Hsslive-XII-zoology-ch-3-Human_reproduction_short_note_minhad_new.pdf

Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® ZLGY-MM: XII 2. HUMAN REPRODUCTION  Humans are sexually reproducing and viviparous. Reproductive E...

Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® ZLGY-MM: XII 2. HUMAN REPRODUCTION  Humans are sexually reproducing and viviparous. Reproductive Events In Human In Male In Female Testes Ovary (Gametogenesis) Sperm Ovum (Insemination) (Fertilisation) Zygote Blastocyst (Implantation) Accessory Glands Contain fructose, (Embryogenesis) Include Ca2+ & enzymes Embryo 1. Paired seminal vesicles (Gestation) 2. A prostate Secretions= Seminal plasma Foetus 3. Paired bulbourethral glands. (Parturition- Delivery of baby) Secretions help in the lubrication of the penis THE MALE REPRODUCTIVE SYSTEM External genitalia (Penis)  It consists of paired testes, accessory ducts, glands and the  It is the copulatory organ made up of erectile tissue to facilitate external genitalia. insemination.  The enlarged end of penis called the glans penis is covered by a loose fold of skin called foreskin. THE FEMALE REPRODUCTIVE SYSTEM  It consists a pair of Ovaries, Accessory ducts (constitute oviducts, uterus & vagina) and the external genitalia. Testes (10 sex organ)  Situated in scrotum (helps in maintaining the low temperature)  Oval in shape, length: 4-5 cm, width: 2-3 cm.  Each testis is subdivided into 250 testicular lobules Ovaries (10 sex organs) Each lobule contains 1-3 highly coiled seminiferous tubules.  Located one on each side of the lower abdomen. Each seminiferous tubule is lined by-  Almond shaped; Length: 2- 4 cm.  Male germ cells (Spermatogonia) undergo meiotic divisions  Each ovary is covered by a thin epithelium which encloses the  sperm ovarian stroma. The stroma is divided into – An outer cortex  Sertoli cells provide nutrition to the germ cells. and an inner medulla.  The regions outside the seminiferous tubules (interstitial spaces), contain - Oviducts (fallopian tubes)  Muscular tubes of 10-12 cm long which carry the ovum from o Small blood vessels ovary to the uterus. o Interstitial cells or Leydig cells (secrete androgens)  It is divided into 3:- (i) Infundibulum- Funnel-shaped opening possessing finger-like Germ cells fimbriae, which help in collection of the ovum after ovulation. Sertoli cells (ii) Ampulla- a wider part. (iii) Isthmus has a narrow lumen and it joins the uterus. Uterus (womb)  It is a large, inverted pear-shaped, supported by ligaments attached to the pelvic wall.  The wall of the uterus has 3 layers - 1. External Perimetrium (thin membrane) 2. Middle Myometrium (thick layer of smooth muscle-exhibits contraction during delivery of the baby). Accessory ducts 3. Inner Endometrium (glandular layer- undergoes cyclical changes  The pathway of transport of sperms is as follows:- during menstrual cycle, zone of implantaion). Seminiferous tubules →Rete testis →Vasa efferentia  Uterus opens into vagina through a narrow cervix. →Epididymis→Vas deferens →Ejaculatory duct →Urethra for HSS LiVE.IN, prepared by: Minhad. M. Muhiyudeen, #- 9846 29 22 27 23  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® Vagina  It is a large, elastic, muscular tube about 7.5cm long. GAMETOGENESIS Cervical canal + vagina = Birth canal The primary sex organs – the testis produce male gamete, sperms and the ovaries produce females gametes, ovum. External genitalia (Vulva)  Consists of mons pubis, labia majora, labia minora, hymen and Spermatogenesis clitoris  It is the production of sperm from spermatogonia (male germ a) Mons pubis is a cushion of fatty tissue covered pubic hair. cell- present on the inside wall of seminiferous tubules). b) Labia majora are fleshy folds of tissue surrounding the vaginal At puberty opening. 1. The spermatogonia (46 chromosomes- 2n) multiply by mitotic c) Labia minora are paired inner folds of tissue. division and increase in numbers. d) Clitoris is a sensitive structure above the urethral opening. 2. Some of the spermatogonia differentiate into primary e) Hymen- The membrane partially covering the opening of the spermatocytes (2n) which undergo 1st meiotic division vagina. (reduction division) leading to formation of 2 secondary spermatocytes (n). 3. The 2 secondary spermatocytes undergo the 2nd meiotic division to produce 4 spermatids (n). 4. The spermatids are transformed into spermatozoa / sperms (n) by the process called spermiogenesis. Then sperm heads become embedded in the Sertoli cells, and are finally released from the seminiferous tubules by the process called spermiation and are transported by the accessory ducts. MAMMARY GLAND (Breasts)  The mammary glands of the female are paired structures that contain glandular and fatty tissue.  