Test: Pregnancy and Embryonic Development (NCERT) - NEET MCQ

Placenta acts as an endocrine gland during pregnancy and produces several hormones including human chorionic gonadotropin (hCG), estrogen, progesterone, etc. hCG stimulates the corpus luteum to secrete progesterone.

• As the zygote is formed, it passes through isthmus towards the uterus.
• Through the passage, it undergoes rapid mitotic divisions.
• This is called cleavage.

Prolactin is secreted by the anterior lobe of pituitary gland. After parturition, secretion and storage of milk in mammary glands is under the influence of this hormone.

• Zygote undergoes cleavage producing an exponential increase in cell mass.
• These new daughter cells formed are called blastomeres.
• They form a blastula with a blastocoel cavity enclosed in between.

During pregnancy, placenta acts as an endocrine gland and secretes some hormones such as estrogen, progesterone, human chorionic gonadotropin (hCG), human placental lactogen (hPL), chorionic thyrotropin, chorionic corticotropin and relaxin.

Placenta is an intimate connection between the fetus and uterine wall of the mother to exchange the materials. Food materials and oxygen pass from the mother's blood into the fetal blood and fetal excretory products diffuse into maternal blood through placenta.

Umbilical Cord  is a flexible, tube-like structure that connects a developing fetus to the placenta during pregnancy. It serves as the lifeline between the mother and the fetus, providing essential nutrients and oxygen to the fetus and removing waste products from the fetal circulation. 

Placental villi or chorionic villi, are tiny, finger-like projections that form the outer layer of the placenta. These villi project into the mother's uterus and play a crucial role in facilitating the exchange of nutrients, oxygen, and waste products between the maternal and fetal bloodstreams. The placenta villi contain fetal blood vessels and are surrounded by maternal blood, allowing for efficient transfer of substances necessary for the developing embryo or fetus.

Yolk Sac is an extraembryonic membrane that is found in the early stages of development in many vertebrates, including humans. Despite its name, it does not function in the same way as the yolk sac in egg-laying animals. In human embryonic development, the yolk sac plays a role in supporting the early embryo by providing some of its initial nutrients and aiding in the formation of blood cells.

Embryo is the early stage of development of a multicellular organism, typically following fertilization and preceding the more advanced fetal stage. In humans, the embryonic stage occurs during the first eight weeks of pregnancy, after which the developing organism is referred to as a fetus. During this stage, the embryo undergoes rapid growth and differentiation, with the formation of various essential organ systems.

• Inner cell mass is the internal layer of blastomere.
• Upon attachment of blastomere, the inner cell mass undergoes differentiation to form the embryo.

Transformation of the blastocyst into gastrula with primary germ layers by rearrangement of the cells is called gastrulation. In all the triploblastic animals three germ layers-ectoderm, mesoderm and endoderm are formed by characteristic morphogenetic movements.

During pregnancy, human chorionic gonadotropin hormone is released by trophoblastic cells which passes out in urine. Thus, if this hormone appears in urine test, it means the woman is pregnant. This hormone maintains the corpus luteum and stimulates it to secrete progesterone which is required for the maintenance of the uterus.

• Fertilization is the fusion of male and female gametes.
• Cleavage is the rapid divisions that lead to the formation of a zygote.
• Implantation is the process that leads to the covering of the blastomere by the uterine endometrium.

Umbilical cord is a narrow. Tube like structure that connects the fetus to the placenta. Through this tube, nutrients and oxygen are supplied from the mother to the baby and waste products are removed from the baby,.

After fertilisation, the zygote undergoes the process of cleavage to form a number of cells which ultimately undergo the process of differentiation and then form tissues, organ and lastly organ systems.

• Limbs and digits, along with external genitalia, are formed during the first trimester.
• This is a period of 12 weeks after pregnancy.

• Trimesters are periods of three months’ post-pregnancy.
• Fetal movements can be observed starting five months’ post-pregnancy i.e., during the second trimester.