31. Why can the amnion also be considered an adaptation to terrestrial life?
The amnion is also an adaptation to dry land since one of its functions is to prevent desiccation of the embryo.
32. 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?
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.
33. In which type of animals does the placenta exist? What is its main function?
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 the mother’s body.
Image Diversity: placenta placental mammals
34. What are the main substances transferred from the mother to the fetus through the placenta and from the fetus to the mother?
From the mother to the fetus the main transferred substances through the placenta are water, oxygen, nutrients, and antibodies. From the fetus to the mother, metabolic wastes including urea (nitrogen waste), and carbon dioxide are transferred.
35. Is there exchange of cells between the mother and the fetus through the placenta?
Under normal conditions, there is no passage of cells across the placenta during gestation. The placenta has a smooth mucosa separating the richly vascularized region in contact with the mother’s endometrium from the umbilical cord in contact with the fetal blood. This barrier is known as placental barrier. Although permeable to some substances (selective permeability), the placental barrier forbids the passage of cells.
Image Diversity: umbilical cord placental barrier
36. What are the endocrine functions of the placenta?
The placenta has endocrine function since it secretes the hormones progesterone and estrogens that maintain the endometrium (internal covering of the uterus) and prevent menses during pregnancy. The placenta also secretes other important hormones for pregnancy regulation.
37. What is the function of the umbilical cord?
The umbilical cord is a set of blood vessels that connect the fetus with the placenta. In the fetus, one extremity of the cord inserts into the center of the abdominal wall (the later scar of this insertion is the umbilicus).
38. What are the three types of germ layers that form tissues and organs in animals?
The three germ layers are the ectoderm, the mesoderm, and the endoderm.
39. How is the mesoderm (third germ layer) of triploblastic animals formed?
The mesoderm appears from differentiation of endodermal cells that cover the dorsal region of the archenteron.
40. What are the archenteron and the blastopore? What is the stage of the embryonic development in which these structures are formed? What are the destinations of the archenteron and of the blastopore?
Archenteron is the tube formed during gastrulation by means of invagination of the blastula wall inside the blatocele. It is the origin of the gastrointestinal tract. Blastopore is the opening of the archenteron to the exterior. The blastopore gives birth to one of the extremities of the digestive tube: the mouth in protostome beings, or the anus in deuterostome beings.
The amnion is also an adaptation to dry land since one of its functions is to prevent desiccation of the embryo.
32. 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?
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.
33. In which type of animals does the placenta exist? What is its main function?
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 the mother’s body.
Image Diversity: placenta placental mammals
34. What are the main substances transferred from the mother to the fetus through the placenta and from the fetus to the mother?
From the mother to the fetus the main transferred substances through the placenta are water, oxygen, nutrients, and antibodies. From the fetus to the mother, metabolic wastes including urea (nitrogen waste), and carbon dioxide are transferred.
35. Is there exchange of cells between the mother and the fetus through the placenta?
Under normal conditions, there is no passage of cells across the placenta during gestation. The placenta has a smooth mucosa separating the richly vascularized region in contact with the mother’s endometrium from the umbilical cord in contact with the fetal blood. This barrier is known as placental barrier. Although permeable to some substances (selective permeability), the placental barrier forbids the passage of cells.
Image Diversity: umbilical cord placental barrier
36. What are the endocrine functions of the placenta?
The placenta has endocrine function since it secretes the hormones progesterone and estrogens that maintain the endometrium (internal covering of the uterus) and prevent menses during pregnancy. The placenta also secretes other important hormones for pregnancy regulation.
37. What is the function of the umbilical cord?
The umbilical cord is a set of blood vessels that connect the fetus with the placenta. In the fetus, one extremity of the cord inserts into the center of the abdominal wall (the later scar of this insertion is the umbilicus).
38. What are the three types of germ layers that form tissues and organs in animals?
The three germ layers are the ectoderm, the mesoderm, and the endoderm.
39. How is the mesoderm (third germ layer) of triploblastic animals formed?
The mesoderm appears from differentiation of endodermal cells that cover the dorsal region of the archenteron.
40. What are the archenteron and the blastopore? What is the stage of the embryonic development in which these structures are formed? What are the destinations of the archenteron and of the blastopore?
Archenteron is the tube formed during gastrulation by means of invagination of the blastula wall inside the blatocele. It is the origin of the gastrointestinal tract. Blastopore is the opening of the archenteron to the exterior. The blastopore gives birth to one of the extremities of the digestive tube: the mouth in protostome beings, or the anus in deuterostome beings.
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