The reproductive system is adapted to carry out the manufacture and storage of gametes, and to allow the physical act of mating to take place.

The male organ used in mating in vertebrates is the penis.

In most males there are two testes, held outside of the body in a pouch of loose skin called the scrotum. The temperature in the scrotum is about 2 degrees Celsius lower than normal body temperature because the body’s internal temperature is too high for the production of sperm.

Unlike animals that fertilize externally, internal fertilization usually requires insertion of the penis inside a receptacle in the female.

The female receptacle that fulfils this purpose is called the vagina. In female mammals a chamber called the uterus connects to the vagina through a narrow opening called the cervix. The uterus is the place where the embryo develops until the time of birth.

Sperm travel from each testis through a tube called the vas deferens. In mammals, the two vas deferens join to form a short ejaculatory duct. The ejaculatory duct in turn joins to the urethra, which carries urine from the bladder to the exterior by way of the penis.

Several glands add secretions to the sperm, forming semen, also called seminal fluid – the fluid that is actually ejaculated.

The seminal vesicles are glands that contribute much of the fluid volume of the semen. The fluid is alkaline, ensuring that the semen neutralizes the acidic environment of the vagina. This neutralization helps increase the sperm’s ability to swim up the vagina to the uterus.

Seminal fluid also produces fructose sugar, providing an energy source for the sperm, and a coagulating enzyme that makes it easier for the semen to be moved up into the uterus by uterine contractions.

The prostate gland secretes anticoagulant enzymes and sperm nutrients. The anticoagulants liquefy the semen after it has moved into the uterus.

In vertebrate animals two ovaries are attached in the abdominal cavity by connective tissue. Each ovary contains many follicles.

By the process of ovulation, an egg is released into the abdominal cavity, near the opening of a paired tube called the oviduct. The egg moves down the oviduct guided by muscular contractions or the movement of cilia lining the oviduct.

The two oviducts join the uterus, which connects to the vagina.

In most nonhuman vertebrates, the oviduct joins to a common opening that serves for excretion as well as reproduction.

In mammals, the egg implants into the wall of the uterus once it is fertilized, and development of the embryo takes place inside the female.

Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education