Transcript right atrium

Cardiovascular & Respiratory
system
Presented by:
N.Barry
A. Narine
J.Hanes
Z. Daniels
Development of
the
Cardiovascular
System in the
Human Embryo
Development of the heart and vascular system begins very
early in mesoderm both within (embryonic) and outside
(extra embryonic, yolk sac and placental) the embryo.
Vascular development therefore occurs in many places, the
most obvious though is the early forming heart, which grows
rapidly creating an externally obvious cardiac "bulge" on the
early embryo.
The heart forms initially in the embryonic disc as a simple paired
tube inside the forming pericardial cavity, which when the disc
folds, gets carried into the correct anatomical position in the
chest cavity.
Throughout the mesoderm, small regions differentiate into
"blood islands" which contribute both blood vessels (walls) and
fetal red blood cells.
These "islands" connect together to form the first vessels which
connect with the heart tube.
Forms initially in splanchnic mesoderm of prechordal plate region cardiogenic region
growth and folding of the embryo moves heart ventrally and
downward into anatomical position
Day 22 - 23, begins to beat in humans
heart tube connects to blood vessels forming in splanchnic and
extraembryonic mesoderm
Week 2 - 3 pair of thin-walled tubes
Week 3 paired heart tubes fuse, truncus arteriosus outflow, heart
contracting
Week 4 heart tube continues to elongate, curving to form S shape
Week 5 Septation starts]], atrial and ventricular
Septation continues, atrial septa remains open, foramen ovale
Week 37-38 At birth, pressure difference closes foramen ovale
leaving a fossa ovalis
Layers of the early Heart
LAYERS
Myocardium: forms from splanchnic mesoderm
surrounding the pericardial coelom. Additional
myocardial cells are added to the outflow tract during
heart looping.
Cardiac Jelly: gelatinous connective tissue separating
the myocardium and heart tube endothelium.
Endocardium: forms from the endothelium of the heart
tube.
Epicardium: develops from mesothelial cells arising
from the sinus venosus which spread cranially over the
myocardium.
The heart primordium arises predominantly
from splanchnic mesoderm in the cardiogenic
region of the trilaminar embryo. The cardiogenic
region can be thought of as bilateral fields that
merge cranially to form a horseshoe-shaped
field. During the third week of development
(approximately day 18) angioblastic
cords develop in this cardiogenic mesoderm and
canalise to form bilateralendocardial heart
tubes.
The sinus venosus is also divided into two
parts: the right horn of the sinus venosus and
the left horn of the sinus venosus.
By day 22, coordinated contractions of the
heart tube are present and push blood
cranially from the sinus venosus.
As the embryo folds, the cranial ends of the
dorsal aortae are pulled ventrally until they
form a dorsoventral loop: the first aortic arch
arteries
LOOPING
The steps in looping can be summarised as:
The straight heart tube begins to elongate with
simultaneous growth in the bulbus
cordis and primitive ventricle.
This forces the heart to bend ventrally and rotate to
the right, forming a C-shaped loop with convex side
situated on the right.
The ventricular bend moves caudally and the distance
between the outflow and inflow tracts diminishes.
The atrial and outflow poles converge and myocardial
cells are added, forming the truncus arteriosus.
Series of scanning EMs showing the rapid change
in the appearance of the heart tube
All of the partitioning of the primitive heart occurs between the
middle of the fourth week and the end of the fifth week
Two endocardial cushions form on the dorsal and
ventral surfaces of the AV canal, referred to as the
superior and inferior cushions respectively. The cardiac
jelly in this region expands while mesenchymal cells
from the endocardium invade the cushions, allowing
them to grow and fuse. This fusion divides the common
AV canal into the right and left canals, hence partially
separating the primitive atrium and ventricle. Two
smaller endocardial cushions also form on the lateral
walls of the AV canal, which later help to form
the mitral and tricuspid heart valves.
