Lecture 11: Body Plan Development III

Question 1

Which signaling factor is necessary for the formation of endoderm?

Answer 1

Nodal

Question 2

Describe the relationship of the expression of nodal and FGF-4 to the establishment of the anterior-posterior gradient

Answer 2

Higher levels of nodal anteriorly

Lower levels of nodal + presence of FGF-4 posteriorly

Question 3

Describe the role of Cdx-2 in the formation of the hindgut and foregut

Answer 3

• Promotes hindgut development
• Suppresses formation of anterior gut structures

Question 4

Describe the relationship of Shh and BMP-4 in the formation of the anterior and posterior intestinal portals

Answer 4

Anterior intestinal portal: Shh

Posterior intestinal portal: Shh followed by BMP-4

Question 5

Which series of Hox genes is involved in the refinement of the differentiation of gut structures?

Answer 5

Anterior: Hex, Sox-2, Foxa-2

Posterior: Cdx-2

Question 6

List major features of the fourth week embryo

Answer 6

• Length of embryo = 4 mm
• Rudiments for most of the major organ systems are present—except limbs and kidneys
• Prominent pharyngeal arches
• Wolffian ridge develops—marks limb buds

Question 7

List each of the three major circulatory arcs in the 4-week embryo and the components and function of each

Answer 7

1. Intraembryonic circulatory arc- circulatory system
2. Omphalomesenteric arc- supplies yolk sac
3. Extraembryonic arc- umbilical vessels

Question 8

List and describe the four extraembryonic layers and the germ layers from which they are derived

Answer 8

Amnion- epiblast derivative

Yolk sac- hypoblast derivative

Chorion- part of fetal maternal interface

Allantosis- interfaces with placenta via umbillical cord

Question 9

List the two trophoblastic derivatives that comprise the fetal-maternal interface

Answer 9

Placenta

Chorion

Question 10

List the functions of the amnion

Answer 10

• Buffer against mechanical injury
• Accommodates growth
• Allows normal movements
• Protects fetus from adhesions

Question 11

Describe hydraminos and indicate what circumstances are often associated

Answer 11

An excessive amount of amniotic fluid

Causes esophageal atresia and anencephaly

Question 12

Describe oligohydramnios and indicate what circumstances are often associated

Answer 12

Too little amniotic fluid

Associated with renal angenesis (absence of kidneys)

Question 13

What information can be learned by testing for A-fetoprotein

Answer 13

a high concentration of this protein in the CNS is an indicator of a neural tube defect

Question 14

What information can be learned by testing for Creatine

Answer 14

assesses fetal maturity

Question 15

What information can be learned by testing for Lecithin-to-sphingomyelin ratio

Answer 15

assesses fetal maturity and specifically shows the maturity of the lungs

Question 16

Describe phase I and phase II formation of the amniotic fluid?

Answer 16

Phase 1: amniotic fluid is similar to fetal fluids, source is maternal serum

Phase 2: contributions from fetal urine, maternal blood vessels, and fetal vessels in the umbilical cord

Question 17

What is the turnover rate in late pregnancy?

Answer 17

the amniotic fluid turns over completely every 3 hours

Question 18

List known and possible functions of the yolk sac in mammals

Answer 18

• May concentrate folic acid, vitamins (A, B₁₂, E)
• Site of origin of primordial germ cells
• Location of blood islands—origin of initial blood cells (extraembryonic hematopoiesis)

Question 19

Describe the development of the allantoic vessels and the relation of the allantois to the urinary baldder and the median umbilical ligament

Answer 19

Allantoic vessels develop in the mesoderm of the allantois (inner cell mass b/w placenta and umbilical cord)

The proximal part of allantois is the urachus, which is associated with the formation of the urinary bladder and becomes the median umbilical ligament

Question 20

Describe each of the four stages in the development of the chorionic villi

Answer 20

1. Previllous embryo: no villi have been formed on the trophoblast
2. Primary villous stage: solid, cytotrophoblastic, ectodermal primary villi appear
3. Secondary villous stage: mesodermal cores appear within the primary villi
4. Tertiary villous stage: characterized by the appearance of blood vessels within the mesenchymal core of the secondary villi

Question 21

What are Hofbauer cells?

