Fertilization Flashcards
A prenatal human is considered an____ for the first 8 weeks.
embryo
The embryo in the first week is considered to be in a “______” stage because it has not yet settled into the uterine lining. Some biologists do not consider a prenatal human an embryo until it begins to develop tissue layers, at about 2 weeks.
preimplantation
Prenatal development after the eighth week is the_____ period, when structures grow and specialize.
fetal
From the start of the ninth week until birth, the prenatal human organism is a_____.
fetus
A sperm cell can survive in the woman’s body for up to____ days, but the oocyte can only be fertilized in the ______hours after ovulation.
3 days
12 to 24 hrs
A process in the female called____ chemically activates sperm, and the oocyte secretes a chemical that attracts sperm.
capacitation
Sperm are also assisted by contractions of the female’s muscles and by their moving tails. Still, only____ or so sperm come near the oocyte.
200
A sperm first contacts a covering of follicle cells, called the______ that guards a secondary oocyte.
The sperm’s____ then bursts, releasing enzymes that bore through a protective layer of glycoprotein (the_____) beneath the corona radiata.
corona radiata
acrosome
zona pellucida
_______, begins when the outer membranes of the sperm and secondary oocyte meet
Fertilization, or conception
Within 12 hours of the sperm’s penetration, the ovum’s nuclear membrane disappears, and the two sets of chromosomes, called______, approach one another.
pronuclei
Fertilization completes when the two genetic packages meet and merge, forming the genetic instructions for a new individual. The fertilized ovum is called a_____.
zygote
About a day after fertilization, the zygote divides by mitosis, beginning a period of frequent cell division called______
The resulting early cells-are called______.
cleavage
blastomeres
When the blastomeres form a solid ball of sixteen or more cells, the embryo is called a_____
morula
The ball of cells hollows out, and its center fills with fluid, creating a_____—the “cyst” refers to the fluid-filled center.
Some of the cells form a clump on the inside lining called the_______
blastocyst
inner cell mass
Formation of the_____ is the first event that distinguishes cells from each other in terms of their relative positions, other than the inside and outside of the morula
inner cell mass
A week after conception, the blastocyst begins to nestle into the woman’s uterine lining (endometrium).
This event, called______, takes about a week
implantation
As implantation starts, the outermost cells of the blastocyst, called the_____, secrete the “pregnancy hormone” _________which prevents menstruation. _____ detected in a woman’s urine or blood is one sign of pregnancy.
trophoblast
human chorionic gonadotropin (hCG)
Key Concepts
- Following sexual intercourse, sperm are_____ and drawn to the secondary oocyte.
2.____ enzymes assist the sperm’s penetration of the oocyte. Chemical and electrical changes in the oocyte’s surface block additional sperm.
- The two sets of chromosomes meet, forming a_____.
- Cleavage cell divisions form a____ and then a_____.
- The outer layer of cells invades and implants in the_____
- The______ develops into the embryo.
- Certain blastocyst cells secrete____.
- capacitated
- Acrosomal
- zygote
- morula/ blastocyst
- uterine lining
- inner cell mass
- hCG
During the second week of prenatal development, a space called the_____ forms between the inner cell mass and the outer cells anchored to the uterine lining.
amniotic cavity
The layer nearest the amniotic cavity is the
ectoderm
the inner layer, closer to the blastocyst cavity, is the
endoderm
Shortly after, a third layer, the______, forms in the middle.
mesoderm
The three-layered structure is called the primordial embryo, or the
gastrula
Cells in the____ become skin, nervous tissue, or parts of certain glands.
ectoderm
cells form parts of the liver and pancreas and the linings of many organs
Endoderm
the____, forms many structures, including muscle, connective tissues, the reproductive organs, and the kidneys.
mesoderm
Genes called____ control how the embryo develops parts in the right places
homeotics
As an embryo develops, structures form that support and protect it. These include
chorionic villi
placenta
yolk sac
allantois
umbilical cord
amniotic sac
By the third week after conception, finger-like outgrowths called ____extend from the area of the embryonic disc close to the uterine wall, and these project into pools of the woman’s blood.
chorionic villi
By 10 weeks, the____ is fully formed.
placenta
The_______ is an organ that links woman and fetus for the rest of the pregnancy.
The ______ secretes hormones that maintain pregnancy and alter the woman’s metabolism to send nutrients to the fetus.
placenta
The________ manufactures blood cells, as does the______, a membrane surrounding the embryo that gives rise to the umbilical blood vessels.
The umbilical cord forms around these vessels and attaches to the center of the placenta.
yolk sac
allantois
Toward the end of the embryonic period, the yolk sac____, and the amniotic sac_____ with fluid that cushions the embryo and maintains a constant temperature and pressure.
The_______ contains fetal urine and cells.
shrinks
swells
amniotic fluid
Key Concepts
1.________ form in the second week. Cells in a specific ____ later become parts of particular organ systems as a result of differential gene expression.
- During week 3, ______extend toward the maternal circulation, and the_____ begins to form.
- Nutrients and oxygen enter the embryo, and wastes pass from the embryo into the maternal circulation.
- The ____&_____manufacture blood cells, the umbilical cord forms, and the amniotic sac expands with fluid.
- Primary germ layers
- chorionic villi ; placenta
- yolk sac and allantois
