Q.Explain "Gastrulation".
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After implantation, the trophoblast develops chorionic villi that interdigitate with maternal endometrial tissue and are bathed in maternal blood, forming the placenta, connected to the foetus by the umbilical cord (two arteries, one vein); maternal and foetal blood do not normally mix, exchange occurring by diffusion/active transport across the villi. The placenta supplies nutrients, exchanges respiratory gases, removes foetal wastes, and acts as a temporary endocrine gland secreting hCG (maintains the c …
After cleavage produces the simple blastula, the embryo must reorganise its cells into distinct layers before any organ can begin to form, and this reorganisation step is what gastrulation refers to. …
Gastrulation converts the simple blastula into a three-layered gastrula, the foundation for all later organ formation.
After cleavage produces the blastocyst/blastula, the embryo undergoes gastrulation — a series of coordinated cell movements (invagination, involution, migration) that reorganise the single layer of blastula cells into three distinct germinal layers:
- Ectoderm (outer layer) — gives rise to skin/epidermis and the nervous system.
- Mesoderm (middle layer) — gives rise to muscles, skeleton, circulatory system, kidneys, gonads.
- Endoderm (inner layer) — gives rise to the lining of the gut and associated organs (liver, pancreas, lungs). …
Showing the 12 most recent of 31 on this concept.
- CBSE 2026Set A1 markMCQQ.After how many months of pregnancy does the limbs and digits of foetus develop?(a) One month(b) Two months(c) Three months(d) Six months
›Reveal solutionSolution
Limbs and digits of the foetus develop by the end of the second month of pregnancy.
Human development follows a set timeline. By the end of the first month the heart forms; by the end of the second month the foetus develops limbs and digits; by the end of about 12 weeks (third month) most major organ systems are formed. Fir …
- CBSE 2026Set A1 markMCQQ.Which of the following placental hormones is produced during pregnancy?(a) hCG(b) hPL(c) relaxin(d) all of these
›Reveal solutionSolution
During pregnancy the placenta acts as an endocrine gland, producing hCG, hPL, relaxin (and oestrogens/progestogens).
Besides connecting the foetus to the mother for exchange of nutrients, gases and wastes, the placenta functions as an endocrine tissue. It secretes several hormones, including human chorionic gonadotropin (hCG), human placental lactogen (hPL), relaxin, oestrogens and progestogens …
- CBSE 2026Set ANNUAL1 markQ.Zygote divide to form ............. which is implanted in uterus.
›Reveal solutionSolution
After fertilisation, the zygote undergoes repeated mitotic divisions (cleavage) while moving down the fallopian tube, forming first a morula and then a blastocyst, which gets implanted in the endometrium of the uterus.
The zygote, formed in the ampullary-isthmic junction, undergoes mitotic cleavage divisions as it travels toward the uterus, forming a 2-celled, then 4-celled, then 8-celled embryo, and eventually a solid ball of cells called the morula. The morula continues dividing and develops into a blastocyst, a hollow structure wit …
- CBSE 2026Set SEM31 markMCQQ.Match the Column-I with Column-II : Column-I : i) Sertoli cells ii) Zona pellucida iii) Placenta iv) Uterine endometrium ; Column-II : a) Layer of the ovum b) Spermiogenesis c) Implantation d) Human chorionic Gonadotropin. Choose the correct answer from the options below :(a) i-a, ii-c, iii-b, iv-d(b) i-c, ii-d, iii-a, iv-b(c) i-b, ii-a, iii-d, iv-c(d) i-d, ii-b, iii-c, iv-a
›Reveal solutionSolution
Matching: Sertoli cells support spermiogenesis; zona pellucida is a coat around the ovum; the placenta secretes hCG; the uterine endometrium is the site of implantation — giving i-b, ii-a, iii-d, iv-c.
- i) Sertoli cells → (b) Spermiogenesis: Sertoli (nurse) cells in the seminiferous tubules nourish and support the differentiation of spermatids into sperm (spermiogenesis).
- ii) Zona pellucida → (a) Layer of the ovum: the zona pellucida is a transparent glycoprotein layer surrounding the plasma membrane of the ovum.
- iii) Placenta → (d) Human chorionic Gonadotropin: the placenta (and early chorion) secretes hCG, which maintains the corpus luteum in early pregnancy. …
- CBSE 2025Set X11 markMCQQ.Which one among the following is essential for the maintenance of endometrium and for the implantation of fertilized ovum?(a) Estrogen(b) Progesteron(c) LH and FSH(d) Androgens
›Reveal solutionSolution
Progesterone maintains the endometrium and supports implantation of the fertilized ovum.
After ovulation, the corpus luteum secretes large amounts of progesterone, which is essential for the maintenance of the endometrium (uterine lining). A maintained, secretory endometrium is necessary for the implantation of the fertilized ovum and for the continuation of pregnancy. Estrogen promotes proliferation of the endometriu …
- CBSE 2025Set F1 markMCQQ.Which of the following cannot pass through placenta?(a) Alcohol(b) Fatty acids(c) Iron(d) Maternal antibodies
›Reveal solutionSolution
The placenta readily passes alcohol, iron and maternal antibodies; it does not directly transfer maternal fatty acids/fats, so fatty acids is the best "cannot pass" answer.
The placenta is a selectively permeable barrier connecting the developing foetus to the mother. Several substances are well documented to cross it: alcohol crosses freely and can cause foetal alcohol syndrome; iron is transferred (receptor/transferrin-mediated) to build the foetal iron store; and maternal IgG antibodies cross the placenta to give the foetus passive immunity (this is explicitly noted in NCERT). Bulk mate …
- CBSE 2025Set F1 markMCQQ.The opening of which of the following is known as blastopore?(a) Gastrula(b) Morula(c) Blastula(d) Neural
›Reveal solutionSolution
The blastopore is the opening seen in the gastrula stage of the embryo.
