- THE FEMALE REPRODUCTIVE ORGANS
THE ANATOMY OF THE FEMALE REPRODUCTIVE SYSTEM
The female reproductive system consists of:
- 2 ovaries
- 2 fallopian tubes (oviducts)
- The uterus
- The cervix
- The vagina
- The vulva
Figure 1: The above are shown in the diagrams below: Anatomy of the Female Reproductive System
THE OVARIES
The ovaries have 2 functions, of which these are:
- The production of eggs
- The secretion of hormones necessary for conception and pregnancy
The ovaries contain many primary cells, each of which is capable of developing into a mature egg. The chief hormones produced are:
- Oestrogen
- Progesterone
- Oestrogen: The female hormone, oestrogen, is produced by the Graafian follicle on the ovary (on next page) Its main effects are:
- The development and function of the secondary sex organs;
- The onset of oestrus (heat) i.e. the period when cows/mares/ewes will stand to be mated;
- Controls the rate of growth and deposition of fat;
- Prepares the female for the start of cyclic sexual activity.
- Progesterone: This is secreted by the corpus luteum on the ovary after oestrus and ovulation.
- It prevents the female from coming back on heat before the end of the oestrus cycle if she does not fall pregnant.
- It suppresses further development of follicles.
- It prepares the uterus to receive the fertilised egg.
- It maintains the correct conditions in the uterus during pregnancy.
Figure 2: The Ovary
The shape of the ovary varies greatly with the species of the animal and depends on whether the female is polytocous (litter bearing), or monotocous (single bearing).
Anterior: nearer the front, especially in the front of the body, or nearer to the head or forepart THE FALLOPIAN TUBES OR OVIDUCTS
The oviducts are paired tubes which receive the eggs from the ovaries and through which the eggs pass to the uterus. The anterior end of the oviduct is expanded into a funnel which has the ability to gather eggs shed from the adjacent ovary. The cells lining the top of the tube have hair-like projections called cilia which, by rhythmic beating, aid the movement of eggs towards the uterus. The oviduct joins the uterus at the utero-tubular junction.
THE UTERUS
The uterus consists of a body and 2 horns, each of which is continuous with one oviduct. Eggs enter the uterus 3 or 4 days after they are shed from the ovary and, if fertilised, develop into embryos and embryonic membranes which attach to the uterus for the duration of the pregnancy.
THE CERVIX
The cervix is a muscular constriction which separates the uterus from the vagina – it varies in structure and appearance between species, for example:
- The Mare – simple, doesn’t protrude markedly into the vagina, easily penetrated.
- The Ewe – projects into the vagina, is more complex, penetration virtually impossible.
- The Cow – Intermediate
- The Sow – Intermediate
THE VAGINA
The vagina extends from the cervix to the vulva. The urethra opens into the floor of the posterior part of the vagina.
THE VULVA
The vulva is the external orifice of the genital tract.
PHYSIOLOGY OF THE FEMALE REPRODUCTIVE SYSTEM
The female reproductive system serves 2 functions:
- It provides ova which carry the chromosomes of the female
- It provides a system whereby the spermatozoa may gain access to the ova, and an environment which permits the fusion of male and female cells.
This fusion is known as fertilisation and occurs in the oviduct. After fertilisation, the egg passes to the uterus which provides a suitable environment for the development of a new individual. When the young is fully formed, the uterus expels it. Lactation follows and is the final stage of the female reproductive cycle.
- 2. OESTRUS CYCLE AND OVULATION
The oestrus cycle of female animals is the period from one oestrus (heat period) to the next, if she does not become pregnant.
For the cow, this period averages 21 days but can vary between 18 and 24 days.
In response to secretions of Follicle Stimulating hormone (FSH) by the pituitary gland, several follicles (egg cells) on the ovaries, start developing. In the cow, which normally only produces one calf per pregnancy, only one of these follicles, the most advanced one, develops fully into a mature follicle. This is then known as a Graafian follicle. At this stage, in response to oestrogen secretions by the Graafian follicle, the cow/mare/ewe starts showing oestrus, or is said to be “on heat”. This is the period when she is receptive to the bull/stallion/ram, and will stand still for mating. With cows, other cows will mount the one on heat, who will stand to be mounted, hence the term “standing heat”. This does not happen with other animals. At the same time, the vulva of the vagina swells and there is often a clear mucous discharge from the vagina. In the cow, oestrus lasts for about 18 hours but varies considerably. About 12 hours after the end of oestrus, the Graafian follicle ruptures (ovulation) in response to a surge of Luteinising hormone (LH) from the pituitary gland. The ovum (egg) released by ovulation goes into the funnel-shaped mouth of the fallopian tube, and is carried down the fallopian tube, where fertilisation will take place if viable sperm are present. Here the ovum is only open to fertilisation for a short time.
| Secreting: produce and discharge (a substance) |
The ovum is carried along and into one of the uterine horns. If it is fertilised, it will become implanted and persist for pregnancy. If it is not fertilised, it will regress and die and the next oestrus cycle will start.
After rupture of the Graafian follicle (ovulation) the cells of the ruptured follicle change, and give rise to a corpus luteum (CL). The CL secretes the hormone progesterone. The CL becomes fully functional by Day 6 of the cycle (Day 1 = oestrus). If the egg is not fertilised, the CL remains fully functional for 10 days (in the cow), after which it regresses and gradually stops secreting progesterone. Then the follicles of the next oestrus cycle begin to develop.
Figure 3: Oestrus Cycle of a Bovine Cow
