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Human Reproduction, Male and Female Reproductive Systems, ● Human beings reproduce sexually and are viviparous., ● In humans, the reproductive phase starts after puberty., ● It involves:, ○ Gametogenesis, ○ Insemination, ○ Fertilisation, ○ Implantation, ○ Gestation, ○ Parturition, The Male Reproductive System, , ● It is located in the pelvic region., ● It consists of:, ○ A pair of testes, ○ Accessory glands and ducts, ○ External genitalia

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Testes, ● Situated within the scrotum, which protects the testes and, also helps in maintaining the temperature., ● Each testis is 4 to 5 cm in length, and 2 to 3 cm in width,, and has about 250 compartments called testicular lobules., ● Testicular lobules have seminiferous tubules which are the, sites of sperm formation., ● Seminiferous tubules are lined by two types of cells:, ○ Male germ cells − They undergo meiosis to form sperms., ○ Sertoli cells − They provide nourishment to the germ cells., ● Region outside the seminiferous tubules is called the, interstitial space, which contains Leydig cells (interstitial, cells). The Leydig cells produce androgens., Accessory Ducts and Glands, ● Accessory ducts include:, ○ Rete testis, ○ Vasa efferentia, ○ Epididymis, ○ Vas deferens, ● The seminiferous tubules open into the vasa efferentia, through the rete testis., ● The vasa efferentia open into the epididymis, which leads, to the vas deferens. The vas deferens opens into the, urethra along with a duct from the seminal vesicle called the, ejaculatory duct., ● The ejaculatory duct stores the sperms and transports them, to the outside

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● The urethra starts from the urinary bladder, extends through, the penis and opens via the urethral meatus., ● Accessory glands include:, ○ A pair of seminal vesicles, ○ Prostate gland, ○ A pair of bulbourethral glands, ● The secretions of these glands make up the seminal plasma,, and provide nutrition and a medium of motility to the, sperms., The Female Reproductive System, , ● It is located in the pelvic region:, ● It includes:, ○ A pair of ovaries, ○ A pair of oviducts, ○ Uterus, ○ Cervix, ○ Vagina, ○ External genitalia, ○ Mammary glands (not part of the reproductive system,

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but aids in child care), Ovaries, ● They are the primary female sex organs. They produce the, ovum and other ovarian hormones., ● They are located in the lower abdomen, and are 2 to 4 cm in, length., ● They are connected by ligaments to the pelvic walls and to, the uterus., ● Each ovary is covered by epithelium, and contains the, ovarian stroma., ● The ovarian stroma is made up of:, ○ Peripheral cortex, ○ Inner medulla, , Oviducts, ● They are also called fallopian tubes., ● They are 10 to 12 cm long, and extend from the ovary to, the uterus., ● The part of each oviduct lying towards the ovary is funnel, shaped, and is called infundibulum. It has finger-like, projections called fimbriae., ● The infundibulum leads to the ampulla, and then to the, isthmus, which has a narrow lumen opening into the uterus., Uterus, ● It is also called womb, and is pear shaped., ● It is connected to the pelvic walls by ligaments.

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● The uterine wall consists of:, ○ External perimetrium, ○ Middle myometrium, ○ Internal endometrium, which lines the uterine cavity, ● The endometrium undergoes changes during the menstrual, cycle., Cervix and Vagina, ● The cervix connects the uterus to the vagina., ● The cervix and the vagina constitute the birth canal., External Genitalia, ● Consists of:, ○ Mons pubis − Fatty tissue covered by skin and pubic hair, ○ Labia majora − Extends from mons pubis and surrounds the, vaginal opening, ○ Labia minora − Fold of skin beneath the labia majora, ○ Hymen − Partially covers the vaginal opening, ○ Clitoris − Lies at the junction of labia minora, Mammary Glands, ● Present in all female mammals, ● It is paired and is glandular., ● Each breast contains 15 to 20 mammary lobes with alveoli, which secrete milk., ● The alveoli open into the mammary tubules, which unite to, form a mammary duct., ● Many mammary ducts constitute the mammary ampulla,, which is connected to the lactiferous duct.

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Gametogenesis, The testis and ovary produce the male and female gametes, respectively by gametogenesis (spermatogenesis in males and, oogenesis in females)., Spermatogenesis, , ● In males, sperms are produced by the spermatogonia, (immature germ cells), which are present in the inner walls, of the seminiferous tubules., ● Spermatogonia increase in number by mitosis. These are, diploid., ● Some of the spermatogonia called primary spermatocytes, periodically undergo meiosis., ● After the first meiotic division, two haploid and equal, secondary spermatocytes are formed., ● These further undergo meiosis to give rise to four haploid

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○ Tail, ● The whole sperm is enclosed in a plasma membrane., ● The head consists of a haploid nucleus and a cap-like, acrosome, which contains enzymes that aid in fertilisation., ● The middle piece contains several mitochondria, which, produce energy for the motility of the sperm., ● Sperms released by the seminiferous tubules are, transported by the accessory ducts., ● Secretions of epididymis, vas deferens, seminal vesicles, and, prostate are essential for maturation and motility of sperms., Oogenesis, , ● The ovum is formed by the process of oogenesis., ● It starts during embryonic growth and millions of gamete, mother cells (oogonia) are formed in the foetal ovary., ● These cells undergo meiosis, but get temporarily arrested at

