Anatomy and Development of the Heart II Flashcards by Joel Glotfelty

The external surface of the heart is covered with the visceral layer of the

Serous pericardium (or epicardium)

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Fused to the heart and also covers the roots of the greater vessels of the heart

Visceral layer of pericardium

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Serous pericardium reflects off the great vessels to become the

Parietal layer

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Located between the visceral and parietal layers of the serous pericardium

Pericardial cavity

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The parietal layer of serous pericardium is fused to the inner surface of the

Fibrous pericardium

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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

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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

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A blind recess that is closed superiorly and laterally but open inferiorly

Oblique sinus

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The oblique sinus is bounded by the

-all inflow vessels

Inferior vena cava and the four pulmonary veins

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The fibrous pericardium is continuous with the adventitial layer of the great vessels and with the superior fascia of the

Diaphragm

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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

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Cardiac tamponade restricts cardiac filling during diastole, thus reducing

Cardiac output

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How is the pressure from cardiac tamponade relieved?

Pericardiocentesis

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Form during the third week in the splanchnic mesoderm, induced by the underlying endoderm

Right and left embryonic heart tubes

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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

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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

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What are the four regions of the embryonic heart tube?

) Sinus venosus
) Primitive atrium
) Primitive ventricle
) Bulbus cordis

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Receives venous return from the embryo, yolk sac, and placenta

-most of the left horn disappears

Sinus Venosus

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Some of the left horn and central portion of the sinus venosus are retained as the

Coronary sinus

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The right portion of the sinus venosus is incorporated into the right atrium to become the

Sinus venarum (smooth walled part of right atrium)

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Receives blood from the sinus venosus

-is retained as part of the right and left atria (the trabeculated parts)

Primitive atrium

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Receives blood from the primitive atrium

-Is retained as the trabeculated part of the left ventricle

Primitive ventricle

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Receives blood from the primitive ventricle and is subdivided into three parts

Bulbus cordis

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The bulbus cordis is subdivided into which three parts?

) Proximal third
) Conus Cordis
) Truncus Arteriosus

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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?

1. ) Atrial septum 2. ) Ventricular septum 3. ) 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?

1. ) 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?

1. ) 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?

1. ) 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 2. ) 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?

1. ) 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

1. ) Left to right (systemic to pulmonary) | 2. ) Right to left (pulmonary to systemic)

What are the following typically? 1. ) Left to right shunts 2. ) Right to left shunts

1. ) Ayanotic | 2. ) Cyanotic

Isolated septal defects are typically

Acyanotic

Atrial septal defects (ASD) may be either

1. ) 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

Anatomy and Development of the Heart II Flashcards

(102 cards)