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Which structure is derived from the trophoblast?
Which structure is derived from the trophoblast?
What is the primary function of the inner cell mass?
What is the primary function of the inner cell mass?
What is a key characteristic of mammalian eggs, specifically those of Eutheria, after fertilization?
What is a key characteristic of mammalian eggs, specifically those of Eutheria, after fertilization?
During gastrulation, what is the first structure formed?
During gastrulation, what is the first structure formed?
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During cleavage, what happens to the ratio between the nucleus and the cytoplasm?
During cleavage, what happens to the ratio between the nucleus and the cytoplasm?
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What is the name of the structure at the anterior end of the primitive streak where cell migration is most intense?
What is the name of the structure at the anterior end of the primitive streak where cell migration is most intense?
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From which germ layer does the yolk sac primarily originate?
From which germ layer does the yolk sac primarily originate?
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What is the process of complete cell division in early mammalian embryonic development called?
What is the process of complete cell division in early mammalian embryonic development called?
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What is the first stage of gastrulation in mammals?
What is the first stage of gastrulation in mammals?
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At what stage of embryonic development does the blastocoele appear?
At what stage of embryonic development does the blastocoele appear?
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Which of the following does NOT form a germ layer in the gastrula?
Which of the following does NOT form a germ layer in the gastrula?
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What does the term 'morula' refer to in early embryonic development?
What does the term 'morula' refer to in early embryonic development?
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Which part of the blastocyst is responsible for forming the main part of the embryo?
Which part of the blastocyst is responsible for forming the main part of the embryo?
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In the blastocyst, which structure is located on the dorsal side?
In the blastocyst, which structure is located on the dorsal side?
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What is the primary function of the trophoblast?
What is the primary function of the trophoblast?
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Where does fertilization of the mammalian egg typically take place?
Where does fertilization of the mammalian egg typically take place?
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Which extraembryonic membrane directly protects the embryo from mechanical damage and drying?
Which extraembryonic membrane directly protects the embryo from mechanical damage and drying?
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What is the primary contribution of the mesoderm to the formation of the chorion?
What is the primary contribution of the mesoderm to the formation of the chorion?
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In humans, how are the chorionic villi arranged within the uterus?
In humans, how are the chorionic villi arranged within the uterus?
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What is the key function of the placental membrane?
What is the key function of the placental membrane?
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What is the structural composition of the placenta?
What is the structural composition of the placenta?
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Which of these describes the primary function of the umbilical arteries?
Which of these describes the primary function of the umbilical arteries?
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In most mammals, what is the primary role of the allantois?
In most mammals, what is the primary role of the allantois?
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Which of the following is NOT a function of the placenta?
Which of the following is NOT a function of the placenta?
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Study Notes
Mammalian Embryonic Development
- Fertilization and embryo development are internal in mammals
- Eggs of higher mammals (Eutheria) are alecytic (oligolecitic), lacking significant yolk
- Embryonic development stages (cleavage, blastula, gastrula, organogenesis) are common to all multicellular organisms
Cleavage
- Cleavage begins hours after fertilization
- Cleavage transforms a single-celled zygote into a multicellular embryo through mitotic divisions without cell growth
- The nucleus-to-cytoplasm ratio changes during cleavage, with the nucleus size remaining relatively constant by maintaining nucleoplasm quantity
- Cleavage is a key process for initial embryonic cell division
- Cleavage morphology in mammals is total-equal (holoblastic), where all blastomeres are similar in size; this distinguishes it from partial (meroblastic) cleavage observed in some other organisms
- During cleavage, DNA synthesis is intensive, increasing the total amount of embryonic DNA along with the number of cells
- A morula forms when the embryo reaches approximately 16 cells
Blastula
- The morula is a short-lived stage transitioning to the blastocyst
- Cavitation results in a fluid-filled blastocoel (blastocyst cavity), defining the blastula stage
- The blastocyst is the blastula stage in mammals
- The blastocyst consists of two distinct cell types: an outer trophoblast layer and an inner cell mass (embryoblast), demonstrating cell specialization
- The inner cell mass will develop into the embryo itself
- The trophoblast will form the placenta in further embryogenesis
Gastrulation
- Gastrulation is the stage where germ layers form from the undifferentiated blastoderm
- Processes of formation such as invagination, migration, delamination, and epiboly shape the gastrula
- The gastrula, particularly in oligolecitic eggs, undergoes invagination
- Primary germ layers (ectoderm and endoderm) are established during the first gastrulation phase
- Mesoderm forms in the second gastrulation stage, a secondary germ layer
- Gastrulation in mammals involves the formation of a primitive streak for cell migration
- Cell migration is focused in the region of Henzen's node, determining head development
- Three germ layers become visibly distinct in gastrulation cross-sections
Germ Layer Differentiation
- The three germ layers (ectoderm, mesoderm, and endoderm) give rise to various body tissues and organs
- The diagrams demonstrate the specialization and derivation of tissues from each layer
Extraembryonic Membranes
- Yolk sac, amnion, chorion, and allantois are extraembryonic membranes that support the developing embryo
- The yolk sac, derived from the endoderm, doesn't have a significant nutritional role in mammals but is crucial in the early development of blood stem cells.
- The amnion, formed early in embryogenesis, is filled with amniotic fluid providing a protective environment for the growing embryo
- The chorion plays a role in forming the chorionic villi, which connect with the maternal blood vessels
- The allantois develops as an outgrowth of the hindgut and helps with waste removal and gas exchange, though its role in mammals is partially reduced
- In humans, the allantois contributes to the umbilical cord's formation
Chorion
- The chorion is the outermost extraembryonic membrane
- The chorion structure, specifically the chorionic villi, plays a critical role in connecting the mammalian embryo to the maternal tissues in the uterus
- The chorion exhibits various arrangements like cotyledonary, diffuse, discoidal, and zonal
- Chorionic villi penetrate the uterine wall (endometrium), forming the placenta during placental development
Placenta
- The placenta is a fetomaternal organ
- The placenta is composed of fetal (chorionic villi) and maternal tissue
- The placenta acts as a transport system for substances between the fetus and the mother
- Blood from the placenta reaches the fetus via the umbilical vein and returns via the umbilical arteries
- The functions of the placenta include nutrition, gas exchange for the embryo, removal of waste, and secretion of hormones such as estrogen, progesterone, and human chorionic gonadotropin (hCG)
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Description
Test your knowledge on the stages of mammalian embryonic development, including fertilization, cleavage, and the different phases of development. This quiz covers key concepts like holoblastic cleavage and the transformation of the zygote into a multicellular embryo.