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the prophase and are called primary oocytes., ● Before reaching puberty, a large number of primary oocytes, degenerate and the remaining ones get surrounded by, layers of granulosa cells and new theca and are called, secondary follicles., ● The secondary follicles are then converted into tertiary, follicles that have characteristic fluid-filled cavity called, antrum. At this stage, the primary oocyte present within the, tertiary follicle completes meiosis, which results in the, formation of haploid secondary oocyte and a tiny polar body., ● This tertiary follicle further changes into the Graafian, follicle. The secondary oocyte is surrounded by the zone, pellucida., ● Then the Graafian follicle ruptures to release the ovum by, ovulation., Menstrual Cycle & Fertilisation

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● Menstrual cycle is the reproductive cycle in all primates and, begins at puberty (menarche)., ● In human females, menstruation occurs once in 28 to 29, days. The cycle of events starting from one menstruation till, the next one is called the menstrual cycle., ● During the middle of the menstrual cycle, one ovum is, released (ovulation)., ● The cycle starts with the menstrual flow (3 to 5 days),, caused due to the breakdown of the endometrium of the, uterus. Blood vessels in liquid state are discharged, but this, occurs only when the ovum is not fertilised., ● It is followed by the follicular phase.In this phase, the, primary follicles mature into the Graffian follicles. This, causes the regeneration of the endometrium.

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These changes are brought about by ovarian and pituitary, hormones. In this phase, the release of gonadotropins (LH, and FSH) increases. This causes follicular growth and the, growing follicles produce oestrogen., ● The LH and FSH are at their peak in the middle of the cycle, (14th day), and cause the rupture of the Graffian follicles to, release ovum. This phase is called the ovulatory phase., ● The remains of the Graffian follicles get converted into the, corpus luteum, which secretes progesterone for the, maintenance of the endometrium., ● In the absence of fertilisation, the corpus luteum, degenerates, thereby causing the disintegration of the, endometrium and the start of a new cycle., ● In humans, the menstrual cycle ceases to operate at the age, of 50 years. This phase is known as the menopause., Fertilisation and Implantation, ● During coitus, the semen is released into the vagina, passes, through the cervix of the uterus and reaches the ampullaryisthmic junction of the fallopian tube., ● The ovum is also released into the junction for fertilisation to, occur., ● The process of fusion of the sperm and the ovum is known, as fertilisation., ● During fertilisation, the sperm induces changes in the zona, pellucida and blocks the entry of other sperms. This, ensures that only one sperm fertilises an ovum., ● The enzymatic secretions of the acrosomes help the sperm

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enter the cytoplasm of the ovum., ● This causes the completion of meiotic division of the, secondary oocyte, resulting in the formation of a haploid, ovum (ootid) and a secondary polar body., ● Then, the haploid sperm nucleus fuses with the haploid, nucleus of the ovum to form a diploid zygote., ● Mitosis starts as the zygote moves through the isthmus of, the oviduct (cleavage) and forms 2, 4, 8, 16 daughter cells, called blastomeres., ● The 8−16 cell embryo is called a morula, which continues to, divide to form the blastocyst. The morula moves further, into the uterus., ● The cells in the blastocyst are arranged into an outer, trophoblast and an inner cell mass., ● The trophoblast gets attached to the uterine endometrium,, and the process is called implantation. This leads to, pregnancy., ● The inner cell mass gets differentiated to form the embryo., Pregnancy, Parturition and Lactation, Pregnancy, ● After implantation, the trophoblast forms finger-like, projections called chorionic villi, surrounded by the uterine, tissue and maternal blood., ● The chorionic villi and the uterine tissue get integrated to, form the placenta, which helps in supplying the developing, embryo with oxygen and nutrients, and is also involved in

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the removal of wastes., ● The placenta is connected to the embryo by the umbilical, cord. The placenta acts as an endocrine gland, and, produces the human chorionic gonadotropins, human, placental lactogen, oestrogen, progesterone and relaxin, (later stages of pregnancy)., ● These hormones support foetal growth and help in the, maintenance of pregnancy. Hormones like oestrogen,, progestogen, cortisol, prolactin, etc., are increased several, folds in the maternal blood., ● Immediately after implantation, the inner cell mass, (embryo) gets differentiated into the ectoderm, mesoderm, and endoderm, which give rise to the different tissues. This, ability of the inner cell mass is due to the presence of multipotent cells called stem cells., ● Most of the major organs are formed at the end of 12 weeks, of pregnancy; during the 5th month, the limbs and body hair, are formed; by the 24th week, the eyelids separate and, eyelashes are formed. At the end of nine months, the foetus, is fully formed., Parturition and Lactation, ● Human pregnancy has the duration of 9 months. This, duration is called the gestation period., ● At the end of this period, vigorous uterine contractions lead, to the delivery of the foetus. This process is called, parturition., ● Parturition is a neuro-endocrine mechanism, and is started

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by the signals from the developed foetus and the placenta,, which produce the foetal ejection reflex., ● This causes the release of oxytocin from the pituitary, which, causes stronger uterine contractions., ● This leads to the expulsion of the baby along with the, placenta., ● During pregnancy, the mammary glands undergo, differentiation, and milk is produced during the end of, pregnancy., ● The milk produced during the first few days of lactation is, known as colostrums.It contains several antibodies that aid, the newborn to develop resistance.