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FETAL MEMBRANES AMNION, CHORION, UMBLICAL CORD, YOLK SAC LEARNING OBJECTIVES • By the end of the lecture, the student will be able to: – Specify the development and functions of fetal membranes, chorion, amnion – Know the details of amnion, chorion. – Describe the formation and function of amniotic fluid and its disorders – Discuss the disorder of related to amniotic fluid volume. – Discuss the development of chorion and its complications. FETAL MEMBRANES • • Fetal membranes, or chorioamniotic membranes, are the amnion and chorion which surround and protect a developing fetus. The Chorion is the outer membrane it surrounds the extraembryonic coelom. AMNION • • Amnion is a membrane building the amniotic sac that surrounds and protects an embryo. It is developed in reptiles, birds, and mammals, which are hence called “Amniota;” but not in amphibia and fishes, which are termed “Anamnia.” AMNIOTIC CAVITY • • In the human embryo the youngest embryo has been studied to have amnion which is already present as a closed sac called the amniotic cavity. Boundaries – – – • • • Roof is made up of a single stratum of flattened, ectodermal cells, the amniotic ectoderm Floor consists of the prismatic ectoderm of the embryonic disk. Outside the amniotic ectoderm is a thin layer of mesoderm, continuous with that of the somatopleure and is connected by the body-stalk with the mesodermal lining of the chorion AMNIOTIC FLUID At first amnion is in contact with the embryo By about 4th week fluid is secreted by the aminoblast begin to accumulate. Fluid increases in quantity and causes the amnion to expand and ultimately to adhere to the inner surface of the chorion, so that the extra-embryonic part of the celom is obliterated. AMNIOTIC FLUID • • • • Amniotic fluid or liquor amnii is the nourishing and protecting liquid contained by the amniotic sac. Amniotic sac grows and begins to fill, mainly with water, approx. two weeks after fertilization. Fluid increases in quantity up to the 6th or 7th month of pregnancy, after which it diminishes somewhat. At the end of pregnancy it is about 1 liter. FUNCTIONS OF AMNIOTIC FLUID • • • Amniotic fluid is "inhaled" and "exhaled" by the fetus. It is essential that fluid be breathed into the lungs in order for them to develop normally. Swallowed amniotic fluid also creates urine and contributes to the formation of meconium. FUNCTIONS OF AMNIOTIC FLUID CONT.. • • • • Amniotic fluid protects the developing baby by cushioning against blows to the mother's abdomen Allows for easier fetal movement Promotes muscular/skeletal development Helps protect the fetus from heat loss. AMNIOCENTESIS • • • Analysis of amniotic fluid, drawn out of the mother's abdomen It can reveal many aspects of the baby's genetic health. This is because the fluid also contains fetal cells, which can be examined for genetic defects. DISORDER OF AMNIOTIC FLUID VOLUME • • Low volumes of amniotic fluid for any particular gestational age-oligohydramnios-result in many cases from placental insufficiency with diminished placental blood flow. Preterm rupture of the amniochorionic membrane occurs in approximately 10% of pregnancies and is the most common cause of oligohydramnios. DISORDER OF AMNIOTIC FLUID VOLUME COT. • When there is renal agenesis (failure of kidney formation), the absence of fetal urine contribution to the amniotic fluid is the main cause of oligohydramnios. OLIGOHYDRAMNIOS • • • A similar decrease in fluid occurs when there is obstructive uropathy (urinary tract obstruction). Complications of oligohydramnios include fetal abnormalities (pulmonary hypoplasia, facial defects, and limb defects) that are caused by fetal compression by the uterine wall. Compression of the umbilical cord is also a potential complication of severe oligohydramnios. DISORDER OF AMNIOTIC FLUID VOLUME • • High volumes of amniotic fluidpolyhydramnios-result when the fetus does not swallow the usual amount of amniotic fluid. Most cases of polyhydramnios (60%) are idiopathic (unknown cause), 20% are caused by maternal factors, and 20% are fetal in origin. POLYHYDRAMNIOS • • • Polyhydramnios may be associated with severe anomalies of the central nervous system, such as meroencephaly (anencephaly). When there are other anomalies, esophageal