Endocrine System
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11.8 Vas Deferens and Seminal Vesicles – After coming out of the testis, the epididymis becomes straight, increases in diameter and becomes a muscular tube, called the sperm duct or vas deferens. Some short tubes called seminal vesicles open into the vas deferens, enter into the abdominal cavity through a wider tube, and merge with the duct leading from the seminal vesicle gland. The seminal vesicles are tightly coiled short tubes that also store sperms. They produce fluid sugars for nourishing the sperms. The prostate gland, which surrounds part of the urethra also contributes acids, trace elements and enzymes to the sperms to form a thick milky fluid known as semen. The penis is the external male genital organ. It is a common passage for both urine and semen.
How does a New Life Begin?
11.9 The ovaries release one egg about every 28 days in a process that is called ovulation. The Fallopian tubes carry the egg to the uterus, which is located between the ovaries. The menstrual cycle is the process that prepares a woman for pregnancy. During the menstrual cycle, changes take place in the uterus. The soft inner lining of the uterus thickens, reaching its full thickness shortly after ovulation. If the egg is fertilised, it attaches itself to the lining of the uterus and starts to develop. If the egg is not fertilised by a sperm within about 21 hours, it dies. The unfertilised egg together with the inner lining of the uterus is then slowly discharged through the vagina in a process called menstruation.
Fertilisation
11.10 For fertilisation to take place in a woman’s body, it is essential that the female egg cell should fuse with the male cell. The female egg starts out very small, about the size of a little dot. The egg is fertilised in the Fallopian tube of the female. Once the egg fuses with the male cell, it undergoes various cell divisions, in which a single cell divides and becomes a number of small cells, to give rise to a zygote. When the egg and the male cell unite, some of the characteristics of the male and some of the female are preserved in the zygote.
11.11 Once the egg has been fertilised in the Fallopian tube, the cell division starts, and the developing embryo moves down the tube. After about three days, it reaches the uterus and attaches itself to the uterine wall. The placenta and other tissues vital to the life of the embryo, form at the attachment point. The placenta is a long tube which connects the mother and the embryo. And through this tube the embryo draws nourishment from the mother while it is developing in the mother’s womb. Unborn babies do not eat food the way we do. They get their food from their mother’s blood. When the mother eats food, much of the nourishment goes into her blood and then to the placenta. The placenta is where the baby’s blood and the mother’s blood meet. It is inside the womb next to the baby. The baby is joined to the placenta by a special thick tube called the umbilical cord. After the baby is born – that is, after it comes out of the mother’s body – the umbilical cord which joins the baby to the mother is cut. Later, the part of the cord left at the baby’s end, shrivels up to form the navel or the belly button. Through the cord the baby gets all the food it needs to go on growing to keep healthy. If the father or mother has some disease, it can also be transferred to the child and the baby born may be malformed. To avoid this mishap, it is important that the concerned person should get his or her disease treated.
