Anatomy and Physiology Answer Key

2 it is necessary to prevent fertilization of the egg

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Unformatted text preview: . Cleavage is the rapid early cell division of the fertilized egg to produce the ball of cells that will become the blastocyst. Cleavage increases the number of cells but not the size of the zygote. 6. (a) Implantation (of blastocyst) is important to establish the close contact between the developing fetus and the uterine lining. The uterine lining can then provide for the early nourishment of the embryo. (b) Chorion and the allantois. (c) The amniotic sac is filled with fluid and so provides shock absorption for the embryo, cushioning it against damage. (d) Early development of the heart and blood vessels is essential for establishing blood flow around the developing fetus, as well as to and from the placenta (the source of nourishment and waste disposal for the fetus for most of its development). 7. This the period during which most organ development occurs and the developing tissues are most prone to damage from drugs. High levels of estrogen-like compounds in the environment are thought to play a part in the feminizing of males during their sexual development and to somehow adversely influence the production of viable sperm in mature males. The evidence for a link between these female hormones and male infertility is tenuous for humans but convincing for some seabird, marine mammal, and fish species. Fertilization and Early Growth (page 217) 1. (a) Capacitation: Changes in the surface of the sperm cell (caused by the acid environment of the vagina) that make possible its adhesion to the oocyte. (b) Acrosome reaction: The release of enzymes from the acrosome at the head of the sperm. These enzymes digest a pathway through the follicle cells and the zona pellucida. Biozone International 2009 Photocopying Prohibited Anatomy and Physiology 1. 36 The Placenta (page 219) 1. A double layered, spongy, vascular tissue, formed from both fetal and maternal tissues in the wall of the uterus. The fetal portion of the placenta sends fingerlike projections (villi) into the maternal endom...
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