Lecture 11: Body Plan Development III Flashcards
Which signaling factor is necessary for the formation of endoderm?
Nodal
Describe the relationship of the expression of nodal and FGF-4 to the establishment of the anterior-posterior gradient
Higher levels of nodal anteriorly
Lower levels of nodal + presence of FGF-4 posteriorly
Describe the role of Cdx-2 in the formation of the hindgut and foregut
- Promotes hindgut development
- Suppresses formation of anterior gut structures
Describe the relationship of Shh and BMP-4 in the formation of the anterior and posterior intestinal portals
Anterior intestinal portal: Shh
Posterior intestinal portal: Shh followed by BMP-4
Which series of Hox genes is involved in the refinement of the differentiation of gut structures?
Anterior: Hex, Sox-2, Foxa-2
Posterior: Cdx-2
List major features of the fourth week embryo
- 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
List each of the three major circulatory arcs in the 4-week embryo and the components and function of each
- Intraembryonic circulatory arc- circulatory system
- Omphalomesenteric arc- supplies yolk sac
- Extraembryonic arc- umbilical vessels
List and describe the four extraembryonic layers and the germ layers from which they are derived
Amnion- epiblast derivative
Yolk sac- hypoblast derivative
Chorion- part of fetal maternal interface
Allantosis- interfaces with placenta via umbillical cord
List the two trophoblastic derivatives that comprise the fetal-maternal interface
Placenta
Chorion
List the functions of the amnion
- Buffer against mechanical injury
- Accommodates growth
- Allows normal movements
- Protects fetus from adhesions
Describe hydraminos and indicate what circumstances are often associated
An excessive amount of amniotic fluid
Causes esophageal atresia and anencephaly
Describe oligohydramnios and indicate what circumstances are often associated
Too little amniotic fluid
Associated with renal angenesis (absence of kidneys)
What information can be learned by testing for A-fetoprotein
a high concentration of this protein in the CNS is an indicator of a neural tube defect
What information can be learned by testing for Creatine
assesses fetal maturity
What information can be learned by testing for Lecithin-to-sphingomyelin ratio
assesses fetal maturity and specifically shows the maturity of the lungs
Describe phase I and phase II formation of the amniotic fluid?
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
What is the turnover rate in late pregnancy?
the amniotic fluid turns over completely every 3 hours
List known and possible functions of the yolk sac in mammals
- 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)
Describe the development of the allantoic vessels and the relation of the allantois to the urinary baldder and the median umbilical ligament
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
Describe each of the four stages in the development of the chorionic villi
- Previllous embryo: no villi have been formed on the trophoblast
- Primary villous stage: solid, cytotrophoblastic, ectodermal primary villi appear
- Secondary villous stage: mesodermal cores appear within the primary villi
- Tertiary villous stage: characterized by the appearance of blood vessels within the mesenchymal core of the secondary villi
What are Hofbauer cells?
Function as macrophages, they are scattered among mesenchymal cells in the mature chorionic villus
Describe cytotrophoblastic column in relation to placental development
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
Describe cytotrophoblastic shell in relation to placental development
formed by the expansion of the cytotrophoblastic columns over the maternal decidual cells
Describe anchoring villi in relation to placental development
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
Describe floating villi in relation to placental development
unattached branches that dangle freely in the maternal blood that fills the space between the chorionic plate and the outer cytotrophoblastic shell
Describe chorionic plate in relation to placental development
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.
Describe hemochorial type placenta in relation to placental development
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
What tissue in the mature placenta directly interfaces with the maternal uterine connective tissue?
Cytotrophoblast
What is decidual reaction?
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
What does the term “decidua” refer to?
tissues that are shed at birth
includes the extraembryonic tissues in addition to the superficial layers of the endometrial connective tissue and epithelium
What is the fate of the decidua capsularis?
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
What maternal tissues are lost at childbirth?
all of the decidua
Trace the maternal-fetal blood flow pattern and indicate where the exchange of materials occurs
q
Describe fetal alcohol syndrome in relation to placental transfer
Since the placenta is highly permeable to alcohol, excessive alcohol produces fetal alcohol sydrome
Describe etiology of erythroblastosis fetalis and explain how it is related to hydrops fetalis
- 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.
Describe hyatidiform mole and relate to the structure of the placenta
- 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
Describe placenta previa and relate to the structure of the placenta
- 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
What is genetic basis for the hydatidiform mole?
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
What is Meckel’s diverticulum?
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
