HUMAN REPRODUCTION
- The reproductive events in humans include formation of gametes (gametogenesis), i.e., sperms in males and ovum in females, transfer of sperms into the female genital tract (insemination) and fusion of male and female gametes (fertilisation) leading to formation of zygote.
- This is followed by formation and development of blastocyst and its attachment to the uterine wall (implantation), embryonic development (gestation) and delivery of the baby (parturition).
- There are remarkable differences between the reproductive events in the male and in the female, for example, sperm formation continues even in old men, but formation of ovum ceases in women around the age of fifty years.
Human Reproduction Class 12 Handwritten Notes
Male and female Reproductive Systems
● Human beings reproduce sexually and are viviparous.
● In humans, the reproductive phase starts after puberty.
● It involves
- Gametogenesis
- Copulation
- Fertilisation
- Implantation
- Gestation
- Labor
The MALE Reproductive System
● It's located in the pelvic region.
● It consists of
- A brace of testes
- Appurtenant glands and tubes
- External genitalia
Human Reproduction Class 12 Biology Notes
Testes
● Positioned 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 range, and has about 250 chambers called testicular lobules.
● Testicular lobules have seminiferous tubules which are the spots of sperm conformation.
● Seminiferous tubules are lined by two types of cells
- male origin cells − They suffer meiosis to form sperms.
- Sertoli cells − They give aliment to the origin cells.
● Region outside the seminiferous tubules is called the interstitial space, which contains Leydig cells (interstitial cells). The Leydig cells produce androgens.
Accessory Tubes and Glands
● Accessory tubes 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 conduit from the seminal vesicle called the ejaculatory conduit.
● The ejaculatory conduit stores the sperms and transports them to the outside
● The urethra starts from the urinary bladder, extends through the penis and opens via the urethral meatus.
● Appurtenant glands include
- A brace of seminal vesicles
- Prostate gland
- A brace of bulbourethral glands
● The concealment of these glands make up the seminal tube, and give nutrition and a medium of motility to the sperms.
Human Reproduction Class 12 Biology Notes
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Class 12 Biology chapter 3 Human Reproduction Notes
The Female Reproductive System
● It's located in the pelvic region
● It includes
- A brace of ovaries
- A brace of oviducts
- Uterus
- Cervix
- Vagina
- External genitalia
- Mammary glands (not part of the reproductive system, but aids in child care) Ovaries
● They're the primary Female coitus organs. They produce the ovum and other ovarian hormones.
● They're located in the lower tummy, and are 2 to 4 cm in length.
● They're 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
- Supplemental cortex
- Inner medulla
Oviducts
● They're also called fallopian tubes.
● They're 10 to 12 cm long, and extend from the ovary to the uterus.
● The part of each oviduct lying towards the ovary is channel shaped, and is called in fundibulum. It has finger like protrusions called fimbriae.
● The infundibulum leads to the ampulla, and also to the island, which has a narrow lumen opening into the uterus.
Uterus
● It's also called womb, and is pear shaped.
● It's connected to the pelvic walls by ligaments.
● The uterine wall consists of
- External perimetrium
- Middle myometrium
- Internal endometrium, which lines the uterine depression
● The endometrium undergoes changes during the menstrual cycle.
Human Reproduction short notes
Cervix and Vagina
● The cervix connects the uterus to the vagina.
● The cervix and the vagina constitute the birth conduit.
External Genitalia
● Consists of
- Mons pubis − Adipose towel 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 − Incompletely covers the vaginal opening
- Clitoris − Lies at the junction of labia minora
Mammary Glands
- Present in all Female mammals
- It's paired and is glandular.
- Each bone contains 15 to 20 mammary lobes with alveoli which cache milk.
- The alveoli open into the mammary tubules, which unite to form a mammary conduit.
- Numerous mammary tubes constitute the mammary ampulla, which is connected to the lactiferous conduit.
Gametogenesis
The testis and ovary produce the male and female gametes independently by gametogenesis (spermatogenesis in males and oogenesis in ladies).
Human Reproduction Class 12 PDF
Spermatogenesis
● In males, sperms are produced by the spermatogonia ( immature origin 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 suffer meiosis.
● After the first meiotic division, two haploid and equal secondary spermatocytes are formed.
● These farther suffer meiosis to give rise to four haploid spermatids.
●These spermatids are converted into sperms by spermiogenesis.
● The sperm head gets bedded in the Sertoli cells after spermiogenesis and is released from the seminiferous tubules by spermiation.
● Spermatogenesis starts at puberty by the action of the gonadotropin releasing hormone (GnRH), which in turn causes the release of two gonadotropins called Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH).
● LH acts on Leydig cells and causes them to release androgens, which stimulate the process of spermatogenesis while the FSH acts on the Sertoli cells, which help in spermiogenesis.
