Basic histology 5/4/2015

Transcription

1 Male reproductive system The male reproductive system is composed of the testes, genital ducts (the adjoining epididymis, and the vas deferens, a accessory sex glands (the seminal vesicles, the prostrate and the bulbourethral gland ), and the penis.(figure 1). The dual function of the testis is to produce of hormones and spermatozoa. The genital ducts and accessory glands produce secretions that,aided by smooth muscle contractions, conduct spermatozoa toward the exterior.these secretions also provide nutrients for spermatozoa. Testes Testis is surrounded by a thick capsule of dense connective tissue, the tunica albuginea.the tunica albuginea is thickened on the posterior surface of the testis to form the mediastinum testis, from which fibrous septa penetrate the gland, dividing it into about 250 pyramidal compartments called the testicular lobules (lobuli testis), which communicate peripherally to form Tubuli recti (figure1). Each lobule contains 1-4 convoluted seminiferous tubules. Interstitial tissue between the convoluted tubules is continuous with a layer of loose vascular connective tissue, the tunica vasculosa testis, which is rich in blood, lymphatic vessels and nerves. Figure 1 1

2 Figure 2 The convoluted seminiferous tubules Each seminiferous tubule that measure about µm in diameter and cm in length, continues near the mediastinum into a straight tubules, a tubuli recti. The straight tubules continue into the rete testis, a labyrinthine system of cavities in the mediastinum, is connected to the cephalic portion of epididymis by ductuli efferentes. (Figure 2) These seminiferous tubules are lined with a complex stratified epithelium called germinal or seminiferous epithelium, enclosed by a thick basal lamina. The innermost layer, adhering to the basal lamina consists of smooth muscle cells (or myoid cells). The insides of the tubules are lined with a complex which consists of two general types of cells :spermatogenic cells and sertoli cells.(figure 3) and interstitial cells also known as Leydig cells occupy much of the space between the seminiferous tubules. Fiure 3 2

3 Spermatogenesis A process by which spermatozoids are formed.it begins with a primitive germ cell, the spermatogonium which relatively small cell,about 12μm in diameter,situated next to the basal lamina of epithelium.at sexual maturity, spermatognia begin dividing by mitosis producing successive generations of cells. The newly formed cells with two type: A type spermatognia : the stem cells can continue dividing. B type spermatognia : the cells can differentiate during progressive mitotic cycles which finally producing successive generations of cells that finally give rise to spermatocytes. Which called Spermatocytogenesis and spermatocytes;meiosis, during which the spermatocytes goes through 2 division,with reduction by half of the number of chromosome, producing spermatids. Spermiogenesis : Includes cell division several times and finally differentiate, producing spermatozoa. Spermatogenesis is regulated by follicle stimulating hormone (FSH),which in males stimulates the spermatogenic epithelium, and luteinizing-hormone (LH), which in males stimulates testosterone production by Leydig cells in the interstitial tissue.(figure 4) (figure 4) 3

4 Spermatogenic cells : It begins with a primitive germ cell,the spermatognia( generation). Spermatognia Which is relatively small cell, about 12µm in diameter,situated next to the basal lamina of the epithelium.spermatogonia remain dormant until puberty, spermatognia begin dividing by mitosis,producing successive generations of cells. Primary spermatocytes Which lie in the cell layer luminal to the spermatogonia. They larger than spermatogonia. A large number of primary spermatocytes is always visible in cross-sections through seminiferous tubules. They immediately enter the prophase of the first meiotic division,which is extremely prolonged ( about) 22 days).results in the formation of Secondary spermatocytes Which are smaller than primary spermatocytes. They rapidly enter and complete the second meiotic division and are therefore seldom seen in histological preparations. Their division results in the formation of Spermatids Which lie in the luminal part of the seminiferous epithelium. They are small ( about 10 µm in diameter) with an initially very light (often eccentric) nucleus. The chromatin condenses during the maturation of the spermatids into spermatozoa, and the nucleus becomes smaller and stains darker. The terminal phase of spermatogenesis is called spermiogenesis and consists of the differentiation of the newly formed spermatids into Spermatozoa The mature human spermatozoon is about 60 µm long and actively motile. It is divided into head, neck and tail.(figure 5) figure 5 4

