BIOLOGY CLASS NOTES FOR CBSE Chapter 03. Human Reproduction 01. Introduction The reproductive system of sexually reproducing animal consist of : Ÿ Primary sex organs (called gonads) which produce gametes and hormones. Ÿ Secondary sex organs which participate in reproduction but not form gametes. Ÿ Accessory sex organs cause difference in the appearance of two sexes.
02. Primary sex organs The primary reproductive organs, or gonads, consist of the ovaries and testes. These organs are responsible for producing the egg and sperm cells and hormones. These hormones function in the maturation of the reproductive system, the development of sexual characteristics, and have important roles in regulating the normal physiology of the reproductive system. All other organs, ducts, and glands in the reproductive system are considered secondary, or accessory, reproductive organs.
03. Male reproductive system The male reproductive system consists of glands with their ducts and supporting structures (i) The glands include a pair of testes, a pair of seminal vesicles, a pair of bulbourethral (Cowper’s) glands, and one prostate gland. (ii) Ducts of testes include a Pair of epididymis, a pair of vas deferens, a pair of ejaculatory ducts, and one urethra. (iii) Supporting structures are divided into: Internal - a pair of spermatic cords and External-Scrotum and penis.
Testes The male gonads, testes, begin their development high in the abdominal cavity. near the kidneys. During the last two month before birth, or shorty after birth, they descend through the inguinal canal into the scrotum, a pouch that extends below the abdomen, posterior to the penis.
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CLASS NOTES FOR CBSE – 03. Human Reproduction
Hormones control The hypothalamus has ultimate control of the testes’ sexual function because it secretes a hormone called gonadotropin releasing hormones, or GnRH, that stimulates the anterior pituitary to secrete the gonadotropic hormones. These are two gonadotropic hormones−follicle-stimulating hormone (FSH) and luteinizing hormone (LH)–in both males and females. In males, FSH promotes the production of sperm in the seminiferous tubules, which also release the hormone inhibin. LH in males is sometimes given the name interstitial cellstimulating hormone (ICSH) because it controls the production of testosterone by the interstitial cells, which are found in the spaces between the seminiferous tubules. All these hormones are involved in a negative feedback relationship that maintains the fairly constant production of sperm and testosterone. Testosterone, the main sex hormone in males, is essential for the normal development and functioning of the organs. Testosterone also bring about and maintains the male secondary sex characteristics the develop at the time of puberty.
Spermatogenesis
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CLASS NOTES FOR CBSE – 03. Human Reproduction
04. Female reproductive system Functions of the female reproductive system are as follows: (i) The ovaries produce secondary oocytes and hormones, including progesterone and estrogens (female sex hormones), inhibin, and relaxin. (ii) The uterine tubes transport a secondary oocyte to the uterus and normally are the sites where fertilization occurs. (iii) The uterus is the site of implantation of the fertilized ovum, development of the fetus during pregnancy. (iv) The vagina receive the penis during sexual intercourse and is a passageway for childbirth. (v) The mammary glands synthesize. secrete and eject milk for the nourishment of newborn.
Ovaries The primary female reproductive organs, or gonads, are the two ovaries. The ovaries are located in shallow depression, called ovarian fosse, one on each side of the uterus, in the lateral walls of the pelvic cavity
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CLASS NOTES FOR CBSE – 03. Human Reproduction
Oogenesis and follicular development
Hormones Follicle-stimulating hormone, luteinizing hormone, estrogen, and progesterone have major roles in regulating the function of the female reproductive system. At puberty, when the ovaries and uterus are mature enough to respond to hormonal stimulating, certain stimuli cause the hypothalamus to start secreting gonadotropin-releasing hormone. This hormone enter the blood and goes to the anterior pituitary gland where it stimulates the secretion of follicle- stimulating hormone and luteinizing hormone. These hormones, in turn, affect the ovaries and uterus and the monthly cycles begin. A woman’s reproductive cycles last form menarche to menopause. The monthly ovarian cycle begins with the follicle development during the follicular phase. continues with ovulation during the ovulatory phase, and concludes with the development and regression of the corpus luteum during the luteal phase. The uterine cycle takes place simultaneously with ovarian cycle. The uterine cycle begins with menstruation during the menstrual phase, continues with repair of the endometrium during the proliferative phase, and ends with the growth of glands and blood vessels during the secretory phase. Menopause occurs when a woman’s reproductive cycles stop, This period is marked by decreased levels of ovarian hormones and increased levels of pituitary follicle-stimulating hormone and luteinizing hormone. The changing hormone levels are responsible for the symptoms associated with menopause.
