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NOTES

HUMAN (CHAPTER- 3)

 Study the following notes along with the N.C.E.R.T  Practice all the diagrams in the practice register  Refer to the video link at the end of the notes for a better understanding of the chapter beings are sexually reproducing, viviparous organisms with and internal development. The reproductive events in human beings include:

- - It is the formation of through the process of inside the organs, that is, testis in males and ovaries in . Gametes are called as in males and ova or in females. - - It is the transfer of sperms from the male body into the genital tract of . - Fertilization- It is the fusion of male and female gametes to form a diploid called . - Cleavage- The zygote undergoes cleavage that is mitotic divisions to first form a morula and then the blastocyst. - Implantation- The blastocyst gets partially embedded in the walls of the for attachment and nourishment. - Establishment of - A foeto-maternal connective called Placenta develops for attachment, , respiration and excretion of . - - The implanted embryo undergoes gastrulation (Establishment of the three primary germ layers) and then organogenesis(Development of various tissues, organs and organ systems) - Development and growth of foetus- There is growth of various parts and Systems of the foetus so that they become fully functional. The foetus is then converted into a young one and the period of total stay of embryo in the body of the mother is called gestation period () - Parturition- The fully formed young one is delivered outside the mother’s body.

DEVELOPMENT is a series of changes that occur in an individual from the beginning of cleavage of zygote to the attainment of maturity that is followed by senescence. It is divisible into two parts: 1) The - It is the embryonic and foetal development that occurs inside the womb of the mother. 2) The postnatal development- It is the development that occurs in the individual after birth.

Various characteristics of the human reproductive systems

1) The are separate and they show , that is, there is a difference in both the external features as well as the sex organs. 2) The stage when primary sex organs (Testes in males and ovaries in female which produce gametes and sex ) become functional is called . 3) Full sexual maturity is attained slowly thereafter when accessory sex organs (Eg: Vas deferens, Epididymis, Prostate, seminal vesicles etc. in males and fallopian tubes, uterus, in females) develop and become functional. 4) Breeding can continue throughout the year, that is, are non-seasonal breeders. 5) Females remain reproductive from (beginning of the first ) to (stoppage of the ) 6) There is a common urinogenital duct in human males whereas the urinary and the genital ducts are separate in females. 7) Fertilization is internal which occurs inside the body of the female in the fallopian tube. 8) The embryo develops inside the uterus of the female where it gets attached and nourished by the Placenta and this phenomenon is called vivipary. 9) Fully formed young ones are delivered by females and this phenomena is called as parturition. 10) are fed on mother’s milk. 11) There is prolonged parental care.

THE MALE

 It is located in the pelvis region.  It includes a pair of testes alongside accessory ducts, glands and the external genitalia.  The testes are situated outside the abdominal cavity within a pouch called as which helps to maintain the low temperature of the testes (that is 2-2.5 degree Celsius lower than the normal internal body temperature) which is necessary for .  In adults, each testis is oval in shape and each testis is covered by a dense covering.  Each testis has about 250 compartments called testicular lobules.  Each lobule contains 1 to 3 highly coiled seminiferous tubules in which sperms are produced.  Each seminiferous tubule js lined on its inside by two types of cells- 1) Male germ cells or the spermatogonia 2) Sertoli cells.

THE

 The male germ cells undergo mitotic division, finally leading to formation while the sertoli cells provide nutrition to the germ cells.  The regions outside the seminiferous tubules are called as interstitial spaces which contain small blood vessels and interstitial cells are the Leydig cells.  The leydig cells synthesise and secrete testicular hormones called androgens.  Other immunologically competent cells are also present.  The male sex accessory ducts include the rete testis, Vasa efferentia, epididymis and vas deferens.  The seminiferous tubules of the testis open into the Vasa efferentia through the rete testis,  The vasa efferentia leave the testis and open into the epididymis located along the posterior surface of each testis.  The epididymis leads to Vas deferens that ascends to the and loops over the urinary bladder.  It receives a duct from the seminal vesicle and opens into the urethra as the ejaculatory duct.  These ducts store and transport the sperms from the testis to the outside through the urethra.  The urethra originates from the urinary bladder and extends through the penis to the external opening called urethral meatus.

