Anatomy and Development of the Heart II Flashcards
The external surface of the heart is covered with the visceral layer of the
Serous pericardium (or epicardium)
Fused to the heart and also covers the roots of the greater vessels of the heart
Visceral layer of pericardium
Serous pericardium reflects off the great vessels to become the
Parietal layer
Located between the visceral and parietal layers of the serous pericardium
Pericardial cavity
The parietal layer of serous pericardium is fused to the inner surface of the
Fibrous pericardium
The pattern of reflection of the serous pericardium from the visceral layer to the parietal layer creates the two pericardial sinuses, which are the
- ) Transverse sinus
2. ) Oblique sinus
Open at both ends and is located under the ascending aorta and pulmonary trunk (outflow vessels), but above the superior vena cava (inflow vessel)
Transverse sinus
A blind recess that is closed superiorly and laterally but open inferiorly
Oblique sinus
The oblique sinus is bounded by the
-all inflow vessels
Inferior vena cava and the four pulmonary veins
The fibrous pericardium is continuous with the adventitial layer of the great vessels and with the superior fascia of the
Diaphragm
Because the fibrous pericardium is not elastic, the rapid accumulation of fluid in the pericardial space causes an increase in pressure which compresses the heart, this is called
Cardiac tamponade
Cardiac tamponade restricts cardiac filling during diastole, thus reducing
Cardiac output
How is the pressure from cardiac tamponade relieved?
Pericardiocentesis
Form during the third week in the splanchnic mesoderm, induced by the underlying endoderm
Right and left embryonic heart tubes
During the fourth week, with the lateral body folding, these heart tubes meet in the ventral midline and fuse to form a single
Heart tube
Blood flows through this tube in a caudal to cranial direction. As a result of a series of constrictions and dilations, four regions of the heart tube are defined from
Caudal to cranial
What are the four regions of the embryonic heart tube?
- ) Sinus venosus
- ) Primitive atrium
- ) Primitive ventricle
- ) Bulbus cordis
Receives venous return from the embryo, yolk sac, and placenta
-most of the left horn disappears
Sinus Venosus
Some of the left horn and central portion of the sinus venosus are retained as the
Coronary sinus
The right portion of the sinus venosus is incorporated into the right atrium to become the
Sinus venarum (smooth walled part of right atrium)
Receives blood from the sinus venosus
-is retained as part of the right and left atria (the trabeculated parts)
Primitive atrium
Receives blood from the primitive atrium
-Is retained as the trabeculated part of the left ventricle
Primitive ventricle
Receives blood from the primitive ventricle and is subdivided into three parts
Bulbus cordis
The bulbus cordis is subdivided into which three parts?
- ) Proximal third
- ) Conus Cordis
- ) Truncus Arteriosus
Retained as the trabeculated part of the right ventricle
Proximal third of bulbus cordis
Retained as the smooth parts of the right and left ventricles
Conus cordis
Retained as the roots of the ascending aorta and pulmonary trunk
Truncus Arteriosus
The heart tube folds upon itself into and S shape, resulting in the
Primitive atrium being more caudal than the primitive ventricle
Venous inflow enters the
Posterior wall of the heart
Arterial outflow exits the
Anterior wall of the heart
The dorsal aorta and the ventral aorta are initially connected by an arching portion of the aorta formed by the
Head fold of the embryo
This arching portion of the artery is called the first aortic arch and passes through the
First pharyngeal arch
There are 6 aortic arches which pass through 6 pharyngeal arches and all connect the
Dorsal and ventral aorta
Which aortic arches almost completely degenerate?
