Human Reproduction PDF Notes

03 HUMAN REPRODUCTION KEYNOTES 2.0 By: Dr. Anand Mani t.me/anandmani001 anand_mani16 anandmani.com  Reproduction is the production of young ones by an organism. Humans are sexually reproducing and viviparous. HUMAN REPRODUCTIV...

03 HUMAN REPRODUCTION KEYNOTES 2.0 By: Dr. Anand Mani t.me/anandmani001 anand_mani16 anandmani.com  Reproduction is the production of young ones by an organism. Humans are sexually reproducing and viviparous. HUMAN REPRODUCTIVE SYSTEM 1) male REPRODUCTIVE SYSTEM It consists of paired testes, Accessory ducts, Accessory glands & external genitalia (penis). PAIRED TESTES Primary sex organs that produce sperms Seminiferous tubule is lined internally & testosterone. with spermatogonia Testes are formed within the abdomen. Sertoli cells give shape and nourishment Soon after the birth or at the 8th month to developing spermatogonia (male germ of pregnancy they descent into the cells) and Sertoli cells (supporting cells). scrotal sac (scrotum) through inguinal canal. The regions outside the seminiferous tubules (Interstitial cells) contain small The low temperature of scrotum (2-2.5 blood vessels, interstitial cells (Leydig degree Celsius less than the body cells) and immunologically competent temperature) helps for proper functioning cells. of testes and for spermatogenesis. Each testis is oval shaped. Length: 4-5 Leydig cells secrete testicular hormones cm, width: 2-3 cm (androgens). Each testis has about 250 testicular Each lobule contains 1-3 coiled lobules. seminiferous tubules. Accessory ducts (Duct system) Include rete testis, vasa efferentia, epididymis and vas deferens. They conduct sperms from testis as follows: rete testis vasa efferentia - epididymis Seminiferous (series of fine (stores sperms tubules (irregular cavities) tubules) temporarily) join with duct of urethral seminal vesicle to vas meatus urethra form common deferens ejaculatory duct Urethra receives ducts of prostate and Cowper’s glands. t.me/anandmani001 anand_mani16 anandmani.com  Accessory glands o Include a prostate gland, a pair of seminal vesicles and a pair of Cowper's glands (bulbo-urethral glands). o Their collective secretion (seminal plasma) is rich in fructose, Ca and enzymes. o Seminal plasma + sperms - semen o Functions of seminal plasma: 1 2 3 4 Provides Secretions of Helps for Supplies alkalinity to Cowper’s transporting nutrients to counteract the glands sperms. sperms. acidity of lubricate the uterus. penis. o Secretions of epididymis, vas deferens, seminal vesicle & prostate help for maturation and motility of sperms. Penis (external genitalia) o It is a copulatory organ made of erectile spongy tissue. Prepare Circumcision Friction PS When spongy tissue The cone-shaped tip Ejaculation Sum is filled with blood, of the penis is the penis erects. It called glans penis. facilitates It is covered by insemination. prepuse (foreskin). E 2. Female Reproductive System o It includes Ovaries, Accessory ducts & External genitalia. Paired ovaries Primary sex organs which produce ova (female gamete) & steroid ovarian hormones (estrogen & progesterone). Each ovary is 2-4 cm in length. They are located on both side of the lower abdomen and connected to the pelvic wall and uterus by ligaments. Each ovary is covered by a thin epithelium which encloses the ovarian stroma. The stroma has outer cortex and inner medulla. Ovary contains groups of cells (Ovarian follicles). Each follicle carries a centrally placed ovum t.me/anandmani001 anand_mani16 anandmani.com  Accessory ducts (Duct system) Include 2 oviducts (Fallopian tubes), a uterus & vagina. cervix oviducts o Each oviduct (10-12 cm long) has 3parts: Infundibulum Ampula Isthmus Funnel-shaped opening provided with many Wider part. Narrow part. It finger-like Fimbriae. It joins the uterus. helps to collect the ovum. siteoffertilization o The ciliated epithelium lined the lumen of the oviduct drives the ovum towards the uterus. uterus (womb) o It is inverted pear shaped. It is supported by ligaments attached to the pelvic wall. o Uterus has 3 parts- 1 Upper fundus 2 middle body 3 terminal cervix o Cervix opens to Vagine. o The uterine wall has 3 layers: Perimetrium: Myometrium: Endometrium: External thin Middle thick layer Inner glandular & membrane of smooth muscle. vascular layer. vagina It opens to the exterior between urethra & anus. The lumen of vagina is lined by a glycogen-rich mucous membrane consisting of sensitive papillae & Bartholin’s glands. Bartholin’s glands secrete mucus that lubricates the penis during sexual act. External genitalia (vulva or pudendum) o Consist of Mons pubis, vestibule, hymen & clitoris. o Mons pubis: A cushion of fatty tissue covered by pubic hair. o vestibule: A median channel. It includes: Labia Majora: Large, fleshy, fatty and hairy outer folds. Labia minora: Small, thin and Surrounds vaginal opening. hairless inner folds. t.me/anandmani001 anand_mani16 anandmani.com  o Hymen (Maiden head) - A membrane which partially cover the vaginal opening. It is often torn during the first coitus.It may also be broken by a sudden fall or jolt, insertion of a vaginal tampon; active participation in some sports items etc. In some women, hymen persists after coitus. So the hymen is not a reliable indicator of virginity. o Clitoris: A highly sensitive organ lying just in front of the urethral opening Mammary glands (breasts) A pair of mammary glands contains glandular tissue & fat. Milkproduction Prolaction Glandular tissue of each breast has 15-20 mammary lobes containing clusters of cells mammary alveoli. Progesterone Milkletdown oxytocin Cells of alveoli secrete milk. It is stored in lumen of alveoli. The alveoli open into mammary tubules 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 lactiferous duct through which milk is sucked out. GAMETOGENESIS o It is the formation of gametes in the gonads. o It is 2 types: Spermatogenesis and Oogenesis. Spermatogenesis It is the process of formation of sperms (spermatozoa) in seminiferous tubules of testis. It has 2 stages: Formation of spermatids In this, Spermatogonia (Sperm mother cells or immature male germ cells) produce spermatids. Spermiogenesis Release ofsperm from Sertolicell Spermatids transform into sperms. Spermiation t.me/anandmani001 anand_mani16 anandmani.com  Schematic representation of Spermatogenesis Spermatogonia-2n (46 chromosomes) Puberty Mitosis differentiation Primary spermatocytes - (2n) 1st meiotic division Secondary spermatocytes-n (23) 2nd meiotic division Spermatids (n) Differentiation Spermatoza (n) o 4 spermatids are formed from each primary spermatocyte. o After spermiogenesis, sperm heads become embedded in the Sertoli cells. Then they are released to lumen of seminiferous tubules. It is called spermiation Role of Hormones in Spermatogenesis o Hypothalamus releases Gonadotropin releasing hormone (GnRH). o GnRH stimulates the anterior pituitary gland to secrete 2 and gonadotropins such as Luteinizing hormone (LH) follicle stimulating hormone (FSH) ABI LH acts on the Leydig FSH acts on the cells and stimulates secretion of Sertoli cells and androgens. Androgens stimulates secretion É stimulate the of some factors for spermatogenesis. the spermiogenesis. mm t.me/anandmani001 anand_mani16 anandmani.com  Structure of spermatozoa (Sperm) o A mature sperm is about 60 µ (0.06 mm) long. o A plasma membrane envelops the whole body of sperm. o A sperm has 3 regions: ProximalCentriole Nick a) Head: Oval b) Middle piece: c) Tail: Consists of a shaped. Formed of Composed of axial central axial nucleus & acrosome. filament surrounded filament. The sperm Acrosome is formed by mitochondria & moves in fluid from Golgi complex. cytoplasm. medium and female It contains lytic Mitochondria genital tract by the enzymes. Behind the produce energy for undulating movement head is a neck. the sperm motility. of the tail. KernSheath Webern o Man ejaculates 200-300 million sperms during a coitus. o For normal fertility, at least 60% sperms must have normal shape and size. o 40% of them must show vigorous motility. Oogenesis It is the process of formation and maturation of ovum. It takes place in Graaflan follicles. Oogenesis is initiated in embryonic stage when millions of egg mother cells (oogonia) are formed within each ovary. No more oogonia are formed and added after birth. Oogonia multiply to form primary oocytes. They enter prophase-I of the meiosis and get temporarily arrested at that stage. diplotone Each primary oocyte gets surrounded by a layer of granulosa cells to form primary follicle. Many primary follicles degenerate during the phase from birth to puberty. Therefore, at puberty, only 60,000 - 80,000 primary follicles are left in each ovary. The