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Class 12 Biology Chapter 3 Human Reproduction
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Human Reproduction
Chapter – 3
REPRODUCTIONS
Very Short Answer Type Questions
Q.1. The process of formation of gametes is called_____
Ans : Gametogenesis.
Q.2. The testes in mammal are situated outside the abdominal cavity within a pouch called ____
Ans : Scrotum.
Q.3. The process of release of ovum from mature follicle is called ____
Ans : Ovulation.
Q.4. Ovulation is induced by hormone called ____
Ans : LH or luteinizing hormone.
Q.5. The fusion of a male and female gamete is called____
Ans : Fertilization.
Q.6. Secondary spermatocytes are formed from_____ by first meiotic division.
Ans : Primary spermatocytes.
Q.7. Zygote divides to form ____ which is implanted in uterus.
Ans : Embryo.
Q.8. The structure which provides connection between foetus amd uterus of the mother is called____
Ans : Placenta.
Q.9. The process which transform zygote to blastula is called _____
Ans : Cleavage.
Q.10. Gestation period of human female is_____
Ans : 9 months. (270 days)
Q.11. Cessation of menstrual cycle in a female is called____
Ans : Menopause.
Q.12. Progesterone is secreted by____
Ans : Corpus luteum.
Q.13. The secretory phase of menstruation cycle is also called the ____
Ans : Luteal phase.
Q.14. Each ovary is connected to the pelvic wall and uterus wall by _____
Ans : Ligament.
Q.15. Acrosome of sperm is formed from the ____
Ans : Golgi Body.
Q.16. ____ is an example of viviparous animal.
Ans : Mammal (man monkey etc)
Q.17. Union of male gamete and the female gamete is called ____
Ans : Fertilization.
Q.18. The function of the sertoli cell is to provide nutrition to the ____ cells.
Ans : Germ cells or spermatozoa.
(B). True or False :
Q.1. Humans are ovoviviparous.
Ans : False.
Q.2. Leydig cells are present in the interstitial spaces between the seminiferous tubules.
Ans : True.
Q.3. The funnel shaped part of the fallopian tube close to ovary is called isthmus.
Ans : False
Q.4. The secondary spermatocytes- contain haploid chromosome.
Ans : True.
Q.5. Spermatogonia undergo mitotic division.
Ans : True.
Q.6. GnRH is an anterior pituitary hormone.
Ans : False.
Q.7. The primary ovarian follicle is also called Graffian follicle.
Ans : False.
Q.8. XY sex chromosomes are found in human male.
Ans : True.
Q.9. Blastocyst is formed from the morula.
Ans : True.
Q.10. Acrosome is found in female gamete.
Ans : False.
(C). Very Short Answer Questions :
Q.1. State the difference in reproductive age of man and woman.
Ans : There äre a remarkable difference in the reproductive age of man and woman i.e. in male sperm formation continues even in old but in females the formation of ovum ceases around the age of fifty year.
Q.2. What is urethral meatus?
Ans : In males the urethra originates from the urinary bladder and extends through the penis to its external opening called urethral meatus.
Q.3. Name two male accessory glands.
Ans : A paired seminal vesicles and a paired bulbourethral glands.
Q.4. State the components of seminal plasma.
Ans : The components of seminal plasma includes rich fructose, calcium and certain enzymes secretions of male accessory glands constitute the seminal plasma.
Q.5. Define spermiation.
Ans : After the formation of sperms by the process of spermiogenesis, sperm heads become embedded in the sertoli cells and are finally released from the seminiferous tubules by the process called spermiation.
Q.6. What is the function of acrosome?
Ans : Acrosome, the cap like anterior portion of the sperm head is filled with enzymes that helps in the fertilization of the ovum.
Q.7. Why sperm contains mitochondria?
Ans : The middle pices of sperm contains numerous mitochondria, which produce energy for the movement of tail that facilitate sperm motility essential for fertilization.
Q.8. Name the hormones which maintain the functions of the male sex accessory ducts and glands.
Ans : Androgen.
Q.9. What is Semen?
Ans : The seminal plasma along with the sperms constitute the semen.
Q.10. Why human female has fixed number of primary follicle in the ovary?
Ans : Oogenesis is initiated during the embryonic development stage in females where a couple of million of oogonia are formed in the fetal ovary and no more oogonia are formed after birth. So females have a fixed number of follicle in ovary.
Q.11. What do you understand by ovulation?
