General Embryology 4 (Fetal membranes & twins)

This presentation explains the membranes of the fetus during pregnancy including Chorion and placenta, Amnion , Umbilical cord , & Yolk sac.
As well as the explanation of twins development and all the fetal periods

Transcript

1. Fetal Membranes
2. Fetal membranes: 1- Chorion and placenta. 2- Amnion. 3- Umbilical cord. 4- Yolk sac.
3. PLACENTA
4. Morphology of Placenta It is the organ of exchange of materials between fetal and maternal blood. Shape: Disc like. Diameter: 15 -25 cm. Thickness: About 3 cm. Weight: About 500 – 600 gm Site: At original implantation site which is upper part of posterior wall of uterus. Surfaces: • Fetal surface: It is covered with amnion and fetal blood vessels. Umbilical cord is attached near the center of this surface. • Maternal surface: Shows 15 – 20 rounded elevations (cotyledons) with grooves inbetween.
5. Formation of Placenta Placenta is formed of 2 components: 1- Fetal part (chorionic plate) 2- Maternal part (decidual plate)
6. Structure of Placenta
7. Chorion frondosum (Chorionic plate) Decidua basalis (Decidual Plate)
8. Decidua basalis Arteriol Venule Decidual septum Cytotrophoblastic shell Decidual plate Stem villous Floating villi Intervillous space Chorionic plate Umbilical vein Umbilical artery Amnion Mesoderm Syncytiotrophoblast Cytotrophoblast Dr. Sherif Fahmy Dr. Sherif Fahmy
9. Placental Circulation A- Maternal part. B- Fetal part.
10. Arteriol (80 – 100) Venule Intervillous space Umbilical vein Umbilical artery Floating villi
11. Placental Barrier
12. Fetal blood vessels Intervillous space Syncytiotrophoblast Cytotrophoblast Tertiary villous Somatic mesoderm
13. Placental barrier: It is the separation between fetal and maternal blood. Structure: 1- Syncytiotrophoblast. 2- Cytotrophoblast. 3- Extraembryonic mesoderm. 4- Endothelium of fetal blood vessels. Functions of the barrier: 1- Separates between fetal and maternal blood. 2- Prevents passage of bacteria, most viruses and damaging factors. 3- Permites gaseous and nutritive exchange. Disappear in 2nd ½ of pregnancy
14. Functions of Placenta
15. 1- Exchange of gases and metabolites. 2- Transmission of maternal antibodies starting from 14th week. 3- Production of hormones as progesterone, estrogen, HCG and somatomammotropin 4- Barrier against bacteria and most of viruses. 5- Excretory function as it excretes urea and creatinine.
16. Anomalies of Placenta
17. Abnormalities in position: ➢ Placenta previa parietalis. ➢ Placenta previa marginalis. ➢ Placenta previa centralis.
18. Placenta previa Marginalis & parietalis Normal site of placenta
19. Placenta previa centralis
20. Abnormality in attachement of umbilical cord: ➢Velamentous placenta. ➢Battle door placenta.
21. Velamentous placenta Dr. Sherif Fahmy Membranes
22. Battle door placenta Dr. Sherif Fahmy
23. Abnormality in number: ➢Twin placenta. ➢Accessory placenta.
24. Accessory placenta
25. Abnormality in shape: ➢Bilobed placenta. ➢Trilobed placenta.
26. Bilobed placenta Dr. Sherif Fahmy
27. Abnormality in infiltration: ➢Placenta accrete. ➢Placenta increta. ➢Placenta percreta.
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29. 1- Abnormalities in position: A- Placenta previa parietalis. B- Placenta brevia marginalis. C- Placenta brevia centralis. 2- Abnormality in shape: A- biloped placenta. B- Triloped placenta. 3- Abnormality in number: A- Twin placenta. B- Accessory placenta. 4- Abnormality in attachement of umbilical cord: A- Velamentous. B- Battle door. 5- Abnormality in infiltration: Placenta accrete, increta and percreta.
30. AMNION (Wall of Amniotic Cavity)
31. Amniotic Cavity ➢Formation. ➢Results of expansion. ➢Sources and constituents of amniotic fluid. ➢Importance of amniotic cavity. ➢Abnormality of amniotic fluid volume.
