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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
(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
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