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Embryology
The study of prenatal development
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Prenatal development consists of what three distinct periods
- the preimplantation period
- the embryonic period
- the fetal period
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What prenatal periods make up the first trimester of the pregnancy
The preimplantation period and the embryonic period
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The first trimester last for how long
8 weeks
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Most of the development of the embryo develops
In the first 9 weeks
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The union of the woman's egg (ovum) and the man's sperm form a
zygote
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When the zygote is formed it contains how many chromosomes
46 23 from mom 23 from dad
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The morula then transforms into a what
Blastocyst or blastula: a hollow ball
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By the end of the first week, the blastocyst stops traveling and
undergoes implantation in the endometrium of the uterus.
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Trophoblast layer
A layer of peripheral cells in the blastula
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Embryoblast
a small inner mass of embryonic cells in the blastocyst
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What group of cells become the future embryo
The embryoblast group of cells will migrate and cluster together
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How long does the pre implantation period last
1 week
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The Embryonic period last from
2nd week to the 8th week
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PROLIFERATION
growth which occurs by the controlled addition of more cells
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interstitial growth
growth which occurs within a tissue
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appositional growth
growth which occurs by addition of layers on the outside of a tissue
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INDUCTION
- the interaction between embryologic cells
- The cells communicate to become different
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DIFFERENTIATION
the change in embryonic cells, which are identical genetically, but become distinct structurally and functionally (transformation of a less specialized cell into a more specialized cell)
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CYTODIFFERENTIATION
–the development of different cell types
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HISTODIFFERENTIATION
–the development of different tissues
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MORPHODIFFERENTIATION
- –the development of differing form or structure
- a change in shape
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MORPHOGENESIS
is the process of development of specific tissue structure which occurs due to migration of embryonic cells and induction of these cells
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MATURATION
is the final process which begins during the embryonic period and continues during the fetal period where the tissue attains adult function and size due to proliferation, differentiation and morphogenesis
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bilaminar embryonic disc
a two-layered, flattened plate of cells
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The top layer of cells in the bilaminar embryonic disc is the
epiblast and is composed of high columnar cells
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The lower layer of the bilaminar embryonic disc is the
hypoblast and is composed of small cuboidal cells.
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The epiblast layer will become the
ectoderm
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The hypoblast layer will become the
endoderm
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When the bilaminar disc becomes suspended in the endometrium the ______ faces the ectoderm and the _____ faces the endoderm layer
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Yolk sac
serves as the initial nutrient for the embryonic disc
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During the third week of prenatal development what forms within the epiblast layer
primitive streak
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During the third week of prenatal development where do some cells migrate to form the mesoderm
epiblast
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Mesenchyme cells
have the ability to differentiate into the different connective tissue cells, such as fibroblasts, chondroblasts and osteoblasts
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What kinds of tissue originate from the ectoderm layer
skin, nerve tissue, lining of mouth
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What kind of tissue originate from the endoderm layer
lining of the digestive tract
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What kind of tissue originate from the mesoderm layer
Bone, cartilage, blood, collagen, muscle, kidney, heart
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When does the central nervous system begins to develop in the embryo
During the last part of the third week
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During the development of the central nervous system cells differentiate from the ectoderm called
- neuroectoderm
- They are localized to the neural plate of the embryo
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The neural plate
a band of cells that runs the length of the embryo on the dorsal surface
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The neural plate undergoes deepening and invaginate centrally to form the
the neural groove
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The neural groove becomes surrounded by
neural folds
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By the beginning of the 4th week, the neural groove deepens to form
a neural tube
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The neural tube fuses and becomes the
future spinal cord
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Specialized group of cells that develop from neuroectoderm
neural crest cells
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somites
38 paired cuboidal aggregates of cells that differentiates from the mesoderm
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Where are the somites located
on each side of the developing midline portion of the central nervous system
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The somites give rise to
most of the skeletal structures of the head, neck and trunk, as well as the associated muscle and dermis of the skin
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During that week does the disc undergoes embryonic folding, into an embryo
During the fourth week of prenatal development
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After the embryonic folding where do the germ layer lie
the endoderm lies inside the ectoderm with mesoderm filling in the the areas between the 2 layers
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The oropharyngeal membrane consists of
ectoderm externally and endoderm internally.
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The oropharyngeal membrane is the location of the
location of the future primitive mouth (stomodeum) and the beginning of the digestive tract
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pharyngeal arches or branchial arches
four pairs of arches that form on the lateral walls lining the pharynx during the development of the digestive tract
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During what week does the face and neck begin to develop with the primitive eyes, ears, nose, oral cavity and jaw areas
4th week
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teratogens
- substances that may cause major congenital malformations of the embryo
- consist of environmental factors such as infections, drugs/alcohol and radiation
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Also known as German measles
- rubella virus
- This infection in the embryo can result in cataracts, cardiac defects and deafness
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Syphilis infection can result in
defects in the incisors and molars
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