Membranous tissue forming the septum
primum grows from the roof of the atrium,
dividing it into left and right halves
Blood flows from the right atrium through the
foramen ovale and foramen secundum to
the left atrium, forming a right-to-left shunt. The
remaining portion of the septum primum acts as
the valve of the foramen ovale. Blood cannot
flow in the opposite direction, as the muscular
strength of the septum secundum prevents
prolapse of the septum primum
Minor trabeculations appear during early development of
the primordial ventricle. Following growth of the ventricles
further trabeculations appear and grow as larger, muscular
structures. Some researchers believe that as the
trabeculations grow they coalesce resulting in the formation
of the ventricular septum. However, the more commonly
described theory of septation begins with the appearance of
a primordial muscular interventricular (IV) ridge developing
in the floor of the ventricle near the apex. As either side of
the ventricle grows and dilates, their medial walls fuse
forming the prominent IV septum. The foramen located
between the cranial portion of the IV septum and the
endocardial cushions: the IV foramen, closes by the end of
the seventh week as the bulbar ridges (see next section) fuse
with the endocardial cushions.
Active proliferation of neural crest mesenchymal cells in
the bulbus cordis during the fifth week creates bulbar
ridges which are continuous in thetruncus arteriosus. The
neural crest cells migrate through the primordial pharynx and
over the aortic arch arteries to reach the outflow tract. The
bulbar ridges undergo a 180° spiral to create the
helical aorticopulmonary septum. As the ridges grow and
develop myocardium they fuse in a distal-to-proximal
direction. Fusion occurs during the sixth week, allowing for
cleavage of the aorta and pulmonary trunk. The spiralling
nature of the ridges causes the pulmonary trunk to twist
around the aorta. Note that the bulbus cordis accounts for the
smooth conus arteriosus (or infundibulum) in the right
ventricle and the aortic vestibule in the left ventricle.
Development of the mitral and
tricuspid valves
There are four valves in the adult heart,
depicted below. There are two AV valves
which comprise leaflets as well as the
structures that tether these leaflets to
the ventricular walls.
The aortic and pulmonary valves, termed
the semilunar valves, are located in the
aorta and pulmonary trunk respectively.
They are each made of three cusps.
The AV valves begin to form between the fifth and eighth
weeks of development. The left AV valve
has anterior andposterior leaflets and is termed
thebicuspid or mitralvalve. The right AV valve has a third,
small, septalcusp and thus is called thetricuspid valve.
The valve leafletsare attached to the ventricular walls by thin
fibrous chords: the chordae tendineae, which insert into small
muscles attached to the ventricle wall: the papillary muscles.
These structures are sculpted from the ventricular wall
The semilunar valves are formed from the bulbar ridges and
subendocardial valve tissue. The primordial semilunar valve
consists of a mesenchymal core covered by endocardium.
Excavation occurs, thinning the valve tissue thus creating its
final shape.
Development of the semilunar valves
Development of the semilunar cusps
Development of Arteries
Upon folding of the embryo the paired dorsal aortae
connecting to the cranial end of the heart tube are
brought ventrally to form the first aortic arches.
Additional aortic arches develop over the next few
weeks which are later remodelled to form the arteries
of the upper body. Caudal to the arches, the paired
dorsal aortae fuse to form a single median dorsal aorta
which develops the following branches:
Ventral (gut) branches - derived from the vitelline
arteries
Lateral branches - supply retroperitoneal structures
Dorsolateral branches (intersegmental arteries) supply the head, neck, body wall, limbs and vertebral
column
The vitelline venous system gives rise to the liver
sinusoids and portal system and forms the ductus
venosus which acts as a shunt from the umbilical
vein to the IVC. The IVC is formed during a left-toright shift in the embryonic veins and is composed
of:
A hepatic segment - from the hepatic vein and
sinusoids
A prerenal segment - from the right subcardinal vein
A renal segment - from subcardinal and
supracardinal anastomosis
A postrenal segment - from right supracardinal vein
The main function of these shunts is to redirect oxygenated blood
away from the lungs, liver and kidney (whose functions are
performed by the placenta).
Oxygenated blood is carried from the placenta to the foetus in
the umbilical vein, most of which then passes through the ductus
venosus to the IVC while some blood supplies the liver via the
portal vein. Blood from the liver drains into the IVC through the
hepatic veins. The blood in the IVC is a mixture of oxygenated
blood from the umbilical vein and desaturated blood from the
lower limbs and abdominal organs (e.g. the liver). This blood
enters the right atrium where most of it is directed to the left
atrium through the foramen ovale and from here to the left
ventricle and aorta. The remainder of the blood in the right
atrium passes with blood from the SVC (from the head and upper
limbs) to the right ventricle and pulmonary artery where most of
it passes to the aorta via the ductus arteriosus. The blood passes
from the aorta to the hypogastric arteries, umbilical arteries and
then back to the placenta.
