Exam 1 Vocab

small cells formed on oocytes by the two meiotic divisions

Embryo surface where the polar bodies form. Yolk is usually less concentrated here. Location of the polar bodies and oocyte nucleus determine pole location.

side of oocyte or early embryo 180 degreees opposite from the animal pole

Any cell of a cleavage-stage or blastula-stage embryo

stage of development of a sea urchin or amphibian in whihc a hollow cavity forms inside the embryo

hollow (water filled) cavity inside a blastula

active movment of cells from the surface into the interior of a blastula

• embryo in which gastrulation has just begun (not many cells have moved into the interior yet)
• followed by mid and late stages

• inward folding of part of epithelial sheet of cells. Caused by contractoin of the concave ends of the cells (1 theory)
• Sea urchin gasturlation occus by invagination, as do formation of the human lungs

future digestive tract, formed during gastrulation

• opening into the archenteron (NOT connected to the blastopore!)
• in sea urchin embryos, blastopore forms at the vegetal pole
• in frog and salamanders, blastopore forms below the equator (on the side of the embryo that will become the posterior)

small invagination that becomes the mouth. connects to the archenteron. in sea urchin gastrulas i forms near the animal pole

movement of epithelial cells out of an epithelium. they change to mesenchymal. partly caused by weakening of cell-cell adhesion and increased adhesion to extracellular fibers on the side of the epithelium toward which the cells move.

• primary and secondary mesenchyme cells of sea urchins are formed by ingression
• in birds, reptiles, and mammals gastrulation is by ingression instead of by invagination. occurs near the animal pole of reptile and bird eggs

variation of invagination (in frog and salamander gastrulation) in whihc epithelial cells "roll" into the interior of the embryo. Blastopore is a curved slit when formed this way. As the slit elongates, its ends curve downward, eventually meet and form a circle (yold plug stage)

examples: fusion of archenteron with the stomodeum and fusion of one neural fold with the other neural fold

(of masses of mesenchymal cells, to form epithelial tubes or sheets, reorientation of cells to form an epithelial sheet surrounding a water-filled cavity)