Flashcards in Reproduction Deck (88):
During ejaculation, _____ sperm are ejected into the vagina, but _____ due
to leakage, destruction, or inability to penetrate the mucus of the cervix.
several hundred million; most
In order to be fertilized, the secondary oocyte must encounter a sperm within _____ of
ovulation. (Sperm can live in the female reproductive tract for up to _____.)
12 to 24 hours; 1 to 3 days
The secondary oocyte is protected by two structures, a cluster of cells called the _____
and a clear glycoprotein coat called the _____.
corona radiata; zona pellucida
To penetrate the egg, the acrosome of sperm must _____ to release _____. To prevent
early release, each sperm's acrosome is inactive until _____.
rupture; digestive enzymes;
long after it enters the vagina
The acrosomes of sperm cannot rupture until they are exposed for several hours to fluids
in the vagina, uterus, and fallopian tubes. This preparation of the acrosome for use is
Only one sperm will actually fertilize the egg, but that one sperm needs the help of many
others in order to _____ so that it can reach the egg. Essentially, the egg's defenses fail
when attacked by hundreds of sperm.
dissolve the zona pellucida
The membrane covering the acrosome contains receptors which bind to proteins of the
zona pellucida. This binding triggers the _____, which causes the _____.
acrosomal reaction; release of
The first sperm to penetrate the zona pellucida will bind to a receptor on the oocyte's
membrane. This triggers two events: the first sperm _____, and other sperm are _____.
enters the oocyte's cytoplasm;
blocked from entry
There are two mechanisms which prevent more than one sperm from entering an oocyte.
The first is the _____, which occurs when the membrane of the _____ and prevents
similar binding by other sperm cells.
fast block to polyspermy;
The _____ block to polyspermy results in the release of _____, which are specialized
vesicles. This leads to the denaturation of the zona pellucida's proteins, including _____.
slow; cortical granules; the
receptors to which sperm bind
The entry of the sperm into the oocyte causes the oocyte to activate. As a result, it _____,
becoming the _____ and producing a small, cytoplasm-free cell, the second polar body.
(Recall that the first one was produced during _____.)
finishes meiosis II; ovum;
Inside the oocyte, the sperm's head and tail separate. The sperm's nucleus swells to form
the _____, and migrates to the center of the ovum where it joins with the _____ (which
was formed when the oocyte completed meiosis II).
male pronucleus; female
It's not until the male and female _____ fuse to form a diploid nucleus that the joined
sperm and egg can be called a(n) _____ (which means _____).
pronuclei; zygote; fertilized,
Fertilization usually occurs in the _____ or _____ of the uterine tube; cell division begins
there, and continues until the growing mass of cells _____.
infundibulum; distal ampulla;
implants in the wall of the
Almost immediately after fertilization, the zygote begins to _____; a small, berry like
structure called the _____ is formed by day 3, and a hollow ball of cells called the _____
has been formed by day 4.
divide rapidly; morula;
The formation of the blastocyst is called _____.
During pre-embryonic development, mitosis and cytokinesis occur without _____. This
process is called _____. As a result, the entire blastocyst, which contains ~100 or so cells,
is roughly _____ .
growth between divisions;
cleavage; the same size that
the ovum was
The blastocyst is a hollow ball. The outer wall is the _____, and the cluster of cells inside
is the _____.
trophoblast; inner cell mass
The cells of the _____ are still pluripotent, and can form any tissue or even complete
inner cell mass
The trophoblast will eventually develop into the _____, while the inner cell mass will
eventually form one or more _____.
placenta and supporting
The _____ reaches the uterus around four days after ovulation. It remains there as the
_____ breaks up, during which time it is nourished by uterine secretions.
blastocyst; zona pellucida
Implantation begins about 6–7 days after ovulation; in this process, the cells of the
trophoblast which are closest to the inner cell mass _____. This process continues until
the blastocyst is _____, and takes several days.
digest their way into the
To prevent menstruation, the cells of the blastocyst release _____ for the first _____
months of pregnancy. This promotes the survival of the corpus luteum until the placenta is
mature enough to produce large amounts of _____ and _____.
human chorionic gonadotropin
(hCG); four; progesterone;
High levels of estrogen and progesterone can cause an unpleasant side effect in the early
months of pregnancy: _____.