5 Sertoli cells Are important for the function of the testes. These cells are elongated pyramidal cells that partially envelop cells of the spermatogenic lineage. The bases of the Sertoli cells adhere to the basal lamina, and their apical ends frequently extend into the lumen of the seminiferous tubule. The nucleus of sertoli cells is ovoid or angular. The long axis of the nucleus is oriented perpendicular to wall of the tubule. Lateral processes of Sertoli cells are interconnected by tight junctions, which are likely to be the structural basis for the blood-testis barrier. Spermatogonia and primary spermatocytes are located in the basal compartment; other cellular stages of spermatogenesis are located in the adluminal compartment. Sertoli cells provide mechanical and nutritive support for the spermatogenic cells. Sertoli cells also secrete two hormones - inhibin and activin - which provide positive and negative feedback on FSH secretion from the pituitary. As the flagellar tails of the spermatids develop, they appear as tufts extending from the apical ends of the Sertoli cells. Spermatozoa are transported to the epididymis in an appropriate medium, testicular fluid, produced by the Sertoli cells and rete testis lining cells. This fluid contains steroids, proteins, ions, and androgen-binding protein (ABP) associated with testosterone.(figure 6) Figure 6 5

6 Interstitial tissue Leydig cells(15-20 µm), located in the interstitial tissue between the convoluted seminiferous tubules, constitute the endocrine component of the testis. They synthesis and secrete testosterone. Ledig cells occur in clusters, which are variable in size and richly supplied by capillaries. The cytoplasm is strongly acidophilic and finely granular. The nucleus is large, round and often located eccentric in the cell.(figure 7) (figure 7) Ducts of the Testis Intratesticular Genital Ducts:- Spermatozoa pass via the tubuli recti (low columnar epithelium) and the rete testis (flattened or cuboidal epithelium) into numerous ductuli efferentes, which are lined by a columnar epithelium, which consists of both absorptive and ciliated cells. The height of the two cells types that form the epithelium of the ductuli efferentes is variable which gives the lumen a characteristic wavy outline. The ductuli efferentes leave the testis and open into a common duct, the ductus epididymidis (transport the spermatozoa produced in the testis toward the penile meatus. These ducts are the1- ductus epididymidis, 2-the ductus (vas) deferens, and3- the urethra). Excretory Genital Ducts 1-epididymidis (about 6 m long!). It is lined by a very tall pseudostratified columnar epithelium. Most cells of the epithelium, called principal cells, have long stereocilia. 6

7 Stereocilia are non-motile structures, which in the EM resemble large microvilli. Towards the basal lamina we see a number of small nuclei, which belong to the basal cells of the ductus epididymidis. These cells regenerate the epithelium. Peristaltic contractions of smooth muscle cells surrounding the ductus epididymidis move the spermatozoa towards the middle segment of the duct, which is the site of final functional maturation of the spermatozoa - now they are motile. The terminal segment of the ductus epididymidis is the site of storage of the mature spermatozoa.(figure 8) AT adipose t.,bv blood vessel,c cilia,ct conn. t. SC stereocilia SM smooth m. Figure 8 2-The Vas deferens (or ductus deferens) The mucosa of the vas deferens forms low longitudinal folds. It is lined by a pseudostratified columnar epithelium. Similar to the epididymis, cells have long stereocilia. The lamina propria is unusually rich in elastic fibers. The muscularis is well developed (up to 1.5 mm thick) and consists of a thick circular layer of smooth muscle between thinner inner and outer longitudinal layers. The vas deferens is surrounded by an adventitia.(figure 9) 7

8 Figure 9 Male Accessory Reproductive Glands The accessory (or secondary) male sex glands consist of the seminal vesicles, the prostrate and the bulbourethral glands. The seminal vesicles :- Consist of two highly tortuous tubes about 15 cm in length. It has a folded mucosa that is lined with cuboidal or pseudostratified columnar epithelium rich in secretory granules. The lamina propria of the seminal vesicles is rich in elastic fibers and surrounded by a thin layer lamina propria of the seminal vesicles is rich in elastic fibers and surrounded by a thin layer of smooth muscle.the seminal vesicles are not reservoirs for spermatozoa. They are glands that produce a, yellowish secretion that 8

9 The prostate:- Figure 10 The prostate is the largest accessory sex gland in men. It contains branched tubuloalveolar glands,which are very irregularly shaped, which empty into independent excretory ducts.(figure 11) These ducts open into the urethra. The glands is surrounded by fibroelastic capsule rich in smooth muscle.septa form this capsule penetrate the gland and divided it into lobes. The epithelium is cuboidal or columnar pseudostratified epithelium. Basal cells are again present. The secretion of the prostate contains citric acid, the enzyme fibrinolysin (liquefies the semen), acid phosphatase, a number of other enzymes and lipids. The secretion of the prostate is the first fraction of the ejaculate. The secretory ducts of the prostate are lined by a simple columnar epithelium, which changes to a transitional epithelium near the openings of the ducts into the urethra. 9 (Figure 11)

10 The prostate has three distinct zones 1-The central zone : occupies 25% of the gland ' s volume, contains mucosal glands. 2-The peripheral zone : occupies 70% of the gland ' s volume so-called main glands, whose ducts run posteriorly to open into the urethra. 3-The transition zone - called submucosal glands (figure 11-12) Figure 12 10