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Flashcards in biology chapter 4 Deck (28):
1

embryology

is the study of the development of a unicellular zygote into a complete multicellular organism

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fertilization

an egg can be fertilized within 12-24 hours following ovulation. Occurs in the lateral, widest portion of the oviduct when sperm traveling from the vagina encounter an egg.

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cleavage

early embryonic development characterized by a series of rapid mitotic divisions

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indeterminate cleavage

is one that results in cells that maintain the ability to develop into a complete organism

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identical twins

are a result of indeterminate cleavage

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determinate cleavage

results in cells whose future differentiation pathways are determined at an eary developmental stage

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morula

solid ball of embryonic cells

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blastulation

begins when the morula develops a fluid-filled cavity called the blastocoel, which by the fourth day becomes a hollow sphere of cells called the blastula

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gastrula

once implanted in the uterus, cell migrations transform the single cell layer of the blastula into a three-layered structure called this

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ectoderm

integument (including the epidermis, hair, nails, and epithelium of the nose, mouth, and anal canal), the lens of the eye, the retina, and the nervous system

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endoderm

epithelial linings of the digestive and respiratory tracts (including the lungs), and parts of the liver, pancreas, thyroid, and bladder lining

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mesoderm

muscoloskeletal system, circulatory system, excretory system, gonads, connective tissue through the body, and portions of digestive and respiratory organs

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neurulation

by the end of gastrulation, regions of the germ layers begin to develop into a rudimentary nervous system

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notochord

a rod of mesodermal cells develops along the longitudinal axis just under the dorsal layer of ectoderm

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neural tube

which gives rise to the brain and spinal cord (central nervous system)

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neural crest

cells at the tip of each neural fold

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peripheral nervous system

including the sensory ganglia, autonomic ganglia, adrenal medulla, and Schwann cells

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chorion

the chorion lines the inside of the shell. It is a moist membrane that permits gas exchange

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allantois

this sac-like structure is involved in respiration and excretion and contains numerous blood vessels to transport O2, CO2, water, salt, and nitrogenous wastes. Fish eggs do not have an allantois or an amnion

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amnion

this membrane encloses the amniotic fluid. Amniotic fluid provides an aqueous environment which protects the developing embryo from shock

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yolk sac

the yolk sac encloses the yolk. Blood vessels in the yolk sac transfer food to the developing embryo

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first trimester

during the first weeks, the major organs begin to develop. The heart begins to beat at approximately 22 days, and soon afterward, the eyes, gonads, limbs, and liver start to form. By 5 weeks the embryo is 10 mm in length; by 6 weeks the embryo has grown to 15 mm. the cartilaginous skeleton begins to turn into bone by the seventh week. by the end of 8 weeks, most of the organs have formed, the brain is fairly developed, and the embryo is referred to as a fetus. at the end of the third month, the fetus is about 9 cm long

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second trimester

during the second trimester, the fetus does a tremendous amount of growing. It begins to move around in the amniotic fluid, its face appears human, and its toes and fingers elongate. By the end of the sixth month, the fetus is 30-36 cm long

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third trimester

the seventh and eighth months are characterized by continued rapid growth and further brain development. During the ninth month, antibodies are transported by highly selective active transport from the mother to the fetus for protection against foreign matter. the growth rate slows and the fetus becomes less active, as it has less room to move about

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labor

a series of strong uterine contractions that can be divided into three distinct stages

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first stage

the cervix thins out and dilates, and the amniotic sac ruptures, releasing its fluids. During this time contractions are relatively mild

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second stage

characterized by rapid contractions, resulting in the birth of the baby, followed by the cutting of the umbilical cord

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final stage

the uterus contracts, expelling the placenta and the umbilical cord