Embryology Ch 4 -

The trilaminar disc develops during this time period

15-16 days

This staging system for determining the age of the embryo is used internationally and is based on the number of somites.

Carnegie

The primitive streak elongates by adding cells to the cranial end

False

The villi that attach to the maternal tissues through the cytotrophoblastic shell are called branch chorionic villi or terminal villi.

False (answer is stem or anchoring villi. Branch chorionic or terminal villi grow from the sides of the stem villi)

What does fetal distress mean? How is the condition recognized? What causes the distress?

Fetal distress refers to a disruption in the flow of oxygen to the fetus, also known as fetal hypoxia. This condition is recognized when the fetal heart rate is less than 100 beats per minute. Fetal distress is caused by decreased maternal oxygen levels in the blood, abnormally low blood flow, constriction of the umbilical cord around the fetus' neck, or compression of the umbilical cord during delivery.

Which of the following does NOT occur during the third week of Human Development a. Formation of the limb buds b. Development of the trilaminar embryonic disc c. Development of the notorchord d. Appearance of the primitive streak

Formation of the limb buds

This is a condition where the blastocyst implants outside of the uterus.

NEED

myelomenigocele

Protrusion of a portion of the spinal cord and meniges through a defect in the spinal column

Implantation of the Blastocyst completes during the ____________________ .

Second week

spina bifida occulta

The mildest form of spina bifida. It results in a small gap in one or more of the vertebrae. The spinal nerves and meninges do not usually protrude through the opening, so most children with this form have no clinical manifestations and experience no neurologic deficits.

What is the scientific basis of the home pregnancy tests that are sold in drugstores?

The scientific basis of the home pregnancy tests that are sold in drugstores is human chorionic gonadotropin. This is synthesized by the syncytiotrophoblast of the chorion and present in a pregnant woman's urine after her first missed period which corresponds with the implantation of the embryo.

The second week of development is known as the week of twos. Formation of what structures supports this statement?

The second week of development is known as the week of 2's due to the fact that several structures differentiate into two different layers or two structures are formed. First, the trophoblast continues on to two layers, the cytotrophoblast, and the syncytiotrophoblast. Next, embryoblast changes result in the formation of the embryonic disc which has two layers, the epiblast, and the hypoblast. Later, the extraembryonic coelom cleaves the extraembryonic mesoderm into the extraembryonic somatic mesoderm and the extraembryonic splanchnic mesoderm. There are also two, primary and secondary, umbilical vesicles. Lastly, two separate cavities are formed called the amniotic cavity and the chorionic cavity.

An implanted embryo can be detected by ultrasonography at the end of the second week. True/False

True

Closure of the neural folds forms the neural tube

True

Folding of the sides of the embryo during the fourth week results from growth of the somites.

True

Neural crest cells differentiate into various cells such as spinal ganglia, pia mater and ganglia of the ANS

True

Neural tube defects are among the most common congenital abnormalites.

True

Remnants of teh primitive streak may persist and give rise to a large tumor known as a sacrococcygeal taratoma.

True

The extraembryonic cavity is a large, isolated cavity that forms from within the extraembryonic mesoderm and surrounds the amnion and umbilical vesicle.

True

The cloacal membrane is the future site of this structure

anus

The tail of the folding caudal end of an embryo during the 22-26 day projects over this developing structure.

anus

Which of the following does NOT occur during week 4-8. a. All major internal and external structure are established b. The notochord develops c. The shape of the embryo changes significantly d. The embryo is most susceptible to teratogens.

b. the notochord develops

As the lateral folds of the embryo develop during the fourth week, the foregut lies between these two structures.

brain and heart

The heart and great vessels form from mesenchymal cells in the hear primordium, or ____________ area.

cardiogenic

anencephaly

congenital deformity in which some or all of fetal brain is missing

The trophoblast differentiates into two layers, the synctiotrophoblast and the ________________ .

cytotrophoblast

Which of the following is NOT an extraembryonic structure. yolk sac embryo chorionic sac

embryo

This layer of the embryonic bilayer disc is related to the amniotic cavity.

epiblast

As the embryo folds during the fourth week, the connecting stalk is attached to the dorsal surface of the embryo

false

Folding only occurs at the cranial end of the embryo during week 4.

false

A source of folic acid is encouraged for pregnant women in the first trimester. You are the doctor. Please explain to your patient, a 28 year old who is trying to conceive, why the addition of folic acid is important in the development of a baby.

folic acid is important for neuralation (formation of the neural tube). Severe birth defects such as ancephaly and spina bifida occur with abnormal neuralation.

During the period of 21-26 days, the forebrain grows and overhangs this developing structure.

heart

The embryonic bilaminar disc that gives rise to the germ layers initially is composed of the epiblast and the ______________ .

hypoblast

`Cells from the primitive streak form this germ layer.

mesoderm

This structure is a cellular rod that defines the axis of the embryo and is the basis for development of the axial skeleton.

notochord

The beginning of morphogenesis begins with this structure

primitive streak

This structure is the source of hCG early in development and is the basis for pregnancy tests.

synctiotrophoblast

meningocele

the congenital herniation of the meninges through a defect in the skull or spinal column involves sac of fluid

The trilaminar embryonic disc folds into a cylindrical embryo

true

Spontaneous movement of the embryo occurs in this week.

week 6

Primary ossification of the femur and disappearance of the caudal eminence occurs during which week?

week 8