Chapter 3 Human Reproduction Notes Part-02  

 6)-What is gametogenesis

spermatocyte completes the first meiotic division (reduction division) leading to formation of two equal, haploid cells called secondary spermatocytes, which have only 23 chromosomes each. The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids . The spermatids are transformed into spermatozoa (sperms) by the process called spermatogenesis. After spermiogenesis, sperm heads become embedded in the Sertoli cells, and are finally released from the seminiferous tubules by the process called spermiation

7.    Explain the structure of sperm

      It is a microscopic structure composed of a head, neck, a middle piece and a tail . A plasma membrane envelops the whole body of sperm. 

      The sperm head contains an elongated haploid nucleus, the anterior portion of which is covered by a cap-like structure, acrosome.

      The acrosome is filled with enzymes that help fertilisation of the ovum. The middle piece possesses numerous mitochondria, which produce energy for the movement of tail that facilitate sperm motility essential for fertilisation.

      The human male ejaculates about 200 to 300 million sperms during a coitus of which, for normal fertility, at least 60 per cent sperm must have normal shape and size and at leas 40 per cent of them must show vigorous motility.

      Sperms released from the seminiferous tubules, are transported by the accessory ducts. Secretions of epididymis, vas deferens, seminal vesicle and prostate are essential for maturation and motility of sperms. 

      The seminal plasma along with the sperms constitute the semen. The functions of male sex accessory ducts and glands are maintained by the testicular hormones (androgens).

7.    Differentiate menarche and menstruation cycle 

       The reproductive cycle in the female  primates (e.g. monkeys, apes and human  beings) is called menstrual cycle. The first  menstruation begin sat puberty and is  called menarche. In human females,  menstruation is repeated at an average  interval of about 28/29 days, and the cycle of events starting from one menstruation till the next one is called  the menstrual cycle.

8. Explain lactation and parturition

     The average duration of human pregnancy is about 9 months which is called the gestation period. Vigorous contraction of the uterus at the end of pregnancy causes expulsion/delivery of the foetus.This process of delivery of the foetus (childbirth) is called parturition. Parturition is induced by a complex neuroendocrine mechanism.

     The mammary glands of the female undergo differentiation during pregnancy and starts producing milk towards the end of pregnancy by the process called lactation

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