Early Human Development
• outer layer of a blastocyst
• develop into a large part of the placenta
• The trophoblast proliferates and differentiates into 2 cell
layers at approximately 6 days after fertilization:
– Cytotrophoblast: inner layer, single celled
– Syncytiotrophoblast: outer layer, thick and
multinucleated. It secretes hCG to maintain progesterone
secretion and sustain pregnancy.
Decidualization/ Decidual reaction
• Increased structural and secretory activity of endometrium, in
response to progesterone.
• The decidual cells become filled with lipids and glycogen and
take the polyhedral shape characteristic for decidual cells.
Parts of decidua
• Decidua basalis – Decidua in
contact with blastocyst.
• Decidua capsularis – Decidua
covering the embryo
• Decidua Parietalis - All other
decidua on the uterine
surface belongs to decidua
• At term pregnancy: Decidua
capsularis and parietalis fuse
together to become one
Chorion and chorionic villi
• Chorion: outermost layer of two fetal membranes
• Syncytotrophoblast layer produce irregular finger like
projections to the maternal decidua, and are lined by
cytotrophoblast, called primary stem villi
• Develops by end of 4th week
• Lacunar spaces appear around these villi
• Secondary stem villi: The villi increase in size and ramify,
while the mesoderm grows into them.
• Develops by 5th week
• Tertiary Villi: Branches of the umbilical vessels grow into the
mesoderm, and in this way the chorionic villi are vascularized.
• Develops by 5th - 6th week
• The chorionic villi invade and destroy the uterine decidua and
at the same time absorb from it nutritive materials for the
growth of the embryo.
• Lacunae in the intervillous
space get connected to the
• the maternal blood fills
intervillous space through
the spiral arteries, bathes
the fetal villi in blood,
allowing an exchange of
gases to take place.
• Deoxygenated fetal blood passes through umbilical arteries to
the placenta. At the junction of umbilical cord and placenta,
the umbilical arteries branch radially to form chorionic
• Chorionic arteries, in turn, branch into cotyledon arteries.
• In the villi, these vessels eventually branch to form an
extensive arterio-capillary-venous system, bringing the fetal
blood extremely close to the maternal blood; but no
intermingling of fetal and maternal blood occurs ("placental
Placental barrier:In spite of close proximate there is no mixing of maternal and
foetal blood. The trophoblast and underlying endothelium of
foetal vessel behave as semi permeable membrane, which is
called placental barrier.
It consist of:1. Syncytotrophoblast
2. Cyto trophoblast
3. Basement membrane
4. Stromal tissue
5. Endothelium of foetal capillary wall.
• embryonic portion of the placenta
• the villi overlying the decidua basalis, that subsequently
• organ that connects the developing fetus
to the uterine wall to allow nutrient
uptake, waste elimination, and gas
exchange via the mother's blood s
• two components: the fetal placenta, or
(Chorion frondosum), which develops from
the fetus; and the maternal placenta, or
(Decidua basalis), which develops from the
maternal uterine tissue
Function of placenta:1. Respiratory function
2. Excretory function
3. Nutritional function:- placenta transfer nutrients from maternal circulation
to fetus, are Glucose, Lipids, Amino acid and minerals (fe, ca), Vitamins
(folic acid, vit. C), Water and electrolytes.
4. Endocrine function:- placenta acts as endocrine gland and secrets:oestrogen, progesterone, human chorionic gonadotrophin (HCG), Human
placental lactogen(HPL), thyroid stimulating hormone (TSH), Hormone
resembling adreno-corticotrophine, Relaxin.
5. Barrier function:- prevents transfer of maternal infection. But some
organism can cross like:- mump, measles, rubella, HIV, syphilis, chicken pox
6. Enzymatic action- (diamine oxidase that inactivates circulatory pressue,
oxytocinase which neutralizes oxytocin, Phospholipase A2 which synthesize
7. Immunological function:- ig G.
• 2 umbilical arteries
– deoxygenated, or "venous-like" blood flows to the
• 1 umbilical vein
– with a significantly higher oxygen content(80% saturation)
• As fetal lungs are not functioning, the fetus obtains oxygen
and nutrients from the mother through the placenta and the
• The core concept behind fetal circulation is that fetal hemoglobin
has a higher affinity for oxygen than does adult hemoglobin, which
allows a diffusion of oxygen from the mother's circulatory system
to the fetus.
• Circulatory system of the mother is not directly connected to that
of the fetus .
• Water, glucose, amino acids, vitamins, and inorganic salts freely
diffuse across the placenta along with oxygen
• Blood from the placenta is
carried to the fetus by the
• About half of this enters the
fetal ductus venosus and is
carried to the inferior vena
cava, while the other half
enters the liver proper from the
inferior border of the liver. The
branch of the umbilical vein
that supplies the right lobe of
the liver first joins with the
• The blood then moves to the right atrium of the heart.
• Between the right and left atrium, the foramen ovale allow
most of the blood flows through it directly into the left atrium
from the right atrium, thus bypassing pulmonary circulation.
• The continuation of this blood flow is into the left ventricle,
and from there it is pumped through the aorta into the body.
• Some of the blood entering the right atrium does not pass
directly to the left atrium through the foramen ovale, but
enters the right ventricle and is pumped into the pulmonary
• In the fetus, connection between the pulmonary artery and
the aorta, called the ductus arteriosus, which directs most of
this blood away from the fluid filled, non functioning lungs
Changes of fetal circulation at birth
• Hemodynamics of fetal circulation undergo profound
changes, soon after birth:
– Caessation of placental blood flow
– Initiation of respiration
1. Closure of umbilical arteries: Functionally, soon after birth,
but actual obliteration takes by 2-3 months
2. Closure of umbilical vein: little later than arteries and allows
few extra volume of blood to go to fetus from placenta
3. Closure of ductus arteriosus: within few hrs of respiration
4. Closure of foramen ovale: functionally , soon after birth but
anatomically, closes in about 1 year
Changes of fetal circulation at birth
• Fetal Structure
• Adult Remnant
• Foramen ovale
• Ductus arteriosus
• Left umbilical vein
• Fossa ovalis of the heart
• Ligamentum arteriosum
– Extra-hepatic portion
– Intra-hepatic portion (ductus
• Left and right umbilical
– Proximal portions
– Distal portions
• Ligamentum teres hepatis
• Ligamentum venosum
• Superior vesical arteries
• Medial umbilical ligaments
Patent ductus arteriosus:
• Failure of a child's DA to close after birth
• generation of a left-to-right shunt as blood flows form hogh
pressure aorta to low pressure pulmonary artery.
• If left uncorrected, patency leads to pulmonary hypertension
and possibly congenital heart disease and cardiac arrythmia
• Prostaglandins are responsible for maintaining the ductus
arteriosus by dilatation of the vascular smooth muscles.
• Closure may be induced with NSAIDs because these drugs
Patent foramen ovale:
• is an incomplete closure of the atrial septum that results in
the creation of a flap or a valve-like opening in the atrial
• is present in everyone before birth but seals in about 80% of
• With each heartbeat, blood can flow in either direction
directly between the right and left atrium.
• When blood moves directly from the right atrium to the left
atrium, this blood bypasses the filtering system of the lungs