Ans : The process of release of the secondary oocyte from the ovary by rupturing the Graffian follicle is known as ovulation.
Q.12. Define menstrual cycle.
Ans : The reproductive cycle in the female primates like monkeys, apes and human being is called menstrual cycle.
Q.13. How the corpus luteum is formed?
Ans : After ovulation the luteal phase starts where the remaining parts of the Graffian follicle transform as the corpus luteum.
Q.14. What happens to corpus luteum in absence of fertilization?
Ans : In absence of fertilization the corpus luteum degenerates.
Q.15. Define menopause.
Ans : The ceasing of the menstrual cycle at a particular age is known as menopause.
Q.16. Name the secretion of corpus luteum.
Ans : The recreation of the corpus luteum is known as proges terone which is a hormone.
Q.17. What is fertilization?
Ans :The process of fusion of sperm of male with the ovum of a female is known as fertilization.
Q.18. You studied the chromosome of a human and found that there present two identical sex chromosomes. What will be the sex of the individual?
Ans : As there found two identical sex chromosome so the sex of the individual will be female.
Q.19. How many sex chromosome is present in the sperm?
Ans : Sperm contains haploid number i.e. half the number of chromosome present in the organisms somatic cells.
Q.20. What are two layers of cells found in the blastocyst.
Ans : The outer layer of the blastocyst is called trophoblast and the inner is inner cell mass.
Q.21. Name an organ which is formed of tissues of two different individuals.
Ans : Placenta.
(D) Short Answer Questions (Two Marks Each):
Q.1. What is the significance of presence of testes within scrotum?
Ans : The scrotum helps in maintaining the low temperature of testes which is 2-2.5°C lower than the normal internal body temperature of necessary for spermatogenesis.
Q.2. Write the functions of two types of cells found within the seminiferous tubule.
Ans : The two types of cells found within the seminiferous tubules are:
(i) Male germ cells that gives rise to sperm.
(ii) Sertoli cells which provide nutrition to germ cells.
Q.3. Name the different events of reproduction occur in human.
Ans : The different events of reproduction occur in human are :
(i) Formation of male and female gametes.
(ii) Transfer of sperms into the female genital tract.
(iii) Fusion of male and female gametes.
(iv) Formation and development of blastocyst.
(v) Implantation.
(vi) Gestation.
(vii) Parturition.
Q.4. What is Leydig cell? State its function.
Ans : The regions outside the seminiferous tubule is called interstitial spaces that contain small blood vessels and interstitial cells or leydig cells. Leydig cells synthesise and secrete testicular hormones called androgens.
Q.5. State the function of FSH and LH.
Ans : (i) Follicular stimulating hormone (FSH) acts on the sertoli cells and stimulates secretion of some factors which help in the process of spermiogenesis.
(ii) Luteinizing hormone (LH) acts at the leydig cells and stimulates synthesis and secretion of androgens which in turn stimulate the process of spermatogenesis.
Q.6. State the structure of sperm head.
Ans : A sperm is a microscopic structure composed of a head, neck, a middle piece and a tail. The sperm head contains and elongated haploid nucleus, the anterior portion of which is covered by a cap like structure, acrosome. The acrosome is filled with enzymes that help fertilization of 6. the ovum.
Q.7. Why unequal division of cytoplasm occurs during formation of ovum?
Ans : In the process of oogenesis the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division. This division is unequal and results 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.
Q.8. What are the changes that occurred during follicular phase of menstrual cycle in human female.
Ans : The second phase of the menstrual cycle is the follicular phase. During this phase, the primary follicles in the ovary grow to become a fully mature Graffian follicle and simultaneously the endometrium of uterus regenerates through proliferation. These change in the ovary and the uterus are induced by changes in the levels of pituitary and ovarian hormones.
Q.9. Differentiate between menarche and menopause.
Ans :
| Manche | Menopause | ||
| (i) | The first menstruation that begins of puberty is known as Menarche. | (i) | The cessation of menstrual cycle at a particular time period is known as menopause. |
| (ii) | It starts at an age of 10-12 years. | (ii) | It occurs at 50-55 age. |
Q.10. State the functions of progesterone.
Ans :The progesterone hormone secreted by corpus luteum is very much essential for maintenance of the endometrium. Endometrium is necessary for implantation of the fertilized ovum and other events of pregnancy.
Q.11. How implantation of human embryo occurs in the mother uterus?
