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The chorion, amnion, yolk sac, and allantois constitute the fetal membranes.
They develop from the zygote but do not participate in the formation of the embryo or fetus, except for parts of the yolk sac and the allantois.
The placenta is the primary site of nutrient and gas exchange between the mother and the fetus.
1. A fetal portion that develops from the chorionic sac
2. A maternal portion that is derived from the endometrium
The vessels in the umbilical cord connect the placental circulation with the fetal circulation.
The placenta and umbilical cord function as a transport system for substances passing between the mother and fetus.
Nutrients and oxygen pass from the maternal blood through the placenta to the fetal blood, and waste material and carbon dioxide passes from the fetal blood through the placenta to the maternal blood.
The placenta and fetal membranes perform the following functions and activities:
e. Hormone Production
Shortly after birth of a baby, the placenta and fetal membranes are expelled from the uterus as the afterbirth.
The decidua refers to the gravid endometrium
the functional layer of the endometrium in a pregnant woman.
the part of the decidua deep to the conceptus that forms the maternal component of the placenta.
is the superficial part of the decidua overlying the conceptus.
is all of the remaining parts of the decidua.
These cells enlarge as glycogen and lipids accumulate in their cytoplasm.
The decidual cellular and vascular changes resulting from pregnancy are referred to as the decidual reaction
Many decidual cells degenerate near the chorionic sac in the region of the synctiotrophoblast and together with maternal blood and uterine secretions, to provide a rich source of nutrition for the embryo.
Decidual regions, clearly recognizable during ultrasonography, are important in diagnosis early pregnancy.
A complex vascular network is established in the placenta by the end of the fourth week
The anatomical arrangements necessary for physiological exchanges between the mother and embryo are established.
Chorionic villi covers the entire chorionic sac until when
This bushy part of the chorionic sac is called
villi associated with the decidua capsularis degenerate
As the villi disappears, those associated with the decidua basalis rapidly increase in number, branch profusely, and enlarge.
the villi associated with the decidua capsularis are compressed, reducing the blood supply to them.
The uterus, chorionic sac, and placenta enlarge as the fetus grows.
Growth in the size and thickness of the placenta continues rapidly until the fetus is about 18 weeks olds.
The fetal component of the placenta is formed by the what?
The fetal component of the placenta is formed by the villous chorion.
The stem villi that arise from it projects into the intervillous space containing maternal blood.
When is the Decidua basalis almost entirely replaced by the fetal component of the placenta.
The maternal component of the placenta is formed by the decidua basalis, the part of the decidua related to the fetal component of the placenta.
What is fetal part of the placenta (villous chorion) is attached to the maternal part of the placenta (decidua basalis) by what?
The fetal part of the placenta (villous chorion) is attached to the maternal part of the placenta (decidua basalis) by the cytotrophoblastic shell–the external layer of the trophoblastic cells on the maternal surface of the placenta.
Stem chorionic villi (anchoring villi) attach firmly to the decidua basalis through the cytotrophoblastic shell and anchor the chorionic sac to the decidua basalis.
Endometrial arteries and veins pass freely through?
Endometrial arteries and veins pass freely through gaps in the cytotrophoblastic shell and open into the intervillous space.
The shape of the placenta is determined by the shape of the persistent area of the chorionic villi.
Usually this is a circular area, giving the placenta a discoid shape.
As the chorionic villi invade the decidua basalis during the placental formation, what happens to the decidual tissue
As the chorionic villi invade the decidua basalis during the placental formation, decidual tissue is eroded to enlarge the intervillous space.
This erosion process produces several wedge-shaped areas of decidua, placental septa, that project toward the chorionic plate–the part of the chorionic wall related to the placenta.
The placental septa divides the fetal part of the placenta into irregular convex areas called cotyledons.
consists of two or more stem villi and their many branch villi.
By the end of the fourth month, the decidua basalis is almost entirely replaced by the cotyledons.
The decidua capsularis, the layer of decidua overlying the implanted chorionic sac, forms what?
The decidua capsularis, the layer of decidua overlying the implanted chorionic sac, forms a capsule over the external surface of the sac.
As the conceptus enlarges, what does the decidua capsularis bulges into
As the conceptus enlarges, the decidua capsularis bulges into the uterine cavity and becomes greatly attenuated.
