report

1. THE STAGES OF HEART
DEVELOPMENT AND
CONGENITAL
MALFORMATIONS

2. 1
Table of Contents
ABSTRACT.................................................................................. 2
INTRODUCTION......................................................................... 3
STAGES OF HEART DEVELOPMENT..................................... 3
Development of primitive heart tube.............................................................................................4
Heart looping stage .......................................................................................................................4
Development of 2 separate chambers ............................................................................................5
Development of 3rd
chamber .........................................................................................................5
Development of 4th
chamber..........................................................................................................5
CONGENITAL MALFORMATIONS OF THE HEART ............ 5
CAUSES OF CONGENTIAL MALFORMATIONS OF THE HEART........................................5
What Causes Tetralogy of Fallot?.................................................................................................6
COMMON TYPES OF CONGENITAL HEART DEFECTS. ......................................................7
AorticValve Stenosis (AVS) ..........................................................................................................7
Atrial Septal Defect (ASD) ............................................................................................................7
Complete Atrioventricular Canal defect (CAVC).............................................................................8
Ebstein's Anomaly.......................................................................................................................8
Patent Ductus Arteriosis (PDA).....................................................................................................8
PulmonaryValve Stenosis............................................................................................................8
Ventricular Septal Defect.............................................................................................................8
Tetralogy of Fallot.......................................................................................................................9
Overriding Aorta .........................................................................................................................9
Right Ventricular Hypertrophy.....................................................................................................9
Congenital mitral valve anomalies..............................................................................................10
CONCLUSION............................................................................11
REFERENCES............................................................................12

3. 2
ABSTRACT
Human heart is the first functional organ to develop which begins beating and
pumping blood around 3 weeks after fertilization. The heart is originated from the
mesodermal tissues. There are five stages of heart development. During the first
stage, the heart begins to beat. In the second stage, the heart begins to form a shape
and in the third stage, 2 separate chambers starts to develop. In the fourth and fifth
stage, the 3 rd and 4 th chamber is formed respectively. The entire process is
completed in about 8 weeks. congenital heart defects are the most common type of
birth defects. This is caused by the abnormal formation of the heart during fetal
development. The most 3common types of congenital heart malformations include
aortic valve stenosis, atrial septal defect, Coarctation of aorta, complete
atrioventricular canal defect, Ebstein’s anomaly, patent ductus arteriosis, pulmonary
valve stenosis, tetralogy of fallot and congenital mitral valve anomalies.

4. 3
INTRODUCTION
The human heart is the first functional organ to develop. It begins beating and
pumping blood around day 21 or 22, a mere three weeks after fertilization. This
emphasizes the critical nature of the heart in distributing blood through the vessels
and the vital exchange of nutrients, oxygen, and wastes both to and from the
developing baby. The critical early development of the heart is reflected by the
prominent heart bulge that appears on the anterior surface of the embryo. The heart
forms from an embryonic tissue called mesoderm around 18 to 19 days after
fertilization. Mesoderm is one of the three primary germ layers that differentiates
early in development that collectively gives rise to all subsequenttissues and organs.
The complexity of the heart leads to the possibility of birth defects and anomalies.
They can be divided into several groups: the anomaly of position, anomalies of
number, violation of the separation of the heart, defects of the interatrial and
interventricular septum and malformations of the valves. Some of them are
incompatible with life, others require serious surgical correction, and others do not
seriously affect the functioning of the heart.
STAGES OF HEART DEVELOPMENT
The mesodermal tissues that give rise to the heart first become evident when the
embryo is undergoing gastrulation. This occurs during the third week of
development. The cells that are destined to form the heart are derived from
mesodermal layer. The mesoderm lies between the ectodermal and endodermal
layers, which are continuous with the amnion and yolk sac. They form a crescent
virtually at the cranial border of the disc. As this heart forming region achieves its
crescentic shape, the central region of the ectoderm transforms into the neural plate.
At this stage, the developing heart itself consists of a plate of promyocardial cells.
The cardiac plate is positioned inferior to the pericardial cavity, which has arisen as
a spacewithin the mesoderm. With continuing folding of the disc, this heart forming
region is moved into the developing neck of the embryo.
There are five major stages ofheart development. The first is the development ofthe
primitive heart tube, in which the heart begins to beat. The second is the heart
looping stage, where the form of the heart starts to take shape. The third marks the
development of two separate heart chambers. The fourth and fifth stages occurwhen
the third and fourth heart chambers are formed, respectively. The entire development
of the heart takes about eight weeks