L.S OF TESTIS SHOWING VARIOUS PARTS

The Penis  It is the male external genitalia.  It is made up of special tissue that helps in of the penis to facilitate the insemination.  The enlarged end of the penis is called as the glans penis which is covered by a loose fold of skin called as the foreskin.  The male accessory glands include the paired seminal vesicles, a prostate and the paired Bulbourethral gland.  Secretions of these glands constitutes the seminal plasma which is rich in Fructose, calcium and certain enzymes. The secretions of Bulbourethral glands also help in the lubrication of the penis.

FEMALE REPRODUCTIVE SYSTEM

 It consists of a pair of ovaries along with a pair of , uterus, cervix, vagina and external genitalia located in the pelvic region.  These parts of the system along with the pair of mammary glands are integrated structurally and functionally to support the process of , fertilization, pregnancy, birth and childcare.  The ovaries are the primary female sex organs that produces the female (ovum) and several steroid hormones (ovarian hormones).  The ovaries are located one on each side of the lower abdomen.  Each ovary is connected to the pelvic wall and uterus by ligaments.

 Each ovary is covered by a thin epithelium which encloses the ovarian stroma.  The stroma is divided into two zones- a peripheral cortex and an inner medulla.  The fallopian tubes (oviducts), uterus and vagina constitute the female accessory ducts.  Each fallopian tube (10-12 cm long) extends from the periphery of each ovary to the uterus.  The part closer to the ovary is the funnel shaped infundibulum.  The ages of the infundibulum possesses finger like projections called fimbriae which helps in the collection of ovum after ovulation.  The infundibulum leads to a wider part of the called the ampulla.  The last part of the oviduct, isthmus, has a narrow lumen and joins the uterus.

THE FEMALE REPRODUCTIVE SYSTEM

The uterus

- It is single and is also called as the womb. The shape of the uterus is like an inverted pear. - It is supported by ligaments attached to the pelvic wall. - The uterus opens into the vagina through a narrow cervix and the cavity of the cervix is called as the cervical Canal which along with the vagina forms the birth Canal. - The wall of the uterus has three layers of tissue: 1) The external thin membranous perimetrium 2) The middle thick layer of smooth muscles myometrium. 3) The inner glandular layer called as the that lines the uterine cavity The endometrium undergoes cyclical changes during menstrual cycle while the myometrium exhibits strong contraction during delivery of the baby.

The female external genitalia - It include mons pubis, labia majora, labia minora, hymen and clitoris. - Mons pubis is a cushion of fatty tissue covered by skin and pubic hair. - Labia majora are 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. - The opening of the vagina is often covered partially by a membrane called hymen. - The clitoris is a tiny finger like structure which lies at the upper junction of the two labia minora above the urethral opening. - The hymen is often torn during the first coitus (intercourse). However it can also be broken by a sudden fall or jolt, insertion of vaginal tampons, active participation in some sports like horseback riding and cycling etc. In some women the hymen persists even after coitus. In fact the presence or absence of hymen is not a reliable indicator of virginity or sexual experience.

FEMALE EXTERNAL GENITALIA

Mammary glands

- It is characteristic of all female mammals t0 possess mammary glands. - The mammary glands are paired structures () that contain glandular tissue and variable amount of fats’ - The glandular tissue of each is divided into 15 to 20 mammary lobes containing clusters of cells called the alveoli. - The cells of alveoli secrete milk which is stored in the cavities (lumen) of the alveoli. - These alveoli open into the mammary tubules and the tubules of each lobe join to form a mammary duct. - Several mammary ducts join to form a wider mammary ampulla which is connected to the lactiferous duct through which milk is sucked out.

SECTIONAL VIEW OF

GAMETOGENESIS

- The primary sex organs that is the testes in males and the ovaries in females produce sperms and ovum by the process called as gametogenesis.

IN MALES - In the testis, the immature male germ cells (spermatogonia) produce the sperms by the process of spermatogenesis which begins at puberty. - The spermatogonia present on the inside wall of the seminiferous tubules multiply by mitotic division and increase in numbers.

- Each is diploid and contains 46 . - Some of the spermatogonia called primary , periodically undergo meiosis. - A primary completes the first meiotic division that leads to the formation of two equal haploid cells called as secondary spermatocytes (n) which have only 23 chromosomes each. - The secondary spermatocytes undergo the second meiotic division to produce 4 equal haploid (n). - The spermatids are transformed into spermatozoa (sperms) by the process called as spermiogenesis. - After spermiogenesis, the sperm becomes embedded in the sertoli cells and are finally released from the seminiferous tubules by the process called as spermiation.