primary oocyte in The secondary follicles Primary follicles tertiary follicle grows and transform into a tertiary undergoes first unequal get surrounded by follicle. It has a fluid more layers of meiotic division to form a filled cavity (antrum). large secondary oocyte granulosa cells and The theca layer (n) & a tiny first polar a new theca to form secondary forms an inner theca body (n). So, secondary follicle. interna and an outer oocyte retains nutrient theca outerna rich cytoplasm of primary oocyte. t.me/anandmani001 anand_mani16 anandmani.com It is unknown Graafian follicle The tertiary that whether Secondary now ruptures to follicle further the first polar oocyte forms release the changes into body divides a new secondary oocyte the mature further or membrane from the ovary. follicle degenerates. This is called OVULATION Schematic representation of oogenesis OOGENESIS oogonia -2n (46 chromosomes) Mitosis differentiation (at foetal stage) Primary oocyte-2n (grows insize) 1st meiotic division (prior to ovulation) Primary oocyte-n & first polar body (n) 2nd meiotic division (during fertilization) Ovum (n) & second Polar body (n) Structure of ovum (egg) o Spherical and non-motile. o About 02 mm in diameter. o Ovum has 3 membranes: Plasma Membrane: Innermost layer. Zona pellucida: Outer to the plasma membrane. Corona radiata: Outer layer formed of follicle cells t.me/anandmani001 anand_mani16 anandmani.com  spermatogenesis & OOgenesis - a comparison Spermatogenesis Oogenesis Occurs in testis Occurs in ovary Limited growth phase Elaborated growth phase Each primary spermatocyte gives 4 sperms Each primary oocyte gives 1 ovum No polar body formation Polar bodies are formed Begins at puberty & extends up to selinity Begins at embryonic stage but suspends upto puberty. It ceases around the age of fifty. MENSTRUAL CYCLE (REPRODUCTIVE CYCLE) It is the cyclic events starting from one menstruation till the next during the reproductive period (from puberty to menopause) of a woman’s life. Start Menarche Its duration is 28 to 29 days. Menstrual cycle is also seen in other primates. Menstrual cycle includes Ovarian cycle (changes in ovary) & Uterian cycle (changes in uterus, oviduct & vagina). - Menstrual cycle has the following phases a) Menstrual phase: b) Follicular (Proliferative) 1 - 5th day phase: 5 13th day The cycle starts with menstrual flow It starts from 5th day after menstruation & (bleeding) completed within 8-12 days. It lasts for 3-5 days. In this phase, the action of gonadotropins Menstruation occurs if the released ovum (FSH &LH) from pituitary occurs. FSH is not fertilized. It results in breakdown of stimulates endometrial lining and uterine blood Development of primary follicles into vessels that comes out through vagina. Graafian follicles. Lack of menstruation indicates pregnancy. Secretion of oestrogens by Graafian follicles. It may also be caused due to stress, poor Proliferation of ruptured uterine health etc. endometrium and mucus lining of oviduct & Menarche - The first menstruation during vagina. puberty. o Development of secondary sexual characters. o Suppression of FSH secretion. o Secretion of LH (Luteinizing hormone). t.me/anandmani001 anand_mani16 anandmani.com c) Ovulatory phase: 14th day o LH & FSH attain a peak level in the middle of cycle. o Rapid secretion of LH (LH surge) induces rupture of Graafian follicle and thereby ovulation (on 14th day). d) Secretory (Luteal) phase: 15-28th day o After ovulation, Graafian follicle is transformed into a yellow endocrine mass called Corpus luteum. It secretes progestrone. Paleyellow o Functions of progestrone: Makes the endometrium Inhibits the FSH maximum vascular, thick secretion to prevent and soft. Thus, the development of a uterus gets ready for second ovarian follicle. implantation. LHHelps in maintaining Corpus luteum o If fertilization does not occur, corpus luteum degenerates. It causes disintegration of endometrium. It leads to next menstruation and new cycle. o If a woman becomes pregnant, all events of menstrual cycle stop and there is no menstruation. o Menstrual cycle ceases around 50 years of age. It is called Menopause. FERTILIZATION AND IMPLANTATION o During copulation, semen is released by the penis into the vagina. It is called insemination. o Fusion of a sperm with ovum is called fertilization. It occurs in