Testes are a pair of oval organs that are present in the scrotal sac, which is situated directly behind the penis. Their function is to produce hormones mainly testosterone and spermatozoa male reproductive cells.
If the embryo is genetically male contains both sex chromosomes, X and Y chromosome , the signal for testis development is mediated by the SRY gene on the Y chromosome. Then, tubules of the rete testis arise, towards the hilum of the gland, due to break up of these cords into very small cell strands. As development continues, a dense layer of fibrous connective tissue is formed, the tunica albuginea, which divides the testis cords from surface epithelium.
In the 4th month major changes happens: testis cords become horseshoe-shaped with their extremities continuous with those of the rete testis and, at this time, they are composed of two types of cells — sustentacular cells of Sertoli, involved in support and protection, and primitive germ cells, both derived from the surface epithelium of the gland. Interstitial cells of Leydig, start developing shortly after the beginning of the differentiation of testis cords and are derived from the original mesenchyme of the gonadal ridge, which is present between the testis cords.
Their function is to produce testosterone. This production starts around the 8th week, time in which the testis are already able to influence sexual differentiation of the genital ducts and external genitalia. At the time of puberty testis cords acquire a lumen and form the seminiferous tubules. Then, after being canalized the seminiferous tubules join the rete testis tubules, which in turn enter the ductuli efferentes.
These efferent ductules are the remaining parts of the excretory tubules of the mesonephric system. Ovaries are almond shaped bodies, found in pairs in the female reproductive system whose main functions are: the production of hormones estrogen and progesterone and oogonia the female reproductive cells. In this case, the embryo is a female, having in this way 2 X chromosomes. By the time of the 7th week, a new generation of cords appears, the cortical cords, due to the constant proliferation of the surface epithelium of the female gonad in male this proliferation does not happen.
These cords penetrate the underlying mesenchyme any loosely organized tissue containing fibroblast-like cells and extracellular matrix regardless of the origin of the cells but remain close to the surface. By the time of the third month, primordial follicles are generated as the cortical cords divide into isolated cell clusters that proliferate and later start to surround the primordial female reproductive cells oogonia with a layer of epithelial cells called follicular cells.
Together, the oogonia and the follicular cells constitute a primordial follicle. Contrary to the male embryos, the medullary cords of the gonads of the female embryos regress and a secondary generation of cortical cords develops. In embryos with an XY sex chromosome complex, medullary cords develop into testis cords and secondary cortical cords fail to develop.
Leydig cell hypoplasia. Others severe hypospadias, cloacal exstrophy. Ovotesticular DSD. CAH congenital adrenal hyperplasia is the most common DSD, which may result from several metabolic effects. In the majority of the people, the block is at the hydroxylase enzyme, which leads to mineralocorticoid deficiency and excessive formation of androgenic products. This condition causes virilization of a child with 46XX chromosomes.
The clinical presentation is dependent on the severity of enzyme deficiency. Another common DSD is androgen insensitivity syndrome AIS , in which a person with a male sex chromosome does not respond to androgens. This abnormality results in a body with a feminine appearance. There are two types, complete and partial androgen insensitivity. Both types of individuals have 46 XY karyotypes. The individual with complete AIS has female external genitalia with normal appearance.
In both cases, the affected individuals have testes and normal production of testosterone and DHT. It results from a mutation in the SRD5A2 gene, which encodes the enzyme 5-alpha reductase type 2. It is the enzyme responsible for the conversion of testosterone to DHT, the more physiological form.
DHT is responsible for the masculinization of external genitalia. Newborns with 5-alpha-reductase deficiency present with ambiguous genitalia with clitoral like phallus, bifid scrotum, and pseudovaginal perineoscrotal hypospadias a form of male pseudohermaphroditism. Whereas in puberty, the child may present with signs of virilization and clitoromegaly.
It is an autosomal dominant condition. Type 1 MRKH is characterized by vaginal and uterine aplasia. Type 2 incorporates other extragenital malformations. The patient usually presents with primary amenorrhea with normal sexual development.
Hypospadias is a congenital condition in which the opening of the urethra is not at the usual position; instead, it is at the underside of the penis. It will lead to problems like abnormal spraying of urine, abnormal curvature of the penis chordee. In epispadias, the urethral opening is at the upper aspect of the penis.
The incidence of Turner syndrome is 1 in liveborn females. Turner syndrome is diagnosable at birth due to features like low birth weight, lymphedema of hands and feet, and short neck. Others may present later with short stature and delay in puberty.
Another one is Klinefelter syndrome; it occurs in 1 in liveborn males. Affected boys can have normal external genitalia. Clinical features include tall stature, weak muscles, small testes, gynecomastia, delayed puberty, and infertility. Pask A, The Reproductive System. Advances in experimental medicine and biology. Journal of molecular endocrinology. Makiyan Z, Studies of gonadal sex differentiation. Results and problems in cell differentiation.
Birth defects research. Part C, Embryo today : reviews. Wiley interdisciplinary reviews. Developmental biology. The FEBS journal. Witchel SF, Disorders of sex development. Endocrine reviews. Sexual development : genetics, molecular biology, evolution, endocrinology, embryology, and pathology of sex determination and differentiation.
Molecular reproduction and development. Differentiation; research in biological diversity. Sajjad Y, Development of the genital ducts and external genitalia in the early human embryo. The journal of obstetrics and gynaecology research. Asian journal of andrology. Baskin LS, Hypospadias and urethral development. The Journal of urology.
Korean journal of urology. Journal of endocrinological investigation. Hormone research in paediatrics. Embryology, Sexual Development.
Free Review Questions. These come from the coelomic epithelium Sertoli's supporting cells , the local mesenchyma and the mesonephros. The testicular cords extend deeply into the region of the future testicles. List of the chapters Next page. Gonads: indifferent stage Testes: differentiation Development of the parenchyma Development of the stroma Summary Ovaries: differentiation Development of the stroma Development of the parenchyma Summary Descent of the testes Displacement of the ovaries.
Gonads: indifferent stage. These cells come from the ectoderm , but they separate themselves from it at a very early stage in the development. The somatic cells with nourishing functions surround the primordial germ cells and form the somatic gonadal blastema.
In the testes the supporting cells Sertoli and the interstitial cells Leydig are involved, in the ovary the follicle cells and the theca cells. Their origin is still a matter of discussion, however, whereby three possible sources come into question: mesonephros , local mesenchyma , as well as superficial epithelial cells coelomic epithelium.
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