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A gonad, sex gland, or reproductive gland [1] is a mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. [2] The male gonad, the testicle, produces sperm in the form of spermatozoa. The female gonad, the ovary, produces egg cells
The first appearance of the gonad is essentially the same in the two sexes, and consists in a thickening of the mesothelial layer of the peritoneum. The thick plate of epithelium extends deeply, pushing before it the mesoderm and forming a distinct projection. This is termed the gonadal ridge. The gonadal ridge, in turn, develops into a gonad.
The primary sex organs are the gonads, a pair of internal sex organs, which diverge into testicles following male development or into ovaries following female development. [8] As primary sex organs, gonads generate reproductive gametes containing inheritable DNA. They also produce most of the primary hormones that affect sexual development, and ...
Gonadal sex refers to the gonads, that is the testicles or ovaries, depending on which genes are expressed. Phenotypic sex refers to the structures of the external and internal genitalia. [6] Six weeks elapse after fertilization before the first signs of sex differentiation can be observed in human embryos. [5]
Male gonad (testes, left) and female gonad (ovaries, right) Males have two testicles of similar size contained within the scrotum, which is an extension of the abdominal wall. [1] Scrotal asymmetry, in which one testicle extends farther down into the scrotum than the other, is common. This is because of the differences in the vasculature's ...
Level of definition Female Male Biological levels Sex chromosomes: XX in humans XY in humans Primary sexual characteristics: Gonads: ovaries: testicles: Levels of sex hormones: high estrogen and gestagens (including progesterone); low androgens (including testosterone) high androgens (including testosterone) Anatomy of internal genitalia
In embryology, the genital ridge (genital fold or gonadal ridge) is the developmental precursor to the gonads. The genital ridge initially consists mainly of mesenchyme and cells of underlying mesonephric origin. Once oogonia [clarification needed] enter this area they attempt to associate with these somatic cells.
In most species, gonads are paired organs of similar size, which can be partially or totally fused. [1] There may also be a range of secondary organs that increase reproductive fitness. The genital papilla is a small, fleshy tube behind the anus in some fishes, from which the sperm or eggs are released; the sex of a fish can often be determined ...