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Human Reproduction

NCERT class 12 for NEET 2018

QuestionAnswer
What are some reproductive organ other than primary sex organs which perform important functions? The growth and maintenance of gonads are regulated by gonadotropins(FSH,LH) of the anterior lobe of pituitary. The other reproductive organs which neither produce gametes nor secrete hormones but are important are called secondary sex organs.
Where do testes start their development? Testes start their development in the abdominal cavity but during 7th month of foetal life, they descend into the scrotal sacs in presence of testosterone hormone. If they fail to descend, the condition is called cryptorchidism.
Name 2 muscles of scrotal sac which help in positioning of testis. Cremaster muscles and dartos muscles. Whenever the outside temp is low, these contract to move the testis close to the abdominal cavity and relax when environment is opposite.
Inguinal canal Oblique passage through the lower abdominal wall through which testes descend into scrotum and it contains the spermatic cord.
Name the mammals which have testes permanently in their abdominal wall. Elephant, aquatic mammals like whales, dolphins, seal and prototherians like Ornithorhyncus. In bat and otter, testes descend seasonally during breeding season.
Outer tough capsule of collagenous connective tissue over testes Tunica albuginea
Define semeniferous tubules. Each testes has 250 compartments called testicular lobules, these compartments contain highly coiled tubules called semeniferous tubules. (3 s.t. in each compartment) Here, sperms are produced.
Types of cells in semeniferous tubules. 2 types:- Male germ cell (spermatogonia) and Sertoli cells.
Work of spermatogonia and sertoli cells. Spermatogonia (lining the semeniferous tubules) give rise to spermatozoa which are released into the lumen of the tubule. In between spermatogonia, sertoli cells are present which provide nourishment to developing spermatozoa and regulate spermatogenesis.
How does seroli cells regulate spermatogenesis? By releasing inhibin to check FSH over-activity.
What are the functions of seroli cells? 1) Absorb the parts being shed by developing spermatozoa. 2) Release ANF (anti mullerian factor) to prevent mullerian duct/oviduct formation in male. 3) Release ABP( androgen binding protein). 4) Form blood-testis barrier.
Define the fate of mullerian duct. Mullerian ducts(mesodermal origin) are paired ducts of the embryo. In the female, they develop to form the fallopian tubes, uterus, cervix and the upper portion of vagina; in males, they degenerate.
Which are the endocrine tissue of testis? Interstitial cells of leydig present in the connective tissue around the semeniferous tubules constitute the endocrine tissue of testis. They synthesise and secrete testicular hormones called Androgens into blood.
Tubuli recti Semeniferous tubules unite to form tubuli recti which open into cuboidal epithelium lined channels called rete testis. Several tubes called vasa efferentia arise from it and conduct spermatozoa out of the testis.
What is intra-testicular genital duct system? Tubuli recti, rete testis and ductuli efferntes form it. The rest tubes which conduct sperms from the testes to the outside are called extra testicular duct system.
Role of vasa efferentia. From each testis, 10-12 vasa efferentia confluent to form a folded and coiled tube called epididymis behind each testis.
Parts of epididymis. It consists of 3 parts:- 1) Caput 2) Corpus 3) Cauda Epididymis stores sperms temporarily.
How does an ejaculatory duct forms? From cauda epididymis, vas deferens ascends into the abdomen through inguinal canal, passes over the urinary bladder, vas deferens dilates to form ampulla which recieves the duct from the seminal vesicle and forms an ejaculatory duct.
What is the final portion of ampulla? Its final portion passes through the prostate to open into the urethra shortly after its origin from the urinary bladder.
Parts of urethra. First part is surrounded by prostate gland and is called glandular part. Second part is the membranous urethra situated behind the lower pubic symphysis and is the shortest. Penile urethra is situated in the penis and is the longest.
Which ducts do urethra recieves? It recieves ducts from prostate and cowper's glands, passes through the penis and opens to the outside.
Membrane over the penile mass? Tunica albuginea
Cords of penis? 3 cords: Two corpora cavernosa, thicker and parallel. The fibres of tunica albuginea surround both the cords jointly and forms a seperate sheath called septum penis. The third, smallest cord is corpus urethrae or spongiosum, urethra runs through it.
Glans penis. Extended part of corpus spongiosum is enlarged and forms a conical structure. The loose skin of penis becomes folded over the glans penis and is called foreskin or prepuce.
