Cuore

Myocardium forms a figure 8 pattern around atria and around ventricula

The muscle of left ventricle is much thicker and generate much more pressure

than

right ventricle in order to overcome the high resistance of systemic circuit

(pulmunary circuit is shorter and provides less resisence).

Inner view

Interatrial septum: extensions of the myocardium lined with endocardium located

between the two atria [Normally in an adult heart, the interatrial septum bears an

oval-shaped depression known as the fossa ovalis, a remnant of an opening in the

fetal heart known as the foramen ovale. The foramen ovale allowed blood in the fetal

heart to pass directly from the right atrium to the left atrium, allowing blood to bypass

the pulmonary circuit. Within seconds after birth the foramen ovale closes]

Interventricular septum: septum between the two ventricles (thicker than the

interatrial septum)

The septum between the atria and ventricles is known as the atrioventricular septum.

In 20% of population fossa ovalis is unable to close at birth -> interatrial septum

pathology called patent foramen ovale (most cases asymptomatic, but can lead to

ictus).

Cardical skeleton and valves

Cardiac skeleton: dense connective tissue in atrioventricular septum that includes four

rings that surround the openings between the atria and ventricles, and the openings to

the pulmonary trunk and aorta, and serve as the point of attachment for the heart

valves. The cardiac skeleton also provides an important boundary in the heart

electrical conduction system.

Between the atria and ventricles there is a valve, a specialized structure that ensures

one-way flow of blood.

atrioventricular valves between atria and ventricles



 semilunar valves that lead to the pulmonary trunk and aorta.

atrioventricular valves

Each flap of the valve is attached to strong strands of connective tissue, the chordae

tendineae (there are several chordae tendineae associated with each of the flaps).

They connect each of the flaps to a papillary muscle that extends from the inferior

ventricular surface. There are 3 papillary muscle in right ventricle (anterior, posterior,

and septal muscles) and 2 (anterior and posterior) in left ventricle which correspond to

the sections of the valves.

When the myocardium of the ventricle contracts, pressure within the ventricular

chamber rises. Blood, like any fluid, flows from higher pressure to lower pressure

areas, in this case, toward the pulmonary trunk and the atrium. To prevent any

potential backflow, the papillary muscles also contract, generating tension on the

chordae tendineae. This prevents the flaps of the valves from being forced into the

atria and regurgitation of the blood back into the atria during ventricular contraction.

Inner view (atrioventricular valves).

Cardical valves

Tricuspid valve (or right atrioventricular valve) consists of three flaps

 (anterior, posterior, medial) made of endocardium reinforced with additional

connective tissue. The flaps are connected by chordae tendineae to the

papillary muscles, which control the opening and closing of the valves.

Pulmonary valve (or right semilunar valve) is comprised of three small flaps of

 endothelium reinforced with connective tissue. When the ventricle relaxes, the

pressure differential causes blood to flow back into the ventricle from the

pulmonary trunk. This flow of blood fills the pocket-like flaps of the pulmonary

valve, causing the valve to close and producing an audible sound. No papillary

muscles or chordae tendineae.

Mitral valve (or bicuspid valve or left atrioventricular valve) consists of two

 cusps (anterior medial cusp and the posterior lateral cusp) attached by chordae

tendineae to two papillary muscles.

 Aortic valve (or left semilunar valve) composed of three flaps. When the

ventricle relaxes and blood attempts to flow back into the ventricle from the

aorta, blood will fill the cusps of the valve, causing it to close and producing an

audible sound.

Discorders of the cardical valves

In valve prolapse, the leaflets of the valve bulge (prolapse) into the atrium like a

parachute during the heart's contraction (due to damage to chordae tendinae).

Sometimes valve prolapse causes blood to leak back into the atrium from the

ventricle, which is called mitral valve regurgitation (valve insufficiency).

Valve stenosis, shown in the heart on the right, is a condition in which the heart's

valve is narrowed. This abnormal valve doesn't open properly, blocking blood flow

coming into ventricle.

Cardiac circulation: coronary a./v

Coronary arteries originates from the first portion of the aorta (ascending aorta).

Coronary vessel branches that remain on the surface of the heart and follow the sulci

are called “epicardial coronary arteries”. The left coronary artery distributes blood to

the left side of the heart, the left atrium and ventricle, and the interventricular

septum. It gives origin to:

the circumflex artery that follows the coronary sulcus to the left;



 the anterior interventricular artery (IVA), (or left anterior descending artery -

LAD), that follows the anterior interventricular sulcus. Along the way it gives rise

to numerous smaller branches that interconnect with the branches of the

posterior interventricular artery, forming anastomoses.