Ans : After the formation of the blastocyst and the trophoblast layer of the blastocyst gets attached to the endometrium and the inner cell mass gets differentiated as the embryo. After attachment, the uterine cells divide rapidly and covers the blastocyst. This become embedded in the endometrium of the uterus which is known as implementation.
Q.12. State the functions of placenta.
Ans : After implementation, finger placenta appear on the trophoblast which plays an important role during pregnancy. The placenta facilitate the supply of oxygen and nutrients to the embryo and also removal of carbon di oxide and excretory or waste mate rials produced by the embryo. The placenta is connected to the embryo through an umbilical cord which help in the transport of substances to and from the embryo. It also plays as an endocrine gland of secretion different hormones.
Q.13. How placenta is formed?
Ans : After implementation, a finger like projections appear on the trophoblast called chorionic villi which are surrounded by the uterine tissue and maternal blood. This chorionic villi and uterine tissue become interdigitated with each other and jointly form a structural and functional unit between developing embryo and maternal body called placenta.
Q.14. What are Stem cells? Where they are found?
Ans: Stem cells are those cells which have the potency to give rise to all the tissues and organs.
These are found in the inner cell mass of the blastocyst.
Q.15. Why breast-feeding during initial period of infant growth is recommended?
Ans :The milk produced during the initial few days of lactation is called colostrum which contains several antibodies absolutely essential to develop resistance for the new born babies. Breast feeding during the initial period of infant growth is recommended by doctors for bringing up a healthy baby.
Q.16. Describe the luteal phase of the menstrual cycle.
Ans : Luteal phase is also called as progestational or premenstrual or secretory or post ovulatory phase. It lasts for about 12-14 days and extends from 16th th 28th day of the menstrual cycle.
It is characterised by the following changes :
(i) Corpus luteum (yellow body) formed from empty graafian follicles, increases in size, so called luteal phase.
(ii) Corpus luteum secrets progesterone hormone whose level in blood gradually increases and in duces the following changes:
(a) Decreases the secretion of FSH and LH from the anterior pituitary so inhibits the maturation of follicle and ovulation.
(b) Uterine endometrium further proliferates and ready for implantation.
(c) Reduces the uterine movements.
(E) Short Answer Question (Three Marks Each):
Q.1. Describe the male accessory duct system of human.
Ans :The male sex accessory ducts include : Rate testes, vasa efferentia, epididymis and vas deferences. The seminiferous tubules of the testis open into the vasa efferentia through the rate testes. The vasa efferentia leave the testis and open into epididymis located along the posterior surface of each testis. The epididymis leads to vas deference that ascends to the abdomen and loops over the urinary bladder. It receives a from seminal vesicle and opens into urethra as the ejaculatory duct which store and transport the sperms from the testes to the outside through urethra. The urethra originates from the urinary bladder extends through the penis to its external opening called urethral meatus.
Q.2. Draw and label the internal structure of the seminiferous tubules.
Ans :
Q.3. Draw and label the sectional view of the female reproductive system.
Ans :
Q.4. Write a note on the layers of tissues of the wall of the uterus.
Ans : The wall of the uterus has three layers of tissue. The external thr membranous layer is called perinectrium. The middle thick layer of smoot muscle is known as myometrium that exhibits strong contraction during delivery of the baby. The inner glandular layer is called endometrium which line the uterine cavity. The endometrium undergoes cyclical change during menstrual cycle.
Q.5. Draw a neat labeled diagram of a human sperm.
Ans :
Q.6. Distinguish between spermatogenesis and oogenesis.
Ans :
| Spermatogenesis | Oogenesis | ||
| (i) | The process of formation of a male gamete is called spermatogenesis. | (i) | The process of formation of a female gamete is known as oogenesis. |
| (ii) | It occurs in the ovary. | (ii) | It Occurs in the Ovary. |
| (iii) | It starts at puberty. embryonic development. | (iii) | It is started during the. |
| (iv) | No polar body is formed, instead 4 sperms are formed 3 polar bodies are formed. | (iv) | Polar body is formed during oogenesis. Generally |
Q.7. Diagrammatically represents the various events of menstrual cycle.
Ans :
Q.8. Discuss the events of fertilization in man.
