The cell theory



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[Frequently Asked Questions]
Extra Embryonic Membranes,

Types & Physiology of Placenta
Subject: Zoology
Course: B.Sc. 3rd Year
Paper No. & Title: Z-305B

Developmental Biology
Topic No. & Title: Topic – 5

Extra Embryonic Membranes, Types & Physiology of Placenta

Lecture Title: Extra Embryonic Membranes, Types & Physiology of Placenta

Frequently Asked Questions

Q1. Why is the human placenta designated as haemochorial type of placenta?

A1. As the placental villi are bathed in maternal blood, the human placenta is designated as haemochorial type of placenta.
Q2. What type of cells invades the maternal spiral arteries and reduces the flow of blood from their open ends?

A2. Cytotrophoblast cells.
Q3. What are extra embryonic membranes?

A3. Extra embryonic membranes are membranous structures that appear in parallel with the embryo and play important role in embryonic development. They form from the embryo, but do not become part of the individual organism after its birth.
Q4. What are extra embryonic membranes present in vertebrates?

A4. The extra embryonic membranes that may be present in vertebrates are the yolk sac, the amnion, the chorion, the allantois and the placenta.
Q5. Are the extra embryonic membranes the same in all vertebrates?

A5. The presence of each extra embryonic membrane varies according to the vertebrate class. In fishes and amphibians, only the yolk sac is present. In reptiles and birds, besides the yolk sac, there are also the amnion, the chorion and the allantois. In placental mammals, besides all these membranes the placenta is also present.
Q6. Which is an extra embryonic membrane whose function is to store nitrogen wastes of the embryo? Is this function present in placental mammalian embryos?

A6. The allantois is the extra embryonic membrane whose function is to store the excreted matter of the embryo. In placental mammals, the allantois is present but it does not exert that function, since the embryonic wastes are collected by the mother’s body through the placenta.
Q7. What is the difference between amnion and chorion?

A7. Amnion is the membrane that covers the embryo. Chorion is the membrane that covers the amnion, yolk sac and allantois. The space delimited by the chorion and the amnion is called amniotic activity and is filled with amniotic fluid.
Q8. Why can amnion also be considered as an adaptation to terrestrial life?

A8. The amnion is also an adaptation to dry land since one of its functions is to prevent desiccation of the embryo.
Q9. What is the chorioallantois membrane present in the embryonic development of reptiles and birds? How does this membrane participate in the energetic metabolism of the embryo?

A9. The chorioallantois membrane is formed by juxtaposition of some regions of the chorion and the allantois. Since it is porous, the chorioallantois membrane allows the passage of gases between the embryo and the exterior thus making aerobic cellular respiration possible.
Q10. In which type of animals does the placenta exist? Mention its main function?

A10. True placenta is present in placental mammals. The placenta is formed from the chorion of the embryo and from the mother’s endometrium. Its main function is to allow the exchange of substances between the fetus and mother’s body.
Q11. What are the main substances transferred from the mother to the fetus through the placenta and vice versa?

A11. From the mother to the fetus, the main substances transferred through placenta are water, oxygen, nutrients and antibodies. From the fetus to the mother, metabolic wastes, including urea (nitrogen waste) and carbon dioxide are transferred through placenta.
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