Revision on General Embryology 2

Fetal Membranes

Dr.Sherif Fahmy

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

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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.

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Connecting stalk

Somatic mesoderm

Syncytio-trophoblast

Cyto-trophoblast

Chorion

Chorionic Vesicle

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Dr. Sherif Fahmy

Primary chorionic villus

Cyto-trophoblast


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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

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Decidua basalis

Chorion frondosum

Chorionic plate

Chorion leave

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Dr.Sherif Fahmy

PLACENTA(Page 38)

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

Cotyledon

Groove between cotyledons

Umbilical cord

Maternal surface

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Dr.Sherif Fahmy

Fetal surface covered with amnion

Umbilical cord

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Dr.Sherif Fahmy

Formation of Placenta

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Dr.Sherif Fahmy

Structure of Placenta

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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

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

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

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

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.

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Dr. Sherif Fahmy

Placenta previa Marginalis & parietalis

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Placenta previa centralis

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Dr. Sherif Fahmy

Velamentous placenta

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Dr. Sherif Fahmy

Battle door placenta

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Dr. Sherif Fahmy

Accessory placenta

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Dr. Sherif Fahmy

Placenta acretaPlacenta percreta

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AMNIONDr.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.

8th day of pregnancy

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Amnioblast

Amniotic cavity

Epiblast Hypoblast

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9th & 10th days

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Cyto-trophoblast

Amnioblast

Amniotic cavity

Epiblast

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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.

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Dr. Sherif Fahmy

Dr. Sherif Fahmy

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Extraembryonic coelom (Chorionic Cavity)

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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

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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

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.

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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 amnion.

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YOLK SACDr.Sherif Fahmy

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 endodermal 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.

7th day:

Dr. Sherif Fahmy

Dr. Sherif Fahmy

8TH Day of PregnancyEndometrium

Cytotrophoblasts Hypoblasts

Amniotic cavity

Epiblast

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Dr. Sherif Fahmy

9th & 10th days

Primary yolk sac

Heuser’s membrane

Hypoblast

Amniotic cavity

Epiblast

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13th day

Endodermal cells

Secondary yolk sac

Exocoelomic cyst

Extra-embryonic coelom Chorionic cavity)

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Chorionic Vesicle

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Dr.Sherif Fahmy

Dr. Sherif Fahmy

Functions of yolk sac:• Formation of 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.

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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

UMBILICAL CORDDr.Sherif Fahmy

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. Dr.Sherif Fahmy

Dr.Sherif Fahmy

Development of the Cord• Primitive umbilical ring: - Expansion 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 intraembryonic and extra-embryonic coelom. Dr.Sherif Fahmy

Primitive umbilical cord:- 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- Intestinal loop in its proximal part.4- Umbilical and vitelline vessels.

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Definitive umbilical cord:- Return of intestinal loop to abdominal cavity at 3rd month.-Obliteration of vitelline duct, allantois, extra-embryonic part of vitelline vessels.-Degeneration of one umbilical vein with persistence of other vein and 2 umbilical arteries.-Transformation of mesoderm of connecting stalk into wharton’s jelly.

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Development

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Embryonic disc with removed ectoderm

Intra-embryonic ceolom Dr.Sherif Fahmy

Dr.Sherif Fahmy

• 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).

Dr.Sherif Fahmy

Dr.Sherif Fahmy

TwinsDr.Sherif Fahmy

Types of TWINSDizygotic (Fraternal) 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 placenta, chorion

and amniotic cavity.- Twins are non-identical and may of same sex

or different.

Dr.Sherif Fahmy

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 occure 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 .

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Morula

stageEmbryonic Disc StageEarly

blastcyste

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SIAMESE (CONJOINED) TWINS• Fused monozygotic twins that occurs

due to incomplete separation of emberyonic disc. They could be either:Craniopagus: Fusion between 2 heads.Thoracopagus: Fusion at thoracic region.Pygopagus: Fusion at the pelvic region.

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Conjoined Twines

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الله إنشاء

كلكم أشوفكم

ثانية سنة فى

طب

.فهمى شريف د

Birth DefectsDr.Sherif Fahmy

Down Syndrome

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Dr.Sherif Fahmy

Cri du Chat Syndrome

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Turner Syndrome

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Achondroplasia

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A Child of A Mother Treated by Antiepileptic drug

A Child of A Mother Treated with Antithyroid drug

A Child of A mother Exposed to Rubella Infection

External Appearance of the Embryo (4th – 8th week)

At the embryonic period (4th – 8th week), human shape becomes easily identified.-Head, body and limb buds are easily identified.-Eyes, nose and ears are seen.

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C-R length in mms Age of embryo in weeks

5 – 8 5

10 – 14 6

17 – 22 7

28 – 30 8

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Fetal PeriodDr.Sherif Fahmy

C-R length in cm Age of embryo in months

5 – 8 cm 3rd month

18 cm 5th month

36 cm Full term fetus at birth

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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.Dr.Sherif Fahmy

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 caesosa.

Fetal movement:It is clearly recognized since the 5th month.

Dr.Sherif Fahmy

The End & Beginning

With my best wishes Dr. Sherif

Fahmy

Revision on General Embryology 2

Education

Transcript of Revision on General Embryology 2