32. Formation
33. 8th day of pregnancy Amnioblast Amniotic cavity Epiblast Hypoblast Blastocele Dr. Sherif Fahmy
34. 9th & 10th days Primary yolk sac Heuser’s membrane Hypoblast Amniotic cavity Dr. Sherif Fahmy
35. 13th day Secondary yolk sac Extra-embryonic coelom (Chorionic cavity) Amniotic cavity Chorionic Vesicle Dr. Sherif Fahmy
36. Expansion of Amniotic Cavity
37. Extraembryonic coelom (Chorionic Cavity) Amnio-ectodermal junction At the 3rd week Dr. Sherif Fahmy
38. Connecting stalk Allantois Vitelline duct Amnio-ectodermal junction (around primitive umbilical ring) Amniotic cavity After folding Amnion Ectoderm (on outer surface of the embryo) Dr. Sherif Fahmy
39. Amnion Chorion Dr. Sherif Fahmy
40. Definitive yolk sac Amniotic cavity Chorionic cavity Chorion Decidua capsularis Decidua parietalis Uterine cavity Amnion
41. Fused amnion, chorion, with obliteration of chorionic cavity at beginning of 3rd month while decidua capsularis and decidua parietalis fuse together with obliteration of uterine cavity at the end of 3rd month During 3rd month Dr. Sherif Fahmy
42. Amniotic fluid Volume - Normal volume is 1000 – 1500 cc Constituents: - Clear watery fluid, rich with electrolytes, protein, lipids, carbohydrate and stem cells at full term. Source: Starts formation from amnioblast and by osmosis from maternal blood, then from kidney.
43. Functions of amniotic fluid: 1- At early pregnancy: 1- Acts as water cushion that absorbs external shocks. 2- Acts as heat insulator. 3- Prevents adhesion of embryo to wall of uterus. 4- Prevents adhesion of fetal parts. 2- At late pregnancy: 1- Give a space to allows fetal movements that help body muscles to develop. 2- Give a space for accumulated urine 3- Help suckling training and development of gut muscles.
44. 3- During labor: 1- Protects against uterine contractions. 2- Formation of bag of water that gradually dilate the cervix. 3- Rupture of amniotic sac is a sign of start of delivery. 4- Sterile amniotic washes vagina before passage of baby. 4- Amniotic fluid & stem cells: Amniotic fluid is a source of stem cells.
45. Abnormalities of amniotic fluid: 1- Polyhydramnios. Causes: 1- No cause (35 %). 2- Maternal diabetes. 3- Congenital malformation e.g. anencephaly and esophageal atresia. 2- Oligohydramnios. Cause: -Renal agenesis. 3- Premature rupture of amniotic sac: It is a common cause of preterm labor.
46. UMBILICAL CORD
47. Morphology of Definitive Umbilical Cord It is the connection between placenta and fetus. Length: 50 – 60 cm Diameter: 2 cm. Shape: Tortous, showing false knots. Contents: 2 umbilical arteries, one umbilical vein embedded in wharton’s jelly and surrounded by amniotic membrane. Attachments: It is attached to fetal surface of placenta near its center, the other attachment is to ventral aspect of fetal abdominal wall. Functions: – It contains umbilical vessels that connect the fetus to the placenta. – Allows free mobility of the fetus.
49. Fetal surface covered with amnion Umbilical cord Dr. Sherif Fahmy
50. Development of the Cord 1- Primitive umbilical ring. 2- Primitive umbilical cord. 3- Definitive umbilical cord.
51. Primitive Umbilical Ring It is formed after folding, surrounded by amnio-ectodermal junction and contains: 1- Vitelline duct with vitelline vessels. 2- Connecting stalk. 3- Allantois with umbilical vessels. .
52. Connecting stalk Allantois Vitelline duct Amnio-ectodermal junction (around primitive umbilical ring) Amniotic cavity After folding Amnion Ectoderm (on outer surface of the embryo) Umbilical vessels Dr. Sherif Fahmy
53. ➢ Expansion of amniotic cavity, leads to formation of a sheath of amnion around the structures that pass through the primitive ring with formation of primitive umbilical cord. Contents: 1- Yolk sac and vitelline duct. 2- Connecting stalk with remnant of allantois. 3- Umbilical and vitelline vessels. 4- Intestinal loop in its proximal part. Primitive umbilical cord
54. Formation of amnion sheath around primitive cord Primitive umbilical ring (surrounded by amnio- ectodermal junction) Placenta
55. Physiological umbilical hernia Primitive umbilical cord Dr. Sherif Fahmy
56. ➢Return of intestinal loop to abdominal cavity at 3rd month. ➢Obliteration of extra-embryonic part of vitelline vessels and one umbilical vein with persistence of other vein (left vein) and 2 umbilical arteries. ➢ Degeneration of vitelline duct, yolk sac and most of allantois. ➢ Transformation of mesoderm of connecting stalk into Wharton’s jelly. Definitive Umbilical Cord
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59. Abnormalities of Umbilical Cord
60. 1- Short cord: leads to premature separation of placenta during delivery of the baby. 2- Long cord: It may encircle neck of fetus and may form true knots. 3- Congenital umbilical hernia (omphalocele): the cord contains coils of intestine. 4- Presence of one umbilical artery. 5- Abnormal attachment of the cord: –Marginal attachment (battledore) –Through membranes (velamentous).