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SPERMATOGENESIS

SPERMATOGENESIS SPERMIOGENESIS 1. It is the process of formation of It is the formation of a spermatozoan from spermatozoa from germinal cells a 2. It involves the conversion of a diploid It involves the conversion of one haploid structure into a haploid structure structure into another 3. There is growth and division during There is reconstruction during spermatogenesis spermiogenesis. No division and growth occurs 4. A spermatogonium forms 4 A spermatid forms a single spermatozoan spermatozoa

Hormonal control of Spermatogenesis

- Spermatogenesis starts at the age of puberty due to significant increase in the secretion of gonadotropin releasing (GnRH). - This is a hypothalamic hormone and this increased levels of GnRH then acts on the anterior pituitary gland and stimulates the secretion of two gonadotropins- Luteinizing hormone (LH) and Follicle Stimulating Hormone (FSH). - LH act on the leydig cells and stimulates the synthesis and secretion of androgens. - Androgen in turn stimulates the process of spermatogenesis. - FSH acts on the sertoli cells and stimulates the secretion of some factors which helps in the process of spermiogenesis. - Structure of sperm

- It is a microscopic structure composed of a head, neck, a middle piece and a tail. - A plasma membrane envelopes the whole body of the sperm. - The sperm head contains an elongated haploid nucleus, the anterior portion of which is covered by a cap like structures called as acrosome. - The acrosome is filled with enzymes which help to fertilize the ovum. - The middle piece possesses numerous mitochondria which produce energy for the movement of the tail to facilitate the sperm motility essential for fertilization. - The Human male ejaculates about 200 to 300 million sperms during coitus of which for normal at least 60% sperms must have normal shape and size and at least 40% of them must show vigorous motility. - Sperms are released from the seminiferous tubules and are transported by the accessory ducts. - The secretions of epididymis, vas deferens, seminal vesicles and prostate are essential for the maturation and motility of the sperms. - The seminal plasma along with the sperms constitute the semen. - The functions of the male accessory ducts and glands are maintained by the testicular hormones (androgens).

STRUCTURE OF A SPERM

IN FEMALES

- The formation of a mature female gamete is called as . - Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cell(oogonia) are formed within each foetal ovary- NO MORE OOGONIA ARE FORMED AND ADDED AFTER BIRTH.. - These cells start division and enter into the prophase I of meiotic division and get temporarily arrested at this stage called as Primary . Each primary oocyte then gets surrounded by a layer of granulosa cells and it is called as the primary follicle. - A large number of these follicles degenerate during the phase from birth to puberty. - Therefore at puberty only 60,000 to 80,000 primary follicles are left in each ovary. - These primary follicles get surrounded by more layers of granulosa cells and a new theca and are called as secondary follicle. - The secondary follicle soon transforms into a tertiary follicle which is characterized by a fluid filled cavity called as antrum. - The theca layer is organized into an inner theca interna and an Outer theca externa. - It is at this stage that the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division. - It is an unequal division resulting in the formation of a large haploid secondary oocyte and a tiny first polar body. - The secondary oocyte retains bulk of the nutrient rich cytoplasm of the primary oocyte to nourish the developing zygote in case fertilization occurs. - The tertiary follicle further changes into the mature follicle or Graafian follicle. - The secondary oocyte forms a new membrane called zona pellucida surrounding it. - The Graafian follicle now ruptures to release the secondary oocyte which is the ovum from the ovary by the process of ovulation. -

STAGES OF DEVELOPMENT OF OVARIAN FOLLICLE

OOGENESIS

SPERMATOGENESIS OOGENESIS 1. All stages are completed inside the Major part of oogenesis occurs inside the testes ovary but the last stage occurs in the oviduct 2. It is a continuous process It is a discontinuous process with early stages taking place inside the foetus and the rest later in life 3. Some cells of the germinal epithelium There is no such differentiation act as support cells called as sertoli cells. 4. All the spermatogonia divide to form Only some oogonia give rise to spermatocyte 5. Primary spermatocyte divides by Primary oocyte undergoes meiosis I to meiosis I to form two secondary form one secondary oocyte and one polar spermatocyte body 6. Secondary spermatocyte divides by Secondary oocyte divides by meiosis II to meiosis II to form two spermatids form one ovum and one polar body 7. Each spermatid requires differentiation No differentiation is required after meiosis II to change into spermatozoan to form the ovum 8. A spermatocyte form four spermatozoa An oocyte forms only one ovum

