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Important points regarding Human Reproductive System


Important points regarding Human Reproductive System

Important definitions:

Below is given a brief introduction of a few terms that are not described in the text book. It may not be much helpful in the board examination neither in entry test but I hope it would help in making up a clear concept of the topic, as I learnt from my teacher.

Vas deferens:
The main ejaculatory duct of the reproductive system of man.

Epididymis:
It is the continuation of vas deferens that forms a layer over the testes where sperms are stored temporarily.

Corona radiate:
It is the outer protective layer of the oocyte/egg.

Zona pellucida:
The part on egg where the sperm has to bind.

Mechanism of gamete formation

Both male and female gametes are formed by the process of meiosis.
It is to be noted that mitosis takes place in all cells of the body but meiosis occurs only in sex cells resulting in gametes.

Production of sperms:

  1. The sex cells also known as spermatogonia are divided by mitosis to produce a primary spermatocyte. One cell remains as such while other divides further.
    This primary spermatocyte divides by MIEOSIS-1 in to two secondary spermatocytes.
  2. The two secondary spermatocytes separately divide by MIEOSIS-2 into two spermatids.
  3. Spermatids differentiate into sperms.


NOTE: Same is the case for production of female gametes with a few inevitable changes.
Four female eggs are formed out which three of them degenerate and only a single develops to become the oocyte.

Now let us discuss the female reproductive cycle.

Menstrual cycle:
In the text book all the important details are written very well, everybody can easily cram it. But let me explain the way I�ve memorized it. I hope it�ll also be simple for you people.
       
Basically there are four steps of the menstrual cycle.

  • Proliferative/follicular stage:
    This cycle starts on the onset of puberty. In our hypothalamus are certain areas that influence glands to release hormones, hence are called hypothalamic factors. The GONADOTROPHIN RELEASING FACTOR in the hypothalamus affects the pituitary gland to release a hormone named FSH (follicle stimulating hormone). FSH acts on the ovaries to produce follicles/eggs.
    In competition to pituitary comes the ovary and releases estrogen. Estrogen comes into play making sure that no more FSH is released and also thickening the uterus.

  • Ovulatory phase:
    Pituitary gland making a comeback secreting LH (luteinizing hormone) and as a result releases an ovum.

  • Secretory phase:
    After ovulation the left over follicle cells differentiate rapidly forming a yellow spongy structure corpus luteum. From this structure is secreted a hormone called progesterone which aids the uterus in zygote implantation after fertilization.

  • Menstruation:
    If fertilization has not occurred, the corpus luteum starts degenerating. Progesterone is no more secreted. The spongy corpus luteum with the walls of uterus and blood vessels is ejected out of the body so that the process can repeat itself for the next cycle. This stage lasts for about 3-4 days.

NOTE: the period of menstrual cycle before ovulation is variable while the phase after ovulation is constant i.e. 14 days.
Hence,
Day of ovulation= total days of menstrual cycle � 14.

All of the above discussion can be concluded as:
Testes and ovary are the respective male and female reproductive structures.
Meiosis results in production of gametes.
Testes and ovary both act as endocrine glands secreting hormones.

Q: At the end a question may arise that how progesterone is used in birth control pills. The answer for this is that it inhibits production of follicles. When no follicles there would be no ovum hence no fertilization.

Q: another question may be, in osteoporosis, estrogen replacement therapy (ENT) is given to aged women. This may again start the menstrual cycle after menopause has taken place. ANS: after the above given description of menstrual cycle it is clear that only estrogen is not responsible for the cycle but it is the gonadotrophin releasing factor in the hypothalamus which induces changes in the reproductive structures of the female.

Entry # 12
By Ahmad Azeem

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