Structure of a Sperm
● A mature sperm consists of
- Head
- Neck
- Middle piece
- Tail
● The whole sperm is enclosed in a tube membrane.
● The head consists of a haploid nexus and a caplike 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 appurtenant tubes.
● Concealment of epididymis, vas deferens, seminal vesicles, and prostate are essential for development and motility of sperms.
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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 suffer meiosis, but get temporarily arrested at the prophase and are called primary oocytes.
● Before reaching puberty, a large number of primary oocytes degenerate and the remaining bones get girdled by layers of granulosa cells and new theca and are called secondary follicles.
● The secondary follicles are also converted into tertiary Follices that have characteristic fluid filled depression called antrum. At this stage, the primary oocyte present within the tertiary follicle completes meiosis, which results in the conformation of haploid secondary oocyte and a bitsy polar body.
● This tertiary follicle farther changes into the Graafian follicle. The secondary oocyte is girdled by the zone pellucida.
● Also the Graafian follicle ruptures to release the ovum by ovulation.
Class 12 Biology chapter 3 Human Reproduction Notes
Menstrual Cycle & Fertilisation
● Menstrual cycle is the reproductive cycle in all primates and begins at puberty (menarche).
● In Humanladies, period occurs formerly in 28 to 29 days. The cycle of events starting from one period till the coming bone is called the menstrual cycle.
● During the middle of the menstrual cycle, one ovum is released (ovulation).
● The cycle starts with the menstrual inflow (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 isn't fertilised.
● It's followed by the follicularphase.In this phase, the primary follicles develop into the Graffian follicles. This causes the rejuvenescence of the endometrium.
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 (14 th day), and beget 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 conservation of the endometrium.
● In the absence of fertilisation, the corpus luteum degenerates, thereby causing the decomposition of the endometrium and the launch of a new cycle.
● In humans, the menstrual cycle ceases to operate at the age of 50 times. This phase is known as the menopause.
Human Reproduction Class 12 Biology Notes
Fertilisation and Implantation
● During commerce, 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 do.
● The process of emulsion 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 concealment of the acrosomes help the sperm enter the cytoplasm of the ovum.
● This causes the completion of meiotic division of the secondary oocyte, performing in the conformation of a haploid ovum (ootid) and a secondary polar body.
● Also, the haploid sperm nexus fuses with the haploid nexus of the ovum to form a diploid zygote.
● Mitosis starts as the zygote moves through the island of the oviduct ( fractionalization) and forms 2, 4, 8, 16 son cells called blastomeres.
● The 8 − 16 cell embryo is called a morula, which continues to peak to form the blastocyst. The morula moves further into the uterus.
● The cells in the blastocyst are arranged into an external trophoblast and an inner cell mass.
● The trophoblast gets attached to the uterine endometrium, and the process is called implantation. This leads to gestation.
● The inner cell mass gets discerned to form the embryo.
Gestation, Labor and Lactation
Gestation
● After implantation, the trophoblast forms fingerlike protrusions called chorionic villi, girdled by the uterine tissue and motherly blood.
● The chorionic villi and the uterine towel get integrated to form the placenta, which helps in supplying the developing embryo with oxygen and nutrients, and is also involved in the junking of wastes.
● The placenta is connected to the embryo by the umbilical cord. The placenta acts as an endocrine gland, and produces the Humanchorionic gonadotropins, Humanplacental lactogen, oestrogen, progesterone and relaxin (after stages of gestation).
●These hormones support foetal growth and help in the conservation of gestation. Hormones like oestrogen, progestogen, cortisol, prolactin,etc., are increased several crowds in the motherly blood.
● Incontinently after implantation, the inner cell mass (embryo) gets discerned into the ectoderm, mesoderm and endoderm, which give rise to the different apkins. This capability of the inner cell mass is due to the presence of multipotent cells called stem cells.
● Utmost of the major organs are formed at the end of 12 weeks of gestation; during the 5 th month, the branches and body hair are formed; by the 24 th week, the eyelids separate and eyelashes are formed. At the end of nine months, the foetus is completely formed.
Human reproduction class 12 Notes ppt
Labor and Lactation
● Humangestation has the duration of 9 months. This duration is called the gravidity period.
● At the end of this period, vigorous uterine condensation lead to the delivery of the foetus. This process is called labor.
● Labor is a neuroendocrine medium, and is started by the signals from the developed foetus and the placenta, which produce the foetal ejection kickback.
● This causes the release of oxytocin from the pituitary, which causes stronger uterine condensation.
● This leads to the expatriation of the baby along with the placenta.
● During gestation, the mammary glands suffer isolation, and milk is produced during the end of gestation.
● The milk produced during the first many days of lactation is known ascolostrums.It contains several antibodies that prop the invigorated to develop resistance.
Human Reproduction Class 12 Biology Notes