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64. YOLK SAC
65. Fate & development of yolk sac • Primary yolk sac: It replaces cavity of blastocyst after the formation of Heuser’s membrane which is formed of flat cells that originate from hypoblast cells at 9th & 10th day. • Secondary yolk sac: additional cells from hypoblast cells will line the Heuser’s membrane, reduction of size of yolk sac and formation of allantois. This occurs in the 13th day. • Definitive yolk sac: It is the part that remains outside the embryo after folding. It is connected to yolk sac by vitello-intestinal (vitelline) duct.
66. 9th & 10th days Primary yolk sac Heuser’s membrane Hypoblast Dr. Sherif Fahmy Dr. Sherif Fahmy
67. 13th day Endodermal cells Secondary yolk sac Exocoelomic cyst Connecting stalk Splanchnic mesoderm Extra- embryonic coelom Chorionic cavity) Chorionic Vesicle Dr. Sherif Fahmy
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69. Definitive yolk sac Dr. Sherif Fahmy
70. Functions of yolk sac: • Gut: foregut, midgut and hindgut. • Allantois: forms part of urinary bladder. • Primordial germ cells: Which are spermatogonia and oogonia which are formed in its caudal part (hind gut). • Vitelline vessels: develop from mesoderm around vitelline duct. Intra-embryonic part form portal vein and arteries of intestine. • Blood cells: develop in the mesoderm around the yolk sac.
71. Twins
72. Types of TWINS Dizygotic twins: - It is the commonest type as it represent 2/3 of twins and 7 – 11 / 1000 births. - Fertilization of 2 separate ova. - Each embryo has its own amniotic cavity, chorion and placenta. - Twins are non-identical and may of same sex or different.
73. Monozygotic (Identical) twins: Developed from division of a fertilized ovum. Twins of this type are identical and of same sex. Its incidence is 0.3 – 0.4 % Division may occur at 3 different stages: 1- At morula stage: Twins has separate amnion, chorion and placentae (as in dizygotic). 2- At blastocyst stage: due to division of inner cell mass. Twins has separate amniotic cavity but single chorion and placenta. 3- At embryonic disc: Midline division of the embryonic disc. Twins has common amniotic cavity, common chorion and common placenta .
74. Early blastcyste Dr. Sherif Fahmy
75. SIAMESE (CONJOINED) TWINS •Fused monozygotic twins that occurs due to incomplete separation of embryonic disc. They could be either: Craniopagus: Fusion between 2 heads. Thoracopagus: Fusion at thoracic region. Pygopagus: Fusion at the pelvic region.
76. Conjoined Twines Dr. Sherif Fahmy
77. Twin defects: 1.Increased incidence of prematurity as about 12 % of premature infants are twins. 2.Low birth weight. 3.High incidence of prenatal mortality.
78. Fetal Period (from 9th week till birth)
79. C-R length Age of embryo 5 – 8 cm 3rd month 18 cm 5th month 36 cm Full term fetus at birth
80. Relative size of head to body: -At the beginning of the 3rd month, the head is ½ the CR length. -At the beginning of the 5th month, the head is 1/3 the CH length. -At birth, the head is ¼ of CH length. Weight growth: -At the end of 5th month, the weight is ½ kg. -At the 7th month, the weight is 1.75 kg. -At full term, the weight is 3.5 kg.
81. Changes in external features: -Face becomes human looking. -Limbs become longer. -External genitalia are differentiated at 12th week. -Lanugo hair covers the fetus since the 4th month. -The skin is wrinkled till the end of 6th month. -Testes descend to scrotum just before birth. -Skin is covered by fatty substance called Vernix caseosa Fetal movement: It is clearly recognized since the 5th month. Time of birth (expected day of delivery) ➢ 280 days from 1st day of last menstruation. ➢ 266 days from day of fertilization (day of ovulation = 14 days after 1st day of menstruation).