Glands on penis neck. Tyson's gland or Preputial glands, present in the skin of penis neck, secrete a white sebaceous substance called smegma. Its microbial infection can cause irritation due to inflammation.
What are the accesory glands of male? Seminal vesicle(paired), Prostate gland and Bulbourethral or cowper's gland(paired).
Seminal vesicle. Secrete viscous fluid which constitutes the main part of ejaculate. Seminal fluid contains fructose, citric acid, inositol and prostaglandins.
Prostate gland. collection of 30-40 tubuloalveolar glands which lie at the base of the bladder. It contributes an alkaline component to semen. Prostatitis- inflammation of prostate gland.
Bulbourethral gland. Secrete a viscous mucus which acts as a lubricant.
Regulation of secondary sex organs. Duct system, accessory glands and the penis are secondary sex organs and their growth and maintenance is regulated by testosterone, secreted by leydig cells.
Regulation of semeniferous tubules and leydig cells. the growth and maintenance of functions of semeniferous tubules and leydig cells are regulated by FSH and ICSH of anterior pituitary respectively.
Semen pH- 7.2-7.7; avg vol.- 2.5-5 ml, with a sperm count of 200-300 million sperms. When it falls below 20 million, the person becomes sterile. Out of these, 60% must have normal shape and size and 40% must show vigorous motility
Role of ovary It produces ova, secretes the female hormone, estrogen and progesterone.
Location of ovary Near kidneys, remain attached to the lower abdominal cavity through mesovarium.
Two zones of stroma? The stoma is divided into 2 zones- a peripheral cortex and an inner medulla. Immediately below the the germinal epithelium, the cortex is covered by tunica albuginea.
Cortex The cortex contains numerous oval sac like masses of cells known as ovarian follicles.
Medulla The medulla contains loose connective tissue, elastic fibres, numerous blood vessels and some smooth muscle fibres.
Ovarian follicles The ovarian follicles contains a large, centrally placed ovum, surrounded by several layers of granular cells. It is suspended in a small cavity called antrum filled with a fluid called liquor folliculi.
Graafian follicle. secondary oocyte in the tertiary follicle also forms a new membrane called zona pellucida. The follicle bulges onto the surface of the ovary. Such a follicle is called graafian follicle.
Corpus luteum(yellow body) After the extrusion of the ovum, what remains in the Graafian follicle is called corpus luteum(yellow body). The cytoplasm of corpus luteum is filled with a yellow pigment called lutein.
Corpus albicans(white body) Corpus luteum continues to grow if ovum is fertilized, else it persists for 14 days. During this period it secretes progesterone and estrogen. At the end of its life, it degenerates and is converted into a mass of fibrous tissue called corpus albicans.
Parts of fallopian duct. 1) Infundibulum- edges of infundibulum possess finger like projections called fimbriae. 2) Ampulla 3) Isthmus Fertilisation occurs at the junction of ampulla and isthmus.
Uterus aka Hystera/Womb. Present in between bladder and rectum and suspended by mesometrium. Implantation of embryo occurs in the uterine fundus.
Cervix opens in the body of uterus by internal os and in vagina below bu external os. It is mainly formed of the most powerful sphincter muscles in the body.
Vagina lined by mucus membrane which is raised into transverse folds called vaginal rugae. Lined with stratified squamous epithelium (non keratinised). Vagina is devoid of glands. Vaginal orifice is partially covered by a membranous diaphragm called hymen.
Homology of vagina to penis Labia majora is homologous to scrotum. Clitoris is homologous to penis as both are supported by corpora cavernosa.
Greater vestibular glands Greater or Bartholin's glands are on each side of vaginal orifice and secrete alkaline secretion for lubrication and neutralising urinary acidity.
Lesser vestibular glands Lesser or Skene's glands are small mucus glands present between urethral and vaginal orifices.
Mammary glands location present over the pectoralis major muscles on the front wall of the thorax.
Path of milk Mammary alveoli-> Mammary tubules--> Mammary ducts--> Mammary ampulla--> Lactiferous duct
Milk production The process is regulated by nervous system. Production is stimulated by hormone prolactin secreted by anterior lobe of pituitary gland. Ejection is stimulated by largely by the hormone oxytocin, released from the posterior lobe of pirtuitary gland.
