Reproduction in man

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 Reproduction (man):

Reproduction is the union of male and female gametes to form a zygote.As it is common with other terrestrials, man has developed a more certain means of bringing the gametes together..

  The sperm is produced in the numerous seminiferous tubules in the testes . From there it passes through the vasa efferentia and epididymis into the VAS deferens. For the sperm to be introduced into the female, it is necessary for the penis to be inserted into the vagina in an act of coitus or corpulation. Under conditions of erotic excitement the arteries in the penis dilates and the veins then constrict.

The resultant high blood pressure in the penis causes the penis to become erect . As the penis move up and down in the vagina , the tactile stimulation of the sensory cells at it's tip triggers off a reflex . This causes the contraction of the VAS deferens. Sperm is then swept down into the urethra . Here, it is mixed with secretions from both the seminal vesicles and the prostrate gland. These secretions keep the sperm in a viable and motile state . The admixture of the sperm and secretions is called "semen". The semen is expelled from the penis Into the vagina by a powerful contraction of the urethra. This processed is termed "ejaculation".

The reflex mechanism that brings about erection and ejaculation inhibits urination.

The sperm reaches the ovum at the upper part of the fallopian tube where fertilisation takes place. Despite the fact that millions of sperm cells are produced only few reach the ovum, and of these few ones, only one is allowed to fertilize the ovum .

After fertilization, the zygote moves down the fallopian tube by peristalsis. it takes about a week for the zygote to reach the uterus and before then it has divided mitotically to form "blastocyst ". The embedding of the blastocyst in the uterus is called" implantation".

After implantation the blastocyst continues to develop by cell division. As development continues, the blastocyst is called the" foetus" .The foetus is enveloped by protective membrane- The chorion and the amnion.

The amnion is the inner membrane and it encloses a fluid filled amniotic cavity which act as a buffer for the fetus. later, the placenta is formed in association with the walls of the uterus and it is connected to the fetus by the umbilical cord. Within the placenta, fetal and material blood vessels come into intimate association with each other and across their walls exchange of respiratory gases , food materials and nitrogenous wastes takes place.

To accommodate the growing foetus , the uterus expands enormously and this is accompanied by the thickening of its walls and increased vascularization. When the fetus reaches a certain age , birth or parturition occurs. The time interval from fertilisation to parturition is known as the gestation period which is affirmed to last for nine months in man under normal circumstances.

For reproduction to occur in man, fertile sperms have to be introduced into the vagina of an ovulating woman with patent fallopian tubes and uterus . From the above , it is clear that not all sperm cells can fertilize an ovum (egg) . Certain qualities are used to measure the potency of a sperm cell. They include> 

1. The volume: The normal volume ranges from one millimetre to six millimetres.

2.mortility: This should be greater than or equal to sixty percent in an hour or seventy percent in two hours .

3.count : Equal to or greater than 20million cells per millimetre of sperm produced.

4.morphology: less than 25% of abnormal forms.

5.pus cells: there should be no pus cells in the sperm.

 Abnormalities associated with the sperm

There are two abnormalities associated with the sperm. These are Azoospermia and oligospermia.

Azoospermia means there is no sperm cell at all in d semen while oligospermia denotes presence of sperm cells that are less available than normal  

oligospermia: Mild;11-19millions\ml

                         Moderate;6-10 millions\ml 

                         Severe; less or equal 5millions\ml.

Author: pius prince

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