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134 terms

Final Ch 28

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occurs when a sperm's chromosomes combine with those of an egg (secondary oocyte) to form a fertilized egg or zygote, the first cell of the new individual
fertilization
motility must be enhanced and their membranes must become fragile so that the hydrolytic enzymes in their acrosomes can be released, prevents the spilling of acrosomal enzymes
capacitation
Events of fertilization
1) after the sperm penetrates the secondary oocycte the oocyte completes meiosis II, forming the ovum and secondary polar body

2) sperma and ovum nuclei swell, forming pronuclei

3) pronuclei approach each other and mitotic spindle forms between them

4) chromosomes of the pronuclei intermix, fertilization is accomplished, then the DNA replicates in preparation for the first cleavage division
Implantation
1) ovulation of oocyte

2) fertilization (sperm meets and enters egg in the uterine tube)
Zygote (fertilized egg) begins to divide about 24 hrs after and continues the rapid mitotic division of cleavage as it travels down the uterine tube

3) Cleavage
2-cell stage
4-cell stage
8-cell ctage

4)Morula - a solid ball of blastomeres 3 days

3 to 4 days after the embryo reaches the uterus and floats freely for 2 to 3 days

5) early blastocyst - morula hollows out, fills with fluid and "hatches" from the zona pellucida

6) late blastocyst (implantation) - consists of a sphere of trophoblast cells and an eccentric cell cluster called the inner cell mass

7) at the late blastocyst stage the embryo implants into the endometrium
viability of the corpus luteum is maintained by an LH like hormone called
human chorionic gonadotropin (hCG)
usually detected in the mother's blood one week after fertilization, blood levels continue to rise until he end of the second month
hCG
all pregnancy test used today are antibody tests that detect ____ in a woman's blood or urine
hCG
form during the first two to three weeks of development include the amnion, yolk sac, allantois, and chorion
extraembryonic membranes
develops when the cells of the epiblast fashion themselves into the a transparent membranous sac
amnion
this sac, the amnion becomes filled with ____

initially derived from the maternal blood, but as fetal kidneys become functional, fetal urine contributes to volume
amniotic fluid
amnion
as the embryonic disc curves to form the tubular body, the amnion curves with it, eventually the sac extends all the way around the embryo, broken only by the umbilical cord

provides a buoyant environment that protects the developing embryo against physical trauma, help maintain homeostatic temperature, prevents rapidly growing embryonic part from adhering and fusing together, allows embryo freedom of movement
yolk sac
forms from the primitive gut which arranges themselves into a sac that hangs from the ventral surface of the embryo

forms part of the gut

is the source of the earliest blood cells and blood vessels
three primary germ layers
serve as primitive tissues from which all body organs derive

ectoderm - (outer skin) fashions structures of the nervous system and the skin epidermis (epidermis, hair nails, glands of skin, brain and spinal cord, neural crests and derivatives - sensory nerve cells, pigment cells, bones and blood vessels of the head)

mesoderm - (middle skin) forms virtually everything else (notochord - nucleus pulposus of intervertebral discs; somite - sclerotome: vertebrae and ribs, dermatome: dermis of dorsal body region, myotome: trunk and limb musclature; intermediate mesoderm - kidneys, gonads; lateral plate mesoderm - somatic mesoderm: parietal serosa, dermis if ventral body region, connective tissue of limbs (bones, joints, ligaments), splanchric mesoderm: wall of digestive and respiratory tract (except epithelial lining), visceral serosa, heart, blood vessels)

endoderm - (inner skin) forms the epithelial linings of the digestive, respiratory, and urogenital systems (epithelial lining and glands of digestive and respiratory tracts)
formation of body organs and organ systems
organogenesis
specialization of the ectoderm
neurulation - produces the brain and spinal cord

process is induced by chemical signals from the notochord

ectoderm overlying the notochord thickens, forming the neural plate

the ectoderm starts to fold inward as a neural groove

neural groove deepens forms neural folds

superior fold fuse forming a neural tube, pinches off from the ectodermal layer and becomes covered by surface ectoderm

anterior end of the neural tube becomes the brain and the rest becomes the spinal cord

neural crest cells migrate widely and give rise to the cranial, spinal, and sympathetic ganglia

end of the first month three primary brain vesicles (fore-, mid-, and hindbrain) apparent

second month all brain flexures are evident, cerebral hemispheres cover the top of the brain stem, brain waves can be recorded

remaining ectoderm forming the surface layer embryonic body differentiates into the epidermis of the skin
specialization of the endoderm
starts off as a flat plate, as it grows, it folds to achieve a cylindrical body shape, which lifts off the yolk sac and protrudes into the amniotic cavity,

folding into a tube, occurs from both ends (head and tail region) and progresses toward the central part of the embryonic body, where the yolk sac and umbilical vessels protrude, as the endoderm come together and fuse it encloses part of the yolk sac

tube of endoderm formed, called primitive gut, forms the epithelial lining (mucosa) of the GI tract