The right coronary artery proceeds along the coronary sulcus and distributes blood to

the right atrium, portions of both ventricles, and the heart conduction system. It gives

origin to: -the marginal arteries that supply blood to the superficial portions of the

right ventricle. -the posterior interventricular artery (or posterior descending artery)

that runs along the posterior portion of the interventricular sulcus toward the apex of

the heart, supplying the interventricular septum and portions of both ventricles.

Coronary veins (great cardiac vein, posterior c. v., middle c. v., small c. v.) drain the

heart and they are generally parallel the large surface arteries. They drain in to the

coronary sinus (large vein in the posterior surface of heart within the atrioventricular

sulcus and emptying directly into the right atrium) except the anterior cardiac vein

that drains directly in the right atrium.

Coronary artery disease

Atherosclerosis occurs when the buildup of plaque (a fatty material) within the walls of

the arteries obstructs the flow of blood. So the flow of blood to the tissues will be

restricted causing ischemia and prevent the cells from receiving sufficient amounts of

oxygen (hypoxia).

Angioplasty is a procedure in which the occlusion is mechanically widened with a

balloon.

Electrical condution system

Cardiac muscle has the exceptional ability to initiate an electrical

potential at a fixed rate that spreads rapidly from cell to cell to

trigger the contractile mechanism. This property is known as

autorhythmicity. Neither smooth nor skeletal muscle can do this.

Even though cardiac muscle has autorhythmicity, heart rate is

modulated by the endocrine and nervous systems.

The conduction system of the heart is formed by the myocardial

conducting cells. Their function is similar in many respects to

neurons, although they are specialized muscle cells. Myocardial

conduction cells initiate and propagate the action potential (the

electrical impulse) that travels throughout the heart and triggers

the contractions that propel the blood. As more myocardial

conducting cells are joined together, the fastest cell continues to assume control of

the rate.

Then a fully developed adult heart has the capability of generating its own

electrical impulse, triggered by the fastest cells, as part of the cardiac

conduction system.

Normal cardiac rhythm is established by the sinoatrial (SA) node, a specialized clump

of myocardial conducting cells located in the right atrium.

SA node has the highest rate of depolarization and is known as the pacemaker of the

heart. It initiates the sinus rhythm, or normal electrical pattern followed by contraction

of the heart.

The components of the cardiac conduction system include:

- the sinoatrial node [60-100 bpm] - the internodal pathways [55-60 bpm]

- the atrioventricular node [45-50 bpm]

- the atrioventricular bundle (of His) [40-45 bpm]

- the atrioventricular bundle branches [40-45 bpm] - the Purkinje cells [35-40

bpm]

This impulse spreads from the SA node throughout the atria through specialized

internodal pathways, to the atrial myocardial contractile cells.

The internodal pathways consist of three bands (anterior, middle, and posterior) that

lead directly from the SA node to the next node in the conduction system, the

atrioventricular node. The impulse takes approximately 50 ms (milliseconds) to travel

between these two nodes. In addition, there is a specialized pathway called

Bachmann’s bundle or the interatrial band that conducts the impulse directly from the

right atrium to the left atrium. As the impulse reaches the atrioventricular septum, the

connective tissue of the cardiac skeleton prevents the impulse from spreading into the

myocardial cells in the ventricles except at the atrioventricular node.

The impulse takes approximately 50 ms (milliseconds) to travel between these two

nodes. In addition, there is a specialized pathway called Bachmann’s bundle or the

interatrial band that conducts the impulse directly from the right atrium to the left

atrium. As the impulse reaches the atrioventricular septum, the connective tissue of

the cardiac skeleton prevents the impulse from spreading into the myocardial cells in

the ventricles except at the atrioventricular node.

There is a critical pause (100 ms) before the AV node transmits the impulse to the

atrioventricular bundle -> This allows the atria to complete their contraction that

pumps blood into the ventricles . The AV node can transmit impulses maximally at 220

per minute typical maximum heart rate in a healthy young individual. From the AV



node, the atrioventricular bundle, or bundle of His, proceeds through the

interventricular septum two atrioventricular bundle branches (left and right).



Portions of the right bundle branch are found in the moderator band and supply the

right papillary muscles -> each papillary muscle receives the impulse at approximately

the same time, so they contract simultaneously just prior to the remainder of the

myocardial contractile cells of the ventricles. This is believed to allow tension to

develop on the chordae tendineae prior to right ventricular contraction. Both bundle

branches descend and reach the apex of the heart where they connect with the

Purkinje fibers. They spread the impulse to the myocardial contractile cells in the

ventricles. They extend throughout the myocardium from the apex of the heart toward

the atrioventricular septum and the base of the heart.

Atrial systole: contractile cells begin contraction from the

superior to the inferior portion of the atria, pumping blood

in ventricles.

Ventricular systole: the