The Heart

OBJECTIVES:

OBJECTIVES

Orientation of heart in thoraxExplain the circuits of blood flowGross Anatomy of HeartBlood Flow to the Heart MuscleHistology of Heart Muscle TissueElectrical Conduction System of HeartDisorders of the Heart

Location and Orientation within the Thorax

Heart – typically weighs 250–350 grams (healthy heart)

Largest organ of the mediastinum (area between the lungs, thoracic inlet superiorly and diaphragm inferiorly, sternum anteriorly and vertebral column posteriorly)

Located between the lungsApex (pointed part) lies to the left of the midline Base is the broad posterior surface (facing

toward left shoulder) The heart is a double pump: one pumps blood to the lung and

the other to the body

Location and Orientation within the Thorax

Figure 18.2

The heart is in contact with the diaphragm inferiorly, lungs laterally, sternum anteriorly and the spinal column and great vessels posteriorly. Superiorly, the vessels which enter and exit the heart fill much of the superior mediastinum.

Four “Corners” of the Heart

Superior right At costal cartilage of third rib and sternum

Inferior right At costal cartilage of sixth rib lateral to the sternum

Superior left At costal cartilage of second rib lateral to the

sternum Inferior left

Lies in the fifth intercostal space at the midclavicular line

The Pulmonary and Systemic Circuits

Figure 18.1

There are three separate circuits of blood involving the heart: the pulmonary, the systemic and the coronary.

The pulmonary circuit goes from the right ventricle to the pulmonary arteries to the lungs and back to the left atrium

The sysemic circuit runs from the left ventricle to the aorta and onto the superior and inferior systemic arteries.

The coronary circuit involves the arteries and veins which supply the heart muscle itself. It runs from the right and left coronary arteries arising from the aorta.

Blood Supply to the Heart

Functional blood supplyCoronary arteries

Arise from the aortaLocated in the coronary sulcusMain branches

Left and right coronary arteries

Coronary Circulation

The left coronary artery (LCA) arises from the left side of the aorta, passes posterior to the pulmonary trunk then divides into two branches: the anterior interventricular and the circumflex arteries. The anterior interventricular artery is referred to as the Left Anterior Descending Artery, or LAD and runs inferiorly down thhe interventricular septum and anterior walls of both ventricles.

The circumflex artery (Cx), follows the coronary sulcus posteriorly and supplies the left atrium and the posterior part of the left ventricle

The Right Coronary Artery (RCA) emerges from the right side of the aorta and descends in the coronary sulcus on the anterior surface of the heart between the right atrium and right ventricle. At the inferior border of the heart, it branches to form the marginal artery. Continuing into the posterior part of the coronary sulcus the right coronary artery gives off a large branch in the posterior interventricular sulcus, the posterior interventricular artery. Clinically this arteries commonly called the posterior descending artery (PDA). The right coronary artery and its branches supply the right atrium and much of the right ventricle

Cardiac veins Cardiac veins collect blood from the arteries and returns it to the right atrium. The

largest vein is the coronary sinus. It occupies the posterior part of the coronary sulcus and returns almost all the venous blood from the heart to the right atrium. Into the coronary sinus drain three large tributaries: the great cardiac vein the middle cardiac vein in the small cardiac vein

Blood Supply to the Heart

Figure 18.16

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Structure of the Heart – Coverings

Figure 18.3

Structure of the Heart – Coverings

Pericardium – two primary layers Fibrous pericardium

Strong layer of dense connective tissue Serous pericardium

Formed from two layers Parietal pericardium – this is the more superficial layer Visceral pericardium – this layer is in direct contact

with the surface of the heart. The function of these layers is to reduce friction while the heart is beating

So in total there are three layers of tissue surrounding the heart. The fibers per cardio and is separated from the serous pericardium and protects the heart.