1st and 2nd
On both the right and left sides, the 3rd aortic arch gives rise to the
Common carotid and internal carotid arteries
The 4th aortic arch on the left becomes the definitive
Adult aortic arch
On the right side, the 4th aortic arch contributes to the
Right subclavian artery
The proximal parts of both 6th aortic arches give rise to the
-distal portion on the right degenerates
Pulmonary arteries
The distal part of the 6th aortic arch on the left is retained and becomes the
-where the left side of the recurrent laryngeal nerve recurs
Ductus arteriosus
Because the distal part of the right 6th aortic arch degenerates, the recurrent laryngeal nerve can not recur there as it usually would and instead must move to the
Right 4th pharyngeal arch (which becomes subclavian artery)
At the end of the fourth week, the atrium is partially separated from the ventricle to create the atrioventricular canals by the growth of four
Atrioventricular endocardial cushions
-contain neural crest cells
The endocardial cushions will contribute to the formation of the
Valves of the heart and the atrial and ventricular septa
From the late fourth week to the early seventh week, the single midline heart tube is divided into right and
left portions by which three septa?
- ) Atrial septum
- ) Ventricular septum
- ) Aorticopulmonary (troncoconal) septum
Divides atrium into right atrium and left atrium
-develops from late 4th to early 6th week
Atrial septum
Partially divides ventricle into right and left ventricles
-develops in 5th week
Ventricular septum
Divides truncus arteriosus into aorta and pulmonary trunk and completes division of ventricle into right and left ventricle
-develops in 6th and early 7th weeks
Aorticopulmonary (Troncoconal) Septum
The atrial septum is formed from which two septa?
- ) Septum Primum (thin and flexible)
2. ) Septum Secundum (Thicker and more rigid)
Begins to form at the end of the fourth week. It grows from the wall of the atrium toward the endocardial cushions
Septum Primum
The gap between the growing septum primum and the endocardial cushion is called the
Ostium (Foramen) Primium
As septum primum grows longer, ostium primum gets
Smaller
Prior to the closure of ostium primum, there develops a perforation in septum primum (apoptosis) called the
Ostium (foramen) Secundum
Forms before the ostium primum closes and thus maintains a continuous communication between the right and left atria
Ostium secundum
An incomplete septum which covers over the ostium secundum and forms on the right side of the septum primum
Septum secundum
The free edges of the septum secundum become the
Limbus of the fossa ovalis
The portion of the septum primum not covered by the septum secundum becomes the
Fossa ovalis
Because septum primum is flexible, it is able to bend (to the left) away from septum secundum under the influence of the right to left pressure gradient that exists in the
Prenatal heart
This allows blood to pass from the right atrium to the left atrium through the
Foramen ovale
Foramen Ovale remains open throughout prenatal life until the pressure gradient reverses at birth resulting in the septum primum being pressed against septum secundum, thus
Closing the foramen ovale postnatally
The adult ventricular septum has which two part?
- ) Muscular septum
2. ) Membranous septum
Develops in the fifth week from the ventricular wall, thus it is formed from cardiac muscle
Muscular septum
The muscular septum partially separates the left and right ventricles, with the area of communication called
the
Interventricular foramen
The membranous septum is formed from the
Aorticopulmonary septum and endocardial cushions
These septa are formed by the ingrowth of two troncoconal ridges (contains neural crest cells)
Aorticopulmonary (troncoconal) septum
As these ridges grow towards eachother they form a spiral, thus, the aorticopulmonary (troncoconal) septum is often called the
Siral septum
The aorticopulmonary septum closes the interventricular foramen and forms the
Membranous ventricular septum
What are some differences between prenatal and post natal circulation?
- ) Prenatally, oxygenated blood is from placenta and enters right side of the heart where as postnatally oxygenated blood is from the lungs and enters left side
- ) Postnatal nutrients come from the digestive tract and must be processed by the liver first
Prenatally, oxygenated blood from the placenta passes through the umbilical vein and mixes with deoxygenated blood from the lower limbs and abdomen in the IVC before reaching the
Heart
Prenatally, deoxygenated blood from the head and upper limbs reaches the heart through the
Superior Vena Cava (SVC)
Blood entering the right atrium through the IVC has a higher oxygen saturation than blood entering the right atrium through the SVC in a
Prenatal
Prenatally, blood entering the right atrium through the IVC is mostly shunted across the
Foramen ovale to the left atrium
Prenatally, blood entering the right atrium through the SVC mostly passes to the
Right ventricle through the tricuspid valve
Prenatally, blood leaving the right ventricle to the pulmonary trunk is mostly shunted from the left pulmonary artery to the aorta through the
Ductus arteriosus
In prenatal, which has a higher oxygen content, blood in the aorta proximal to the ductus arteriosus or distal?
