Revision on General Embryology 2
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Transcript of Revision on General Embryology 2
Fetal Membranes
Dr.Sherif Fahmy
Fetal membranes:1- Chorion 2- 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
Connecting stalk
Somatic mesoderm
Syncytio-trophoblast
Cyto-trophoblast
Chorion
Chorionic Vesicle
Dr. Sherif FahmyDr. Sherif Fahmy
Dr.Sherif Fahmy
Dr. Sherif Fahmy
Primary chorionic villus
Cyto-trophoblast
Syncytio-trophoblast
Dr.Sherif Fahmy
Dr. Sherif Fahmy
Syncytio-trophoblast
Cyto-trophoblast
Somatic mesoderm
Secondary chorionic villus
Dr.Sherif Fahmy
Dr. Sherif Fahmy
Syncytio-trophoblast
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
Dr. Sherif Fahmy
Dr.Sherif Fahmy
Fetal surface covered with amnion
Umbilical cord
Dr. Sherif Fahmy
Dr.Sherif Fahmy
Formation of Placenta
Dr.Sherif Fahmy
Dr.Sherif Fahmy
Dr.Sherif Fahmy
Dr.Sherif Fahmy
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
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.
Dr. Sherif Fahmy
Dr. Sherif Fahmy
Placenta previa Marginalis & parietalis
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Dr. Sherif Fahmy
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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Dr. Sherif Fahmy
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
Dr. Sherif Fahmy
Amnioblast
Amniotic cavity
Epiblast Hypoblast
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9th & 10th days
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Cyto-trophoblast
Amnioblast
Amniotic cavity
Epiblast
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
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
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.3- Premature rupture of amnion.
Dr. Sherif Fahmy
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
Dr.Sherif Fahmy
Dr. Sherif Fahmy
9th & 10th days
Primary yolk sac
Heuser’s membrane
Hypoblast
Amniotic cavity
Epiblast
Dr. Sherif Fahmy
13th day
Endodermal cells
Secondary yolk sac
Exocoelomic cyst
Extra-embryonic coelom Chorionic cavity)
Dr.Sherif Fahmy
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.
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
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
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.
Dr.Sherif Fahmy
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
Dr.Sherif Fahmy
Dr.Sherif Fahmy
Dr.Sherif Fahmy
Dr.Sherif Fahmy
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
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 .
Dr.Sherif Fahmy
Morula
stageEmbryonic Disc StageEarly
blastcyste
Dr.Sherif Fahmy
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.
Dr.Sherif Fahmy
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
Dr.Sherif Fahmy
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