Ans : The process of fusion of a sperm with an ovum is called fertilization. During fertilization, at first a sperm comes in contact with the zone 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 fertilize an ovum. The secretion of the acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane and this induces completion of meiotic division results in the formation of haploid ovum. After this the haploid nucleus of the and the ovum fuse together to form zygote.
| Sl. No. | CONTENTS |
| Chapter 1 | Reproduction in Organisms |
| Chapter 2 | Sexual Reproduction in Flowering Plants |
| Chapter 3 | Human Reproduction |
| Chapter 4 | Reproductive Health |
| Chapter 5 | Principles of Inheritance and Variation |
| Chapter 6 | Molecular Basis of Inheritance |
| Chapter 7 | Evolution |
| Chapter 8 | Human Health and Disease |
| Chapter 9 | Strategies for Enhancement in Food Production |
| Chapter 10 | Microbes in Human Welfare |
| Chapter 11 | Biotechnology: Principles And Processes |
| Chapter 12 | Biotechnology and its Applications |
| Chapter 13 | Organisms and Populations |
| Chapter 14 | Ecosystem |
| Chapter 15 | Biodiversity and Conservation |
| Chapter 16 | Bioresources of Assam |
| Chapter 17 | Environmental Issues |
Q.9. State how sex of human is determined?
Ans : The sex of human can be determined in the zygotic stage itself. The chromosome pattern in the human female is XX and that in the male is XY. Therefore, all the haploid gametes produced by the female (ova) have the sex chromosome X whereas in the male gametes (sperms) the sex chromosome could be either X or Y. So 50% of the sperms carry A chromosome while other 50% carry the Y. After fusion the zygote many carry either XX or XY depending on whether sperms carrying X or Y fertilised the ovum the zygote carrying XX would develop into a female body and XY would form a male. So it can be said that the sex of the body is determined by the father and mother is not responsible for this.
Q.10. Discuss briefly the embryonic development up to blastocyst stage.
Ans : The zygote developed after fertilisation moves through the isthmus of the oviduct and at that time mitotic division starts. This process is known a cleavage. The zygote moves towards the uterus and forms 2, 4, 8, 16 daughter cells called blastomeres. The embryo with 8 to 16 blastomeres is called a morula. The morula continues to divide and transforms into blastocyst as it moves further into the uterus.
Q.11. What is parturition? Discuss the process of parturition in human.
Ans : Vigorous contraction of the uterus at the end of pregnancy causes expulsion or delivery of the foetus. This process of the delivery of the foetus is known as parturition.
Parturition in the pregnant female is induced by a complex neuroendocrine mechanism. The signals for parturition origination from the fully developed fetus and the placenta which induce mild uterine contractions called foetal ejection reflex. This triggers release of oxytocin from the maternal pituitary and this acts causes stronger uterine contractions which in turn further secretion of oxytocın. The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger contraction. This leads to expulsion of the baby out of the uterus through the birth canal known as parturition.
Q.12. “Placenta acts as an endocrine tissue”. Justify.
Ans : Placenta not only facilitate the supply of oxygen and nutrients to the embryo and removal of carbon dioxide and waste or excretory materials produced by the embryo but also acts as an endocrine gland by secreting different types of hormones.
The hormone produced by the placenta are human chorionic gonadotropin (hcG), human placental lactogen (hPL), estrogens, progestogens etc. which helps in the fetal growth and in the maintenance of pregnancy.
Q.13. Discuss the role of hormones in menstrual cycle.
Ans : The hormones play a key role in the menstruation cycle are :
(i) FSH-RF of hypothalamus stimulates the secretion of FSH from the anterior pituitary gland.
(ii) FSH stimulates the changes of primary follicle of the ovary into a graafian follicle.
(iii) Inhibit the secretion of FSH and stimulate the secretion of luteinising hormone (LH) from the anterior pituitary.
(iv) Ovulation is controlled by the increased level of LH in blood.
(v) Decreased the secretion of FSH and LH from anterior pituitary which inhibit the maturation of follicle and ovulation.
(vi) Decrease in the level of progesterone and estrogens in the blood stimulates the hypothalamus and anterior pituitary to release FSH- RF and FSH respectively. FSH starts the follicular phase of next menstrual cycle.
(F). Long Answer Question : (Five Marks Each):
Q.1. Describe the structure of testes with neat labeled diagram.
Ans : The testes are situated outside the abdominal cavity within a pouch called scrotum. The scrotum helps in maintaining the low temperature of the testis necessary for spermatogenesis. In adults each testis is oval in shape, with a length of about 4 to 5 cm and a width of above 2 to 3 cm. The testis is covered by a dense covering. Each testis has about 250 compartments called testicular lobules.
