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The study of prenatal development


consists of three primary germ layers called ectoderm, mesoderm and endoderm


most common site of fertilization

movement from vagina

movement from vagina: cervical canal-> uterus->uterine tube. Must meet egg in upper 1/3 of uterine tube.


Sperm cannot fertilize an egg for about 10 hours. While migrating, sperm must undergo a process of _____ that makes it possible to penetrate an egg. In fresh sperm, the plasma membrane is toughened by cholesterol. This prevents the premature release of acrosomal enzymes while sperm are still in the male, and thus avoids wastage of the sperm.


genetic material from sperm & secondary oocyte merges into single diploid zygote in uterine tube


Fertilization by two or more sperm

fast block

oocyte membrane depolarizes so another sperm can't fuse

slow block

creates an inpenetrable membrane btwn egg & zone pellucida

Dizygotic Twins

fraternal; produced by release of 2 secondary oocytes & fertilization by separate sperm

Monozygotic Twins

identical; develop from a single fertilized ovum

preembryonic stage

first 16 days of the development, culminating the existence of an embryo.

Cleavage of zygote

1st step in preembryonic stage; rapid mitotic cell divisions; makes morula (sold sphere of cells)

Blastocyst Formation

2nd step; morula moves thru tubes to uterus; forms blastocyst


The process of attachment when the blastocyte adheres to the endometrium usually on the fundus or the posterior wall of the uterus. (6 days after ovulation)

embryonic stage

begins when all 3 primary germ layers are present after gastrulation


arrangement of the blastomeres into three primary germ layers: ectoderm, mesoderm, and endoderm.

amniotic cavity

space btwn embryoblast & trophoblast


multiplying epiblast cells migrate medially toward the primitive groove and down into it.


process where germ layers differentiate into organs and organ systems

accessory organs

a placenta, umbilical cord, and four embryonic membranes called the amnion, yolk sac, allantois, and chorion.


transparent sac that develops from cells of the epiblast. It grows to completely enclose the embryo and is penetrated only by the umbilical cord.

amniotic fluid

protects the embryo from trauma, infection, and temperature fluctuations; allows the freedom of movement important to muscle development; enables the embryo to develop symmetrically; prevents body parts from adhering to each other, and stimulates lung development as the fetus "breathes" the fluid.

yolk sac

small sac suspended from the ventral side of the embryo. It contributes to the formation of the GI tract and produces the first blood cells and future egg of sperm cells

placental nutrition

nutrients diffuse from the mother's blood through the placenta into the fetal blood.


disc-shaped organ attached to the uterine wall on one side and on the other side, attached by way of an umbilical cord to the fetus.

placental phase

The placenta begins to develop about 11 days after conception, becomes the dominant mode of nutrition around the beginning of week 9, and is the sole mode of nutrition from the end of week 12 until birth. The period from week 9 until birth is called WHAT of the pregnancy.

placental sinus

The development of the placenta, or placentation. Roots (villi) during this penetrate uterine blood vessels. They become surrounded by luacunae, or endometrial spaces filled with maternal blood. The lucunae eventually merge to form a single blood-filled cavity, the WHAT. Exposure to maternal blood stimulates increasingly rapid growth of the villi. Villi gives rise to the blood vessels that connect to the embryo by way of the umbilical cord.

umbilical arteries

The umbilical cord contains two of these

Umbilical veins

the umbilical cord contains one of these


Oxygen and nutrients pass from the maternal blood to the fetal blood, while fetal wastes pass the other way to be eliminated by the mother; also permeable to nicotine, alcohol, and most other drugs that may be present in the maternal bloodstream.


final stage of prenatal development

ductus venosus

leads directly to the inferior vena cava

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