The Heart

Functions of the Heart

• The heart works in conjunction with cardiovascular centers and peripheral blood vessels to achieve this goal

• The function of the heart • Generates blood pressure to produce a

gradient that pushes blood through the vascular system

• Regulates blood supply - changes in contraction rate & force match blood delivery to metabolic needs

• Routes blood, ensuring one-way blood flow, separates pulmonary and systemic circulations

The Heart

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

• A muscular double pump• Pulmonary circuit –

takes blood to and from the lungs

• Systemic circuit – vessels transport blood to and from body tissues

Location and Orientation within the Thorax

Figure 18.2

• Largest organ of the mediastinum• Located between

the lungs

• Apex lies to the left of the midline

• Base is the broad posterior surface

Structure of the Heart• Right and left atria - Superior chambers, receive blood from the pulmonary

and systemic circuits• Right and left ventricles - Inferior chambers, the pumping chambers of the

heart• External markings

• Left/right auricles• Apex

• Internal Structures• Interventricular septa• Fossa ovalis

Chambers• Right Atrium

• Forms right border of heart• Receives blood from systemic

circuit• Fossa ovalis - depression in

interatrial septum, remnant of foramen ovale

• Right Ventricle• Receives blood from right

atrium through the tricuspid valve (right atrioventricular valve)

• Pumps blood into pulmonary circuit via the pulmonary semilunar valve into pulmonary trunk

• Internal walls of right ventricle• Trabeculae carneae • Papillary muscles• Chordae tendineae

Chambers• Left atrium

• Makes up heart’s posterior surface

• Receives oxygen-rich blood from lungs

• Opens into the left ventricle through the Mitral valve (left atrioventricular valve)

• Left Ventricle• Forms apex of the heart• Internal walls of left ventricle

• Trabeculae carneae • Papillary muscles• Chordae tendineae

• Pumps blood through systemic circuit via the Aortic semilunar valve (aortic valve)

Heart Valves – Valve Structure• Each valve composed of -

endocardium with connective tissue core

• Atrioventricular (AV) valves between atria and ventricles

• Aortic and pulmonary valves at junction of ventricles and great arteries

Function of the Atrioventricular Valves

Figure 18.9a

Function of the Semilunar Valves

Figure 18.10a, b

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

• Visceral pericardium

• Pericardial cavity

Structure of the Heart – Layers of the Heart Wall• Epicardium - Visceral layer of the serous pericardium

• Myocardium

• Consists of cardiac muscle

• Muscle arranged in circular and spiral patterns

• Endocardium

• Endothelium resting on a layer of connective tissue

• Lines the internal walls of the heart

Structure of Heart Wall• Walls differ in thickness

• Atria – thin walls• Ventricles – thick walls

• Left ventricle – three times thicker than right• Exerts more pumping force• Flattens right ventricle into a

crescent shape• Systemic circuit

• Longer than pulmonary circuit• Offers greater resistance to blood

flow

Blood Flow Through the Heart

Figure 18.6

• Beginning with oxygen-poor blood in the superior and inferior venae cavae

• Go through pulmonary and systemic circuits

• A blood drop passes through all structures sequentially

Cardiac Muscle Tissue• Forms a thick layer called myocardium

• Striated like skeletal muscle

• Contractions pump blood through the heart and into blood vessels

• Contracts by sliding filament mechanism

• Cardiac muscle cells

• Short

• Branching

• Have one or two nuclei

Cardiac Muscle Tissue

• Cells join at intercalated discs• Complex junctions

• Form cellular networks

• Cells are separated by delicate endomysium• Binds adjacent cardiac fibers

• Contains blood vessels and nerves

Electrical Activity of Heart• Heart beats rhythmically as result of action potentials it

generates by itself (autorhythmicity)

• Two specialized types of cardiac muscle cells• Contractile cells

• 99% of cardiac muscle cells

• Do mechanical work of pumping

• Normally do not initiate own action potentials

• Autorhythmic cells• Do not contract

• Specialized for initiating and conducting action potentials responsible for contraction of working cells

Cardiac Conduction System

70-80/min

40-60/min

20-40/min

• SA node ~ 75 bpm - sets the pace of the heartbeat

• AV node ~ 50 bpm - delays the transmission of action potentials

• Purkinje fibers ~ 30 bpm - can act as pacemakers under some conditions