Both sexes have a pair of sexual organs or gonads (ovaries or testes), the main functions of which are to produce eggs or sperm, respectively, and hormones.
Ovaries are female gonads that produce eggs and female sexual hormones, including estrogen and progesterone. Estrogen is necessary for the development of eggs, and progesterone prepares the uterus for pregnancy. Once puberty is reached and the cat starts having estrous (heat) cycles, the size and form of the ovaries change. Within the ovary, a special group of cells called a follicle surrounds each egg.
The estrous cycle begins when follicle stimulating hormone causes follicles to grow, leading to maturation of eggs. Follicle stimulating hormone also stimulates the production and release of estrogen. Cats are induced ovulators, which means that the mechanical stimulation of the vagina and cervix during mating causes the release of luteinizing hormone from the brain, which stimulates the ovary to release the eggs (a process called ovulation). Progesterone, which is released from the ovaries, prepares the uterus for pregnancy and the mammary glands for milk production. Estrogen and progesterone are required for the development of female characteristics and sexual behavior.
Estrual cycling is seasonal in cats and is controlled by light. Cats require at least 12 hours of light in order to have estrous cycles. In the Northern Hemisphere, under natural lighting, cats reproduce in the spring and summer, with reduced or absent cycling during the shorter days of winter. Cats that are kept indoors under artificial light will tend to have heat periods more often than cats housed under natural lighting conditions.
The testes are male gonads that produce sperm and male sexual hormones. Sperm maturation is stimulated by the production and release of follicle stimulating hormone and testosterone. During ejaculation, sperm are transported from the testes through the ductus deferens (narrow tubes connecting the testicles to the urethra). Testosterone is required for development and function of accessory glands (such as the prostate), sexual organs, male sex characteristics, and sexual behavior. For normal sperm production, testes must descend into the scrotum (a pouch of skin outside the abdomen), because normal body temperature is too high for sperm to develop normally. The function of the testicles can be assessed by an evaluation of semen samples and hormonal tests. In addition, testicle examination and measurement can help evaluate fertility and may reveal reproductive diseases.
The female genital tract consists of the vulva, vagina, cervix, uterus, oviducts, and ovaries. The oviducts (also called Fallopian tubes) are small tubes that connect the ovaries to the uterus. The end of the uterus is called the cervix. It separates the uterus from the vagina and provides a barrier against infection. The vagina, a muscular tube that extends from the cervix to the outside, is connected to the vulva, which is the external opening of the female genitals. Oviducts are associated with each ovary. After ovulation, mature eggs are transported to the uterus via the oviducts. Secretion of fluid in the tubes provides a proper environment for survival of the mature egg, fertilization, and the first few critical days of embryonic life. The proper functioning of the uterus and cervix are also required for the establishment and maintenance of pregnancy.
Infections may cause female infertility because they interfere with the proper function of the uterus. Infertility in female cats can be diagnosed through various tests, including x-rays, ultrasonography, abdominal examination, evaluation of vaginal cells and discharge, and blood tests. The vagina and vulva serve as the copulatory organ and as the last part of the birth canal. They also provide a route for infections, particularly when the vulva cannot function properly due to trauma, relaxation, or deformities.
In male cats, the genital tract provides a pathway for semen, which contains the sperm cells. The epididymis connects the testicle to the ductus deferens, which carries ejaculated sperm to the urethra. Sperm mature and are stored in the epididymis. The accessory sex glands, such as the prostate, create the fluid portion of semen. Cancer and inflammation of the genital tract can be diagnosed by several means, including physical examination, laboratory tests, and ultrasonography. Other diseases or abnormal functioning can be diagnosed by testing semen samples. Reproductive tract disease in male cats is very uncommon.
Also see professional content regarding the gonads and genital tract.