5. 4
Development of primitive heart tube
The first stage of heart development involves the primitive heart tube. The heart
begins to develop near the head of the embryo in a region known as the cardiogenic
area. The cardiogenic area begins to form two strands called the cardiogenic cords.
As the cardiogenic cords develop, a lumen rapidly develops within them.
At this point, they are referred to as endocardial tubes. The two tubes migrate
together and fuse to form a single primitive heart tube. The primitive heart tube
quickly forms five distinct regions.
From head to tail, these include the truncus arteriosus, bulbus cordis, primitive
ventricle, primitive atrium, and the sinus venosus. Initially, all venous blood flows
into the sinus venosus, and contractions propel the blood from tail to head, or from
the sinus venosus to the truncus arteriosus. This is a very different pattern from that
of an adult.
The five regions of the primitive heart tube develop into recognizable structures in
a fully developed heart. The truncus arteriosus will eventually divide and give rise
to the ascending aorta and pulmonary trunk. The bulbus cordis develops into the
right ventricle. The primitive ventricle forms the left ventricle. The primitive
atrium becomes the anterior portions of both the right and left atria, and the two
auricles. The sinus venosus develops into the posterior portion of the right atrium,
the SA node, and the coronary sinus.
The heart begins to beat during the first stage of heart development. Usually during
week five of pregnancy, about 22 or 23 days after conception, a tiny flickering heart
beat can be seen from a vaginal ultrasound. This very primitive but functional tube-
shaped heart is a close resemblance to a fish heart.
Heart looping stage
The second stage of heart development occurs rapidly, within 24 hours. It is called
heart looping. As it grows, the tube-shaped heart contorts into an S shape and bends
to the right, which is called d-looping. This new shapecreates a primitive region for
the ventricle to grow. This stage of development is triggered by activated heart-
specific proteins.
Once formed, the ventricular loop itself has inlet and outlet components, with the
outlet part supporting the outflow tract. The outflow tract, in turn, feeds the arteries
that arise from the aortic sac and extend into the increasing number of pharyngeal
arches. This arrangement is seen at around the 25th day in the human. The stage is

6. 5
now set for formation of the definitive cardiac chambers, along with the arterial
trunks.
Development of 2 separate chambers
The two chambers consist of one atrium and one ventricle. During this stage, the
heart continues to grow rapidly. The cardiac jelly serves as a valve between the
ventricular areas and the atria. Thetwo-chambered stage of the growing human heart
resembles the heart of a frog.
Development of 3rd
chamber
The fourth stage of heart development is triggered by the atria dividing. This stage
is called the three-chambered heart. The three chambers include the two atria, which
have split, that rest on top of the ventricle, the third chamber. This stage of the
developing heart looks like a three-chambered snake or turtle heart.
Development of 4th
chamber
The final stage of heart development occurs by the end of the tenth week of
pregnancy. It is marked by the development of the fourth heart chamber. The heart
is now fully formed with two atria, two ventricles, and two large blood vessels to
carry blood to and from the heart.
CONGENITAL MALFORMATIONS OF THE HEART
Congenital heart defects are the most common type of birth defect that can involve
the walls of the heart, the valves ofthe heart, and the arteries and veins near the heart
CAUSES OF CONGENTIALMALFORMATIONS OF THE HEART
A congenital heart defect (CHD) is a heart problem which is present at birth. It is
caused by abnormal formation of the heart during fetal development. In most
cases, when a baby is born with congenital heart disease, there is no known reason
for it. Scientists know that some types of congenital heart defects can be related to
an abnormality in the number of an infant's chromosomes, single gene defects, or
environmental factors. In most cases, there is no identifiable cause for the heart
defect, and they are generally considered to be caused by multifactorial
inheritance.
Multifactorial inheritance means that "many factors" (multifactorial) are involved in
causing a birth defect. Thefactors are usually bothgenetic and environmental, where
a combination of genes from both parents, in addition to unknown environmental
factors, combine to produce the trait or condition.