GI organs become apparent, then oral and anal opening perforate

mucosal lining of the respiratory tract forms as an outpocketing from foregut (pharyngeal endoderm) and glands arise as endodermal outpocketing at various points

pharyngeal endoderm forms thyroid, parathyroid, and thymus
specialization of the mesoderm
appearance of the notochord in the embryonic discs, replaced by the vertebral column, remnants persist in the springy nucleus pulpose of the intervertebral discs (notochord)

three mesodermal aggregates appear on either side of notohcord

largest somites - all 40 pairs present by week 4, three functional parts
sclerotome - "hard piece", produce vertebra and rib at the associated level
dermatone - cells help form the dermis of the skin in the dorsal part of the body
myotome - cells help develop in conjunction with the vertebra, they form the skeletal muscles of the neck, body trunk, and via their limb buds the muscles of the limbs

intermediate mesoderm - form the gonads and kidneys

lateral plate mesoderm - consists of paired mesodermal plates: somatic mesoderm & splanchnic mesoderm
somatic mesoderm - help form the dermis of the skin in the ventral body region, forms the perietal serosa that lines the ventral body cavity, migrate into the forming limbs and produce the bones, ligaments, and dermis of the limbs
splanchnic mesoderm - provides the mesenchymal cells that form the heart and blood vessels and most connective tissue of the body, forms the smooth muscle, connective tissues, and serosal coverings of the digestive and respiratory organs
first blood cells aries from the
yolk sac
carries freshly oxygenated blood returning from the placenta into the embryonic body, where it is conveyed to the liver, some of the returning blood percolates through the liver sinoids and out the hepatic veins
umbilical vein
most of the blood coursing through the umbilical vein enter the ____ a venous shunt that bypasses the liver sinusoids
ductus venosus
both the hepatic veins and the ductus venosus empty into the ______ where the placental blood mixes with deoxygenated blood returning from the lower parts of the fetus's body
inferior vena cava
in turn conveys this "mixed load" of blood directly to the right atrium of the heart
vena cava
after birth, the _____ plays an important role in nutrient processing, but during embryonic life the mother's ____ preforms these functions, blood flow through the fetal ____ during development is important only to ensure that the ____cells remain healthy
liver
some if the blood entering the right atrium flows directly into the left atrium via the ______, an opening in the interatrial septum loosely closed by a flap of tissue
foramen ovale
blood that enters the right ventricle is pumped out into the pulmonary trunk, however the second shunt ____, transfers most of that blood directly into the aorta, bypassing the pulmonary circuit
ductus arteriosus
unique cardiovascular modifications seen only during prenatal include______, all of these structures are occluded at birth
umbilical arteries and vein, and three vascular shunts
blood flowing distally through the aorta eventually reached the _____, which are branches of the internal iliac arteries serving the pelvis, from here the deoxygenated blood, laden with metabolic wastes, is delivered back to the capillaries in the chrorionic villi of the placenta
umbilical arteries
carries oxygen and nutrient-rich blood from the placenta to the fetus
umbilical vein
carry waste laden blood from the fetus to the placenta
umbilical arteries
bypass the nonfunctional lungs
ductus arterious ans foramen ovale
allows blood to partially bypass the liver
ductus venosus
the umbilical vessels as well as the liver and lung bypasses are occluded
changes in the cardiovascular system at birth
Stages of labor
stage 1 - dilation stage is the time from labor's onset until the cervix is fully dilated by the baby's head, weak but regular contractions begin int the upper part of the uterus and move toward the vagina, contraction 15- 30 min apart, last for 10 - 30 seconds, contractions become more vigorous and rapid, lower part of the uterus gets involved, as the infants head is forced against the cervix with each contraction, cervix softens, thins and dilates, amnion ruptures, longest part of labor, lasting 6 - 12 hours or more, engagement occurs when infants head enters the true pelvis, descent continues baby's head rotates