atresia (blockage), for example, amniotic fluid accumulates because it is unable to pass to the fetal stomach and intestines for absorption. Ultrasonography has become the technique of choice for diagnosing oligo- and polyhydramnios. CHORION • Chorion consists of two layers: – Outer formed by the primitive ectoderm or trophoblast. – Inner formed by the somatic mesoderm; which is in contact with amnion. CHORION • Trophoblast is made up of: – – Internal layer of cubical or prismatic cells, the cytotrophoblast or layer of Langhans External layer of richly nucleated protoplasm devoid of cell boundaries, the syncytiotrophoblas CHORIONIC VILLI • • • • Chorion undergoes rapid proliferation and forms numerous processes, the chorionic villi which invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth of the embryo. Chorionic villi are at first small and nonvascular, and consist of trophoblast only, called as Primary Villi They increase in size and ramify, CHORIONIC VILLI • The mesoderm, carry branches of the umbilical vessels, grows into them, and in this way they are vascularized. • Villi cover the entire chorion by the end of the second month pregnancy. HYDATIDIFORM MOLE • • • • • • • • Hydatidiform mole is an overgrowth of placental tissue or an abnormal growth develops from a non-viable, fertilized egg at the beginning of a pregnancy. It often is referred to as a molar pregnancy. Instead of the normal embryonic cell division that results in the development of a fetus, the placental material grows uncontrolled and develops into a shapeless mass of watery, small, blisterlike sacs (vesicles). The cause of hydatidiform mole is unknown, but is thought to be caused in part by chromosomal abnormalities. CHORIOCARCINOMA Choriocarcinoma is a malignant, trophoblastic and aggressive cancer, usually of the placenta. t is characterized by early hematogenous spread to the lungs. It belongs to the malignant end of the spectrum in gestational trophoblastic disease (GTD). • It is also classified as a germ cell tumor and may arise in the testis or ovary CHORIOCARCINOMA • Characteristic feature is the identification of intimately related syncytiotrophoblasts and cytotrophoblasts without formation of definite placental type villi. UMBILICAL CORD • • • • • • • • • The umbilical cord attaches the fetus to the placenta. Length At full time, as a rule, is about equal to the length of the fetus i.e., about 50 cm. (20 inch) It contains: – – Two arteries (carries deoxygenated blood) One vein (carries oxygenated blood) Embedded in wharton’s jelly DEVELOPMENT OF UMBILICAL CORD Developed from yolk sac and allantois. Replaces yolk sac for the supply of nutrients to the fetus by the end of 5th week. Not directly connected to mother but connected to placenta. Blood flow through umbilical cord increases as the size of fetus increases Yolk sac • • • • • The yolk-sac is situated on the ventral aspect of the embryo It is lined by endoderm, outside of which is a layer of mesoderm. It is filled with vitelline fluid, which may be utilized for the nourishment of the embryo during the earlier stages of its existence. VITELLINE CIRCULATION Blood is conveyed to the wall of the yolk sac by the primitive aortae, and after circulating through a wide-meshed capillary plexus, is returned by the vitelline veins to the tubular heart of the embryo. Function – Nutritive material is absorbed from the yolk-sac and conveyed to the embryo. VITELLINE DUCT • • At the end of the fourth week the yolk-sac presents the appearance of a small pear-shaped vesicle (umbilical vesicle) opening into the digestive tube by a long narrow tube, called vitelline duct. Persistence of vitelline vein is called as Meckel’s Diverticulum MECKEL’S DIVERTICULUM • • • • As a rule the vitelline duct undergoes complete obliteration during the 7th week. in about 2 to 3% of cases its proximal part persists as a diverticulum from the small intestine, Meckel’s diverticulum. which is situated about 2 or 3 feet from the ileocolic junction. Diverticulum is 2 inch long MECKEL’S DIVERTICULUM CONT.. • • May be attached by a fibrous cord to the abdominal wall at the umbilicus. Sometimes a narrowing of the lumen of the ileum is seen opposite the site of attachment of the duct. REFERENCES • • Gray’s human anatomy. Langman book of embryology Thank you