HUMAN REPRODUCTION

Uterus:

• It is single and is called womb.
• It is inverted pear shaped.
• Attached the pelvic wall by ligaments.
• The uterus opens into vagina through a narrow cervix.
• The lumen of cervix is called cervical canal.
• Cervical canal along with vagina form the birth canal.
• The wall of the uterus has three layers of tissues
  • Perimetrium: external thin membranous.
  • Myometrium: middle thick layer of smooth muscles
  • Endometrium: inner glandular layer.
• Endometrium undergoes cyclical changes during menstrual cycle.
• Myometrium exhibits strong contraction during delivery of the baby.

External genitalia:

• It includes following structure:
  • Mons Pubis: cushion of fatty covered by skin and pubic hair.
  • Labia majora: fleshy folds of tissue which extends down from the mons pubis and surrounds the vaginal opening.
  • Labia minora: are paired folds of tissue under the labia majora.
  • Hymen: the opening of vagina is often covered partially by a membrane called hymen.
  • Clitoris: a tiny finger-like structure lies at the upper junction of two labia minora above the urethral opening.

Mammary glands:

• Mammary gland consists of glandular tissue and fat.
• Glandular tissue of each breast divided into 15-20 mammary lobes.
• Mammary lobes contain cluster of cells called alveoli.
• The cells of alveoli secrete milk, stored in the lumen of alveoli.
• The alveoli open into mammary tubules.
• The tubules of each lobe join to form a mammary duct.
• Several mammary ducts join to form a wider mammary ampulla.
• Mammary ampulla connected to lactiferous duct, through which milk is sucked out.

GAMETOGENESIS: (formation of gametes)

Spermatogenesis:

• Formation of sperm from the germ cell in the testes is spermatogenesis.
• The process begins at puberty.
• Spermatogonia present in the lining of seminiferous tubules undergo mitotic division to increase their number.
• Each spermatogonium is diploid (2n) which contain 46 chromosomes.
• Innermost layer of spermatogonial becomes larger called primary spermatocyte.
• Primary spermatocyte undergoes meiosis-I to form two equal haploid (n) secondary spermatocytes (n).
• Each secondary spermatocyte undergoes meiosis-II to form two equal, haploid spermatids.
• Each primary spermatocyte produces four spermatids.
• Spermatids transformed into spermatozoa (sperms) by the process called spermiogenesis.
• The sperm head embedded in the Sertoli cell.
• Release of sperm from the seminiferous tubule is called spermiation.

Hormonal control of spermatogenesis:

• This process is initiated at puberty due to secretion of gonadotrophins releasing hormone (GnRH)
• GnRH secreted form hypothalamus and stimulate anterior pituitary to secrete two gonadotrophins.
  • Luteinizing hormone (LH) and
  • Follicle stimulating Hormone (FSH)
• LH acts on Leydig cells and stimulates synthesis of androgens.
• Androgen stimulates spermatogenesis.
• FSH acts on Sertoli cells and stimulates spermatogenesis in other ways.

Structure of sperm:

• Ultrastructure of sperm consists of a head, neck, a middle piece and a tail.
• Whole body of sperm surrounded by plasma membrane.
• The sperm head contain an elongated haploid nucleus.
• Above the nucleus a cap like structure present called acrosome.
• The acrosome contains enzymes which help in fertilization of ovum.
• The middle piece contains mitochondria, which provide energy for movement of tail that facilitate sperm motility.
• Human male ejaculates 200-300 million sperms during coitus.
• 60 percent must have normal shape and size and 40 percent of them must show vigorous motility.
• Sperm released from seminiferous tubules enters into accessory ducts.
• On their way fluids from seminal vesicle and prostate gland added which collectively called as Semen.
• The function of male accessory ducts and glands are maintained by testicular hormone androgen.

CBSE Biology (Chapter Wise) Class XII ( By Mr. Hare Krushna Giri )
Email Id : [email protected]