stage 2 - expulsion stage, lasts from full dilation to delivery of the infant (childbirth), cervix is fully dilated, strong contractions occur every 2 - 3 min and last about 1 min, increasing urge to push/bear down with abdominal muscles, may last 2 hours, is typically 50 mins in first births and 20 min in subsequent births, crowning occurs when the largest dimension of the baby's head distends the vulva. episiotomy may be done to reduce tissue tearing, baby's neck extends as the head exits from the perineum, once head has been delivered, rest of baby's body is delivered much more easily, umbilical cord is clamped and cut

stage 3 - placental stage, delivery of the placenta and its attached fetal membranes, called afterbirth, accomplished in 30 min after the birth of infant, strong contractions continue after birth compress uterine blood vessels, limit bleeding and shear the placenta off the uterine wall, important that all placental fragments be removed to prevent uterine bleeding after birth
1 to 5 min after birth, the infants physical status is assessed based on five signs: heart rate, respiration, color, muscle tone, and reflexes, each is given a score from 0-2, total called ____, a score of 8-10 indicates a healthy baby
apgar score
contractions called Braxton Hicks contractions
false labor
stimulates the myometrial cells of the uterus to form abundant oxytocin receptors also antagonizes progesterone's quieting influence on uterine muscles
rise of estrogen
certain fetal cells begin to produce ______, causes the placenta to release______, both hormones are powerful uterine muscle stimulants, since the myometrium is now highly sensitive, contractions become more frequent and vigorous
oxytocin
prostaglandins
It is impossible for sperm to be functional (able to fertilize the egg) until after ________.
they undergo capacitation
The umbilical arteries carry ________.
waste products to the placenta
The dorsal surface cells of the inner cell mass form ________.
the primitive streak
Derivatives of the ectoderm include ________.
epithelium of the pineal and pituitary glands
Derivatives of the mesoderm include ________.
endothelium of blood and lymph vessels
Which of the following is a highly unlikely method of producing a child?
ectopic implantation
Milk ejection or letdown reflex is stimulated by which of the following hormones associated with pregnancy?
oxytocin
Which of the following is not a correct matching of a fetal structure with what it becomes at birth?
ductus arteriosus-ligamentum teres
The cardiovascular system of a newborn must be adjusted after the infant takes its first breath. Which of the following is also true?
The ductus arteriosus constricts and is converted to the ligamentum arteriosum.
During which stage of labor is the fetus delivered?
expulsion stage
Relaxin is a hormone produced by the placenta and ovaries. The function of this hormone is to ________.
relax the pubic symphysis
Developmental events during weeks 9-12 include ________.
sex readily detected from the genitals
Derivatives of the endoderm include ________.
epithelium of the respiratory tract
A blastocyst is a hollow ball of cells, while the morula is a solid ball of cells.
true
A pregnancy test involves antibodies that detect GH levels in a woman's blood or urine.
false
Which of the choices below occurs if fertilization of the ovum occurs and implantation takes place?
The corpus luteum is maintained until the placenta takes over its hormone-producing functions
The trophoblast is mostly responsible for forming the ________.
placental tissue
The period from fertilization through week eight is called the embryonic period.
true
The correct sequence of preembryonic structures is ________.
zygote, morula, blastocyst
Select the correct statement about fertilization.
Millions of sperm cells are destroyed by the vagina's acidic environment.
Protective water filled sac surrounding the embryo.
amnion
extraembryonic membranes that develops from the trophoblasts and forms part of the placenta
chorion
site of early blood cell production, and site from which progenitors of the future germ cells migrates to reach the genital ridges
yolk sac
structure in humans that is the base for the umbilical cord; the solid waste disposal site in nonplacental animals
allantois
leads to the development of a morula and then a blastocyst
cleavage
embedding of the blastula in the uterine wall
implantation
leads to the formation of the first cell of the new individual
fertilization
leads to the establishment of the three primary germ layers
gastrulation
conceptus is a term used to describe the developing offspring in a woman
true
the first weeks of gestation are called the embryonic period
false
fertilization occurs while the egg is still in the ovarian follicle
false
freshly deposit sperm are not capable of penetrating an oocyte
true
by 72 hrs after fertilization, the egg has divided into more than 160 cells and is called the morula
false
implantation begins six days after ovulation
true
growth hormone is responsible for the integrity of the corpus luteum
false
the organs of the developing fetus are recognizable in the first eight weeks
true
the first major event in oogenesis is development of the gut
false
of the germ layers, the mesoderm forms more body parts
true
a pregnant woman urinates more often than usual because the uterus compresses the bladder and she must also dispose of fetal metabolic waste
