together by cytoplasmic bridges, type AP spermatogonia mature into type B-cells which divide by mitosis to produce further type B-cells, these cells then mature in a clusters to produce (1ry spermatocytes).
2-The 1ry spermatocytes replicate their DNA shortly after their formation (i.e. they are 4N), more 1ry spermatocytes formed by mitosis then they undergo the 1st meiotic division thus they pass through long prophase lasting about 22 days, during which changing nuclear chromatin patterns (preliptotane liptotane, zygotane, pachytene and diplotene) can be identified. The first meiotic division occurs after the late [pachytene-diplotene] stage leading to the formation of diploid secondary spermatocytes which rapidly within few hours undergo the 2nd meiotic division to produce spermatids.
Is the process by which haploid spermatids are transformed into spermatozoa, spermiogenesis can be divided into 4 stages all of which occur while the spermatids are embedded within small hollows in the free luminal surface of the sertoli cells, these stages are:
The mature spermatozoon is formed from (head, tail, the latter 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 contains 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, neuraminidase and hyaluronidase), it can be regarded as specialized giant lysosome.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: is responsible for the spermatozoon motility, it is a long specialized cilium with 9 outer douplets tubules around a central pair of tubule forming what is called axoneme runs throughout its length, the tail consists of :
Neck: a short narrow segment forming the proximal portion of the tail consists of a pair of centriole & connected to the remaining parts by a connecting piece which consists of nine fibrous rings around the axoneme surrounded by outer zone of highly packed elongated mitochondria.
Middle piece: through which runs the axoneme surrounded by nine coarse longitudinal fibers, the lower limit of the middle piece is marked by a sudden narrowing associated with an annular thickening of the cell membrane forming the (annulus).
Principle piece: Is the longest part of the tail & comprises the axoneme surrounded by the nine coarse longitudinal fibers which in turn enclosed by another circumferential external sheath fibers.
End piece: is composed of axoneme only because both the longitudinal & circumferential fibers disappear.
Male Reproductive System PAGE 1
Lecture 1 Dr. Muna Zuhair