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Home , Spermatocytogenesis

HISTOLOGY of

Mr. Babatunde, D.E. Male Reproductive System

❖ Consists of the testes contained in the , the genital ducts and their associated glands (accessory glands) and the . ❖ Testes function to produce spermatozoa (sperm) and to synthesize the hormone testosterone. ❖ Major accessory glands include the paired and the single gland. ❖ Minor accessory glands include the two bulbourethral glands located at the root of the penis. ❖ Accessory glands function to manufacture the fluid portion of the semen, which transports and nourishes the spermatozoa as they pass through the excretory ducts. ❖ Penis is the male copulatory organ that delivers spermatozoa into the female reproductive tract and serves as a conduit for excretion of urine from the body. Fig 22-1 (Text)

Bladder Prostate Menbranous Ampulla

Urethra Seminal vesticle Penis Corpus cavernosum of the penis Ductus deferens Corpus cavernosum Ductus epididymids of the urethra Ductus efferentes Prepuce Glands penis Testicular lobule Tunicia albuginea Tunicia vaginalis Tubuli recti Testes Testis ❖ Is an ovoid body, about 4 to 5cm long, that is housed within the scrotum. ❖ Develops retroperitoneally in the abdominal cavity and descends into the scrotum,carrying parietal and visceral layers of the peritoneum (the ) that partially cover the testis on its anterior and lateral surfaces. Seminiferous epithelium

Seminiferous tubules Tunica Tunica vasculosa albuginea Lumen Blood vessel

septum Seminiferous tubules Seminiferous epithelium Tunica albuginea

Tunica vasculosa

Seminiferous tubules Tunica Albuginea

❖ Is the thick fibrous connective tissue capsule of the testis. ❖ Is thickened posteriorly to form the mediastinum testis from which connective tissue septa arise to divide the organ into approximately 250 compartments (lobuli testis). Lobule Testis

⚫ Are pyramidal-shaped incomplete compartments that intercommunicate. ⚫ Contain from 1 to 4 seminiferous tubules each, embedded in a meshwork of loose connective tissue where nerves, vessels, and scattered interstitial cells of Leydig are present. Tunica albuginea Seminiferous epithelium

lobule

Seminiferous tubules Interstitial Cells of Leydig ❖ Are located in the interstitial spaces between the seminiferous tubules. ❖ Mature and begin to secrete during puberty and are richly supplied with capillaries and lymphatic vessels. ❖ Are round to polygonal in shape, possessed a large central nucleus, many mitochondria, a well-developed Golgi apparatus, smooth endoplasmic reticulum, and many lipid droplets. ❖ Are endocrine cells that produce the male sex hormone testosterone, when stimulated by luteinizing hormone (interstitial cell stimulating hormone) from the pituitary gland. Primary

Sertoli cell

Blood vessel

Spermatogonium

Interstitial cells

Figure 22–8. Interstitial cells and cells of the seminiferous epithelium. H&E stain. High magnification. Connective tissue Figure 22–3. Epithelium of seminiferous tubules surrounded by myoid cells. The spaces between the tubules contain connective Interstitial tissue, blood and lymphatic cells vessels, and interstitial cells. PT stain. Medium magnification. Myoid cells Figure 22–14. Electron micrograph of a section of an interstitial cell. There is abundant smooth endoplasmic reticulum as well as mitochondria. Medium magnification. Seminiferous Tubules ❖ Are the sites where spermatozoa are produced. ❖ Are 30 to 70 cm long, with a diameter of 150 to 250 um. ❖ Are lined by a complex, stratified epithelium. ❖ Are enveloped by a fibrous connective tissue tunic, composed of several layers of fibroblasts. Myoid cells, resembling smooth muscle, are present in the inner layer of some species. ❖ Form tortuous pathways through the organ before they become continuous with the short straight tubuli recti. Figure 22—6. Spermatocytes and in the epithelium of a . The tubule is covered by myoid cells. Picrosirius- hematoxylin (PSH) stain. Medium magnification.

