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Exercise 44

Survey of Embryoic Development

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