amnion & umbilical cord (general embryology)

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)

Dr. Sherif Fahmy

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.

Dr. Sherif Fahmy

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

Dr. Sherif Fahmy

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).