THE MENSTRUAL CYCLE

- The reproductive cycle in female primates (Eg: monkeys, apes, humans) is called as the menstrual cycle. - The first menstruation begins at puberty and is called as Menarche. - In human females menstruation is repeated at an average interval of about 28 to 29 days and the cycle of events starting from one menstruation till the next one is called as the menstrual cycle. - Ovulation- 1 ovum is released during the middle of each menstrual cycle. - The cycle starts with the menstrual phase when menstrual flow occurs and it lasts for 3 to 5 days. The menstrual flow results due to The breakdown of the endometrial lining of the uterus and its blood vessels which forms liquid that comes out from the vagina. - Menstruation only occurs if the released ovum is not fertilized .Lack of menstruation maybe indicative of pregnancy. However it may also be caused due to some other underline causes like stress, poor health, hormonal problems etc. - The menstrual phase is followed by the during which the primary follicles in the ovary grow to become a fully mature Graafian follicle and simultaneously the endometrium of the uterus regenerate through proliferation.

FATE OF AN OVARIAN FOLLICLE DURING MENSTUATION-

- These changes in the ovary and the uterus are induced by changes in the levels of pituitary and ovarian hormones. - The secretion of gonadotropins (LH and FSH) increases gradually during the follicular phase and stimulates follicular development as well as secretion of estrogens by the growing follicles. - Both LH and FSH attain a peak level in the middle of the cycle (about the14th day). - Rapid secretion of LH leading to its maximum level during the mid-cycle called LH Surge induces rupture of the Graafian follicle thereby releasing the ovum (Ovulation). - This ovulatory phase is followed by the during which the remaining part of the Graafian follicle is transformed into the Corpus luteum. - The Corpus luteum secretes large amounts of progesterone which is essential for maintaining the endometrium which is necessary for implantation of the fertilized ovum and other events of pregnancy. - During pregnancy all events of the menstrual cycle stop and there is no menstruation. - In the absence of fertilization, the Corpus luteum degenerate which causes disintegration of the endometrium leading to menstruation, marking a new cycle. - In human beings, the menstrual cycle ceases around 50 years of age and this is termed as menopause. - Cyclic menstruation is an indicator of normal reproductive phase and extends between menarche and menopause.

PLASMA CONCENTRATION OF OVARIAN HORMONES AND GONADOTROPINS

FERTILISATION AND IMPLANTATION

- During (coitus) semen is released by the penis into the vagina this is called as insemination. - the motile sperms swims rapidly, pass through the cervix, enters into the uterus and finally reaches the ampullary region of the fallopian tube. - The ovum released by the ovary is also transported to the ampullary region where fertilization takes place. - can only occur if the ovum and sperms are transported simultaneously to the ampullary region. - This is the reason why not all copulations lead to fertilization and pregnancy. - The process of fusion of a sperm and ovum is called fertilization. - During fertilization, a sperm comes in contact with the zona pellucida layer of the ovum and induces changes in the membrane that block the entry of additional sperms. thus this ensures that only one sperm can fertilise an ovum. - The secretions of the acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane. - This induces the completion of the meiotic division of the secondary oocyte. - The second meiotic division is also unequal and results in the formation of a second polar body and haploid ovum (ootid). - Soon the haploid nucleus of the sperms and that of the ovum fuse together to form a diploid zygote (2N).

OVUM SURROUNDED BY A FEW SPERMS

Sex of the Child - The sex of the child has been decided at this stage only. - The pattern in the human female is XX and that in male is XY. - Therefore all the haploid gametes produced by the female (ova) have the as X whereas in the male gametes (sperms) the sex chromosome could be either X or Y. Hence 50% of the sperms carry while the other 50% carry . - After fusion of the male and female gametes, the zygote would either carry XX or XY depending on whether the sperm carrying X or Y fertilized the ovum. - The zygote carrying XX would develop into a female where as the one carrying XY would develop into a male.(HENCE THE SEX OF THE BABY IS DETERMINED BY THE FATHER AND NOT BYTHE MOTHER).