7. 6
There are an estimated 70,000 genes contained on the 46 chromosomes in each cell
of the body. Genes come in pairs, one of which is inherited from the mother, the
other from the father. Genes not only help to determine our individual traits, but
also may be responsible for health problems when gene alterations (mutations) are
present. When a single gene is mutated, a number of health problems may occur in
a person. When several health problems occurfromone genetic causethat is referred
to as a syndrome. Some of the genetic syndromes associated with a higher incidence
of heart defects include, but are not limited to, the following:
 Marfan syndrome (genetic disorder of the connective tissue )
 Smith-Lemli-Opitz syndrome (Mutations in the DHCR7 gene )
 Ellis-van Creveld syndrome ( inherited as an autosomal recessive genetic
condition)
 Holt-Oram syndrome (an autosomal dominant disorder )
 Noonan syndrome (caused by changes in one of several autosomal dominant
genes)
 Mucopolysaccharidoses ) inherited metabolic diseases caused by the absenceor
malfunctioning of certain enzymes needed to break down molecules called
glycosaminoglycans )
There are a number of chromosome abnormalities associated with congenital heart
defects. Some of these include the following:
 Down syndrome (trisomy 21)
 Trisomy 18 and trisomy 13
 Turner's syndrome
What Causes Tetralogy of Fallot?
Doctors don'tknow what causes most cases of tetralogy of Fallot and
other congenital heart defects.
Certain conditions or factors that occur during pregnancy may raise your risk for
having a child with tetralogy of Fallot. These conditions and factors include:
 German measles (rubella) and some other viral illnesses
 Poornutrition
 Overuse of alcohol
 Age (being older than 40)
 Diabetes

8. 7
Heredity may play a role in causing tetralogy of Fallot. An adult who has tetralogy
of Fallot may have an increased chance of having a baby with the condition.
Children who have certain genetic disorders, such as Down
syndrome and DiGeorge syndrome, often have congenital heart defects, including
tetralogy of Fallot.
COMMON TYPES OF CONGENITALHEART DEFECTS.
Aortic Valve Stenosis (AVS)
Aortic stenosis (AS) occurs when the aortic valve didn't form properly. A normal
valve has three parts (leaflets or cusps), buta stenotic valve may have only one cusp
(unicuspid) or two cusps (bicuspid), which are thick and stiff, rather than thin and
flexible. In most children, the cause isn't known. It's a common type of heart defect.
Some children can have other heart defects along with AVS.
Atrial Septal Defect (ASD)
An atrial septal defect (ASD) is a hole in the wall between the two upper chambers
of the heart (atria). This defect allows oxygen-rich blood to leak into the oxygen-
poor blood chambers in the heart.
If the atrial septal defect is large, this extra blood volume can overfill the lungs and
overwork the right side of the heart. If not treated, the right side of the heart
eventually enlarges and weakens. If this process continues, the blood pressure in
your lungs may increase as well, leading to pulmonary hypertension.
Coarctation of the Aorta (CoA)
Coarctation of the aorta or aortic coarctation is a narrowing of the aorta, the large
blood vessel that branches off the heart and delivers oxygen-rich blood to the body.
When this occurs, the heart must pump harder to force blood through the narrowed
part of the aorta.