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CLASS NOTES FOR CBSE – 03. Human Reproduction
Uterus The uterus serves as part of the pathway for sperm deposited in the vagina to reach the uterine tubes. Anatomical subdivision of the uterus include. (i) A dome-shaped portion superior to the uterine tubes called the fundus. (ii) A tapering central portion called the body, and (iii) An inferior narrow portion called the cervix that opens into vagina. Histologically, the uterus consists of three layers of tissue: perimetrium, myometrium, and endometrium. The outer layer- the perimetrium or serosa is part of visceral peritoneum. The middle layer of the uterus, the myometrium consists of three layers of smooth muscle fibers that are thickest in the funds and thinnest in the cervix. The inner layer of the uterus, the endometrium is highly vascularized and has three components: when properly inserted, a contraceptive diaphragm rests on the fornix, covering the cervix.
vagina The vagina is tubular, 10-cm long fibromuscular canal lined with mucous membrane that extends form the exterior of the body to the uterine cervix. It is the receptacle for the penis during sexual intercourse, the outlet for menstrual flow, and the passageway for childbirth. Situated between the urinary bladder and the rectum, the vagina is directed superiorly and posteriorly, where it attaches the uterus. A recess called the fornix surrounds the vaginal attachment to the cervix.
Vulva The external genital organs of the female are known collectively as the Vulva. The vulva includes tow large, hair-covered folds of skin called the labia majora. The labia minora are tow small folds laying just inside the labia majora. They extend forward from the vaginal opening to encircle and form a foreskin for the glans clitoris. The glans clitoris is the organ of sexual arousal in females and, like the penis, contains a shaft of erectile tissue that becomes engorged with blood during sexual stimulation. The cleft between the labia minora contains the openings of the urethra and the vagina.
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CLASS NOTES FOR CBSE – 03. Human Reproduction
Female reproductive cycle Ovarian cycle Follicular phase (pre-ovulatory phase): An ovary is made up of an outer cortex and an inner medulla. These are many follicles in the cortex, and each one contains an immature egg, called an oocyte. As the follicle undergoes maturation, it develops form a primary follicle to a secondary follicle to a vesicular (Graafian) follicle. As the vesicular follicle develops, the primary oocyte divides, producing a secondary oocyte. Ovulatory phase: The vesicular follicle bursts, releasing the secondary oocyte (called an egg) surrounded a by a clear membrane. This is referred to as ovulation. One ovarian follicle per month produces a secondary oocyte Luteal phase (post-ovulatory phase): Once a follicle has lost its egg, it develops into a corpus luteum, a glandlike structure. If pregnancy does not occur, the corpus luteum begins to degenerate after about 10 days Hormonal control of ovarian cycle: These events, called the ovarian cycle, are under the control of the gonadotropic hormones, FHS and LH. The gonadotropic hormones are not present in constant amount but instead are secreted at different rates during the cycle.
Uterine cycle Menstrual phase : During days 1-5, a low level of female sex hormones in the body causes the endometrium to disintegrate and its blood vessels to rupture. On day one of the cycle, a flow of blood and tissues, known as the menses, passes out of the vagina during menstruation, also called the menstrual period. Proliferative phase : The proliferative phase is the time between the end of menstruation and ovulation. During days 6-13, increased production of estrogen by a new ovarian follicle in the ovary causes the endometrium to thicken and to become vascular and glandular. Estrogens are the dominate ovarian hormones during the preovulatory phase. Secretory phase : During days-15-28, increased production of progesterone by the corpus luteum in the ovary cause the endometrium of the uterus to double or triple in thickness (from 1 mm to 2-3 mm) and the uterine glands to mature, producing a thick mucoid secretion. This is called the secretory phase of the uterine cycle.
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CLASS NOTES FOR CBSE – 03. Human Reproduction
05. Embryonic development Embryonic is a development process that usually beings once the egg has been fertilized. It involves multiplication of cell by mitosis an their subsequent growth, movement, and differentiation into all the tissues and organs of a living baby. Fertilization Fertilization is the process whereby tow gametes fuse together to form a zygote. The male gamete, the sperm cell, is a small cell with a greatly reduced cytoplasm and a haploid nucleus. The nucleus is highly condensed and transcriptionally inactive because the normal histones are replace by a special class of packaging proteins known as protamines. The female gamete, the egg cell (or ovum), is a large cell, which contain the vitelline envelope, outside the plasma membrane. In mammals, it is a separate and thick extracellular matrix known as the zona pellucida. Fertilization begins with attachment of a sperm of the zona pellucida followed by the release of the enzyme form the acrosomal vesicle, which cause local digestion of the zona. The ova release a chemical substance called fertilizin and the sperms produce a substances called antifertilizin. These two substances interact and there is agglutination of sperms near the egg. Usually, only one sperm enter an egg cell. This is called monospermy. In some cases of arachnids and some insects, there is the phenomenon of polyspermy i.e, a number of sperms enter the egg.
