anatomy & physiology of the heart. heart anatomy size, location, and orientation enclosed in the...

Anatomy & physiology of the heart

Heart Anatomy

Size, Location, and Orientation Enclosed in the mediastinum Base (posteriorsuperior

portion) and Apex (inferioranterior portion)

Heart Anatomy Coverings

Pericardium protects the heart anchors the heart to

surrounding structures such as the diaphragm and the great vessels

prevents overfilling of the heart with blood

Heart AnatomyCoverings

pericardial cavity contains a film of serous fluid

pericarditis: inflammation of the pericardium which may lead to adhesions between the layers or the buildup of fluid in the pericardial cavity (cardiac tamponade)

Heart Anatomy Heart Wall

Epicardium Myocardium

bulk of the heart consisting mainly of cardiac muscle

Heart Anatomy Heart Wall

Endocardium simple squamous

epithelium and a thin CT layer that lines the heart chambers and valves and is continuous with the endothelial lining of the blood vessels

Heart Anatomy Chambers

Atria Features

small, thin-walled chambers Functions

receiving chambers for blood returning to the heart from the circulation

push the blood into the adjacent ventricles.


Atria Receive blood from

right side Superior and Inferior Vena

Cava Coronary Sinus (draining the

myocardium) left side Pulmonary Veins


Ventricles Features

make up most of the mass of the heart

the walls of the left ventricle are 3X thicker than those of the right


Ventricles Functions

discharging chambers of the heart propel blood to Pulmonary Trunk (right

ventricle), Aorta (left ventricle)

Heart Anatomy Pathway of Blood Through the

Heart Pulmonary Circuit

functions strictly as gas exchange

the right side of the heart is the pulmonary circuit pump

this is a short, low-pressure circuit

Heart Anatomy Pathway of Blood Through the

HeartSystemic Circuit

o functions as both gas and nutrient exchange

o the left side of the heart is the systemic circuit pump

o this is a long, high-resistance pathway through the entire body

Heart Anatomy Heart Valves

These enforce the one-way flow of blood through the heart

The valves open and close in response to differences in blood pressure on their two sides


Atrioventricular Valves the valves close when the

ventricular pressure increases and forces blood against the valve flaps

Tricuspid (right side) Bicuspid (Mitral) (left side)


Semilunar Valves located between the ventricles

and the large arteries these open when the pressure

produced by the contracting ventricle exceeds that in the artery and close when the arterial pressure exceeds the pressure produced by the relaxing ventricle

Pulmonary (right side) Aortic (left side)

Coronary Circulation Coronary Arteries

the coronary arteries arise from the base of the aorta and actively deliver blood only when the heart is relaxed

the heart is 0.5% of body weight and receives 5% of the body's blood supply (most to the left ventricle)


left main coronary artery left anterior descending artery:

serves the interventricular septum and anterior walls of both ventricles

circumflex artery: serves the left atrium and posterior wall of the left ventricle


Right main coronary artery posterior descending artery: serves

the posterior walls of both ventricles

marginal artery: lateral wall of the right side of the heart

Cardiac Veins follow arteries and join at the Coronary Sinus which empties blood into the right atrium

Heart Physiology Electrical Events

Intrinsic Conduction System of the Heart the ability of cardiac muscle to

depolarize and contract is intrinsic (no nervous stimulation is required)

nerve impulses can alter the basic rhythm of heart activity set by intrinsic factors


Action Potential Generated by Autorhythmic Cells Sequence of Excitation

o Sinoatrial Node o Atrioventricular Node o Atrioventricular Bundle

(bundle of His) o Bundle Branches o Purkinje Fibers


Extrinsic Innervation of the Heart fibers of autonomic nervous

system accelerate or inhibit the basic rate of heartbeat set by the intrinsic conduction system


Electrocardiography electrical currents generated

and transmitted through the heart spread throughout the body and can be monitored

the graphic recording of electrical changes during heart activity is called an electrocardiogram (ECG or EKG)

Heart Physiology

Electrical Events Electrocardiography

the ECG consists of series of three waves o P Wave: atrial depolarization

starting at the SA node o QRS Complex: ventricular

depolarization


Electrocardiographyo P-R (P-Q) interval: time from

the beginning of atrial excitation to the beginning of ventricular excitation and includes the contraction of the atria and the passage of the depolarization wave through the rest of the conduction system


ElectrocardiographyoT Wave: ventricular repolarization oQ-T interval: time from the

beginning of the ventricular depolarization through their repolarization and includes the contraction of the ventricles

Heart Physiology Mechanical Events: The Cardiac Cycle

Terms Systole: contraction period of

heart activity Diastole: relaxation period of

heart activity


Cardiac Cycle o pressure in the heart is low and the

blood is returning passively (70% of ventricle filling occurs)

o atria depolarize (P wave) and contract and force the remaining 30% of the blood into the ventricles

o the atria relax and remain in diastole through the rest of the cycle


o the ventricles depolarize (QRS complex)

o ventricles begin their contraction o ventricular pressure rises rapidly

and the AV valves close o as ventricular pressure rises above

arterial pressure the semilunar valves open and the ventricles empty during the ventricular ejection phase


o ventricular systole ends with the repolarization of the ventricles (T wave)

o ventricles relax and ventricular pressure drops

o semilunar valves close o the atria have been filling with blood

since ventricular systole and when the atrial pressure exceeds the ventricular pressure the AV valves open ventricular filling begins again

Heart Physiology Cardiac Output

General cardiac output is the amount of

blood pumped out by each ventricle in 1 minute and is the product of heart rate (HR) and stroke volume (SV)

stroke volume is the volume of blood pumped out by one ventricle with each beat and is the difference between end diastolic volume (EDV) and the end systolic volume (ESV)


Regulation of Stroke Volume Preload: Degree of Stretch

affected by the EDV and operates intrinsically

Frank Starling Law of the Heart: The greater the degree of stretch of cardiac muscle fibers the greater the force of contraction and the greater the stoke volume


resting cardiac fibers are normally shorter than the optimal length and stretching them (increasing EDV) produces dramatic increases in contractile force

anything that increases the volume or speed of venous return (slow heart rate or exercise) increases EDV which increases the force of contraction which increases stroke volume


Contractility affects the ESV and are

extrinsic factors that increase the contractile strength of heart muscle

many chemicals enhance contractility (positive inotropic agents)


Afterload: Back Pressure affects the ESV the pressure exerted on the

aortic (80 mm Hg) and pulmonary (20 mm Hg) valves by arterial blood

important in people with hypertension where ESV is increased and stroke volume is reduced

SA

AV

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