9. 8
Complete Atrioventricular Canal defect (CAVC)
Atrioventricular canal defectis a combination ofheart problems resulting in a defect
in the center of the heart. The condition occurs when there's a hole between the
heart's chambers and problems with the valves that regulate blood flow in the heart.
Sometimes called endocardial cushion defect or atrioventricular septal defect,
atrioventricular canal defect is present at birth (congenital). The condition is often
associated with Down syndrome.
Ebstein's Anomaly
Ebstein anomaly is a rare heart defect that's present at birth (congenital). In Ebstein
anomaly, tricuspid valve: the valve between the two right heart chambers (right
atrium and right ventricle) doesn'tworkproperly. The tricuspid valve sits lower than
normal in the right ventricle, and the tricuspid valve's leaflets are abnormally formed.
Patent Ductus Arteriosis (PDA)
Patent ductus arteriosus (PDA) is a persistent opening between the two major blood
vessels (aorta & pulmonary artery) leading from the heart. The opening, called the
ductus arteriosus, is a normal part of a baby's circulatory system before birth that
usually closes shortly after birth. If it remains open, however, it's called a patent
ductus arteriosus.
Pulmonary Valve Stenosis
Pulmonary valve stenosis is a condition in which a deformity on or near the
pulmonary valve narrows the pulmonary valve opening and slows the blood flow.
The pulmonary valve is located between the lower right heart chamber (right
ventricle) and the pulmonary arteries. Adults occasionally have pulmonary valve
stenosis as a complication of another illness, but mostly, pulmonary valve stenosis
develops before birth as a congenital heart defect.
Ventricular Septal Defect
The heart has a wall that separates the two chambers on its left side from the two
chambers on its right side. This wall is called a septum. The septum prevents blood
from mixing between the two sides of the heart.

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A VSD is a hole in the part of the septum that separates the ventricles, the lower
chambers of the heart. The hole allows oxygen-rich blood from the left ventricle to
mix with oxygen-poor blood from the right ventricle.
Tetralogy of Fallot
Tetralogy of Fallot is a rare condition caused by a combination of four heart defects
that are present at birth (congenital). The four abnormalities that make up the
tetralogy of Fallot include:
 Pulmonary valve stenosis.
 Ventricular septal defect.
 Overriding aorta.
 Right ventricular hypertrophy.
Overriding Aorta
This is a defect in the aorta, the main artery that carries oxygen-rich blood to the
body. In a healthy heart, the aorta is attached to the left ventricle. This allows only
oxygen-rich blood to flow to the body.
In tetralogy of Fallot, the aorta is between the left and right ventricles, directly over
the VSD. As a result, oxygen-poor blood from the right ventricle flows directly into
the aorta instead of into the pulmonary artery to the lungs.
Right Ventricular Hypertrophy
This defectoccurs ifthe right ventricle thickens becausethe heart has to pump harder
than it should to move blood through the narrowed pulmonary valve.

11. 10
Figure A shows
the structure and
blood flow in the
interior of a
normal heart.
Figure B shows a
heart with the four
defects of
tetralogy of Fallot.
Babies and children who have tetralogy of Fallot have episodes of cyanosis. This is
a bluish tint to the skin, lips, and fingernails. Cyanosis occurs becausethe oxygen
level in the blood is below normal.
Tetralogy of Fallot must be repaired with open-heart surgery, either soonafter birth
or later in infancy. The timing of the surgery depends on how severely the
pulmonary valve is narrowed.
Over the past few decades, the diagnosis and treatment of tetralogy of Fallot have
greatly improved. As a result, most children who have this heart defect survive to
adulthood. However, they'll need lifelong medical care from specialists to help
them stay as healthy as possible.
Congenital mitral valve anomalies
Congenital mitral valve anomalies are defects presentat birth (congenital) that affect
the heart's mitral valve. The mitral valve is located between the heart's upper left
chamber (left atrium) and lower left chamber (left ventricle).
Various types of mitral valve anomalies exist, including:
Thickened, stiffened, deformed or fused valve flaps (leaflets)
Abnormalities with the cords that support the valve, such as short and thick cords,
cords attaching to a heart muscle near the mitral valve, or missing cords
Heart tissue or heart muscle problems near the mitral valve

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CONCLUSION
This researched essay about stages of heart development and congenital
malformations concludes that human heart undergoes five stages during fetal
development. These include development of primitive heart tube, heart looping
stage, development of 2 separate chambers. Development of 3rd chamber and
development of 4th chamber. This researched essay also concludes that congenital
heart defects are the most common 10 type of birth defects. This is caused by the
abnormal formation of the heart during fetal development. The most common types
of congenital heart malformations include aortic valve stenosis, atrial septal defect,
Coarctation of aorta, complete atrioventricular canal defect, Ebstein’s anomaly,
patent ductus arteriosis, pulmonary valve stenosis, tetralogy of fallot and congenital
mitral valve anomalies.

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