The mammary glands undergo differentiation during pregnancy and starts producing milk towards the end of pregnancy by the process called lactation. This helps the mother in feeding the newborn. Hormonal control of spermetogenesis Structure of a sperm  A plasma membrane envelops the whole body of sperm. Sperm consists of- a. Head: Oval shaped. Containing nucleus and capped by acrosome Structure- contains lytic enzymes- helps in penetrating ovum.  Each glandular tissue is divided into 15-20 mammary lobes b. Middle piece: Contain mitochondria which produce energy for the containing clusters of cells called alveoli. The cells of alveoli sperm motility. secrete milk, which is stored in the cavities (lumens). c. Tail: It helps the sperm moves in fluid medium. Path of milk ejection: The alveoli open into mammary tubules → mammary duct → mammary ampulla → lactiferous duct → nipple through which milk is sucked out.  The human male ejaculates about 200 to 300 million sperms during coitus. for normal fertility 60% sperms must have normal shape and size 40% of them must show vigorous motility  Sperm (10%) + seminal plasma = Semen for HSS LiVE.IN, prepared by: Minhad. M. Muhiyudeen, #- 9846 29 22 27 24  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® MENSTRUAL CYCLE Oogenesis It is the cyclic changes in the activity of ovaries and accessory  It is the process of formation of ovum from oogonia (female germ ducts as well as hormones during the reproductive phase in a cell- formed within each fetal ovary) female body, with bleeding (menstruation), repeated at an average interval of about 28/29 days During embryonic stage- The first menstruation begins at puberty and is called menarche. 1. The oogonia (46 chromosomes- 2n) divide mitotically to form In human beings, menstrual cycles stop around 50 years of age; 2 millions of oogonia. that is termed as menopause. 2. All oogonia undergo first meiotic division and get temporarily Menstrual cycle has the following phases:- arrested at prophase-I, called primary oocytes (n). I. Menstrual / Bleeding Phase: 1-5th day Each primary oocyte then gets surrounded by a layer of granulosa cells and is called the primary follicle.  The cycle starts with menstrual flow and it lasts for 3-5 days.  It is due to breakdown of endometrial lining of the uterus and its Birth to puberty- blood vessels that comes out through vagina. - A large number of primary follicles degenerate and only 60,000-  Menstruation only occurs if the released ovum is not fertilised. 80,000 of them are left in each ovary. Lack of menstruation may be indicative of pregnancy. It may At puberty, in each menstrual cycle- also be caused due to stress, poor health etc. - One primary follicle of either ovary gets surrounded by more layers II. Proliferative / Follicular Phase: 5-13th day of granulosa cells and a new theca and are called secondary follicles.  In this phase, the secretion of gonadotropins (LH & FSH) - The secondary follicle soon transforms into a tertiary follicle increases gradually from pituitary. They stimulates:- which is characterised by a fluid filled cavity called antrum. The o Development of 10 follicles into Graafian follicles. theca layer is organised into an inner theca interna and an outer Developing follicles secretes estrogens. theca externa. Estrogens stimulates- 3. The primary oocyte within the tertiary follicle grows in size and o Regeneration of ruptured uterine endometrium. completes its first meiotic division resulting in the formation of a large secondary oocyte (n) and a tiny first polar body (n). III. Ovulatory Phase: 14th day - The tertiary follicle further changes into the mature follicle or  Both LH and FSH attain a peak level. Graafian follicle. The secondary oocyte forms a new membrane  Rapid secretion of LH (LH surge) induces rupture of Graafian called zona pellucida surrounding it. follicle and thereby ovulation. - The Graafian follicle now ruptures to release the secondary IV. Secretory / Luteal Phase: 15-28th day oocyte from the ovary by the process called ovulation.  After ovulation, Graafian follicle is transformed into a yellow After fertilisation- glandular mass called Corpus luteum. nd 4. The secondary oocyte undergoes 2 meiotic division and results in - It secretes large amount of progesterone which is essential for the formation of an ovum (ootid-n) and a 2nd polar body. maintenance of the endometrium. Thus the uterus gets ready for implantation of the fertilised ovum and other events of pregnancy. - During pregnancy all events of menstrual cycle stop and there is Differences between spermatogenesis and oogenesis no menstruation. Spermatogenesis Oogenesis - If fertilization does not occur, corpus luteum degenerates. This i. It occurs in the testis i. In ovary causes disintegration of the endometrium leading to ii. Gamete is called sperm ii. Ovum menstruation, marking a new cycle. iii. Continuous process iii. Discontinuous It begins at puberty and It begins at embryonic stage and FERTILISATION & IMPLANTATION extends up to senility suspended at the time of birth. The  During copulation (coitus), semen is released by the penis into remaining part takes place only after the vagina (insemination). puberty.  