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==Introduction==

==Introduction==

Spermatogenesis is the process of the gradual transformation of germ cells into spermatozoa. It occurs mainly within the seminiferous tubules of the testes and can be divided into three phases, each of which is associated with different germ cell types:

Spermatogenesis is the process of the gradual transformation of germ cells into spermatozoa. It occurs mainly within the seminiferous tubules of the testes and can be divided into three phases, each of which is associated with different germ cell types:

*Proliferative phase - spermatogonia → spermatocytes

*Proliferative phase: spermatogonia → spermatocytes

*Meiotic phase - spermatocytes → spermatids

*Meiotic phase: spermatocytes → spermatids

*Differentiation phase / spermiogenesis - spermatids → spermatozoa

*Differentiation phase (also known as spermiogenesis): spermatids → spermatozoa

Unlike the female production of gametes which occurs entirely before birth, with gamete maturation occurring in a pulsatile fashion after puberty, males produce gametes continuously from puberty onwards for the rest of their reproductive lives and the release of the gametes is constant.  

Unlike the female production of gametes which occurs entirely before birth, with gamete maturation occurring in a pulsatile fashion after puberty, males produce gametes continuously from puberty onwards for the rest of their reproductive lives and the release of the gametes is constant.  

==The meiotic phase==

==The meiotic phase==

Each 1^o spermatocyte divides to give rise to two short-lived 2^o spermatocytes, which in turn give rise to two '''spermatids''' each, each of which contain a haploid number of chromosomes (half the number of a somatic cell).  

Each 1^o spermatocyte divides to give rise to two short-lived 2^o spermatocytes, which in turn give rise to two '''spermatids''' each. The spermatids contain a haploid number of chromosomes (half the number of a somatic cell).  

1^o spermatocytes are the largest cells in the spermatogenic series and are located approximately midway within the seminiferous epithelium.

1^o spermatocytes are the largest cells in the spermatogenic series and are located approximately midway within the seminiferous epithelium.

This phase is also known as spermiogenesis.

This phase is also known as spermiogenesis.

Spermatids undergo transformation into spermatozoa. Many changes occur within the cells, the 3 major ones being  

Spermatids undergo transformation into '''spermatozoa'''. Many changes occur within the cells, the 3 major ones being:

i) formation of the acrosome, which covers the cranial part of the head. The acrosome will contain hydrolytic enzymes to allow fusion of sperm and egg for fertilisation.

i) formation of the acrosome, which covers the cranial part of the head. The acrosome will contain hydrolytic enzymes to allow fusion of sperm and egg for fertilisation.

The morphological changes occurring during this process can be seen if sections of different seminiferous tubules are examined.  

The morphological changes occurring during this process can be seen if sections of different seminiferous tubules are examined.  

=Hormonal Control of spermatogenesis=

=Hormonal Control of spermatogenesis=

The production of sperm is controlled by hormones influencing sertoli cells rather than sperm cells directly. Hormonal control is via the two gonadotrophins luteinising hormone (LH) and follicle-stimulating hormone (FSH).

Spermatogenesis is controlled by a complex feedback mechanism involving the hypothalamus, anterior pituitary and testes. Gonadotrophic releasing hormone (GnRH)is released by the hypothalamus in a pulsatile manner and travels through portal vessels to the anterior pituitary, where it acts of the gonadotrophic cells. These cells respond to the stimulation by producing either follicle stimulating hormone (FSH) or luteinising hormone (LH) depending on the pattern of GnRH secretion.  

*LH acts on the interstitial leydig cells stimulating them to produce the androgen testosterone.

 

*FSH acts on the sertoli cells within the seminipherous tubules stimulating production of Androgen Binding Protein as well as Inhibin

LH and FSH travel in the bloodstream to the testes, where LH acts on the Leydig cells to stimulate them to convert steroids to testosterone and other androgens, which in turn contribute to the stimulation of Sertoli cells.

 

FSH acts on the receptors of Sertoli cells and, in combination with testosterone, stimulates many functions, including synthesis and secretion of oestrogen, inhibin and many other products, meiosis, spermatocyte maturation and Leydig cell function.

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