Answer 21

Function as macrophages, they are scattered among mesenchymal cells in the mature chorionic villus

Question 22

Describe cytotrophoblastic column in relation to placental development

Answer 22

It is the terminal portion of a villus remains trophoblastic, con- sisting of a solid mass of cytotrophoblast

Under the hypoxic environment, the cytotrophoblastic column expands distally and penetrates the syncytiotrophoblastic layer

Question 23

Describe cytotrophoblastic shell in relation to placental development

Answer 23

formed by the expansion of the cytotrophoblastic columns over the maternal decidual cells

Question 24

Describe anchoring villi in relation to placental development

Answer 24

villi that are anchored to the cytotrophoblastic shell (as opposed to floating villi)

they represent the attachment points between the embryo complex and maternal issues

Question 25

Describe floating villi in relation to placental development

Answer 25

unattached branches that dangle freely in the maternal blood that fills the space between the chorionic plate and the outer cytotrophoblastic shell

Question 26

Describe chorionic plate in relation to placental development

Answer 26

bounds the chorionic cavity

• chorionic villi extend out from the chorionic plate, and their trophoblastic covering is continuous with that of the chorionic plate. The villi and the outer surface of the chorionic plate are bathed in a sea of continually exchanging maternal blood.

Question 27

Describe hemochorial type placenta in relation to placental development

Answer 27

the villi and the outer surface of the chorionic plate are bathed in a sea of continually exchanging maternal blood… because of this, the human placenta is designated the hemochorial type

*maternal blood comes in direct contact with the fetal chorion

Question 28

What tissue in the mature placenta directly interfaces with the maternal uterine connective tissue?

Answer 28

Cytotrophoblast

Question 29

What is decidual reaction?

Answer 29

when the stromal cells of the endometrium undergo a transformation

• after the stromal cells swell as the result of the accumulation of glycogen and lipid in their cytoplasm, they are known as decidual cells. The decidual reaction spreads throughout stromal cells in the superficial layers of the endometrium.
• endometrial cells prepare for pregnancy, thickening of endometrium

Question 30

What does the term “decidua” refer to?

Answer 30

tissues that are shed at birth

includes the extraembryonic tissues in addition to the superficial layers of the endometrial connective tissue and epithelium

Question 31

What is the fate of the decidua capsularis?

Answer 31

The decidual tissue that overlies the embryo and its chorionic vesicle is the decidua capsularis, whereas the decidua that lies between the chorionic vesicle and the uterine wall is the decidua basalis.

With continued growth of the embryo, the decidua basalis becomes incorporated into the maternal component of the definitive placenta. The remaining decidua (decidua capsularis), which consists of the decidualized endometrial tissue on the sides of the uterus not occupied by the embryo, is the decidua parietalis.

*it becomes the decidua parietalis

*it encircles the remainder of the chorion like a capsule

Question 32

What maternal tissues are lost at childbirth?

Answer 32

all of the decidua

Question 33

Trace the maternal-fetal blood flow pattern and indicate where the exchange of materials occurs

Answer 33

q

Question 34

Describe fetal alcohol syndrome in relation to placental transfer

Answer 34

Since the placenta is highly permeable to alcohol, excessive alcohol produces fetal alcohol sydrome

Question 35

Describe etiology of erythroblastosis fetalis and explain how it is related to hydrops fetalis

Answer 35

• Maternal antibodies cause hemolysis of the Rh-positive fetal erythrocytes, Rh-positive fetuses are attacked by the maternal anti-Rh antibodies
• Occurs when fetal erythrocytes are Rh positive and the mother is Rh negative, so the presence of fetal erythrocytes in maternal circulation stimulates the formation of anti-Rh antibody by the maternal immune system
• In severe cases, the bilirubin released from the lysed red blood cells causes water accumulation in the fetus (hydrops fetalis), with accompanying jaundice and brain damage in addition to anemia.

Question 36

Describe hyatidiform mole and relate to the structure of the placenta

Answer 36

• Chorionic villi on the placenta that swell, giving them the appearance of grapes (chorionic villi are attached to the placenta to provide maximal contact with maternal blood, their genetic make-up is the same as the fetus)
• Embryo is either absent or not viable

Question 37

Describe placenta previa and relate to the structure of the placenta

Answer 37

• If the embryo is implanted close to the cervix, the placenta forms a partial covering over the cervical canal
• Results in hemorrhage during late pregnancy and will cause death of fetus and mother b/c of placental detachment after the hemorrhage

Question 38

What is genetic basis for the hydatidiform mole?

Answer 38

Result of paternal imprinting, chromosomes are paternally derived 46/XX, two sperm fertilize one egg

• the female pronucleus of the egg does not participate in development

Question 39

What is Meckel’s diverticulum?

Answer 39

traces of yolk duct persist as a fibrous cord or an outpouching of the small int.

results in an outpouching or buldge in the small intestine