Fertilisation (sperm + ovum → zygote) can only occur if the 0 iv. Each 1 spermatocyte iv. Each 10 oocyte gives only 1 ovum ovum and sperms are transported simultaneously to the gives 4 sperms and 3 polar bodies ampullary region.  During fertilisation, 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, it ensures that only one sperm can fertilise an ovum. for HSS LiVE.IN, prepared by: Minhad. M. Muhiyudeen, #- 9846 29 22 27 25  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ®  In the later phase of pregnancy, a hormone called relaxin is also  The secretions of the acrosome help the sperm enter into the secreted by the ovary. cytoplasm of the ovum through the zona pellucida and the plasma membrane.  In addition to hCG, hPL and relaxin, during pregnancy the levels of other hormones like estrogens, progestogens, cortisol, prolactin, thyroxine, etc., are increased several folds in the maternal blood. They support:- o The fetal growth o Metabolic changes in the mother o Maintenance of pregnancy.  Immediately after implantation, the inner cell mass (embryo) differentiates into an outer ectoderm, middle mesoderm and an inner endoderm. These 3 layers give rise to all tissues (organs) in adults. Developmental stages of human embryo during  Soon the haploid nucleus of the sperms and that of the ovum fuse together to form a zygote (2n). pregnancy  The human pregnancy lasts 9 months (gestation period).  The mitotic division (cleavage) starts as the zygote moves through the isthmus towards the uterus and forms 2, 4, 8, 16 Month Embryonic development daughter cells called blastomeres. 1st month Heart is formed.  The embryo with 8 to 16 blastomeres is called a morula. 2nd month Limbs and digits develop.  The morula continues to divide and transforms into blastocyst. 3rd month Limbs and external genital organs well develops The blastomeres in the blastocyst are arranged into an outer layer 5th month Shows movements and appear hair on the head (trophoblast) and an inner group of cells (inner cell mass) The body is covered with fine hair, eye-lids attached to trophoblast. 6th month separate, and eyelashes are formed. The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated as the embryo. The foetus is fully developed and is ready for 9th month delivery. PARTURITION & LACTATION  Vigorous contraction of the uterus at the end of pregnancy causes delivery of the foetus (parturition). Neuroendocrine mechanism of parturition Step 1. The signals from the fully developed foetus and the placenta which induce mild uterine contractions (foetal ejection reflex). Step 2. This induce release of oxytocin from the maternal pituitary. Step 3. Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates further secretion of oxytocin. Step 4. Contraction get stronger, which leads to expulsion of the baby out of the uterus through the birth canal. Soon after the infant is delivered, the placenta is also expelled out  After attachment, the uterine cells divide rapidly and cover the of the uterus. blastocyst. As a result, the blastocyst becomes embedded in the endometrium of the uterus (implantation) and it leads to pregnancy. PREGNANCY & EMBRYONIC DEVELOPMENT  After implantation, finger-like projections (chorionic villi) appear on the trophoblast which is surrounded by the uterine tissue and maternal blood. Mammary glands differentiate during pregnancy and secrete The chorionic villi and uterine tissue become inter digitated milk after child-birth. with each other and jointly form a structural and functional unit o The milk produced during the initial few days of lactation between developing embryo (foetus) and maternal body called (colostrum) which contains several antibodies absolutely placenta. essential to develop resistance for the new-born babies. o Placenta is connected to the embryo by an umbilical cord. It transports substances to and from the embryo. Functions of placenta:  Supply O2 and nutrients to the embryo  Remove CO2 and waste materials produced by the embryo.  Acts as an endocrine gland by secreting human chorionic gonadotropin (hCG), human placental lactogen (hPL), oestrogens, progesterone. for HSS LiVE.IN, prepared by: Minhad. M. Muhiyudeen, #- 9846 29 22 27 26