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CLASS NOTES FOR CBSE – 03. Human Reproduction
06. Cleavage Cleavage is the development stage in which the zygote divided to form a number of smaller cells called blastomeres. This first cleavage plane is vertical, but in the second round of cell division, one of the cells cleaves vertically and th other horizontal. The result of cleavage is a ball of cells, surrounding a fluid-filled cavity called the blastocoel. The ball of cells with fluid-filled bastocoel is known as a blastocyst. As about the 16- cell moral stage it become possible to discriminate between two type of cell: external polarized cell and internal cells nonpolar cells (amnion, yolk sac, allantois ). The outer polarized cell comprise the trophoblast that will go on the form one of the four extra- embryonic membrane, the chorion, which provides the embryonic portion of the placenta. The inner nonpolar cells comprise the embryoblast.
07. Implantation After day 5 of human development, the blastocyst hatches. In the uterus, the blastocyst attaches tightly to the uterine epithelium (implantation). Trophoblast cells proliferate rapidly and differentiate into an inner layer of cytotrophoblast and an outer multinucleated cell layer, the syncytiotrophoblast.
08. Gastrulation Gastrulation take place during the third week of human development and is the first major morphogenetic process in development. During gastrulation, the orientation of the body is laid down, and the embryo is converted into a structure of three germ layers: ectoderm, endoderm and mesoderm, all of which are derived form the epiblast. The major structure characterizing gastrulation is a linear, one the primitive streak.
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CLASS NOTES FOR CBSE – 03. Human Reproduction
This appears at about day 15 in human development At day 16 in human development of epiblast cells near the primitive streak being to proliferate, flatten and lose their connections with one another, Starting on day 16- more of the epiblast cells migrating through the primitive streak diverge into the space between the epiblast and the nascent definitive endoderm to form a third layer, the intraembryonic mesoderm. When the intraembryonic mesoderm and definitive endoderm have formed, the residual epiblast is now described as the ectoderm and the new three-layered structure is referred to as the trilaminar germ disc. By day 20 of human development the notochordal process is completely formed, but then transform form a hollow tube to a solid rod, the notochord. The notochord will later induce formation of components of the nervous system.
Organogenesis The development of the embryo is now programmed toward organizing tissues into the precursors of the many organs and systems contained in the adult. During organogenesis, the various organs of the foetus are established and they attain a functional state.
09. Extra-embryonic membranes and placenta Early mammalian development is primarily concerned with the formation of the four extra-embryonic membranes (yolk sac, amnion, chorion and allantois) and the placenta, derived from combination of embryonic tissue (the chorion ) and maternal tissue. Amnion provides a fluid medium to the developing embryo: it prevent desiccation of the embryo and function as a shock absorber. As the human egg is devoid of yolk, the yolk sac develops as an evolutionary process. It is very small and gradually degenerates and shrinks. The chorion and allantois and take part in the formation of the placenta The human placenta is, thus, referred to as chorioallantoic placenta. The foetal placenta grow intimacy and invades the uterine mucosa with its chorionic villi. The placenta acts as a barrier between the foetus and the mother. Although there is no blending of the two blood supplies, the placenta acts as an ultrafilter; soluble inorganic and organic materials nutrients, hormones, antibodies against diphtheria, smallpox, scarlet fever, measles, etc. can pass form the mother to the foetus. It also helps in the exchange of gases between the mother and the foetus.
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CLASS NOTES FOR CBSE – 03. Human Reproduction
The placenta also helps in the elimination of nitrogenous discharge and other wastes of the foetus. The placenta acts as an endocrine gland and synthesizes large quantities of proteins and some hormones. The umbilical cord connects the foetus to the placenta.
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CLASS NOTES FOR CBSE – 03. Human Reproduction
CBSE Pattern Exercise (1)
(Q. No. 1 to 4) One Mark 1. Mention the function of zona pellucida. 2. Write the function of oxytocin. 3. Name the embryonic stage that gets implanted in the uterine wall of a human female. 4. What stimulates pituitary to release the hormone responsible for parturition? Name the hormone. (Q. No. 5 to 6) Two Marks 5. Where does fertilisation occur in humans? Explain the events that occur during this process. 6. Mention the number of cells of the following stages. Embryonic Stage Zygote Morula Blastocyst
No. of cells (a) (b) (c)
(Q. No. 7 to 8) Three Marks 7. Describe the process of parturition in human. 8. (i) (ii)
How is placenta formed in human female? Name any two hormones which are secreted by it and are also present in a non-pregnant woman.
(Q. No. 9 to 10) Five Marks 9. (i) Briefly explain the events of fertilisation and implantation in an adult human female. (ii) Explain the process of spermatogenesis. 10. (i)
(ii)
Write the specific location and the functions of the following cells in human males (a) Leydig cells (b) Sertoli cells (c) Primary spermatocyte Explain the role of any two accessory glands in human male reproductive system.
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