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 : harekrushnagiri@yahoo.com
Biology - Mr. Hare Krushna Giri
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