Placenta and fetal circulation


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Placenta and fetal circulation

  1. 1. Placenta and fetal circulation
  2. 2. Early Human Development • • • • • • • Zygote Blastomeres Morula Blastocyst Embryo Fetus Conceptus
  3. 3. Trophoblast: • outer layer of a blastocyst • develop into a large part of the placenta • The trophoblast proliferates and differentiates into 2 cell layers at approximately 6 days after fertilization: – Cytotrophoblast: inner layer, single celled – Syncytiotrophoblast: outer layer, thick and multinucleated. It secretes hCG to maintain progesterone secretion and sustain pregnancy.
  4. 4. Decidualization/ Decidual reaction • Increased structural and secretory activity of endometrium, in response to progesterone. • The decidual cells become filled with lipids and glycogen and take the polyhedral shape characteristic for decidual cells.
  5. 5. Parts of decidua • Decidua basalis – Decidua in contact with blastocyst. • Decidua capsularis – Decidua covering the embryo • Decidua Parietalis - All other decidua on the uterine surface belongs to decidua parietalis. • At term pregnancy: Decidua capsularis and parietalis fuse together to become one
  6. 6. Chorion and chorionic villi • Chorion: outermost layer of two fetal membranes • Syncytotrophoblast layer produce irregular finger like projections to the maternal decidua, and are lined by cytotrophoblast, called primary stem villi • Develops by end of 4th week • Lacunar spaces appear around these villi
  7. 7. • Secondary stem villi: The villi increase in size and ramify, while the mesoderm grows into them. • Develops by 5th week • Tertiary Villi: Branches of the umbilical vessels grow into the mesoderm, and in this way the chorionic villi are vascularized. • Develops by 5th - 6th week • The chorionic villi invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth of the embryo.
  8. 8. • Lacunae in the intervillous space get connected to the maternal blood • the maternal blood fills intervillous space through the spiral arteries, bathes the fetal villi in blood, allowing an exchange of gases to take place.
  9. 9. Fetoplacental circulation • Deoxygenated fetal blood passes through umbilical arteries to the placenta. At the junction of umbilical cord and placenta, the umbilical arteries branch radially to form chorionic arteries. • Chorionic arteries, in turn, branch into cotyledon arteries. • In the villi, these vessels eventually branch to form an extensive arterio-capillary-venous system, bringing the fetal blood extremely close to the maternal blood; but no intermingling of fetal and maternal blood occurs ("placental barrier")
  10. 10. Placental barrier:In spite of close proximate there is no mixing of maternal and foetal blood. The trophoblast and underlying endothelium of foetal vessel behave as semi permeable membrane, which is called placental barrier. It consist of:1. Syncytotrophoblast 2. Cyto trophoblast 3. Basement membrane 4. Stromal tissue 5. Endothelium of foetal capillary wall.
  11. 11. Chorionic frondosum: • embryonic portion of the placenta • the villi overlying the decidua basalis, that subsequently forms placenta
  12. 12. Placenta • organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood s • two components: the fetal placenta, or (Chorion frondosum), which develops from the fetus; and the maternal placenta, or (Decidua basalis), which develops from the maternal uterine tissue
  13. 13. Function of placenta:1. Respiratory function 2. Excretory function 3. Nutritional function:- placenta transfer nutrients from maternal circulation to fetus, are Glucose, Lipids, Amino acid and minerals (fe, ca), Vitamins (folic acid, vit. C), Water and electrolytes. 4. Endocrine function:- placenta acts as endocrine gland and secrets:oestrogen, progesterone, human chorionic gonadotrophin (HCG), Human placental lactogen(HPL), thyroid stimulating hormone (TSH), Hormone resembling adreno-corticotrophine, Relaxin. 5. Barrier function:- prevents transfer of maternal infection. But some organism can cross like:- mump, measles, rubella, HIV, syphilis, chicken pox etc. 6. Enzymatic action- (diamine oxidase that inactivates circulatory pressue, oxytocinase which neutralizes oxytocin, Phospholipase A2 which synthesize AA) 7. Immunological function:- ig G.
  14. 14. Fetomaternal circulation • 2 umbilical arteries – deoxygenated, or "venous-like" blood flows to the placenta • 1 umbilical vein – with a significantly higher oxygen content(80% saturation)
  15. 15. • As fetal lungs are not functioning, the fetus obtains oxygen and nutrients from the mother through the placenta and the umbilical cord • The core concept behind fetal circulation is that fetal hemoglobin has a higher affinity for oxygen than does adult hemoglobin, which allows a diffusion of oxygen from the mother's circulatory system to the fetus. • Circulatory system of the mother is not directly connected to that of the fetus . • Water, glucose, amino acids, vitamins, and inorganic salts freely diffuse across the placenta along with oxygen
  16. 16. Circulation • Blood from the placenta is carried to the fetus by the umbilical vein. • About half of this enters the fetal ductus venosus and is carried to the inferior vena cava, while the other half enters the liver proper from the inferior border of the liver. The branch of the umbilical vein that supplies the right lobe of the liver first joins with the portal vein
  17. 17. • The blood then moves to the right atrium of the heart. • Between the right and left atrium, the foramen ovale allow most of the blood flows through it directly into the left atrium from the right atrium, thus bypassing pulmonary circulation. • The continuation of this blood flow is into the left ventricle, and from there it is pumped through the aorta into the body.
  18. 18. • Some of the blood entering the right atrium does not pass directly to the left atrium through the foramen ovale, but enters the right ventricle and is pumped into the pulmonary artery. • In the fetus, connection between the pulmonary artery and the aorta, called the ductus arteriosus, which directs most of this blood away from the fluid filled, non functioning lungs
  19. 19. Changes of fetal circulation at birth • Hemodynamics of fetal circulation undergo profound changes, soon after birth: – Caessation of placental blood flow – Initiation of respiration
  20. 20. 1. Closure of umbilical arteries: Functionally, soon after birth, but actual obliteration takes by 2-3 months 2. Closure of umbilical vein: little later than arteries and allows few extra volume of blood to go to fetus from placenta 3. Closure of ductus arteriosus: within few hrs of respiration 4. Closure of foramen ovale: functionally , soon after birth but anatomically, closes in about 1 year
  21. 21. Changes of fetal circulation at birth • Fetal Structure • Adult Remnant • Foramen ovale • Ductus arteriosus • Left umbilical vein • Fossa ovalis of the heart • Ligamentum arteriosum – Extra-hepatic portion – Intra-hepatic portion (ductus venosus) • Left and right umbilical arteries – Proximal portions – Distal portions • Ligamentum teres hepatis • Ligamentum venosum • Superior vesical arteries • Medial umbilical ligaments
  22. 22. Patent ductus arteriosus: • Failure of a child's DA to close after birth • generation of a left-to-right shunt as blood flows form hogh pressure aorta to low pressure pulmonary artery. • If left uncorrected, patency leads to pulmonary hypertension and possibly congenital heart disease and cardiac arrythmia • Prostaglandins are responsible for maintaining the ductus arteriosus by dilatation of the vascular smooth muscles. • Closure may be induced with NSAIDs because these drugs inhibit prostaglandin
  23. 23. Patent foramen ovale: • is an incomplete closure of the atrial septum that results in the creation of a flap or a valve-like opening in the atrial septal wall • is present in everyone before birth but seals in about 80% of people. • With each heartbeat, blood can flow in either direction directly between the right and left atrium. • When blood moves directly from the right atrium to the left atrium, this blood bypasses the filtering system of the lungs