ABNORMALITIES
A variety of developmental defects occur as a result of
prenatal exposure to alcohol (ethanol) in utero.
In humans, those defects are collectively classified as
Fetal Alcohol Spectrum Disorders, with Fetal Alcohol
Syndrome (FAS) representing the more severe defects.
FAS is defined by pre- and post-natal growth retardation,
minor facial abnormalities, and deficiencies in
the central nervous system (CNS). In addition to those
defects, prenatal exposure to alcohol impacts
cardiogenesis, the developmental stage of heart
formation.
Prenatal exposure to alcohol induces a variety of
abnormalities in the developing heart which include:
atrial and ventricular abnormalities, issues with valve
formation, and a potential increase in the risk of heart
disease later in adulthood. The specific defects that
have been observed from prenatal alcohol exposure
include defects to the atrioventricular valves (tricuspid
and mitral) that allow blood to flow backward into the
atria; ventricular septal defects, commonly known as a
“hole in the heart” between the left and right
ventricles; enlargement of the left ventricle, the
primary pumping chamber in the heart; and an
increased risk of developing heart disease later in adult
life.
Lymphatic system
this development occurs after the
cardiovascular system.
It appears in the fifth week
The lymphatic vessels forms from the
mesenchyne in situ or saclike out grows
from the endothelum of veins
Six primary sacs are formed:
Two jugular
Two iliac
One retroperitoneal
One cisterna chyli
Two main channels
Thoraic duct
Right lymphatic duct
Thoraic duct- develops from the distal portion of
the right thoraic ,anaostomis.
The right and the left thoraic duct joins the jugular
sacs with the cisterna and soon an anastomis from
between these ducts
Right lymphatic duct- derives from the cranial
portion of the right thoratic duct
Both he thoratic duct maintain their connection
with the venous system and empties into the
junction of the internal jugular and subclavin
veins
When development does occur and
description of the Respiratory
System?
The respiratory system develops after the fourth week of
gestation. The development of the respiratory system
has many constituent components. The respiratory
system begins at the nasal cavity and consists of a
conducting portion and a respiratory portion. The
conducting portion includes nasal cavity, pharynx, larynx,
trachea, bronchi, and bronchioles. The respiratory
portion consists of the respiratory bronchioles, alveolar
ducts, alveolar sacs and the alveoli. Gaseous exchange
occurs in the alveoli. The development of the respiratory
system involves the endoderm and the mesoderm that
surrounds it. The mesoderm surrounding the trachea
inhibits branching whereas the mesoderm surrounding
the bronchi stimulates branching.
Formation of the respiratory system is regulated by
a flow of molecules:
•Fibroblast growth factor 10 (FGF10)
•The Hox genes:
•Sonic hedgehog
Other molecules in the mesoderm regulate
branching and differentiation of epithelia of lung
buds. The main regulatory molecules are:
•. N-Myc
•Fibronectin and Collagen types I and II
•Syndecan and Tenascin
•Epimorphin
Early Development
The early development of the lungs lags behind
the development of the heart and great vessels.
However, as development proceeds the lungs
will eventually occupy more of the thoracic
cavity than the heart. This will be discussed
further in the partitioning of the body cavities.
Development of the Respiratory
System
Larynx: The larynx is first seen as an outgrowth from the
foregut. The outgrowth of tissue is called the respiratory
diverticulum or the lung bud. The formation of the lung bud
occurs when two lateral folds of splanchnic mesoderm and
endoderm meet in the midline and separate the larynx and
trachea from the esophagus. The lung bud is a ventral
diverticulum of endoderm that arises from the floor of the
foregut caudal to the pharynx. The diverticulum forms a
groove in the floor of the pharynx called the
laryngotracheal groove. Cephalic to the laryngotracheal
groove is the epiglottal swelling. On either side of this
groove are the developing arytenoids swellings.
The epithelium of the larynx develops from the endoderm of
the foregut. However, the muscles and cartilage arise from
the 4th and the 6th arches. The development of these
structures will be discussed in a later.
Laryngeal orifice and surrounding swellings at
successive stages of development A. 6 weeks. B. 12
weeks
Trachea: The trachea or voice box develops caudal to
the larynx. The epithelium develops from the
endoderm and the tracheal cartilage and muscles
develop from splanchnic mesoderm. Early in
development the trachea bifurcatesinto the left and
right bronchi.