Proximal
Prenatally, the shunting of blood from the right atrium to the left atrium through the foramen ovale and
shunting of blood from the pulmonary artery to the aorta through the ductus arteriosus both
depend on a prenatal pressure gradient from
Right to left
In prenatals, brings placental blood toward the liver, which is then shunted past the liver to the IVC by the ductus venosus towards the heart
Umbilical vein
Postnatally, closing of the umbilical vein reduces blood flow to the
Right atrium
Reduces vascular resistance in the pulmonary circuit resulting in increased pulmonary flow to the lungs and increased pulmonary venous return to the left atrium
Expansion of the lungs
The decrease in flow to the right atrium and the increase in flow to the left atrium results in a
Post natal reversal of the pressure gradient (left to right)
The left to right pressure gradient causes a reversal of flow through the ductus arteriosus such that becomes an
Aorta to pulmonary shunt
Causes the ductal smooth muscle to contract resulting in closure of the ductus arteriosus
Postnatal increase in oxygen tension and bradykinin and decreased prostaglandins
The closure of the ductus arteriosus eventually becomes fibrotic and is called the
Ligamentum arteriosum
The umbilical vein closes to become the
Ligamentum teres hepatis
The ductus venosus closes and becomes the
Ligamentum venosum
Postnatally, venous blood entering the liver from the portal vein passes through the liver sinusoids before entering the
IVC
Congenital heart defects may fall under one of which two categories?
- ) Cyanotic
2. ) Acyanotic
When deoxygenated blood enters systemic circulation resulting in a “blue baby”
Cyanotic congenital heart defects
The primary determinant of whether a defect is cyanotic or not is whether the shunting of blood through that defect is
- ) Left to right (systemic to pulmonary)
2. ) Right to left (pulmonary to systemic)
What are the following typically?
- ) Left to right shunts
- ) Right to left shunts
- ) Ayanotic
2. ) Cyanotic
Isolated septal defects are typically
Acyanotic
Atrial septal defects (ASD) may be either
- ) Primum type
2. ) Secundum type
Results from a failure of the septum primum to fuse with the endocardial cushion, thus leaving a patent ostium primum
Primum type ASD
Results from the ostium secundum not being covered over completely by the septum secundum, thus preventing acomplete closure of the foramen ovale
Secundum type ASD
Which is more common, a primum or secundum ASD?
Secundum
A result of excessive resorption of the embryonic ventricular septum during growth of the ventricle
Muscular ventricular septal defect (VSD)
A result of defective formation of the aorticopulmonary septum and a failure of this septum to fuse with the embryonic ventricular septum
Membranous VSD
Which is more common, membranous or muscular VSD?
Membranous
Are VSD’s typically cyanotic or acyanotic?
Acyanotic
In VSD’s, if there the pressure in the pulmonary circuit rises so that it is greater than the systemic circuit, the left to right shunt through the VSD will become a
Right to left shunt
This right to left shunt results in the development of “late cyanosis” which is known as the
Eismenger complex
Failure of the ductus arteriosus to close results in a postnatal aorta to pulmonary (left to right) shunt. This
is an
Acyanotic defect
When the ductus arteriosus fails to completely close
-Much more common in pre-term babies than full-term babies
Patent ductus arteriosus (PDA)
Often successful in getting the PDA to close in preterm babies
Inhibition of prostaglandin synthesis with indomethicin along with oxygen therapy