Milk constituents fat droplets, casein(milk protein), lactose(milk sugar), mineral salts and vitamins. Milk is poor in iron content. Vit C is present in very small quantity.
Stages of spermatogenesis 1) Spermatocytogenesis 2) Meiosis-1 3) Meiosis-2 4) Spermiogenesis
Spermatocytogenesis Some spermatogonia undergo changes and increase in size and are called primary spermatocytes.
Meiosis-1 Primary spermatocyte(diploid) completes its first meiotic division and form 2 equal, haploid cells called secondary spermatocytes, which have only 23 chromosomes.
Meiosis-2 secondary spermatocytes undergo second meiotic division to produce four equal haploid spermatids. The no of chromosomes in each spermatid is 23.
Spermiogenesis Transformation of spermatids into sperms. Nucleus becomes compact forming the major part of head of spermatozoa. Golgi complex of spermatid give rise to acrosome. The two centrioles of the spermatids become arranged one after the other behind the nucleus.
contd.,Spermiogenesis Mitochondria from different parts of spermatid get arranged in the mid piece around the axial filament. The sperm heads finally becoem embedded in the sertoli cells and get released from the semeniferous tubules.
Who saw sperm first? Human sperm was first seen by Hamm and Leeuwenhoek.
Sperm lysins Acrosome is filled with enzymes called sperm lysins that dissolve the membranes enveloping the ovum and help the sperm cell to enter the ovum.
Hormonal control of Male Reproductive system. Spermatogenesis starts at puberty due to significant increase in the secretion of GnRH( gonadotropin releasing hormone) from hypothalamus. Its increased levels then acts at the anterior pituitary gland and stimulates secretion of 2 gonadotropins.
contd., The gonadotropins are Luteinising hormone (LH) and follicle stimulating hormone (FSH). LH acts at the leydig cells and stimulates synthesis and secretion of androgens. Androgens, in turn, stimulate the process spermatogenesis.
contd., FSH acts on the sertoli cells and stimulates the secretion of some factors which help in spermiogenesis. Sertoli cells also secrete inhibin protein which suppresses FSH synthesis. Andogens maintain the function of male accessory glands.
Structure of sperm composed of head, neck, a middle piece and a tail. a plasma membrane envelops the body of sperm. Sperm head contains haploid nucleus, anterior portion of head is covered by acrosome.
Semen constitution seminal plasma along with the sperms constitute semen.
Oogenesis process of formation of a mature female gamete. It is initiated during the embryonic development stage when a million of gamete mother cells (oogonia) are formed in each fetal ovary; no more oogonia are formed and added after birth.
Primary oocytes Oogonia start division and enter into prophase-1 of the meiotic division and get temporarily arrested at that stage, called primary oocytes.
Primary follicle Each primary oocyte gets surrounded by a layer of granulosa cells and is called primary follicle. A large number of these follicles degenerates during the phase from birth to puberty. Only 60K-80K primary follicles are left in each ovary.
Seconday follicle The primary follicles get surrounded by more layer of granulosa cells and more theca and are called secondary follicles.
Antrum The secondary follicle soon transforms into a tertiary follicle which is characterised by a fluid filled cavity called antrum.
Secondary oocyte 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. In humans, polar body degenerates.
Graafian follicle The tertiary follicle further changes into the mature follicle called graafian follicle. The secondary oocyte forms a new memebrane called zona pellucida surrounding it.
Ovulation The graafian follicle now ruptures to release the secondary oocyte from the ovary by the process called ovulation.
Menstrual cycle The cycle of events starting from one menstruation till the next one is called the menstrual cycle. It is of 28/29 days. One ovum is released in the middle of each menstrual cycle.
Menstrual flow Each cycle starts with menstrual flow and it lasts for 3-5 days. It is the result of breaking down of endometrial lining of the uterus and its blood vessels which forms liquid that comes out through vagina. It only occurs if the ovum is not fertilised. `
Folicular phase Menstrual phase is followed by the follicular phase. During this phase, the primary follicles in the ovary grow to become a fully mature graafian follicle and simultaneously the endometrial lining of uterus regenerates through proliferation.
Hormonal control of Menstruation. Changes in ovary and uterus are induced by changes in pituitary and ovarian hormones level. Secretion of gonadotropins(LH and FSH) increases during follicular phase, and stimulates follicular development and estrogen secretion by the growing follicles.