Tubuli Recti

❖ Have a narrow lumen lined by a simple cuboidal epithelium. ❖ Lead into the rete testis, a network of epithelial-lined channels located in the mediastinum. Epithelium Rete testis Mediastinum testis

Connective tissue Tubuli recti

Seminiferous tubules Ductuli Efferentes

❖ Lead from the rete testis into the epididymis. Epithelium

Spermatozoa Ductuli efferentes

Connective tissue

Spermatozoa Ductuli Efferentes Rete testis Seminiferous Epithelium

❖ Is composed of two different types of cells, the spermatogenic cells from which the germ cells eventually develop and the Sertoli cells, which support and provide nutrition to the spermatogenic cells. ❖ Is 4 to 8 cell layers thick. Cytoplasmic bridges Late Early spermatids

Initial spermiogenesis Secondary spermatocytes meiosis Primary Basal lamina

fibroblast

Interstitial cells Figure 22–4. Part of a seminiferous tubule with its surrounding tissues. The seminiferous epithelium is formed by 2 cell populations: the cells of the spermatogenic lineage and the supporting or Sertoli cells. Late spermatids

Young spermatids

Primary spermatocyte

Sertoli cell spermatogonium

Figure 22–5. Part of the wall of a seminiferous tubule. Several cells of the spermatogenic lineage are present: a spermatogonium, primary spermatocytes, and young and late spermatids. The approximate limits of a Sertoli cell holding several spermatids are delineated. H&E stain. High magnification. Sertoli Cells

❖ Are columnar, extremely complex in shape, and extend from the basal lamina to the lumen. ❖ Their apical and lateral plasma membranes are markedly irregular in outline since they envelope the developing germ cells. Cytoplasmic bridges Late spermiogenesis Early spermatids

Initial spermiogenesis Secondary spermatocytes meiosis Primary spermatocyte Basal lamina spermatogonium

fibroblast

Interstitial cells Figure 22–4. Part of a seminiferous tubule with its surrounding tissues. The seminiferous epithelium is formed by 2 cell populations: the cells of the spermatogenic lineage and the supporting or Sertoli cells. ❖ Contain a well-developed smooth endoplasmic reticulum, some rough endoplasmic reticulum, an abundance of mitochondria and lysosomes, and an extensive Golgi apparatus. Spermatocytogenesis ❖ refers to division of the spermatogonia to provide a continuous supply of cells that will give rise to primary spermatocytes.

Meiosis ❖ are two successive divisions that reduce the chromosome number from diploid to haploid and produce spermatids.

Spermiogenesis ❖ is cytodifferentiation and transformation of spermatids to form spermatozoa. ❖ Nucleus is pale, oval, displaying frequent indentations and a large nucleolus. ❖ Form occluding junctions with adjoining Sertoli cells, thus subdividing the lumen of the seminiferous tubule into a basal and an adluminal compartment. ❖ Zonulae occludentes are responsible for establishing the blood-testis barrier that serves to protect the developing sperm cells from autoimmune reactions. Adluminal compartment (blue) Figure 22–12. The Sertoli cells form the blood-testis barrier. Neighbor Sertoli cells are attached by occluding junctions that divide the seminiferous tubules into 2 compartments and impede the Late spermatids passage of substances between both compartments. The basal Early spermatids compartment comprises the interstitial space and the spaces Sertoli cell occupied by the spermatogonia. The adluminal compartment Spermatocyte comprises the tubule lumen and the intercellular spaces down to the Spermatogonium level of the occluding junctions (OJ). In this compartment are Basal compartment spermatocytes, spermatids, and spermatozoa. Cytoplasmic residual(red) bodies from spermatids undergo Myoid cell phagocytosis by the Sertoli cells and are digested by lysosomal Endothelial enzymes. The myoid cells surround cells the seminiferous epithelium. Lumen of capillary Functions

Of Sertoli cells are manifold. ❖ Support, protect, and nourish developing spermatozoa. ❖ Phagocytose excess cytoplasm discarded by spermatids in the process of spermiogenesis. ❖ Form the blood- testis barrier which plays an essential role in isolating spermatogenic cells from the immune system. ❖ Secrete a fluid into the seminiferous tubules that transports spermatozoa to the genital ducts. ❖ Contain FSH receptors and under FSH influence synthesize androgen-binding protein (ABP) that binds testosterone, concentrating it to permit sperm maturation. ❖ Secrete inhibin, a hormone that inhibits synthesis and release of FSH from the anterior pituitary. Sertoli cells(continued)

⚫ Produce Mullerian Inhibiting Factor/Hormone that inhibits the paramesonephric duct/Mullerian duct ⚫ Produces plasminogen activator which converts plasminogen to active proteolytic hormone plasmin ⚫ Transferrin, an iron-transporting protein ⚫ Ceruloplasmin, a copper-transporting protein ⚫ Stem cell factor Figure 22–13. Hypophyseal control of male reproduction. Luteinizing hormone (LH) acts on the Leydig cells, and follicle- stimulating hormone (FSH) acts on the seminiferous tubules. A testicular hormone, inhibin, inhibits FSH secretion in the pituitary. ABP, androgen- binding protein. (Modified and reproduced, with permission, from Bloom W, Fawcett DW: A Textbook of Histology, 10th ed. Saunders, 1975.) Spermatogenic Cells