During embryonic development, the blastula (a hollow ball of cells) undergoes gastrulation to form the gastrula, which has the primary germ layers and a primitive gut cavity called the archenteron. The opening of this archenteron to the …
- CBSE 2025Set ANNUAL1 markQ.Fill in the blank: The structural and functional unit formed between embryo (foetus) and maternal body is called ___.
›Reveal solutionSolution
The placenta is the structural and functional link between the developing foetus and the mother.
The placenta is formed by the intimate fusion of the foetal chorionic villi with the uterine (maternal) tissue. It is a highly vascularised structure through which nutrients, oxygen and other required substances are transported from mother to foetus, while carbon dioxide and excretory/waste subst …
- CBSE 2025Set ANNUAL1 markMCQQ.Human chorionic gonadotropin (hCG) is secreted by(a) Corpus Luteum(b) Placenta(c) Mammary gland(d) Ovary
›Reveal solutionSolution
Human Chorionic Gonadotropin (hCG) is a hormone secreted by the placenta soon after implantation, and its presence in blood/urine is the basis of pregnancy tests.
After implantation of the blastocyst, the developing chorionic villi (part of the placenta) start secreting hCG. This hormone signals the corpus luteum in the ovary to continue secreting progesterone, which maintains the endometrium and supports the pregnancy …
- CBSE 2025Set ANNUAL1 markQ.The structure that provides vascular connection between the foetus and uterus is called _________.
›Reveal solutionSolution
The placenta, connected to the embryo by the umbilical cord, is the structural link that allows exchange of nutrients, oxygen and waste between maternal and foetal blood.
After implantation, finger-like chorionic villi develop and, along with the surrounding uterine (endometrial) tissue, form a specialised structure called the placenta. The placenta is connected to the embryo through an umbilical cord, which contains blood vessels carrying blood between the foetus and the placenta. The placenta facilitates the supply of oxygen and nutrients to the embryo and the removal of carbon dioxide and excretory/w …
- CBSE 2025Set ANNUAL1 markMCQQ.Hormones secreted by the placenta to maintain pregnancy are(a) HCG, HPL, progesterone, prolactin(b) HCG, HPL, estrogens, relaxin(c) HCG, HPL, estrogens, progesterone(d) HCG, progesterone, estrogen, glucocorticoids
›Reveal solutionSolution
The placenta secretes hCG, hPL, estrogens, and progesterone, together maintaining pregnancy.
The placenta, in addition to its role in nutrient/gas exchange between mother and foetus, functions as a temporary endocrine gland during pregnancy, producing several hormones required to maintain the pregnancy:
- hCG (human Chorionic Gonadotropin) — maintains the corpus luteum, ensuring continued progesterone secretion, especially in early pregnancy.
- hPL (human Placental Lactogen) — a hormone with growth-hormone-like effects, contributing to maternal metabolic adaptations.
- Estrogens — rising levels help prepare the body for parturition and lactation.
- Progesterone — essential to maintain the uterine endometrium in a state suitable for the ongoing pregnancy. …
- CBSE 2024Set 57/1/11 markMCQQ.Which one of the following hormones is secreted by the human placenta that helps in the maintenance of pregnancy? (A) Relaxin (B) Human Chorionic Gonadotropin (C) Oxytocin (D) Human Placental Lactogen
›Reveal solutionSolution
The human placenta secretes Human Chorionic Gonadotropin (hCG), which is crucial for maintaining the corpus luteum and thus the pregnancy in its early stages. The correct option is (B).
The maintenance of pregnancy is a complex process heavily reliant on a delicate balance of hormones. The placenta, a temporary organ formed during pregnancy, plays a central role not only in nutrient and gas exchange but also as a major endocrine gland, producing hormones essential for the continuation of pregnancy and fetal development. Understanding which hormones are produced by the placenta and their specific functions is key to grasping the physiological mechanisms of gestation.
Here's a breakdown of the hormones mentioned and their roles:
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Understanding the Role of the Placenta in Pregnancy Maintenance:
Initially, after ovulation, the corpus luteum (formed from the ruptured follicle in the ovary) produces progesterone and estrogen. These hormones are vital for maintaining the uterine lining (endometrium) and preventing its shedding, which would lead to menstruation and loss of the embryo. If pregnancy occurs, the corpus luteum must be sustained until the placenta is fully developed and can take over hormone production. This is where a specific placental hormone becomes critical.
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Analyzing Option (A) Relaxin:
Relaxin is indeed secreted by the placenta (and also by the corpus luteum). Its primary function is to relax the pelvic ligaments and soften the cervix, particularly towards the end of pregnancy, to facilitate childbirth. While important for the overall process of pregnancy and delivery, its direct role in the maintenance of pregnancy, especially in the early stages to prevent miscarriage, is not as central as other hormones.
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Analyzing Option (B) Human Chorionic Gonadotropin (hCG):
This hormone is secreted by the trophoblast cells of the developing placenta shortly after implantation. Its most critical role in the maintenance of pregnancy is to rescue and sustain the corpus luteum. hCG is structurally similar to Luteinizing Hormone (LH) and binds to LH receptors on the corpus luteum, stimulating it to continue producing progesterone and estrogen. Without hCG, the corpus luteum would degenerate, progesterone levels would drop, and the uterine lining would be shed, leading to menstruation and termination of the pregnancy. This makes hCG absolutely vital for the early maintenance of pregnancy. It is also the hormone detected in pregnancy tests.
ImportanthCG is the primary hormone responsible for maintaining the corpus luteum, which in turn produces progesterone and estrogen to sustain the uterine lining and prevent early pregnancy loss.
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Analyzing Option (C) Oxytocin: …
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