Formation of Embryo and Implantation - As the zygote moves through the isthmus of the oviduct towards the uterus, the mitotic division called as cleavage starts in the zygote. - The zygote forms 2, 4, 8 and 16 daughter cells called blastomeres. - The embryo with 8 to16 blastomeres is called as a morula. - The morula continues to divide and transforms into a blastocyst.as it moves further into the uterus. - The blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to the trophoblast called as the inner cell mass. - The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated into the embryo. - After attachment the uterine cells divide rapidly and cover the blastocyst. As a result the blastocyst becomes embedded in the endometrium of the uterus.This is called as implantation and it leads to pregnancy. -

- DEVELOPMENT OF BLASTOCYST

FERTILISATION AND IMPLANTATION STAGES IN THE REPRODUCTIVE TRACT OF HUMAN FEMALE

PREGNANCY AND EMBRYONIC DEVELOPMENT

- After implantation finger like projections appear on the trophoblast called as chorionic villi which are surrounded by the uterine tissue and maternal blood. - The chorionic villi and uterine tissue become interdigitated with each other and jointly form a structural and functional unit between developing embryo (foetus) and the maternal body called as Placenta. - The Placenta facilitates the supply of Oxygen and nutrients to the embryo and also removal of carbon dioxide and excretory products produced by the embryo. - The Placenta is connected to the embryo through an which helps in transport of substances to and from the embryo. - Placenta also acts as an endocrine tissue and produces several hormones like: 1) Human chorionic gonadotropin (hCG) 2) human Placental lactogen (hPL) 3) Estrogens 4) Progestogens etc. - In the latter phases of pregnancy a hormone called relaxin is also secreted by the ovary. - hCG, hPL and relaxin are produced in women only during pregnancy. - In addition, during pregnancy the levels of the other hormones like Estrogen, progesterone, cortisol, prolactin, thyroxine etc. are increased several folds in the maternal blood. - Increased production of these hormones is essential for supporting the fetal growth, metabolic changes in the mother and maintenance of pregnancy. - Immediately after implantation, the inner cell mass (embryo) differentiate into an outer layer call ectoderm and inner layer call endoderm. Mesoderm soon appears between the ectoderm and the endoderm. - These three layers give rise to all the tissues and organs in adults. - The inner cell mass contains certain cells which are called as the stem cells which have the potential to give rise to all the tissues and organs. - The human pregnancy last for 9 months. In other animals like: Elephant- lasts for 22 months Dog- lasts for 58 to 68 days Cat- lasts for 58 to 68 days Cow- 40 weeks - After 1 month of pregnancy, the embryo’s heart is formed. The first sign of growing foetus maybe noticed by listening to the heart sound carefully through a stethoscope. - By the end of the second month of pregnancy, the foetus develop limbs and digits. - By the end of 12 weeks (first trimester) most of the major organ systems like the Limbs and external genital organs are formed. - The first movements of the foetus and appearance of hair on the head are usually observed during the fifth month. - By the end of about 24 weeks (end of second trimester), the body is covered with fine hair, the eye-lids separate and eyelashes are formed. - By the end of 9 months of pregnancy, the foetus is fully developed and is ready for delivery.

HUMAN FOETUS WITHIN UTERUS

PARTURITION AND

- The average duration of human pregnancy is about 9 months and this is called as the gestation period. - Vigorous contraction of the uterus at the end of pregnancy causes expulsion/delivery of the foetus. - This process of delivery of foetus is called as parturition (). - Participation is induced by a complex neuroendocrine mechanism. - The signal for parturition originates from the fully developed foetus and the placenta which induces mild uterine contractions called foetal ejection reflex. - This triggers release of Oxytocin from the maternal pituitary. - Oxytocin acts on the uterine muscles and causes stronger uterine contractions which in turn stimulate further secretion of Oxytocin. - The stimulatory reflex between the and Oxytocin secretion continues resulting in stronger and stronger contractions. - This results to the expulsion of the baby out of the uterus through the birth canal and this is called as parturition.

- Soon after the is delivered, the placenta is also expelled out of the uterus. - The mammary glands of the female undergo differentiation during pregnancy and start producing milk towards the end of pregnancy by the process called as lactation. - This helps the mother in feeding the newborn. - The milk produced during the initial few days of lactation is called as colostrum which contains several antibodies absolutely essential to develop resistance for the newborn babies. - during the initial period of Infant growth is recommended by doctors for bringing up a healthy baby

REFER TO THE FOLLOWING VIDEO LINK FOR BETTER UNDERSTANDING OF THE CHAPTER:

https://www.youtube.com/watch?v=Lbv6WbjIQW0