❖ Include several characteristic cell types in the seminiferous epithelium: spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids, and spermatozoa. ❖ Each of these cells represents a distinct stage in the differentiation of male germ cells. The entire process is known as . Figure 22–7. Diagram showing the clonal nature of the germ cells. Only the initial spermatogonia divide and Type A spermatogonia produce separate daughter cells. Once (stem cells) committed to differentiation, the cells of all subsequent divisions stay Type B spermatogonia connected by intercellular cytoplasmic (progenitor cells) bridges. Only after they are separated from the residual bodies can the spermatozoa be considered isolated Mitosis cells. (Modified and reproduced, with permission, from Bloom W, Fawcett DW: A Textbook of Histology, 10th ed. Saunders, 1975.) Primary spermatocytes First meiotic division secondary spermatocytes Second meiotic division

Residual bodies

Spermatids

Spermiogenesis

Residual bodies Spermatozoa Spermatogenesis

❖ Is divided into three phases: spermatocytogenesis(spermatogonial phase) , meiosis( spermatocyte phase), and spermiogenesis( phase). ❖ In man takes approximately 74 days; its cell divisions are unusual, in that the daughter cells remain connected to each other via intercellular bridges (forming a syncytium). Syncytium

❖ May be responsible for the synchronous development of germ cells along any one seminiferous tubule. ❖ Is disrupted at the completion of spermatogenesis, when the individual spermatozoa are released into the lumen ( The process known as spermiation) Spermatogonia

❖ are the diploid germ cells that sit upon the basal lamina. ❖ are of three types: pale type A, dark type A, and type B. Pale spermatogonia Arterioles

Seminiferous epithelium Spermatogonia B Sertoli cell Nucleolus

Dark spermatogonia Venule Pale Type A

❖ are small (about 12 um diameter) and possess a pale-staining nucleus and cytoplasm containing spherical mitochondria, a small Golgi complex, and abundant free ribosomes. ❖ at puberty these cells undergo mitosis and give rise to either more pale type A spermatogonia (to maintain the supply of spermatogonia) or type B spermatogonia (which undergo mitosis and give rise to primary spermatocytes). Dark Type A

❖ (with dark nuclei) represent noncycling, reserve cells that have the potential to produce more pale type A cells. Seminiferous epithelium Spermatozoa Spermatogonia Primary Connective tissue spermatocyte

myoid cell lumen Basal Adluminal compartment compartment

Fibroblast Sertoli cell

Spermatid Primary Spermatocytes

❖ are identified as the largest germ cells in the seminiferous epithelium. ❖ are diploid cells (46 chromosomes) that undergo meiosis.

Prophase

❖ of the first meiotic division is long (it takes more than 22 days). ❖ Including several stages: leptotene, zygotene, pachytene, diplotene (during which crossing over, the exchange of genetic material between homologous chromosomes, occurs) and diakinesis. ❖ is followed by metaphase I, anaphase I, and telophase I, which compose the first meiotic division.

First Meiotic Division

❖ results in the formation of small secondary spermatocytes. Secondary Spermatocytes

❖ possess the haploid number of chromosomes (23), and the amount of DNA has been reduced (from 4N to 2N). ❖ undergo the second division, producing spermatids. Spermatids

❖ are haploid cells with 23 chromosomes and one-half the amount of DNA (since no S phase took place). ❖ are small (7 to 8 um diameter) and located near the lumen of the seminiferous tubule. ❖ their nuclei often display regions of condensed chromatin. ❖ contain a pair of centrioles, mitochondria, free ribosomes, smooth endoplasmic reticulum, and a well- developed Golgi apparatus. ❖ undergo the cytodifferentiation process known as spermiogenesis. Spermiogenesis

