Spermatogenesis PDF

Spermatogenesis  Introduction Spermatogenesis is initiated in the male testis with the beginning of puberty. This comprises the entire development of the spermatogonia (former primordial germ cells) up to sperm cells. The gonadal cords that are solid up till then in the juveni...

Spermatogenesis  Introduction Spermatogenesis is initiated in the male testis with the beginning of puberty. This comprises the entire development of the spermatogonia (former primordial germ cells) up to sperm cells. The gonadal cords that are solid up till then in the juvenile testis develop a lumen with the start of puberty. They then gradually transform themselves into spermatic canals that eventually reach a length of roughly 50-60 cm. They are termed convoluted seminiferous tubules (Tubuli seminiferi contorti) and are so numerous and thin that in an adult male testicle their collective length can be 300 to 350 meters. They are coated by a germinal epithelium that exhibits two differing cell populations: some are sustentacular cells (= Sertoli's cells) and the great majority are the germ cells in various stages of division and differentiation. Definition:- It is the process by which spermatozoa are produced. The whole process take about 70-74 days. It is acontinuous process. 1 Basal lamina (membrane) (not recognizable) 2 Myofibroblast 3 Fibrocyte 4 Sertoli's cell 5 Spermatogonia 6 Various stages of the germ cells during spermatogenesis 7 Spermatozoon 8 Lumen  Control Of Spermatogensis 1- Age-from puberty to death. 2- Normal Testicles 3- Optimal temperature below body temperature by 0.5 C 4- Endocrine Control a)-testosterone b)-FSH C)-LH d)-inhibin 5-Nutritional status 6-psychological conditions 7-vitamin B The development of the germ cells begins with the spermatogonia at the periphery of the seminal canal and advances towards the lumen over spermatocytes I (primary spermatocytes), spermatocytes II (secondary spermatocytes), spermatids and finally to mature sperm cells Developmental stages of spermatogenesis  A-spermatogonium B-spermatogonium Primary spermatocyte (= spermatocyte order I) Secondary spermatocyte (= spermatocyte order II) Spermatid Sperm cell (= spermatozoon) The spermatogenesis can be subdivided into two successive sections: The first comprises the cells from the spermatogonium up to and including the secondary spermatocyte and is termed spermatocytogenesis. The second one comprises the differentiation/maturation of the sperm cell, starting with the spermatid phase and is termed spermiogenesis (or spermiohistogenesis Fig. The stem cell population of the germinal cells lies on the basal lamina of the convoluted seminiferous tubules. These are Type A spermatogonia. These cells undergo mitosis: one of the daughter cells renew the stock of type A spermatogonia, the other becomes a type B spermatogonia. These divide and their daughter cells migrate towards the lumen. In roughly 64 days they differentiate themselves thereby into sperm cells up to the outer surface of the epithelium (one should note that in these cellular divisions, the separation of the cytoplasm is not complete. Whole networks of connected cells arise. So, for example in the last generation, the spermatids, far more cells are bound to each other than as shown here).  Local course of spermatogenesis - the spermatogenesis wav In examining a cross-section of a convoluted seminiferous tubule one notices that cells appear in groups having the same maturation stages. However, not all the spermatogenesis stages are found in a cross-section. Fig. Various developmental stages in a light microscope cross- section through a convoluted seminiferous tubule. 1 Leptotene/zygotene of the 2 spermatocytes typ I Pachytene of the 3 spermatocytes 4 typ I Young spermatids 5 Older spermatids 6 (sperm cells heads can be recognized) Sertoli's cells Spermatogonia On the one hand, the reason for this appearance lies in the fact that the daughter cells, generated by each meiotic step, remain bound together by thin cytoplasmic bridges. Thus with each meiotic step the following generation is twice as large, until the cells have formed a relatively complex network. The result is that cells of the same development stages are seen there in groups. On the other hand, in addition, other spermatogenesis generations are wound around each other in spirals along the seminiferous tubule. This is why one meets with groupings of various generations in a tubule cross-section. Thus, it is highly improbable that all of the development stages will be seen in a single section at the same time. Spermiogenesis (spermatohistogenesis) and structure of the sperm cell The differentiation of the spermatids into sperm cells is called spermiogenesis. It corresponds to the final part of spermatogenesis and comprises the following individual processes that partially proceed at the same time Nuclear condensation: thickening and reduction of the nuclear size, condensation of the nuclear contents into the smallest space. Acrosome formation: Forming a cap (acrosome) containing enzymes that play an important role in the penetration through the pellucid zone of the oocyte. Flagellum formation: generation of the sperm cell tail. Cytoplasma reduction: elimination of all unnecessary cytoplasm. 1 Axonemal structure, first flagellar primordium 2 Golgi complex 3 Acrosomal vesicle 4 Pair of centrioles (distal and proximal) 5 Mitochondrion 6 Nucleus 7 Flagellar primordium 8 Microtubules 9 Sperm cells tail 10 Acrosomal cap  Leydig's interstitial cells and hormonal regulation Between the seminal canals lie Leydig's interstitial cells. These are endocrine cells that mainly produce testosterone, the male sexual hormone, and release it into the blood and into the neighboring tissues. An initial active stage of these cells occurs during the embryonic development of the testis. Later in juvenile life, due to the influence of the LH (luteinizing hormone) secreted by the anterior hypophysis (pituitary gland), Leydig's interstitial cells enter a second, long lasting stage of activity. Together with the hormones secreted by the adrenal cortex, testosterone initiates puberty and thus the maturation of the sperm cells. 1 Leydig's interstitial cells 2 Crystalloids of Reinke fertilization Implantation  Predecidualization The endometrium increases thickness, becomes vascularized and its glands grow to be tortuous and boosted in their secretions. These changes reach their maximum about 7 days after ovulation. Furthermore, the surface of the endometrium produces a kind of rounded cells, which cover the whole area toward the uterine cavity. This happens about 9 to 10 days after ovulation. These cells are called decidual cells, which emphasises that the whole layer of them is shed off in every menstruation if no pregnancy occurs, just as leaves of deciduous trees. The uterine glands, on the other hand, decrease in activity and degenerate already 8 to 9 days[after ovulation in absence of pregnancy. The decidual cells originate from the stromal cells that are always present in the endometrium. However, the decidual cells make up a new layer, the decidua. The rest of the endometrium, in addition, expresses differences between the luminal and the basal sides. The luminal cells form the zona compacta of the endometrium, in contrast to the basalolateral zona spongiosa, which consists of the rather spongy stromal cells  Decidualization Decidualization succeeds predecidualization if pregnancy occurs. This is an expansion of it, further developing the uterine glands, the zona compacta and the epithelium of decidual cells lining it. The decidual cells become filled with lipids and glycogen and take the polyhedral shape characteristic for decidual cells.