Placenta & Amnion (General Embryology)

13th day

Endodermal cells

Secondary yolk sac

Exocoelomic cyst

Somatic mesoderm

Connecting stalk

Somatic mesoderem

Splanchnic mesoderm

1ry chorionic villi

Extra-embryonic coelom Chorionic cavity)

Dr. Sherif Fahmy

13th day

Somatic mesoderm

Connecting stalk

1ry chorionic villi

Cyto-trophoblast

Intervillous space

Syncytio-trophoblast

Dr. Sherif Fahmy

Tertiary Chorionic Velli

Dr. Sherif Fahmy

Syncytio-trophoblastCyto-

trophoblast

Somatic extraembryonic mesoderm

Fetal blood vessels

Dr. Sherif Fahmy

Types of Tertiary Chorionic Velli

Decidua basalis (Decidual plate)

Chorion frondosum

Chorionic plate

Chorion leave

Dr. Sherif Fahmy

Fetal Membranes

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Fetal membranes:1- Chorion and placenta.2- Amnion.3- Umbilical cord.4- Yolk sac.

Dr. Sherif Fahmy

Chorion

Dr. Sherif Fahmy

It is the wall of chorionic vesicle.Time: Chorionic vesicle is formed at the 12th day by the formation of extra-embryonic mesoderm.Structure of chorion:1- Syncytiotrophoblast.2- Cytotrophoblast.3- Somatic extra-embryonic mesoderm.Chorionic velli:1- Primary.2- Secondary.3- Tertiary.

Dr. Sherif Fahmy

Somatic mesoderm

Connecting stalk

Secondary yolk sac

Somatic mesoderm

Extra-embryonic coelom

Amniotic cavity

Splanchnic mesoderm


Cyto-trophoblast

Chorion

Exocoelomic cyst

Embryonic disc

Chorionic Vesicle

Dr. Sherif Fahmy

Endodermal cells

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Primary chorionic villus

Cyto-trophoblast


Dr. Sherif Fahmy

Dr. Sherif Fahmy


Cyto-trophoblast

Somatic mesoderm

Secondary chorionic villus

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Dr. Sherif Fahmy


Cyto-trophoblast

Mesoderm

Fetal blood vessels

Tertiary chorioniv villus

Dr. Sherif Fahmy

Dr. Sherif Fahmy

1- Primary chorionic velli (start of 3rd week): cyncytiotropholblasts and cytotrophoblast.

2- Secondary chorionic velli (middle of 3rd week):

Cyncytiotrophoblast, cytotrophoblast and mesoderm (in the central core).

3- Tertiary chorionic velli (end of 3rd week): formation of fetal blood vessels in the mesoderm.

-Tertiary velli, opposite decidua basalis form side branches and called chorion frondosum while under decidua capsularis it will degenerates to form chorion leave.

Dr. Sherif Fahmy

Dr. Sherif Fahmy

PLACENTA

Dr. Sherif Fahmy

Morphology of Placenta• It is the organ of exchange of materials between fetal

and maternal blood.• Shape: Disc like.• 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 septa inbetween).

• 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.Dr. Sherif Fahmy

Dr. Sherif Fahmy

Cotyledon

Groove between cotyledons

Umbilical cord

Maternal surface

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Fetal surface covered with amnion

Umbilical cord

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Formation of Placenta

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Structure of Placenta

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Decidua basalis

Arteriol

Venule

Decidual septum

Cytotrophoblastic shell

Decidual plate

Stem villous

Floating velli

Intervillous space

Chorionic plate

Umbilical veinUmbilical arteryAmnion

MesodermSyncytiotrophoblast

Cytotrophoblast

Dr. Sherif Fahmy

Structure of Placenta• The placenta is developed from 2 parts:

Chorion frondosum (tertiary velli) and Decidua basalis. The internal structure of placenta is described as follow:

• 1- Chorionic velli: They are stem and absorbing (floating). They are composed of syncytiotrophoblast, cytotrophoblast, mesoderm and fetal blood vessels.

• 2- Intervillous spaces: They are spaces between stem villi that are filled with maternal blood.

