In the female, the internal genital organs consist of the ovaries, the fallopian tubes, the uterus and the vagina.
Ovary
It is a paired organ. Each ovary of the adult female is an oval body (8cm x 2cm x 1cm) and weight 2-8 g. The ovum drops into the body cavity. The process of release of ovum from the ovary is called ovulation. The ovum which is released in to abdominal cavity is drawn towards the oviducal funnel. The ovum finally enters the funnel and starts coming down the duct. In about 24 hours, the ovum is passed out of the body through the vagina. The ovum is very small, almost the size of a pinhead, and is, therefore, hardly noticeable. The ovary releases one ovum every 28 days.
Oviduct:
There are two oviducts or tubes. They are joined to the uterus on either side. The oviduct is about 10-15 cm long. It curves outwards towards the sides of the abdomen. The oviduct is wider towar5ds the sides, but very narrow towards the uterus. The opening of the oviduct in the abdominal cavity has longitudinal folds and fringes resembling a carnation in flower.
Uterus:
The uterus (womb) is a hollow, pear-shaped muscular structure. Its upper broader portion is called the corpus uteri (body of the womb) and the narrow portion is the cervix uteri or the neck of the womb. The cavity of the womb is 7-8 cm in length.
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The external genital parts of the female include the outer lips (labia majora), the inner lips (labia minora) and the clitoris. The outer and inner lips close the openings of the vaginal tube, the vestibule. The clitoris is found in the pubic cleft. It is a small projected part which is comparable to the penis of the male.
Fertilization
If coitus takes place just after the ovulation, and if sperms discharged in the vagina, manage to climb up to the fallopian tube there is a good chance that one of the sperms will enter the ovum (egg) so as to bring about fertilization.
Post-fertilization Changes
Implantation:
After fertilization the reproductive organs are geared towards a different set of activities. As the fertilized egg trickles down the oviduct, it is continuously undergoing mitotic cell division. It is a nonstop process, but for our convenience we divide the post-fertilization events in to a number of stages. When the resultant cells form a group or a mass of cells in which there is no space within the group, we call it morula stage. The cells of morula rearrange afterwards in such a manner as to leave some space within. This stage is called blastula. It is blastula which is embedded in the uterus. This process is called implantation. The wall of the uterus is thick and its wall has muscles, glands and a large number of blood capillaries. As the blastula erodes into the uterine wall, there is some erosion of blood capillary. As a result the blood oozes out and the blastula gets nutrition from the blood. This blastula will subsequently develop in to foetus and finally into an infant.
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Important Changes during Pregnancy:
When the blastula becomes implanted in the uterus of mother, it continues to grow by cell division. There important layers of cells develop. These are the germ layers. Subsequently, membranes are developed. The outermost membrane of the embryo is called chorion. Second covering of the embryo is amnion, which immediately surrounds the foetus. Withins this covering there is an amniotic fluid which protects the embryo from shocks. A portion of the gut wall of the embryo is sprouted.
This out-pushing grows out further, and occupies a space between amnion and chorion, and is called allantois, which acts as the urinary bladder of the foetus. From the outermost membrane (chorion) a number of outpushings arise arise a get inserted in to the inner wall of the uterus of mother to form placenta. This device draws nutrition from the maternal blood. There is an intimate contact between the blood vessels of the uterus and that of the foetus through the placenta. Umbilical cord serves as a link between the foetal and maternal circulation. When the embryonic development is completed, the young is born. The young is expelled by the contraction of the uterine muscles, this is called birth or parturition. The contraction of the uterine muscles is induced by the hormone oxytocin.
The total period of embryonic development is different for different mammals. In man, it is 280 days. This period is called the gestation period. Elephants have the longest gestation period (2 years).
Relationship of Ovary and Uterus
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Menstruation:
If there is no occasion for the released ovum to be fertilized then the ovum is passed out. It will never be implanted in the uterus in the unfertilized state. After about two weeks of ovulation, in the event of egg not being fertilized, the uterus begins to contract. This is a sign of undoing the preparations it had made to receive the fertilized egg. Upon the contraction of uterus, the blood capillaries rupture, and the blood flows out through the vagina. This process is called menstruation. The blood along with tissue debris is called menses. Menstruation lasts for 3-4 days. Afterwards, the uterus starts preparing itself afresh for the arrival of the ovum in the next two weeks. To sum up, menstruation takes place 14 days after the ovulation. Again 14 days after menstruation, there is fresh ovulation. In this way, ovulation and menstruation alternate. Both these processes stop once pregnancy had set in.
Menarche and Menopause
When a girl attains the age of 13-15, she begins to ovulate. This is the age of her sexual maturity. The age of sexual maturity in both male and female is called puberty. What happens in this age? The onset of puberty is marked by changes in the body. For example, in the female the breasts start developing, pubic hairs also grow besides the commencement of periodical menstruation. The first menstruation in the life of a girl is called menarche. Somewhere between 45-55 years the ovary stops releasing the egg. We can say that the ovary has become nonfunctional. It does not develop further to receive the fertilized egg. So, the question of its contraction resulting in menstruation does not arise. When menstruation stops in a woman, it is taken for granted that she will not be able to bear child any more. Ending of menstruation is called menopause.