Question 1

________ Nuclear aggregation

Accepted Answer

At some sites,the syncytiotrophoblast of the placental membrane in mature placentas shows protuberances or sprouts of cytoplasm that contain aggregations of syncytiotrophoblastic nuclei-syncytial knots.Some knots break off and float in the intervillous space.They may pass into the maternal circulation through the uterine veins and lodge in the capillaries of the lungs.This occurrence is not usually considered to be of clinical significance because these nuclear masses are believed to degenerate and disappear.

Question 2

________ Decidua parietalis

Accepted Answer

The decidua parietalis refers to the endometrium lining parts of the uterus not directly involved with the conceptus (i.e. ,endometrium not designated as decidua capsularis or decidua basalis).

Question 3

________ Forms on the surfaces of chorionic villi

Accepted Answer

Fibrinoid is an eosinophilic,homogeneous substance that forms on the surfaces of chorionic villi and reduces the area of tissues through which exchange of materials between the maternal and fetal circulations may take place.It consists of fibrin and other unidentified substances.

Question 4

________ Extends into cervical canal during labor

Accepted Answer

The chorion,with which the amnion is fused,extends into the cervical canal during the first stage of labor and helps to dilate the cervix.When the fused layers of amnion and chorion (amniochorionic membrane)rupture,the amniotic fluid escapes through the cervix and vagina.

Question 5

________ Placental membrane

Accepted Answer

The placental membrane may be defined as the fetal tissues that are interposed between the fetal and placental circulations.The structure and thickness of the membrane vary at different stages of pregnancy.The placental membrane becomes extremely thin as pregnancy advances,and its permeability increases.The thickness of the membrane is also affected by the extent of distention of the capillaries in the villus.

Question 6

________ Fibrinoid material

Accepted Answer

Fibrinoid material develops as a homogeneous layer at various places on the maternal aspect of the villi.Because it is at the fetomaternal junction of tissues,fibrinoid is believed to be important in preventing rejection of the fetus by the mother.Composed of fibrin and other unidentified substances,fibrinoid decreases the permeability of the placental membrane for exchange of material between the fetal and maternal blood streams.

Question 7

________ Smooth chorion

Accepted Answer

The smooth chorion is continuous with the chorionic plate ("roof")of the placenta.From the third to eighth weeks,the chorionic sac is covered by villi.The villi degenerate as the amniotic sac enlarges and presses the chorion against the decidua capsularis.This reduces the blood supply to the villi and results in their degeneration.

Question 8

________ Fetal capillaries

Accepted Answer

Fetal capillaries are tiny blood vessels in the branch villi that transport poorly oxygenated blood and waste products from the fetus and carry well-oxygenated blood and nutrients to the fetus.Exchange of material occurs between the blood in the fetal capillaries and in the intervillous space.

Question 9

________ Fetal surface of placenta

Accepted Answer

The amnion adheres to the smooth fetal surface of the placenta and is continuous with the epithelial membrane covering the umbilical cord.The umbilical vessels radiate over the fetal surface of the placenta deep to the amnion.

Question 10

________ Syncytial knot

Accepted Answer

Syncytial knots consist of aggregations of nuclei in protuberances of cytoplasm of the syncytiotrophoblast.They form at intervals along a villus;occasionally they break off and enter the maternal circulation.Apparently these nuclear aggregations have a short life in the maternal blood.

Question 11

________ Ensheaths umbilical cord

Accepted Answer

As the amniotic sac enlarges,it obliterates the chorionic cavity and ensheaths the umbilical cord.The amnion becomes the epithelial covering of the cord.

Question 12

________ Decidua capsularis

Accepted Answer

The decidua capsularis is the part of the decidua (gravid endometrium)that encapsulates the luminal surface of the implanted conceptus.At the stage shown,it is fused with the smooth chorion (chorion laeve).Together the amnion and chorion form the amniochorionic membrane.

Question 13

________ Forms part of early placental membrane

Accepted Answer

The cytotrophoblast consists of large,pale cells with relatively large nuclei.Their cytoplasm contains vacuoles and some glycogen.The placenta synthesizes glycogen early in pregnancy,and its declining ability to perform this activity later in pregnancy may be related to the assumption of this function by the fetal liver and to the retrogression of the cytotrophoblast.

Question 14

________ Fetal capillary

Accepted Answer

The fetal capillaries,embedded in the connective tissue of the chorionic villi,are part of an arterio-capillary-venous system that carries the fetal blood.As pregnancy advances,the capillaries increase in size and their walls eventually come into intimate relation with the syncytiotrophoblast.The endothelium of the capillary is separated from the syncytiotrophoblast by only an extremely delicate network of reticular fibers.

Question 15

________ Occurs only in monozygotic twins

Accepted Answer

A monochorionic twin placenta,associated with twins in separate amniotic sacs,occurs only with monozygotic twins;thus,this type of placenta is diagnostic of monozygotic twinning.The twins often have a common fetal-placental circulation.

Question 16

________ Features of maternal surface of placenta

Accepted Answer

Cotyledons are characteristic features of the maternal surface of the placenta.The placental septa divide the maternal surface into 15 to 30 cotyledons,which gives the expelled placenta a cobblestone appearance.During examination of the placenta after delivery,special attention should be given to determining whether the cotyledons are all present and intact.If they are not all recognizable and complete,placental tissue may still be in the uterus and must be removed.

Question 17

________ Maternal part of placenta

Accepted Answer

The decidua basalis forms the maternal part of the placenta.The fetal part is formed by the villous chorion (chorion frondosum).Together they form a unique fetomaternal organ,the placenta,the basic function of which is to bring the maternal and fetal circulations into proximity to permit effective exchange of materials.

Question 18

________ Branch villus

Accepted Answer

The main stem villi give rise to numerous branch villi that are bathed by maternal blood in the intervillous spaces.Exchange of gases,nutrients,and waste products between mother and fetus occurs between maternal blood in the intervillous space and fetal vessels in the branch villi.

Question 19

________ Marginal attachment of umbilical cord

Accepted Answer

When the umbilical cord and vessels are attached to the margin of the placenta,it is called a battledore placenta because of its resemblance to the bat used in the medieval game of battledore and shuttlecock.This is a common variation of placental form.Battledore placenta (marginal insertion of cord)has some clinical significance because slight bleeding occasionally occurs.It has also been shown that many patients with battledore placentas have premature labor.

Question 20

________ Places of attachment to decidua basalis

Accepted Answer

The main means of attachment of the conceptus to the uterus is by anchoring stem villi that pass from the chorionic plate to the decidua basalis.Columns of cytotrophoblastic cells extend through the syncytiotrophoblast at the tips of these villi and cover the maternal tissue.Soon cytotrophoblastic cells from adjacent villi join to form a cytotrophoblastic shell around the conceptus.This shell is also attached to the decidua basalis.

Quiz 6: Placenta and Fetal Membranes