The placenta is a temporary organ which forms in the uterus to allow the blood of the
mother and the unborn child to _____. It also acts as a(n) _____ to shield the fetus from
at least some harmful substances.
exchange chemicals and gases
without mixing; filter
Before implantation, the boundary between the inside of the blastocyst and the outside is
a single layer of cells called the _____. Eventually, cell division and differentiation lead to
a more complex boundary called the _____.
After implantation, trophoblast cells divide rapidly and the outermost cells _____. _____
grow from the surface, and become _____ as surrounding blood vessels are dissolved.
This is the very early _____.
fuse to form a syncytium; Villi;
bathed in maternal blood;
The placenta forms from the _____ and the _____ which lie between the embryo and the
wall of the uterus. The _____ in other regions deteriorate, forming the smooth chorion.
endometrium; chorionic villi;
The placenta is fully functional by _____ .
the 3rd month after fertilization
The _____ connects the developing embryo to the placenta until birth.
The _____ channels blood from the umbilical cord past the fetal liver, directly to the vena
Together, the foramen ovale, ductus arteriosus, and ductus venosus are known as the
The development of ectoderm, mesoderm, and endoderm from the _____ is called _____,
and the embryo is referred to as a(n) _____. All three layers are present roughly _____
inner cell mass; gastrulation;
gastrula; 16 days
Early in gastrulation, a two-chambered ball of cells on a connecting stalk forms. One
chamber is the _____, and the other the _____: the wall between them is the _____, and
will actually form the embryo.
amnion; yolk sac; embryonic
The _____ is a fluid-filled sac which will eventually surround the fetus. At first the fluid is
derived directly from the _____, but by birth much of its volume is _____. It provides
cushioning and support, and _____, during development.
amnion; maternal blood; fetal
urine; room to move
Cells of the yolk sac form the earliest _____, contribute the formation of the _____, and
become the _____ or _____ of the fetus.
blood cells; gut;
A projection formed by the yolk sac, the _____, eventually helps to form the umbilical cord
and its base becomes the _____.
allantois; urinary bladder
The brain and spinal cord begin to form within two weeks of fertilization, a process called
The cerebrum and other brain regions become recognizable roughly _____
after fertilization, although its development is far from complete - the central sulcus, for
example, does not appear until roughly _____ after fertilization.
eight weeks; twenty weeks
A rudimentary circulatory system and a beating heart are present by the start of the _____
Organogenesis is the formation of organs and organ systems; by the end of the _____, all
organ systems are recognizable.
The medical community assumes that the mother will not know which sexual act led to
conception, and calculates fetal age based on the time that has passed since _____.
Developmental biologists, however, calculate age based on the time since _____.
the last menstrual period;
From the beginning of the _____ after conception, when organ systems
are _____, the developing child is no longer an embryo, but is instead called a(n) _____.
9th week; present but not yet
fully functional; fetus
Survival of the fetus outside the mother is not possible until at least _____ weeks after
fertilization, a time referred to as the edge of viability. At this point, major _____ will be
required, and lifelong _____ may result even if the child survives.
22; medical intervention;
Even late in pregnancy, chemicals and disease affecting the mother can still cause _____:
the brain, for example, continues to develop even _____. Chemicals that cause
developmental abnormalities in the developing embryo or fetus are ______.
birth defects; after birth;
The last two months of _____ ('before birth') development include the production of _____
by the lungs, to allow breathing, and the storage of _____ for use as energy and
During pregnancy, the uterus enlarges dramatically: the woman’s center of gravity _____
and an accentuated _____ often results.
shifts forward; lumbar curvature
Heartburn and constipation may result due to _____ and _____ of the GI tract.
Upward pressure of the abdominal organs against the diaphragm as pregnancy reaches
its final stages causes many women to suffer from _____.
difficult breathing OR dyspnea
Near the end of pregnancy, placental production of the hormone relaxin causes _____
and _____ to soften and relax. A side-effect is that _____ of the body also respond.
pelvic ligaments; the pubic
symphysis; other ligaments
The placenta produces _____, which helps to promote the maturation of the breasts for
lactation and shifts the mother's metabolism to burn more fat, sparing glucose for the
human placental lactogen (hPL)
Metabolic wastes are transferred from the fetal blood to the mother's and so the mother's
_____ to cope.
kidneys must produce more
_____ during pregnancy can cause difficulties ranging from discomfort to incontinence.
Uterine pressure on the bladder
Blood volume increases to accommodate the needs of the fetus, leading to increases in
the mother's _____.
blood pressure and heart rate
Parturition is the process of giving birth, and usually occurs between _____ and _____
days after the last menstrual period (LMP).