Ovulation (hormonal) Both LH and FSH attain a peak level in the middle of cycle. Rapid secretion of LH leading to its max level called LH surge induces rupture of graafian follicle and thereby the release of ovum.
Luteal phase The ovulatory phase is followed by luteal phase during which the remaining parts of the graafian follicle transforms as the corpus luteum. It secretes a large amount of progesterone which is essential for maintenance of the endometrium for implantation.
Condition for fertilisation Fertilisation can only occur if the ovum and sperms are transported simultaneously to the ampullary-ishtmic junction.
Sperm and ovum meeting During fertilisation, sperms comes in contact with zona pellucida layer of ovum and induces changes in the membrane that block the entry of additional sperms.
Second polar body. Sperm and ovum contact in induces the completion of meiotic division of the secondary oocyte. It is also unequal and thus results into second polar body and a haploid ovum(ootid).
Zygote formation Haploid nuclues of sperm and that of the ovum fuses together to form a diploid zygote.
Blastomeres and morula Mitotic division starts as the zygote moves through the ishthmus of the oviduct called cleavage towards the uterus and forms 2,4.8,16 daughter cells called blastomeres. The embryo with 8 to 16 blastomeres is called morula.
Blastocyst Morula continues to divide and transforms into blastocyst as it moves further into the uterus. Blastomeres in blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast called inner mass of cells.
Implantation Trophoblast layer gets attached to the endometrium and the inner cell mass gets differentiated as the embryo. After attachment, the uterine cell divide rapidly and covers the blastocyst. Thus, blastocyst become embedded in endometrium.
Gastrulation movement of cells in small masses or sheets so as to form primary germ layers. These cell movements are called morphogenetic movements since they lead to initiation of morphogenesis. The product of gastrulation is called gastrula.
Amniotic cavity Space appears between the ectoderm and the trophoblast. It is filled with amniotic fluid. Epiblast is the source of all the germ layers in the embryo.
Chorionic villi after implantation, finger like projections appear on the trophoblast called chorionic villi which are surrounded by the uterine tissue and maternal blood.
Placenta The chorionic villi and uterine tissue become interdigitated with each other to form structural and functional unit between developing embryo and maternal body called placenta.
Function of placenta Facilitate the supply of oxygen and nutrients to the embryo and also the removal of carbon dioxide and waste produced by the embryo. It also acts as an endocrine tissue and several hormones.
Hormones of placenta human chorionic gonadoropin(hCG), human placental lactogen(hPL), estrogens, progestogens etc. In the later phase of pregnancy, a hormone relaxin is also produced by the ovary. hCG, hPL and relaxin is produced only during pregnancy.
Umbilical cord The placenta is connected to the embryo through an umbilical cord which helps in the transport of the substances to and from the embryo.
Germ layers Immediately after implantation, the embryo gets differentiated into an outer layer called ectoderm and inner layer called endoderm. A mesoderm soon appears in between.
Stem cells Inner cell mass (embryo) contains several cells called embryo which have the potency to give rise to all the tissues and organs.
Development of embryo after 1 month, heart is fromed. By the end of 2nd month, limbs and digits are developed. By the end of 12 weeks (first trimester), most of the organ systems are formed.
contd., By the end of 24 weeks (second trimester), body is covered with hairs, eye lids seperate and eyelashes are formed. By the end of 9 months, foetus is fully developed.
Gestation period Duration of human pregnancy which is of 9 months.
Parturition Delivery of the foetus is called parturition. It is induced by a complex neuroendocrine mechanism. Signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex.
Expulsion of the baby Foetal ejection reflex triggers the release of oxytocin from the maternal pituitary, Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates the further secretion of oxytocin.
contd., Expulsion of the baby The stimulatory reflex between the uterine contractions and oxytocin secretion continues resulting stronger and stronger secretions. This leads to expulsion of the baby. Soon after parturition, placenta is also expelled out of the uterus.
lactation Mammary glands of the female undergo the differentiation during pregnancy and starts producing milk towards the end of pregnancy by the process called lactation.
Colostrum Milk produced during the initial days of lactation is called colostrum which contains several antibodies absolutely essential to develop resistance for the new born.
Created by: sherickp