The reproduction system of a female dog is similar to a female human. The reproductive system includes the ovaries, the uterus, the cervix and the vagina. The ovaries are where the unfertilised eggs for pregnancy formulate. The Fallopian tubes are where fertilisation occurs between the sperm and egg. The fertilised eggs travel to the uterus where it attaches to the inside of the uterine lining. Once attached, the egg develops into an embryo.
The female dog has a reproductive cycle of three months with four phases. The first phase, proestrus, lasts from five to nine days and the external genitals become swollen and emit a bloody discharge. In phase two, oestrus, ovulation occurs for five to nine more days. In phase two the female dog mates with a male. Phase three is the diestrus period lasting two months and phase four is the anestrus period lasting three months. During phase three and four the female dog cannot mate.
The uterus is where the fertilised eggs develops into an embryo. The uterus of a female dog looks like a "Y" and the cervix is at the bottom of the "Y." The fertilised egg attaches to the inside of the uterus and forming a placenta. Placenta is how the nutrients from the mother transfer to the embryo allowing it to mature. Dogs breed in litters. A litter is multiple fertilised eggs.
The vulva is located below the anus on a female dog. The vulva has two purposes: one is for the discharge of urine and the other as part of the mating cycle. The vulva swells when the female dog is ready to mate. The vulva's lips expel hormones to attract a male dog for mating. Part of the swelling function of the vulva is the beginning stimulation of the female dogs teats to produce milk for her litter.
The ovaries are where unfertilised eggs form. The Fallopian tubes carry the egg to the sperm of the ejaculating male dog for fertilisation. Once fertilised, the eggs continue to travel to the uterus. There are two ovaries in the female dog's reproductive system. Within the ovary, the eggs mature in a fluid-filled sac. The follicles or the sac holds the eggs until phase two of the reproduction cycle. Within the ovary are oviducts. The oviducts move the ovulated egg into the Fallopian tubes for fertilisation.