Ampullary-isthmic junction of fallopian tube. r ngion cervical 1 Sperms 2 vagina 3 canal 4 uterus 5 isthmus isthmic 3 Fertilization 2 Ampullary 1 Junction 1 Ovum (from ovary) 2 fimbriae 3 infundibulum 4 ampulla t.me/anandmani001 anand_mani16 anandmani.com  Fertilization happens only if ovum and sperms are The embryo with 8-16 blastomeres is called a transported simultaneously. So all copulations do morula. not lead to fertilization & pregnancy. i week Morula continues to divide and transforms into A sperm contacts with zona pellucida. It induces blastocyst. changes in the membrane that block entry of additional sperms. In blastocyst, blastomeres are arranged into trophoblast (outer layer) and an inner cell mass attached to trophoblast. The secretions of the acrosome help sperm to enter the egg cytoplasm via zona pellucida & plasma membrane. This causes second meiotic The trophoblast layer gives nourishment to division of secondary oocyte to form an ovum inner cell mass. Also, it gets attached to (ootid) and a second polar body. endometrium. After attachment, uterine cells divide rapidly The haploid nuclei of the sperm and ovum fuse and cover the blastocyst. Thus, the blastocyst together to form a diploid zygote. becomes embedded in the endometrium. This is called implantation. Zygote undergoes mitotic division (cleavage) as it The inner cell mass gets differentiated to 3 moves through the isthmus towards the uterus germ cells. (outer ectoderm, middle mesoderm and forms 2, 4, 8, 16 daughter cells called & inner endoderm). This 3-layered structure blastomeres. (gastrula) forms the embryo. PREGNANCY AND EMBRYONIC DEVELOPMENT After implantation, finger-like projections (chorionic villi) appear on the trophoblast which is surrounded by the uterine tissue and maternal blood. The chorionic villi & Placenta is uterine tissue are connected to the interdigitated to form embryo by an placenta. It is a It transports UMBIICALCORD structural and functional unit b/w substances to and embryo (foetus) and from the embryo. maternal body Functions of placenta Acts as barrier between the foetus and mother. Supply O 2 nutrients etc. from mother to foetus. Remove CO 2 and excretory wastes from foetus. Acts as an endocrine gland. It secretes human Chorionic Gonadotropin (hCG), human placental lactogen (hPL) t.me/anandmani001 anand_mani16 anandmani.com  Oestrogens, progesterone and relaxin Relaxin is also secreted by ovary. During pregnancy, levels of estrogens, progestogens, cortisol, prolactin, thyroxin etc. are also increased in maternal blood. They support the fetal growth, metabolic changes in the mother and maintain pregnancy. The germ layers give rise to all tissues (organs). The stem cells in inner cell mass have the potency to give rise to all the tissues and organs. Human pregnancy (gestation period) lasts 9 months (for cats: 2 months, dogs: 2 months, elephants: 21 months) Changes in embryo during pregnancy End of 12 weeks (first 1 2 3 End of second trimester): The major After one month: month: organs (limbs, Heart is informed Limbs and digits are external genital developed. organs etc.) are well developed. End of 24 weeks During 5th month: 4 5 6 (second trimester) First movement of End of 9 months: Body is covered with foetus and Ready for fine hair, eyelids appearance of hair delivery. separate and eye on the head. lashes are formed. PARTURITION AND LACTATION Parturition (labour): Process of giving birth to After parturition, the umbilical cord is cut off. young ones. Parturition is induced by neuroendocrine The placenta & remnants of umbilical cord are mechanism. expelled from the maternal body after parturition. It is called "after birth". The signals originating from the foetus and placenta induce mild uterine contractions (fetal ejection reflex). This causes the release of The mammary glands produce milk towards oxytocin from maternal pituitary. the end of pregnancy. It is called lactation. Oxytocin causes stronger uterine muscle - The yellowish milk produced during the initial contractions which in turn stimulate further few days of lactation is called colostrum. It secretion of oxytocin. This process is continued contains several antibodies essential to leading to expulsion of the baby out of the develop resistance for the new born babies. uterus through the birth canal. IgA t.me/anandmani001 anand_mani16 anandmani.com