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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


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


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


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


all pregnancy test used today are antibody tests that detect ____ in a woman's blood or urine


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


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


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


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


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


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?


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.


A pregnancy test involves antibodies that detect GH levels in a woman's blood or urine.


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.


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.


extraembryonic membranes that develops from the trophoblasts and forms part of the placenta


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


leads to the development of a morula and then a blastocyst


embedding of the blastula in the uterine wall


leads to the formation of the first cell of the new individual


leads to the establishment of the three primary germ layers


conceptus is a term used to describe the developing offspring in a woman


the first weeks of gestation are called the embryonic period


fertilization occurs while the egg is still in the ovarian follicle


freshly deposit sperm are not capable of penetrating an oocyte


by 72 hrs after fertilization, the egg has divided into more than 160 cells and is called the morula


implantation begins six days after ovulation


growth hormone is responsible for the integrity of the corpus luteum


the organs of the developing fetus are recognizable in the first eight weeks


the first major event in oogenesis is development of the gut


of the germ layers, the mesoderm forms more body parts


a pregnant woman urinates more often than usual because the uterus compresses the bladder and she must also dispose of fetal metabolic waste


the 2 hormones responsible for initiating labor are thyroxine and human chronic thyrotropin


The "fluid filled, hollow ball of cells" stage of development is the


the embryonic stage lasts until the end of the eighth week


the embryo is directly enclosed in and protected by the amnion


in fetal circulation, one-way blood bypasses the nonaerated lungs by the way of the foramen ovale


a episiotomy is an incision made to widen the vaginal orifice, aiding fetal expulsion


the placenta and its attached fetal membranes are collectively called afterbirth


human placental lactogen initiates labor


surfactant production in premature infants is rarely a factor providing normal respiratory activity


a zygote is usually formed within the uterus


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


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


the formation of endodermal and ectodermal germ layers occurs at


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


hormones concerned with the events of lactation include


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


neural tissue is formed by the


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


which hormone is not produced by the placenta


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


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


as the newborn suckles, her mother's pituitary produces _____ to assist in producing milk


the act of giving birth is called


after the egg is fertilized, it is called a


the____cells of the blastocyst will take part in placental formation


the stage of development is the first in which all three germ layers of the tissue are evident


a tissue with star-shaped cells that are free to migrate widely throughout the embryo


neural tissue develops from the


during pregnancy some woman develop increased pigmentation of the skin of the nose and cheek, a condition called


the first axial support for the embryo is called the


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