A gonad, sex gland, or reproductive gland is a mixed gland and

sex organ A sex organ, also known as a reproductive organ, is a part of an organism that is involved in sexual reproduction. Sex organs constitute the primary sex characteristics of an organism. Sex organs are responsible for producing and transporting ...

that produces the

gamete A gamete ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as s ...

s and sex hormones of an organism.

Female An organism's sex is female ( symbol: ♀) if it produces the ovum (egg cell), the type of gamete (sex cell) that fuses with the male gamete (sperm cell) during sexual reproduction. A female has larger gametes than a male. Females and ...

reproductive cells are

egg cell The egg cell or ovum (: ova) is the female Reproduction, reproductive cell, or gamete, in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female game ...

s, and

male Male (Planet symbols, symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or Egg cell, ovum, in the process of fertilisation. A male organism cannot sexual repro ...

reproductive cells are

sperm Sperm (: sperm or sperms) is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm ...

. The male gonad, the

testicle A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is Homology (biology), homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of Androgen, androgens, p ...

, produces sperm in the form of spermatozoa. The female gonad, the

ovary The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/ oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are end ...

, produces egg cells. Both of these gametes are

haploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Here ''sets of chromosomes'' refers to the num ...

cells. Some hermaphroditic animals (and some humanssee Ovotesticular syndrome) have a type of gonad called an ovotestis.

Evolution

It is hard to find a common origin for gonads, but gonads most likely evolved independently several times.

Regulation

The gonads are controlled by luteinizing hormone (LH) and follicle-stimulating hormone (FSH), produced and secreted by gonadotropes or gonadotrophins in the anterior pituitary gland. This secretion is regulated by

gonadotropin-releasing hormone Gonadotropin-releasing hormone (GnRH) is a releasing hormone responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. GnRH is a tropic peptide hormone synthesized and rele ...

(GnRH) produced in the

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

Development

The gonads develop from three sources; the mesothelium, underlying mesenchyme and the primordial germ cells. Gonads start developing as a common primordium (an organ in the earliest stage of development), in the form of genital ridges, at the sixth week, which are only later differentiated to male or female

s (except when they are not differentiated). The presence of the SRY

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

, located on the short arm of the

Y chromosome The Y chromosome is one of two sex chromosomes in therian mammals and other organisms. Along with the X chromosome, it is part of the XY sex-determination system, in which the Y is the sex-determining chromosome because the presence of the ...

and encoding the testis determining factor, usually determines male sexual differentiation. In the absence of the SRY gene from the Y chromosome, usually the female sex (ovaries instead of testes) will develop. The development of the gonads is a part of the

development of the urinary and reproductive organs The development of the urinary system begins during prenatal development, and relates to the development of the urogenital system – both the organs of the urinary system and the sex organs of the reproductive system. The development continues as ...

Disease

The gonads are subject to many diseases, such as

hypergonadism Hypergonadism is a condition where there is a hyperfunction (medicine), hyperfunction of the gonads. It can manifest as precocious puberty, and is caused by abnormally high levels of testosterone or estrogen, crucial hormones for sexual developmen ...

hypogonadism Hypogonadism means diminished functional activity of the human gonad, gonads—the testicles or the ovary, ovaries—that may result in diminished biosynthesis, production of sex hormones. Low androgen (e.g., testosterone) levels are referred t ...

agonadism Gonadal dysgenesis is classified as any Disorders of sex development, congenital developmental disorder of the reproductive system characterized by a progressive loss of primordial germ cells on the developing gonads of an embryo. One type of go ...

, tumors, and cancer, among others.

Aging

Ovarian aging

A delay in having children is common in the developed world and this delay is often associated with ovarian

female infertility Female infertility refers to infertility in women, which is the inability to Fertilisation, conceive after sexual intercourse. It affects an estimated 48 million women, globally. Female infertility varies widely by region. The highest rates of ...

and subfertility. Ovarian aging is characterized by progressive decline of the quality and number of oocytes. This decline is likely due, in part, to reduced expression of genes that encode proteins necessary for

DNA repair DNA repair is a collection of processes by which a cell (biology), cell identifies and corrects damage to the DNA molecules that encode its genome. A weakened capacity for DNA repair is a risk factor for the development of cancer. DNA is cons ...

and meiosis. Such reduced expression can lead to increased DNA damage and errors in meiotic recombination.

Testicular aging

The testes of older men often have

abnormalities that can ultimately lead to

male infertility Male infertility refers to a sexually mature male's inability to impregnate a fertile female. Male infertility can wholly or partially account for 40% of infertility among couples who are trying to have children. "A problem with the male is the s ...

. These abnormalities include accumulation of DNA damage and decreased DNA repair ability. During spermatogenesis in the testis, spontaneous new mutations arise and tend to accumulate with age.

References

{{Authority control Glands Endocrine system Human reproductive system Sex organs