Physiology of testis

 

 

The testis is the male generative organ which produces the sperm in the process of gametogenesis called spermatogenesis. It is located in the scrotal sac which is placed relatively outside the body and below the trunk, this position is to ensure lower temperature in order to allow for adequate spermatogenesis.  It is divided into lobules by septa running from the tunica albuginea. The lobules contain seminiferous tubules (3 or 4 in number), these tubules open by straight ductules that enter into the epididydmis. The epididydmis becomes confluent to form single tube known as the vas or ductus deferens.

 

The seminiferous tubules are responsible for spermatogenesis. The development starts from the primordial or primitive germ cells known as the dark type A spermatogonium which divides into 2 light type A and another dark type A by mitosis. The light type A divides into 2 light type B spermatogonia which divide mitotically again to form the primary spermatocyte.

The primary spermatocyte represents the beginning of meiosis. Cells do not pass to the state of primary spermatocyte until puberty. At puberty, waves of meiotic cycle becomes evident in seminiferous tubules. The spermatogonia are found in the periphery of the tubules, while spermatocytes are nearer the center of the tubules. The mature sperm cells are liberated into the center of the tubules for onward transportation into the straight tubules that lead into the epididydmis. where further maturation takes place.

The plan of meiosis is to decrease the diploid state of spermatogonia to haploid state of the spermatocyte. The division is divided into two stages. The first meiotic division is over with the formation of the two daughter cells known as secondary spermatocyte (from primary spermatocyte). This is the actual reduction division since after this division the chromosomal complement is reduced from diploid (2N) to haploid (1N) state

 

Secondary spermatocytes prepare for the second division once they are formed. This second division ends in the formation of spermatids

 

Spermatids are immature sperm cells that have completed their meiotic division and are now ready for the morphological maturation that finally leads to the formation of recognizable sperm cell. The process of sperm formation from spermatid is called spermiogenesis. The morphological maturation of spermatogenesis allows the development of 5 regions on the mature sperm cell which has a streamlined morphology presumably for active movement in fluid medium is opposed to the spherical spermatid. Regions of the mature sperm include, the head, neck, body, middle piece, tail piece and end piece

 

The following processes occur during maturation of the sperm the head becomes transformed into pear shaped structure. Within the head is the peripheral acrosomal vesicle followed by acrosomal granule which is developed from Golgi apparatus. The neck is a short straight structure which leads from the head and joins the middle piece (or body) and it contains the anterior and posterior centrioles for the attachment of axial filaments which run form the body to tail. Axial filaments are arranged in 9:2 configuration of cilioflagellar ultrastructure with two filaments in the middle and 9 surrounding the two at the periphery. It is covered by mitochondrial sheath in the body. The tail tapers from the body and also contains the 9:2 axial filament structure but is covered by fibrillar sheath. The axial filament ends at the junction between the tail and the end piece.

A maturation known as spermiogenesis takes place through the Sertoli cells which are large supporting cells found n the margin of the seminiferous tubule. The spermatid is handled by the first process of the Sertoli cell from where it is passed to the second and then to the 3rd process. By the time it reaches the 3rd process the cytoplasm has been pushed down the tail and the body by the spermatozoa. It is now found mainly in the head of the spermatozoa (cytoplasm).

Mature cells are transported through the various ducts straight ducts to rete testis then into efferent ducts and to the caput epididymis. Sperm cells do not move in the testis. They acquire their ability for locomotion in the epididydmis especially at the tail of the epididymis hence it is believed that epdidymal maturation is paramount for fertilizability of the sperm cell. The processes of maturation which occurs in the epididydmis are chemical in nature, glycoproteins are produced in the epithelium of the epididymis which aid maturational process of the sperm cell. But the maturation which occurs in the epididymis are of a chemical nature and not morphological. It is believed that these maturational processes act on the membrane modifying considerably the membrane chemistry and thus changing such chemical and physical properties of membrane such as membrane charges etc. Sperm cells which do not have the influence of epididydmal environment cannot fertilize any egg.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Meiosis 1

Meiosis 2

 

 

 

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