The Foetus and Placenta.pptx

EMBRYOLOGY

1. The Foetus and Placenta Themba Hospital FCOG(SA) Part 1 Tutorials By Dr N.E Manana

2. Foetus The period from the beginning of the ninth week to birth is known as the fetal period Characterized by maturation of tissues and organs and rapid growth of the body The length of the fetus is usually indicated as the CRL (sitting height) or as the CHL (standing height) Length of pregnancy: 280 days after LNMP or 266 after fertilization Growth in length is particularly striking during the third, fourth, and fifth months, while an increase in weight is most striking during the last 2 months of gestation

3. Foetus One of the most striking changes taking place during fetal life is the relative slowdown in growth of the head compared with the rest of the body At the beginning of the third month, the head constitutes approximately half of the CRL , at birth, it is approximately one quarter of the CHL During the third month, the face becomes more human looking The eyes , initially directed laterally, move to the ventral aspect of the face, and the ears come to lie close to their definitive position at the side of the head

4. Fetal Growth At 12 weeks : CRL 6-7cm 1. Swallowing 2. Primitive ossification centers 3. External genitalia developed 4. Bowel withdrawn in the abdomen 5. Muscular activity 6. Chorion cavity obliterated At 16 weeks: CRL 12cm, Weight 110g Eye movement Gender visible Respiratory movements At 20 weeks : CRL 15cm , Weight 500g Hair: lunago , head, eye brows Fetal movement felt At 24weeks: CRL 20cm, Weight 650g Suckling movements Hearing Skin wrinkled Lungs at Canalicula stage At 28 weeks: CRL25cm, Weight 1kg (90% Survival) Skin thin wrinkled and red with vernix ceseosa Eye site At 32 weeks: Weight 1.8kg Tastes descended At 36 weeks: Weight 2.6kg Skin smooth

5. Time of Birth Fertilization date rarely used, LNMP preferred In women with regular 28-day menstrual periods, the method is fairly accurate, but when cycles are irregular, substantial miscalculations may be made Most foetuses are born within 10 to 14 days of the calculated delivery date Ultrasound, which can provide an accurate (1 to 2 days) measurement of CRL during the 7th to 14th weeks

6. Fetal membranes and placenta The placenta facilitates nutrient and gas exchange It increases in surface area after 12weks due to demands The fetal component : trophoblast and extraembryonic mesoderm (chorionic plate) The maternal component : uterine endometrium By the end of the second month the placenta has Tertiary villi , with sterm ( anchoring ) villi

7. Placenta Maternal blood is delivered to the placenta by spiral arteries in the uterus Invasion of the spiral arteries by cytotrophoblast cells transforms these vessels from small-diameter, high-resistance vessels to larger-diameter, low resistance vessels By the beginning of the fourth month, cytotrophoblastic cells and some connective tissue cells disappear. The syncytium and endothelial wall of the blood vessels are then the only layers that separate the maternal and fetal circulations

8. Placenta During the fourth and fifth months , the decidua forms a number of decidual septa , which project into intervillous spaces but do not reach the chorionic plate As a result of this septum formation, the placenta is divided into a number of compartments( cotyledon ) Because the decidual septa do not reach the chorionic plate , contact between intervillous spaces in the various cotyledons is maintained. As a result of the continuous growth of the fetus and expansion of the uterus, the placenta also enlarges

9. Full-Term Placenta Discoid with a diameter of 15 to 25 cm , is approximately 3 cm thick , and weighs about 500 to 600 g When the placenta is viewed from the maternal side, 15 to 20 slightly bulging areas, the cotyledons , covered by a thin layer of decidua basali s, are clearly recognizable Grooves between the cotyledons are formed by decidual septa. The fetal surface of the placenta is covered entirely by the chorionic plate . A number of large arteries and veins converge toward the umbilical cord Attachment of the umbilical cord is usually eccentric and occasionally even marginal . Rarely, however, does it insert into the chorionic membranes outside the placenta ( velamentous insertion).

10. Circulation of the Placenta Cotyledons receive their blood through 80 to 100 spiral arteries that pierce the decidual plate and enter the intervillous spaces at more or less regular intervals As the pressure decreases, blood flows back from the chorionic plate toward the decidua, where it enters the endometrial veins Collectively, the intervillous spaces of a mature placenta contain approximately 150 mL of blood , replenished 3 to 4x per minute The chorionic villi have a surface area of 4 to 14 m2 , but not all villi exchange

11. Placental membrane Initially composed of 4 layers 1 . Endothelial of fetal vessels, 2. connective tissue in the villi core, 3. cytotrophoblast layer 4. syncytium From 16 weeks the placenta membrane thins out, increasing gasias exchange Normally the is no mixing but small number of fetal blood cells occasionally escape

12. Function Exchange of gases : O2,CO2,CO simple diffusion Exchange of nutrients and electrolytes Transmission of maternal antibodies Hormone production Prog, E2, HCG, PL,

13. Umbilical cord 1. Connective stalk 2. The yolk stalk (vitelline duct), accompanied by the vitelline vessels ; 3. The canal connecting the intraembryonic and extraembryonic cavities The amniotic cavity enlarges rapidly at the expense of the chorionic cavity, and the amnion begins to envelop the connecting and yolk sac stalks, Crowding them together and giving rise to the primitive umbilical cord Distally, the cord contains the yolk sac stalk and umbilical vessels . More proximally, it contains some intestinal loops and the remnant of the allantois

14. Umbilical cord The abdominal cavity is temporarily too small for the rapidly developing intestinal loops , and some of them are pushed into the extraembryonic space in the umbilical cord. These extruding intestinal loops form a physiological umbilical hernia At approximately the end of the third month , the loops are withdrawn into the body of the embryo, and the cavity in the cord is obliterated. When the allantois and the vitelline duct and its vessels are also obliterated , all that remains in the cord are the umbilical vessels surrounded by Wharton’s jelly .

15. Amniotic fluid Increases from 30ml at 10 weeks ( Ultrafiltration of maternal plasm), 450ml at 20 weeks ( Fetal urine ), to 1l at 37weeks Fetal kidneys start producing urine at 12 weeks Amniotic fluid also contains : fetal cells, vernix, lunago and various secreations Function: cushin , lubricant, allows movement, maintain Temp, Growth factors Its volume is replaced every 3hrs From 20weeks the fetus drinks about 400ml per day

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