❖ Is the unique differentiation process whereby spermatids transform into spermatozoa that are release into the lumen of the seminiferous tubule. ❖ Acrosome and sperm tail are formed during spermiogenesis, the nucleus becomes condensed and elongated, and excess cytoplasm not directly involved in forming the spermatozoa is shed and phagocytosed by Sertoli cells. ❖ Is divided into four phases: Golgi, cap, acrosome, and maturation phases. Golgi Phase ❖ of spermiogenesis is characterized by the formation of proacrosomal granules in the Golgi complex. Proacrosomal Granules ❖ coalesce to form a single acrosomal granule enclosed within an acrosomal vesicle, which becomes attached to the anterior end of the nuclear envelope. Centrioles ❖ migrate away from the nucleus to form the flagellar axoneme and then retreat toward the nucleus and assist in forming the connecting piece associated with the tail. Cap Phase ❖ Involves the expansion of the acrosomal vesicle over much of the nucleus, to form the acrosomal cap. Acrosomes ❖ contain hydrolytic enzymes (acid phosphatase, neuraminidase, hyaluronidase, protease, and phosphatase).

Acrosomal Reaction ❖ refers to the release of enzymes that facilitate the dissociation of the cells of the corona radiata and the digestion of the zona pellucida. Acrosome Phase ❖ is characterized by the nucleus becoming condensed and flattened, mitochondria aggregating around the proximal portion of the flagellum to form the middle piece, and elongation of the spermatid.

Elongation ❖ may be facilitated by a cylinder of microtubules, the manchette. By the end of the acrosome phase the spermatids are oriented with their acrosomes pointing toward the base of the seminiferous tubule. ⚫ Figure 22—10. Electron micrograph of a mouse spermatid. In the center is the nucleus, covered by the acrosome. The flagellum can be seen emerging in the lower region below the nucleus. A cylindrical bundle of microtubules, the manchette, limits the nucleus laterally. (Courtesy of KR Porter.) Maturation Phase

❖ is characterized by excess cytoplasm being discarded (including the intercellular bridges that connected the spermatids) and phagocytosed by Sertoli cells. ❖ is completed when nonmotile spermatozoa are released (tail first) into the lumen of the seminiferous tubule. Cycle of Seminiferous Epithelium

❖ refers to the wave-like sequence of maturation that occurs along the seminiferous tubules.

One Cycle

❖ is the reappearance of identical cell associations within the epithelium. ❖ in humans is approximately 16 days, so that 4.6cycles (approximately 74 days) must occur for a spermatogonium to be transformed into a . ⚫ Figure 22—9. Top: The principal changes occurring in spermatids during spermiogenesis. The basic structural feature of the spermatozoon is the head, which consists primarily of condensed nuclear chromatin. The reduced volume of the nucleus affords the sperm greater mobility and may protect the genome from damage while in transit to the egg. The rest of the spermatozoon is structurally arranged to promote motility. Bottom: The structure of a mature spermatozoon. Histophysiology

Temperature

❖ of 35˚C is critical for the development of spermatozoa. ❖ is achieved in the scrotum by the pampiniform plexus of veins that wrap around the testicular artery and function to dissipate heat. ❖ is achieved also by evaporation of sweat from the skin of the scrotum. ❖ below 35˚C, contraction of the cremaster muscle in the brings the testis close to the body wall to increase the temperature. Cryptorchidism

❖ is a condition when the testes fail to descend into the scrotum during development. ❖ the normal body temperature inhibits spermatogenesis, resulting in sterility. However, this condition does not affect testosterone production. Luteinizing Hormone (LH)

❖ of the pituitary gland stimulates the interstitial cells of Leydig to secrete testosterone, which is responsible for the normal development of male germ cells and secondary sex characteristics.

Follicle-Stimulation Hormone (FSH)

❖ of the pituitary gland acts on the Sertoli cells, promoting the synthesis of androgen-binding protein (ABP). ABP

❖ binds with testosterone and maintains a high concentration of testosterone in the seminiferous tubules, where it is essential for spermatogenesis. ❖ binds estrogens and inhibits spermatogenesis. Increased testosterone levels inhibit LH release, whereas FSH release is stopped by inhibin (secreted by Sertoli cells). Figure 22–13. Hypophyseal control of male reproduction. Luteinizing hormone (LH) acts on the Leydig cells, and follicle- stimulating hormone (FSH) acts on the seminiferous tubules. A testicular hormone, inhibin, inhibits FSH secretion in the pituitary. ABP, androgen- binding protein. (Modified and reproduced, with permission, from Bloom W, Fawcett DW: A Textbook of Histology, 10th ed. Saunders, 1975.) Genital Ducts

❖ convey the spermatozoa and semen to outside of the body. ❖ extend from the seminiferous tubules to the urethra. Although they are continuous, they are structurally and histologically different. Their names identify the regional division and unique characteristics they possess.