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Exercise 44
Survey of Embryoic Development
| Question | Answer |
|---|---|
| what are the three basic types of activities which are integrated to ensure the formation of a viable offspring | (1) an increase in cell number & subsequent cell growth (2) cellular specialization (3) morphogenesis, the formation of functioning organ systems |
| blastomeres | happens after fertilization has occurred, and the zygote begins o divide, forming a mas of successively smaller & smaller cells |
| cleavage | the series of mitotic divisions wo intervening growth periods ; it provides a large number of building blocks (cells) with which to build the forming body |
| the product of early cleavage is a | solid ball of cells |
| at the 16-cell stage it is called the | morula; the embryo resembles a raspberry in form |
| blastula | when the cell mass hollows out to become the embryonic form; it is a ball of cells surrounding a central cavity; more commonly called the blastocyst in humans (final product of cleavage) |
| ICM; inner cell mass | the cells seen at one side of the blastocyst; only a portion of the human blastocyst cells contribute to the formation of the body |
| trophoblast | the rest of the blastocyst--that portion enclosing the central cavity & overriding the ICM; becomes an extraembryonic membrane called the CHORION, which forms the fetal portion of the placenta |
| the portion of the uterine wall beneath the ICM, destined to take part in placenta formation is called the | decidua basalis |
| what surround sthe rest o fthe blastocyst is called the | decidua capsularis |
| by the time implantation is complete, the blastocyst has undergone what? | gastrulation |
| as a result of gastrulation a 3-layered embryo called a ___ forms | gastrula |
| each of the gastrula's 3 layers corresponds to a _______ from which specific body tissues develop | primary germ layer |
| ectoderm | is the outermostlayer, it gives rise to the epidermis of the skin & the nervous system |
| endoderm | the deepest layer; forms the mucosa of the digestive & respiratory tracts & associated glands |
| mesoderm | the middle layer, forms virtually everything lying between the 2 (skeleton, walls of digestive organs, urinary system, skeletal muscles, circulatory system & others) |
| by the 9th week of development, the embryo is reffered to as a | fetus |
| what is present in the placenta | a composite of uterne tissue & chorionic villi |
| what is going on during the placenta | all exchanges to & from the embryo occur through the chorionic membranes |
| what does the amnion do? | it encases the young embryonic body in a fluid-filled chamber that protects the embryo against mechanical trauma & temperature extremes |
| what does the yolk sac do? | (in humans it has lost its original function); was suppose to pass nutrients to the embryo after digestion the yolk mass; the placenta has taken over that task; embryo's first blood cells originate here & the primordial germ cells migrate from it into the |
| allantois | protrudes from the posterior end of the yolk sac, is also largely redundant in humans bc of the placent |
| umbilical cord | attaches the embryo to the placenta; the structural basis on which the mesoderm migrates to form the body stalk |
Created by:
Brina
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