Each lobule contains one to three highly coiled seminiferous tubules in which sperms are produced. Each seminiferous tubule is lined on its inside by two types of cells called male germ cells amd sertoli cells. The male germ cells undergo meiotic division and form sperm while sertoli cells provide nutrition to the germ cells. The interstitial space present in the outside region of the seminiferous tubule contain blood vessels and leydig cells.
Q.2. Describe the female reproductive system in human.
Ans : The female reproductive system consists of a pair of ovaries along with a pair of oviducts, uterus, cervix, vagina and the external genitalia located in pelvic region. These parts of the system along with a pair of mammary glands are integrated structurally and functionally to support the processes of ovulation, fertilization, pregnancy, birth and child care.
Ovaries are the primary female sex organs that produce the female gametes and several steroid hormones. The ovaries are located on each side of the lower abdomen. Each ovary is about 2-4 cm in length and is
connected to epithelium wall and uterus by ligaments. Each ovary is covered by a thin epithelium which encloses the ovarian stroma and it is divided into two zones a peripheral cortex and an inner medulla.
The oviduct or fallopian tube, uterus and vagina constitute the female accessary ducts. Each fallopian tube is about 10-12 cm long and extends from the periphery of each ovary to the uterus. The part closer to the ovary is funnel shaped infundibulum, the edges of which possess fingers like projections called fimbriae while help in collection of ovum after ovulation. The infundibulum leads to an ampulla and the last part of the oviduct is isthmus. The narrow lemon of the isthmus joins the oviduct.
The uterus is also known as womb which is like an inverted pear. It is supported by ligaments attached to the pelvic wall. The uterus opens into vagina through a narrow cervix.
The female external genitalia include mons pubis, labia majora, labia minora, hymen and clitoris.
The diagrammatic view of the female reproductive system is shown below :
Q.3. Give the structure of the mammary gland with neat diagram.
Ans : The characteristics of all female mammals is a functional mammary gland. The glands are paired structures that contain glandular tissue and variable amount of fat. The glandular tissue of each breast is divided into 15-20 mammary lobes containing clusters of cells called alveoli which secrete milk that is stored in the cavities of alveoli. The ovary opens 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.
Q.4. Explain the process of spermatogenesis.
Ans : The process by which sperms are produced in the testes is known as spermatogenesis. It begins at the puberty. The spermatogonia present on the inside wall of seminiferous tubules multiply by mitotic divition and increase number. The spermatogonium is diploid. Some of the spermatogonia called primary spermatocyte periodically undergo meiosis and after completion of first meiotic division two equal haploid cells known as secondary spermatocytes. The secondary spermatocyte undergo second meiotic division to produce four equal haploid spermatids. The spermatids are transformed into spermatozoa or sperms by the process cells spermiogenesis.
Q.5. Describe the role of hormones in initiating spermatogenesis at puberty.
Ans : Spermatogenesis starts at the age of puberty due to significant increase in the secretion of gonadotropin releasing hormone (GNRH). It is a hypothalamic hormone. The increased levels of GnRH hormone acts at the anterior pituitary gland and stimulates secretion of two gonadotropins – Luteinizing hormone (LH) and follicle stimulating hormone (FSH) LH acts at the leydig cells and stimulates synthesis and secretion of androgens. Androgen in turn stimulates and process ofs FSH acts to help in the process of spermatogenesis.
Q.6. Describe the process of development of human embryo since one month of pregnancy.
Ans : Human pregnancy lasts 9 months and during this period of time the embryo undergoes different developmental stages. After one months of pregnancy, the embryo heart is formed. By the end of the second month, the foetus develops limbs and digits. By the end 12 weeks (first trimester), most of the major organ systems are formed like limbs and external genital organs are well developed. The first movement of the foetus and appearance of hair on the head are usually observed during fifth month. By the end of 24 weeks (second trimester), the body is covered with fine hair, eye lids separate and eyelashes are formed. By the end of nine months of pregnancy the fetus is fully developed and is ready to delivery.
Give One Word Technical Term : (Special One Mark Questions)
Q.1. The process by which spermatids are transformed into spermatozoa.
Ans : Spermiogenesis.
Q.2. The fluid filled cavity of the ovarian follicle.
Ans : Antrum.
Q.3. The membrane surrounds the secondary ocyte.
Ans : Zona pellucida.
Q.4. The first mensuration which begins at puberty.
Ans : Menarche.
Q.5. The daughter cells formed by cleavage.