Bronchi and Bronchioles: As the bronchi develop they
continue to branch. The right bronchus gives off three
diverticula and the left bronchus gives off two
diverticula. These diverticula become the lobar bronchi
and indicate that the right lung will have three lobes
and the left lung will have two lobes. Each of the
bronchi at this stage will divide into smaller bronchi. The
branching of the bronchi continues until the
bronchioles begin to form. In all there are 17 divisions
of the bronchi until the sixth fetal month is reached.
However, by early childhood there will be a total of 24
generations of branching that occurs.
Maturation of the Lungs
As the lungs develop and divide into smaller divisions
there are changes in the vascular supply of the lungs as
well. The lungs can be described as undergoing 4 phases
of development.
During the first phase of development, the pseudo
glandular period, the bronchi are dividing into smaller
and smaller units, the bronchioles. This period occurs
from the 2nd month through the end of the 4th month.
During the next 2 and 1/2 months the respiratory
bronchioles are formed. They will give rise to alveolar
ducts. This is called the canalicular period. During this
time period the epithelium remains as a cuboidal
epithelium and the capillaries while proliferating do not
approach the respiratory epithelium.
The next phase of development occurs from the 7th month until
birth. During this period, the terminal sac phase / saccular phase,
the number of capillaries increases and the capillaries approach
the respiratory epithelium. At the same time the terminal sacs
form. These result in the formation of a squamous epithelium,
made up of type I alveolar epithelial cells, which will permit
gaseous exchange. Hence, from the 7th month on the fetus is
capable of survival. It is also starting with the 7th month that type
II alveolar epithelial cells develop. These type II cells produce
surfactant, the fluid that reduces the surface tension at the
alveolar cell surface. Finally, from the 8th month on, the mature
alveoli continue to be formed with an increase in the amount of
surface area where capillaries and alveolar cells are in contact. This
period of lung development is the alveolar period and actually can
last through age ten. The growth of the lungs after birth is mainly
the result of increases in the number of alveoli during this time.
Clinical implications
The absent or insufficient surfactant in the premature baby causes
respiratory distress syndrome (RDS) because of collapse of the
primitive alveoli (hyaline membranedisease).
Congenital cysts of the lung; which are formed by dilation of
terminal or larger bronchi. These cysts may be small and multiple,
giving the lung a honeycomb appearance on radiograph, or they may
be restricted to one or more larger ones. Cystic structures of the lung
usually drain poorly and frequently cause chronic infections.
Babies born before 28 weeks have very small chances of
survival because they lack pulmonary alveoli. A few manage to
survive following intensive respiratory assistance.
Babies born between 32 and 36 weeks usually suffer from the
respiratory distress syndrome due to lack of surfactant
secreted by pneumocytes type II. The respiratory distress
syndrome is treated by:
•Intensive respiratory assistance
•Surfactant therapy including surfactant lipoprotein and
surfactant associated proteins A,B and C.
REFERENCES
Bellusci S, et al.: Fibroblast growth factor 10 (FGF 10)
and branching morphogenesis in the embryonic
mouse lung. Development 124:4867, 1997.
http://embryology4genius.weebly.com/maturationof-the-lungs.html
http://php.med.unsw.edu.au/embryology/index.php?title=Re
spiratory_System_Development
http://search.medicinenet.com/search/search_results/defaul
t.aspx?Searchwhat=1&query=mesoderm&I1=Search
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767109/
http://php.med.unsw.edu.au/embryology/index.php?title=C
ardiovascular_System_Development
Longman's Medical Embryology 11th ed., Sadler, T
W, (Thomas W.); Langman, Jan. Philadelphia :
Wolters Kluwer Lippincott Williams & Wilkins
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Developmental Biology, 6th ed., Gilbert, Scott F;
Sunderland (MA): Sinauer Associates; 2000
Larsen's human embryology 4th ed. Schoenwolf,
Gary C; Larsen, William J, (William James).
Philadelphia, PA : Elsevier/Churchill Livingstone
O'Neil, Erica, "Effects of Prenatal Alcohol Exposure on
Cardiac Development". Embryo Project
Encyclopedia (2011-04-30). ISSN: 1940-5030
http://embryo.asu.edu/handle/10776/2097.