Structure of the Heart – Layers of the Heart Wall

Figure 18.4

This muscle arrangement is very efficient to squeeze out all of the blood

Structure of Heart Wall

Left ventricle – three times thicker than rightExerts more

pumping forceFlattens right

ventricle into a crescent shape

Figure 18.7

Heart Chambers

Figure 18.5b

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Heart Chambers

Figure 18.5e

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Posterior View of the Heart

Figure 18.5d

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The Heart

A muscular double pump (left and right)Pulmonary circuit (right side) – takes

blood to and from the lungsSystemic circuit (left side) – vessels

transport blood to and from body tissuesAtria – receive blood from the pulmonary

and systemic circuitsVentricles – the pumping chambers of the

heart

Heart Chambers

Right and left atria Superior chambers

Right and left ventricles Inferior chambers

Internal divisions Interventricular septa Interatrial septa

External markings Coronary sulcus posterior interventricular sulcus

Right Atrium

Forms right border of heart Receives blood from systemic circuit Auricle - the auricle is a separate part of the main atrium

known as the atrial appendages Pectinate muscles

Ridges inside anterior of right atrium - associated with auricle

Fossa ovalis Depression in interatrial septum

Remnant of foramen ovale

Right Ventricle

Receives blood from right atrium through the tricuspid valve

Pumps blood into pulmonary circuit viaPulmonary trunk

Internal walls of right ventricleTrabeculae carneae Papillary musclesChordae tendineae

Left Atrium

Makes up heart’s posterior surfaceReceives oxygen-rich blood from lungsOpens into the left ventricle through

Mitral valve (left atrioventricular valve)

Left Ventricle

Forms apex of the heartInternal walls of left ventricle

Trabeculae carneae Papillary musclesChordae tendineae

Pumps blood through systemic circuit viaAortic semilunar valve (aortic valve)

Blood Flow Through the Heart

Figure 18.6

Heartbeat

70 – 80 beats per minute at restSystole – contraction of a heart chamberDiastole – expansion of a heart chamber

Systole and diastole also refer toStage of heartbeat when ventricles contract

and expand

Heart Valves – Valve Structure

Each valve composed ofEndocardium with connective tissue core

Atrioventricular (AV) valvesBetween atria and ventricles

Aortic and pulmonary valvesAt junction of ventricles and great arteries

Fibrous Skeleton

Surrounds all four valvesComposed of dense connective tissue

FunctionsAnchors valve cuspsPrevents overdilation of valve openingsMain point of insertion for cardiac muscleBlocks direct spread of electrical impulses

Heart Valves – Valve Structure

Figure 18.8a

Function of the Atrioventricular Valves

Figure 18.9a

Function of the Atrioventricular Valves

Figure 18.9b

Function of the Semilunar Valves

Figure 18.10a, b

Microscopic Anatomy of Cardiac Muscle

Figure 18.12a, b

Cardiac Muscle Tissue

Figure 18.12c, d

Cardiac Muscle Tissue

Not all cardiac cells are innervatedWill contract in rhythmic manner without

innervation Inherent rhythmicity

Is the basis for rhythmic heartbeat

Conducting System

Cardiac muscle tissue has intrinsic ability to generate and conduct impulses

Conducting system A series of specialized cardiac muscle cellsSinoatrial (SA) node sets the inherent rate

of contraction (overrides autorhythmicity)

Conducting System

Figure 18.14

Innervation

Heart rate is altered by external controls

Nerves to the heart include Visceral sensory fibers Parasympathetic branches

of the vagus nerve Sympathetic fibers –

from cervical and upper

thoracic chain ganglia

Figure 18.15

Heart Sounds

“Lub-dub” – sound of valves closingFirst sound “lub”

The AV valves closingSecond sound “dub”

The semilunar valves closing

Heart Sounds

Each valve sound – best heard near a different heart cornerPulmonary valve – superior left cornerAortic valve – superior right cornerMitral (bicuspid) valve– at the apexTricuspid valve – inferior right corner

Heart Sounds

Figure 18.11

Disorders of the Heart

Coronary artery disease – caused by a buildup of fatty plaque called atherosclerosis in the coronary arteries resulting in decreased blood supply to the myocardium of the heart and diminished heart function. The causes of CAD may be lifestyle or genetic. The first step is to make lifestyle changes. If this is insufficient to open the arteries then surgical intervention may be necessary.

Atherosclerosis – fatty deposits Angina pectoris – chest pain Myocardial infarction – blocked coronary artery

Heart attack

Silent ischemia – no pain or warning. Loss of blood supply to a portion of the cardiac muscle.

Disorders of the Heart

Heart failureProgressive weakening of the heartCannot meet the body’s demands for

oxygenated bloodCongestive heart failure (CHF)

Heart enlargesPumping efficiency declines

Cor pulmonale Enlargement and potential failure of right

ventricle