true
the 2 hormones responsible for initiating labor are thyroxine and human chronic thyrotropin
false
The "fluid filled, hollow ball of cells" stage of development is the
blastocyst.
true
the embryonic stage lasts until the end of the eighth week
true
the embryo is directly enclosed in and protected by the amnion
true
in fetal circulation, one-way blood bypasses the nonaerated lungs by the way of the foramen ovale
true
a episiotomy is an incision made to widen the vaginal orifice, aiding fetal expulsion
true
the placenta and its attached fetal membranes are collectively called afterbirth
true
human placental lactogen initiates labor
false
surfactant production in premature infants is rarely a factor providing normal respiratory activity
fasle
a zygote is usually formed within the uterus
false
the ectodermal cells migrate to form a raised groove known as the
primitive streak
the result of polyspermy in humans is
a nonfunctional zygote
it is impossible for sperm to be functional (able to fertilize the egg) until after
they undergo capacitation
estrogen and progesterone maintain the integrity of the uterine lining and prepare the mammary glands secrete milk. which of the following structures makes this possible during the first three months of pregnancy?
corpus luteum
the placenta, a vitally important metabolic organ, is made up of a contribution from mother and fetus, which portion is from the fetus
chorion
hyaluronidase and proteinase are enzymes, how do he function is reproduction
they act to break down the protective barriers around the egg, allowing the sperm to penetrate
which of the following is not a germ layer
epiderm
the formation of endodermal and ectodermal germ layers occurs at
cleavage
the lateral mesoderm forms
the epithelial lining of the GI tract
failure of the foramen ovale to close at birth may result in
mixing of oxygenated and nonoxygenated blood
implantation involves
embedding of the blastula in the uterine wall
one sign of an infant's physical condition that is first notices at birth is which of the following
color
hormones concerned with the events of lactation include
oxytocin
just after implantation occurs, nutrition of the young embryo is primarily provided by
digestion of the endometrial cells
onset of labor may be a result of all the following factors except
aspirin and similar drugs
select the correct statement about fertilization
millions od sperm cells are destroyed by the vagina's acidic environment
Implantation ______
signals the division of the trophoblast into two distinct layers
the surface cells of the inner cell mass become
the primitive streak
muscle tissue is formed by the
mesoderm
neural tissue is formed by the
ectoderm
the trophoblast is responsible for forming the
placental tissue
the cardiovascular system of a newborn must be adjusted after the infant rakes its first breath, which of the following is true
the ductus arteriosus constricts and is converted to the ligamentum arteriorsum
sperm move to the uterine tube through uterine contractions and the energy of their own flagella, what other factor id involved in sperm movement
reverse peristalsis of the uterus and uterine tubes
at which stage of labor is the "afterbirth" expelled
placental
which hormone is not produced by the placenta
inhibin
during which stage of labor is the fetus delivered
expulsion stage
implantation of the blastocyst is the result of all of the following except
phagocytosis by the trophoblast cells
cleavage as part of embryonic development is distinctive because it involves
cell division by mitosis with little or no growth between successive divsions
which part of the following id true in reference to what may pass through the placental barriers
nutrients, respiratory gases, wastes, and alcohol
which of the following id not usually considered a teratogen
aspirin
developmental events during the weeks 13-16 include
the face looking human and the body beginning to outgrow the head
developmental events during weeks 17-21 include
limbs achieving final proportions
developmental events during weeks 21-30 include
distal limp bones beginning to ossify
which metabolic change does not occur as the placenta enlarges
increased levels of calcitonin
select the correct statement about the special fetal blood vessels
the umbilical vein becomes the ligamentum teres
which of the following statement about the events of fertilization is not true
the two pronuclei divide
which developmental event occurs during the embryonic period
weak spontaneous muscle contractions just begin
the decidua basalis is
located between the developing embryo and the myometrium
the first "milk" the mother produces is called
colostrum
as the newborn suckles, her mother's pituitary produces _____ to assist in producing milk
oxytocin
the act of giving birth is called
parturition
after the egg is fertilized, it is called a
zygote
the____cells of the blastocyst will take part in placental formation
trophoblast
the stage of development is the first in which all three germ layers of the tissue are evident
gastrula
a tissue with star-shaped cells that are free to migrate widely throughout the embryo
mesenchyme
neural tissue develops from the
ectoderm
during pregnancy some woman develop increased pigmentation of the skin of the nose and cheek, a condition called
chloasma
the first axial support for the embryo is called the
notochord