Dr. Sherif Fahmy

Dr. Sherif Fahmy

3- Cytotrophoblastic shell; complete sheet of cytotrophoblastic cells that is present between decidua basalis and intervillous spaces.4- Decidual septa: They descend from roof of intervillous spaces. Each septum is composed of decidua basalis, cytotrophoblast and cyncytiotrophoblasts. There is a groove opposite each septum which are separated from each other by cotyledones.5- Chorionic plate: composed of amnion, extraembryonic mesoderm,cytotrophoblast and syncytiotrophoblast.

Dr. Sherif Fahmy

Dr. Sherif Fahmy

6- Decidual plate: composed of:- Syncytiotrophoblast.- Cytotrophoblast.- Decidua basalis.

Dr. Sherif Fahmy

Dr. Sherif Fahmy

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- Permites gaseous and nutritive exchange.3- Prevents passage of bacteria, most viruses and damaging factors.

Disappear in 2nd ½ of pregnancy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Placental circulation:1- Maternal part: Maternal blood flow from endometrial arterioles to the intervillous spaces where floating velli are bathed in maternal blood. Exchange of gases and nutritive materials occurs. Then blood flows back from chorionic plate to endometrial veins.2- Fetal part: umbilical arteries carry venous blood of the fetus to placenta while umbilical veins carry blood loaded with nutritive material and oxygen. Dr. Sherif Fahmy

Dr. Sherif Fahmy

Functions of placenta1- Exchange of gases and metabolites.2- Transmission of maternal antibodies

starting from 14th week.3- Production of hormones as progesterone,

estrogen, HCG and somatomammotropin 3- Barrier against bacteria and most of viruses.4- Excretory function as it excretes urea and

creatinine.Dr. Sherif Fahmy

Dr. Sherif Fahmy

Anomalies of Placenta1- 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.

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Placenta previa Marginalis & parietalis

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Dr. Sherif Fahmy

Placenta previa centralis

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Velamentous placenta

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Battle door placenta

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Accessory placenta

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Placenta acretaPlacenta percreta

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Dr. Sherif Fahmy

AMNION

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Extraembryonic coelom (Chorionic Cavity)

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

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

Dr. Sherif Fahmy

8th day of pregnancy

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Endometrium


CytotrophoblastBlastocele Amnioblast

Amniotic cavity

Epiblast Hypoblast Trophoblast

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9th & 10th days

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Cyto-trophoblast

Amnioblast

Amniotic cavity

Epiblast

HypoblastHeuser’s membrane

Primary yolk sacFibrin clot

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

-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.

-Expansion of amniotic cavity leads to folding of the embryonic disc and amnio-ectodermal junction will be present at primitive umbilical ring.

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Extraembryonic coelom (Chorionic Cavity)

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Decidua basalis

Decidua parietalis

Decidua capsularis

Chorion frondosum

Uterine cavity

Amniotic cavity

Chorion frondosum

Fused decidua parietalis and capsularis

Amniotic cavity

Decidua basalis

Chorionic cavity

Dr. Sherif Fahmy

Amniotic fluid- Normal volume is 1000 – 1500 cc clear

watery fluid.- 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

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

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

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

Dr. Sherif Fahmy

YOLK SAC

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.

• Defenitive yolk sac: During 3rd week, hypoblast become replaced by endoderm. After folding, it shares in formation of gut and the part remains outside the embryo is called defenitive yolk sac. It is connected to yolk sac by vitello-intestinal duct.

Dr. Sherif Fahmy

7th day:

Dr. Sherif Fahmy

Dr. Sherif Fahmy

8TH Day of PregnancyEndometrium

Cytotrophoblasts Hypoblasts

Amniotic cavity

Epiblast

Dr.Sherif Fahmy

Dr. Sherif Fahmy

9th & 10th days

Primary yolk sac

Heuser’s membrane


Hypoblast

Amniotic cavity

Epiblast

Cyto-trophoblast Dr. Sherif Fahmy

13th day

Endodermal cells

Secondary yolk sac

Exocoelomic cyst

Connecting stalk

Splanchnic mesoderm

Extra-embryonic coelom Chorionic cavity)

Dr.Sherif Fahmy

Chorionic Vesicle

Dr. Sherif Fahmy

Dr. Sherif Fahmy

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.

Dr. Sherif Fahmy

Abnormalities of Yolk Sac• 1- Vitelline cyst and fistula

due to persistence of vitelline duct.

• 2- Urachal cyst and fistula due to persistence of urachus from allantois.

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Placenta & Amnion (General Embryology)

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