What does the decidua capsularis contact and fuse with? What does this do?
decidua capsularis contacts and fuses with the decidua parietalis, thereby slowly obliterating (wiping out) the uterine cavity.
By 22-24 weeks, the reduced blood supply to the decidua capsularis causes it to degenerate and disappears.
The intervillous space containing maternal blood is derived from the lacunae that developed in the syncytiotrophoblast during the second week of development.
result from the coalescence and enlargement of the lacunar networks.
The intervillous space of the placenta is divided into compartments by the placental septa; however, there is free communication between the compartments because the septa do not reach the chorionic plate.
There is free communication between the compartments because the septa do not reach the chorionic plate.
Maternal blood enters the intervillous space from the spiral endometrial arteries in the decidua basalis.
The spiral arteries pass through gaps in the cytotrophoblastic shell and discharge blood into the intervillous space.
This large space is drained by endometrial veins that also penetrate the cytotrophoblastic shell.
Endometrial veins are found over the entire surface of decidua basalis.
The numerous branch villi-arising from stem chorionic villi are continuously showered with maternal blood that circulates through intervillous space.
The blood carries oxygen and nutritional materials that are necessary for fetal growth and development.
The maternal blood contains fetal waste products such as carbon dioxide, salts, and products of protein metabolism.
The amniotic sac enlarges faster than the chorionic sac.
As a result, the amnion and smooth chorion soon fuse to form the amniochorionic membrane.
This composite membrane fuses with the decidua capsularis and, after disappearance of this capsular part of the decidua, adheres to the decidua parietalis.
What membrane ruptures during labor?
It is the amniochorionic membrane that ruptures during labor.
Preterm rupture of the membrane is the most common event leading the premature labor.
When the amniochorionic membrane ruptures, amniotic fluid escapes through the cervix and vagina to the exterior.
The many branch chorionic villi of the placenta provide a large surface area where material may be exchanged across the very thin placental membrane interposed between the fetal and maternal circulations.
How does the main exchange of material between mother and fetus take place
It is through the numerous branch villi, which arise from the stem villi, that the main exchange of material between mother and fetus takes place.
The circulation of the fetus and the mother are separated by the placental membrane consisting of extrafetal tissues.
Poorly oxygenated blood leaves the fetus and passes through the umbilical arteries to the placenta.
At the site of attachment of the cord to the placenta, these arteries divide into a number of radially disposed chorionic arteries that branch freely in the chorionic plate before entering the chorionic villi.
The blood vessels form an extensive arterio-capillary-venous system within the chorionic villi, which bring the fetal blood extremely close to the maternal blood.
This system provides a very large area for the exchange of metabolic and gaseous products between the maternal and fetal blood.
There is normally no intermingling of fetal and maternal blood; however, very small amounts of fetal blood may enter the maternal circulation through minute defects that sometimes develop in the placental membrane.
The blood in the intervillous space is temporally outside the maternal circulatory system.
It enters the intervillous space through 80 to 100 spiral endometrial arteries in the decidua basalis.
These vessels discharge into the intervillous space through gaps in the cytotrophoblastic shell.
The blood flow from the spiral arteries is pulsatile and is propelled in jetlike fountains by the maternal blood pressure.
The yolk sac forms early and by the 20th week it is very small and thereafter it usually not visible.
The yolk sac can be observed sonographically early in the fifth week.
The presence of the amnion and yolk sac enables early recognition and measurement of the embryo.
The yolk sac is recognizable in ultrasound examinations until the end of the first trimester.
1. 2nd n 3rd wks- transfers nutrients 2 embryo during 2. Blood development occurs in mesoderm covering wall of the yolk sac 3. incorporated into the embryo as the primitive gut. 4. Primordial germ cellsi n endodermal lining of the wall of the yolk sac
At 10 weeks the small yolk sac lies in the chorionic cavity between the amnion and chorionic sac.
The yolk sac usually detaches from the midgut loop by the end of the sixth week.
In about 2% of adults, the proximal intra-abdominal part of the yolk stalk persists as an ileal diverticulum or a Meckel diverticulum
A. Higher risks of fetal morbidity and mortality
B. Risk increases with number of fetuses
C. Infertility drugs-ovulatory failure
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