amnion & umbilical cord (general embryology)
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AMNION
AMNION-It is a membrane that enclose amniotic cavity.-Formation: -It is formed at the 8th day as a small cavity in
epiblast cells with formation of amnioblasts. -So, floor of the cavity is epiblast while the
roof is formed from amnioblasts. -By the 12th day it becomes separated from cytotrophoblasts by primary mesoderm (Extraembryonic).-Amnio-ectodermal junction is at the margin of oval embryonic disc at the 3rd week.Dr. Sherif Fahmy
-During 4th week, expansion of amniotic cavity leads to folding of the embryonic disc and amnio-ectodermal junction will be present at primitive umbilical ring.-At 3rd month amnion comes in contact with chorion to form amnio-chorionic membrane with obliteration of chorionic cavity.-By the end of 3rd month, uterine cavity is obliterated due to expansion of amniotic cavity. -Finally, the amniotic cavity surrounds the fetus and forms a tubular sheath around the umbilical cord.
Dr. Sherif Fahmy
8th day of pregnancy
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Endometrium
CytotrophoblastAmnioblast
Amniotic cavity
Epiblast Hypoblast
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9th & 10th days
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Cyto-trophoblast
Amnioblast
Amniotic cavity
Epiblast
Hypoblast
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13th daySecondary yolk sac
Connecting stalk
Extra-embryonic coelom
(Chorionic cavity)
Dr.Sheri f FahmyAmniotic cavity
Chorionic Vesicle
Amnion & Folding
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Dr. Sherif Fahmy
Dr. Sherif Fahmy
Dr. Sherif Fahmy
Definitive yolk sac Vitelline duct
Midgut
Expansion of Amniotic Cavity
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Extraembryonic coelom (Chorionic Cavity)
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Dr. Sherif Fahmy
Dr. Sherif Fahmy
Dr. Sherif Fahmy
Decidua parietalis
Decidua capsularis
Uterine cavity
Amniotic cavity
Fused decidua parietalis and capsularis
Amniotic cavity
Chorionic cavity
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Amniotic fluid- Normal volume is 1000 – 1500 cc clear
watery fluid at full term.- Source: 1st from amnioblast then from
kidney.
- If the volume is less than 500 cc it is called oligohydramnios.
-If the volume is more than 2000 cc is called polyhydramnios. Dr. Sherif Fahmy
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- A space for accumulated urine.2- Allows fetal movements to help body muscles to develop.3- Help suckling training and development of gut muscles. Dr. Sherif Fahmy
3- During labor:1- Protects against uterine contractions.2- Formation of bag of water that gradually dilate the cervix.3- Sterile amniotic washes vagina before passage of baby.4- Rupture of amniotic sac is a sign of start of delivery.
Dr. Sherif Fahmy
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.
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UMBILICAL CORD
Morphology of Umbilical CordIt is the connection between placenta and
fetus.• Length: 50 – 60 cm• Diameter: 2 cm.• Shape: Tortous, showing false notes.• 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.
Fetal surface covered with amnion
Umbilical cord
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Dr. Sherif Fahmy
Development of the Cord
1- Primitive umbilical ring.
2- Primitive umbilical cord.
3- Definitive umbilical cord.
Primitive Umbilical RingExpansion of amniotic cavity, leads to folding with ventral shifting of amnio-ectodermal junction and formation of primitive umbilical ring.
Contents: Connecting stalk containing allantois and
umbilical vessels.Vitelline duct and vitelline vessels.Connection between intra-embryonic and extra-
embryonic coelom.
Expansion of amniotic cavity, leads to elongation of 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
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 and 2 umbilical arteries.
Degeneration of vitelline duct and allantois
Transformation of mesoderm of connecting stalk into wharton’s jelly.
Definitive Umbilical Cord
Development
1- Primitive umbilical ring
Embryonic disc with removed ectoderm
Intra-embryonic ceolom
Connecting stalk
Allantois
Umbilical vessels
Definitive yolk sac
Vitelline vesselsVitelline duct
Primitive umbilical ring
2- Primitive umbilical cord
3-Definitive umbilical cord
• Abnormalities of Umbilical Cord• 1- Short cord: leads to premature separation
of placenta.• 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).