Anatomy lecture 5 Flashcards
➢ Distinguish between the inner cell mass and trophoblast in terms of their developmental potential
o Trophblast:
• At the time of implantation into the uterine wall, the trophobolast will attach to the lining of the uterus (endometrium) and will form two kinds of tissue: a cytotrophblast and a Syncytiotrophoblast.
• The cytotrophoblast consists of a layer of cells on the inside of the blastocyst separated from each other by cell membranes.
• The cytotrophoblast will give rise to the chorion which, in mammals, contributes to the placenta
• The cytorophblost and synctiotrophoblast will combine to form the placenta
o Inner cell mass:
• Cells of the inner cell mass will form the embryo proper as well as additional membranes that surround and support the embryo
• These membranes include the ammion, yolk sac, and allatonic stalk
➢ List advantages for embryos developing in an aquatic environment
o A number of developmental problems are resolved when organisms undergo development in an aquatic environment
• Carbon dioxide and oxygen diffuse readily between the embryo and the environment
• Nitrogenous waste products (usually ammonia) can be readily excreted
• Problem of desiccation (state of extreme dryness) is reduced
➢ List disadvantages for embryos developing in a terrestrial environment
o Keeping cell membranes moist, a must if diffusion is to occur, becomes difficult
o Copious amounts of water are not available to dilute the highly toxic ammonia waste product
o Food for the developing embryo may not be readily available in a terrestrial environment
➢ List the four extraembryonic membranes and functions for each
o Amnion (Composed of ectoderm and mesoderm) • Surrounds the embryo proper except where the yolk sac and allantoic sac are attached • Creates a fluid-filled environment important in protecting the embryo from desiccation
o Chorion (composed of ectoderm and mesoderm)
• Surrounds the embryo as well as other membranes
• Not directly attached to the embryo
• In reptiles and birds, it fuses with allantois to form chorioallantoic membrane which is important for gas exchange
• In mammals, it is involved in the formation of the placenta
o Yolk sac (composed of endoderm and mesoderm)
• Continuous with gut endoderm of the embryo
• In reptiles, birds, and egg laying mammals, the yolk sac contains a massive amount of yolk necessary for nutrition for the developing embryos
• In other mammals, the yolk sac eventually disappears but serves as the preliminary site for the formation of blood cells and germ cells
o Allantois (composed of endoderm and mesoderm) • Projects from gut endoderm of embryo just caudal to yolk sac • In reptiles and birds, the allantois stores nitrogenous waste in the form of uric acid and fuses to the chorion to form the chorioallantoic mbrnae necessary for gas exchange • In mammals, only the proximal part of the allantois is retained; it forms the umbilical cord connecting the embryo to the placenta (chorion)
o Chorioallantoic membrane (fusion of the chorion and allantois)
Remember, birds, reptiles and mammals are considered amniotes
State the function of Amnion
Surrounds the embryo proper except where the yolk sac and allantoic sac are attached
• Creates a fluid-filled environment important in protecting the embryo from desiccation
State the function of Chorion
In reptiles and birds, it fuses with allantois to form chorioallantoic membrane which is important for gas exchange
• In mammals, it is involved in the formation of the placenta
State the function of Yolk sac
In reptiles, birds, and egg laying mammals, the yolk sac contains a massive amount of yolk necessary for nutrition for the developing embryos
• In other mammals, the yolk sac eventually disappears but serves as the preliminary site for the formation of blood cells and germ cells
State the function of allantois
In reptiles and birds, the allantois stores nitrogenous waste in the form of uric acid and fuses to the chorion to form the chorioallantoic mbrnae necessary for gas exchange
• In mammals, only the proximal part of the allantois is retained; it forms the umbilical cord connecting the embryo to the placenta (chorion)
