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A&P 2 Lab pgs46-48
embryology and pregnancy
24
Anatomy
Undergraduate 1
04/19/2013

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Term
unfertilized egg
Definition
showing a large distinct nucleus containing a small, dark, spherical nucleolus
Term
fertilized egg
Definition
a one-celled stage but too opaque to show a nucleus; may be distinguished from blastula due to its being solid and therefore darker than the blastula
Term
two-cell stage
Definition
composed of 2 equal and very evident cells
Term
four-cell stage
Definition
composed of four smaller but evident cells
Term
eight-cell stage
Definition
a solid sphere of eight cells
Term
morula
Definition
3 days of development; ball of cells
Term
blastula
Definition
hollow sphere stage in which the cells form a single layer called the blastoderm; the lighter cavity is called the blastocoel
Term
gastrula
Definition
hollow but with one side invaginated (pushed in); ectoderm, mesoderm, endoderm forming
Term
chorionic sac
Definition
includes the whole complex embryo and extra-embryonic membranes
Term
chorion
Definition
outer extra-embryonic membrane of the chorionic sac; part is thin at either end, whereas the middle portion is a thick band--this representst the cat's fetal placenta
Term
amnion
Definition
delicate, transparent membrane close to the developing cat; between this structure and the developing cat is the amniotic fluid which prevents embryonic dessication and also prevents the embryo from sticking to surrounding tissues
Term
umbilical cord
Definition
links developing cat to the placenta; within this structure are the umbilical vein (carries oxygen and nutrients from placenta to the embryo) and two umbilical arteries (carries wastes such as urea and carbon dioxide from the embryo to the placenta); ceases to function at birth
Term
umbilicus
Definition
spot on the abdomen where the umbilical cord would be attached to the cat
Term
area pellucida
Definition
first evident in 18-hr chick; light central area; region which is free from underlying yolk; area where embryo will develop
Term
area opaca
Definition
first evident in 18hr chick; marginal darker area; representing area attached to the yolk
Term
primitive streak
Definition
first evident in 18hr chick; longitudinal groove bordered by 2 ridges; located in the area pellucida; with continued incubation the embryo will develop in front of this streak
Term
somites
Definition
first evident in 24hr chick; laterally placed segments which develop into such things as muscle, vertebral elements, and inner portions of skin; paired along the midline; number will increase with continued development
Term
neural tube
Definition
first evident in 24hr chick; in midline; will become the brain and spinal cord with further development
Term
proencephalon
Definition
first evident in 33hr chick; cranial enlargement of the neural tube; forebrain; later gives rise to the telencephalon and diencephalon
Term
optic vesicle
Definition
first evident in 33hr chick; lateral bulge of the proencephalon; will become the retina of the eye with further development
Term
mesencephalon
Definition
first evident in 33hr chick; bulblike and immediately behind proencephalon; midbrain
Term
rhombencephalon
Definition
first evident in 33hr chick; narrower than mesencephalon and immediately behind it; provided with a number of minor constrictions; its caudal border is indefinite at this time; hindbrain; later gives rise to metencephalon and myelencephalon
Term
heart
Definition
first evident in 33hr chick; saclike structure bulging to the right at the level of the rhombencephalon
Term
vitelline veins
Definition
first evident in 33hr chick; one on either side behind heart where 2 vessels angle medially and unite; these vessels carry blood into the heart
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