During the last few weeks of pregnancy, estrogen levels rise, stimulating myometrial cells
of the uterus to form _____, and antagonizing progesterone's inhibition of _____.
oxytocin receptors; uterine
As the time of birth approaches, the fetus usually changes position until _____.
the head is below the feet
Labor is thought to be triggered by the release of _____ by the fetal adrenals, which
causes the placenta to produce _____ which _____, leading to contractions.
irritate the wall of the uterus
Contraction of the uterus pushes the fetus against the cervix. _____ signals the posterior
pituitary to release _____, which further increases uterine contractions.
Stretching of the cervix;
Labor is divided into three stages: the _____, _____ and _____ stages.
dilation; expulsion; placental
The dilation stage of labor extends from onset of labor to the time when _____.
the cervix is fully dilated (about
10 cm in diameter)
At some time during the dilation stage, the amniotic sac will _____ (or a medical care
worker will see that it happens when dilation is nearly complete, if necessary). This is
known as the _____.
rupture; water breaking
Uterine contractions lasting ~ 10 to 30 seconds each generally occur _____
early in the dilation stage of labor.
every 15 to 30 minutes
The dilation stage of labor varies greatly in length, but the average is _____ .
6 - 12 hours
Thinning out and softening of the cervix is called _____ and must occur before or in
conjunction with dilation.
The expulsion stage extends from _____ until the time the infant is delivered. As this
stage approaches, the urge to assist the labor process with _____ becomes intense. (This
urge varies depending on which method is chosen for pain reduction.)
full dilation; the abdominal
Normally, the head is delivered first. Deliveries in which the baby is in another position
may require interventions ranging from _____ to _____.
repositioning; surgical delivery
Surgical deliveries (_____) are sometimes needed (although it is argued by many that
they are not needed nearly so often as they are performed) to ensure that the blood flow
to the fetus is not _____.
Cesarean sections; interrupted
_____ occurs when the infant's head enters the _____ early in the dilation stage of labor.
Engagement; true pelvis
Uterine contractions lasting ~ 1 minute each generally occur _____ during
the expulsion stage of labor.
every 2 to 3 minutes
The expulsion stage of labor is typically_____ in length.
30 minutes to 2 hours
_____ refers to the point in time at which the widest part of the infant's head enters the
_____ during the expulsion stage of labor.
The third and final stage of labor is the _____, in which the placenta and attached fetal
membranes, no longer needed, are expelled.
The newborn baby is called a(n) '_____.'
The placental stage of labor occurs _____ following the birth of the neonate.
within the half hour
Within the first few seconds of postnatal life, _____ will cause it to take the first breath,
inflating the lungs.
rising carbon dioxide levels in
the neonate's blood
Within five minutes of birth in a medical environment, the Apgar score is used to assess
the infant’s physiological status based on _____, _____, _____, _____ and _____.
Appearance; Pulse rate;
Grimacing reflex; Activity;
Within a half an hour after birth, the umbilical arteries and veins close and begin to
fibrose; eventually all that will remain are _____
A flap of tissue covers the foramen ovale: _____, it is sealed to become the _____.
within a year; fossa ovalis
Blood flow through the ductus arteriosus stops within a half hour of birth, and it eventually
becomes the _____.
During pregnancy, high hormonal levels stimulate the growth of the _____ and _____ of
the breasts. In addition, the _____ , presumably to make them easy for the
infant to find.
glandular structure; adipose
tissue; areolae darken and
Prolactin, as its name suggests, promotes _____.
Prolactin production by the anterior pituitary begins before birth, but milk production is
limited until _____ after birth.
estrogen and progesterone fall
The baby's suckling stimulates the nipples to send signals to the hypothalamus, which
responds by causing the posterior pituitary to release _____, and the anterior pituitary to
Oxytocin causes the _____ reflex, resulting in the _____ by both breasts.
let-down; expulsion of milk
For the first few days after birth, the breasts secrete _____ instead of true milk. This fluid
is rich in protein, vitamin A, and protective antibodies which escape digestion in the
newborn's stomach and thus offer protection.
Nursing partially disrupts the _____. However, if nursing is continued, it eventually
resumes (although the timing may initially be irregular).