Ans : Blastomere.
Q.6. The milk produced during initial few days of lactation.
Ans :Colostrum.
Q.7. Discuss the process of fertilization in human.
Ans : Fertilization in human involves the fusion of haploid male and female gamete to form diploid zygote. Fertilization in human beings is internal and takes place in the proximal part of the fallopian tube of the female. Fertilization involves the following processes-
(a) Approach of sperm to ovum : During the copulation, male insert his erectile penis in the vagina of female and releases about 3.5 ml of seminal fluid. It is called ejaculation. Seminal fluid contains around 200- 300 million sperms. The acidity of the vagina kills most of the sperms and only 100 sperm can reach the fallopian tube. The sperms can swim in the seminal fluid with lashing movement at the rate of 1-4 mm/minute. The sperms physiologically getting matured in the female genital tract which is called capacitation. It takes about 5-6 hours.
Ovum released from the Graafian follicle of ovary on 15th day of the menstrual cycle and the process is called ovulation. Ovum is traped by the fimbriae of the ampulla of fallopian tube. Ovum moves in the tube towards the uterus by peristalsis. At the time of ovulation egg is at secondary oocyte stage.
The fertilizability of human sperm is the female genital tract is of 12-24 hrs while the survival value is upto three days. Fertilizer liability period of ovum is only 24 hrs though it can live for 72 hrs.
To thin out the number of sperms, the ovum secretes a chemical substance, called fertilizin which has a spermophillic site-where sperms of species specific type can be found by their antifertilizin site. The fertilizin antifertilizin reaction is highly specific and to stop the polyspermy.
(b) Penetration of sperm : The sperm generally comes in contact (9) with ovum in the animal pole while the opposite site of ovum is called vegetative pole. Ovulation in human female occurs at secondary oocyte stage in which meiosis – I has been completed and first polar body has been released. Penetration of sperm is a chemical mechanism. Here, acrosome of sperm undergoes acrosomal reaction and releases sperm lysins which dissolve the egg envelop locally and make a passage for the penetration of sperm. Sperm lysins are acidic protein which contain an enzyme hyaluronidase. Only the sperm nucleus and middle piece enter the ovum. The tail is lost. In human, there is always monospermy.
(c) Cortical reaction: The penetration of sperm into the egg in a series of process where the egg membrane prevents the polyspermy. Sperm penetration into ovum also includes the following metabolic activities.
(i) The rate of protein synthesis increases.
(ii) The rate of respiration also increases.
(iii) The permeability of plasma membrane also increases.
(d) Fusion of gametic nuclei : The sperm entry stimulates the secondary oocyte to undergo meiotic II division which produces the ovum and second polar body. Inside the ovum, the sperm nucleus takes a definite path called copulation path. The centriole of the middle piece form a spindle. The nuclear membrane of the gametic nuclei degenerates and two sets of chromosomes initially lie on two poles and then mix up and this process is called amphimixis. The fertilised egg is new called zygote.
Q.8. Describe pregnancy and embryonic development in human.
Ans : After the fertilization, the fertilized egg undergoes a series of changes that taking place in side the female reproductive tract to form the embryo and this stage is called pregnancy. The pregnancy is mainly maintained by the progesterone hormone, so it is called pregnancy hormone. The embryonic development during pregnancy is discussed bellow:
(i) By the end of one month : Embryo’s heart starts to beat (4th week) and heart sound can be listened. Fore and hind limb develops. Optic vesicles are established. Liper and pancreatic bud is formed.
(ii) By the end of second month : Limbs become paddle like (5th week). Knees and elbows become distinct (8th week). Epidermis become single layered. Fusiform stomach is found with coiled intestine. Metanephros kidneys are formed. Brain, vesicle is formed.
(iii) By the end of third month : Epidermis multilayered, intestinal coil is found, islets of langerhans developed in pancreas, thymus, thyroid and parathyroid developed. External genitalia and limbs well developed. Prostate gland formation starts. Cerebellum and corpus callosum formed.
(iv) By the end of 4th month : Medullated nerve fibre formation begins.
(v) By the end of 5th month : First movement of foetus is found. Eruption of hair on head begin, Vagina canalised.
(vi) By the end of Sixth month : Fine hair on whole body is found. Separation of eye lids and fermentation of eye lashes takes place.
(vii) By the end of Eighth month : Testes descends in the scrotal sacs.
(viii) By the end of Ninth month : Fetus is fully developed and ready for birth.
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