Chapter 12The Heart

Location, Size, and Position of the Heart

In mediastinum 2/3 to the left of the body midline Apex = point

Most inferior portion

Shape and size of a closed fist Septum divides right and left sides(internally)

Pericardium

Two-layered fibrous sac

Inner layer = visceral pericardium or epicardium

Outer layer = parietal pericardium

Pericardial cavity is filled with pericardial fluid

Approximately 15-30 ml pericardial fluid present

Three layers of the Heart Wall

Epicardium Outer layer Connective tissue

Myocardium Middle layer Thick Muscle

Endocardium Inner layer (lining) Very thin, smooth

Summary of layers

Outside (external) to Inside (internal) Parietal Pericardium Pericardial cavity (filled with fluid) Visceral Pericardium/Epicardium Myocardium Endocardium

Anatomy of the Heart

Heart chambers Two upper chambers are

Right and left atria (atrium) Small chambers Receive blood

Two lower chambers called ventricles Right and left ventricles Larger chambers Pump blood out of heart

Vessels

Pulmonary Arteries Carry blood from R ventricle to lungs R pulmonary artery to R lung L pulmonary artery to L lung

Pulmonary Veins Carry blood from lungs to L atria R pulmonary veins from R lung L pulmonary veins from L lung

Vessels cont.

Vena Cava Inferior and superior Empties blood into heart from body

Valves

Cuspid valves Tricuspid: between right atrium and ventricle Bicuspid (mitral): between left atrium and ventricle Open and close from chordae tendineae

Semilunar valves Pulmonary Semilunar: base of pulmonary arteries Aortic Semilunar: base of aorta Open and close from pressure within heart

The 4 valves

The heart is where pulmonary circulation starts and ends.

The valves support 1-way movement through the heart.

The heart acts as two pumps

Right atrium and ventricle pump deoxygenated blood to the lungs

Left atrium and ventricle pump oxygenated blood to the body

Sequence of Blood Flow

Heart Sounds

Two distinct heart sounds in every heartbeat or cycle—“lubb-dupp”

First (lubb) sound is caused by the vibration and closure of AV valves during contraction of the ventricles

Second (dupp) sound is caused by the closure of the semilunar valves during relaxation of the ventricles

Heart Actions

Contraction is called systole

Relaxation is called diastole

These actions create Blood Pressure

Practical Application

Supposed an individual was injured by falling off a roof and he severely damaged his right arm with copious blood loss. His blood pressure steadily dropped to dangerous levels. How would you explain the drop in his blood pressure?

Continued

In response to the drop in blood pressure, the heart begins beating more rapidly. The increase in HR increases overall blood flow and thus causes even more rapid blood loss from a wound. The more blood lost, the faster the heart beats and the faster blood volume is lost. How can you explain this? What type of feedback is this?

Cardiac Cycle

Heart beat is regular and rhythmic—each complete beat called a cardiac cycle—average is about 72 beats per minute

Each cycle, about 0.8 seconds long, subdivided into systole (contraction phase) and diastole (relaxation phase)

Cardiac Cycle

Stroke volume is the volume of blood ejected from one ventricle with each beat

Cardiac output is amount of blood that one ventricle can pump each minute—average is about 5 L per minute at rest

Benefit of exercise!

Conduction System of the Heart

SA (sinoatrial) node The pacemaker In wall of right atrium near superior vena cava

AV (atrioventricular) node In the floor of right atrium near septum

AV bundle (bundle of His) Located in the septum of the ventricle

Purkinje fibers— Located in the walls of the ventricles Cause contraction of myocardium

Conduction System of the Heart

Electrocardiography Measures the electrical impulses that result in

contraction of the heart Impulses transformed into visible tracings by a

machine called an electrocardiograph The visible tracing of these electrical signals is called

an electrocardiogram or ECG

Conduction System of the Heart

The normal ECG has three deflections or waves called the P wave, the QRS complex, and the T wave P wave—associated with depolarization of the

atria QRS complex—associated with depolarization of

the ventricles T wave—associated with repolarization of the

ventricles

Issues with the heart’s conduction system

Bradycardia—slow heart rate (under 60 beats/min) Tachycardia—rapid heart rate (over 100 beats/min) Sinus dysrhythmia—variation in heart rate during

breathing cycle Premature contraction (extrasystole)—contraction

that occurs sooner than expected in a normal rhythm Fibrillation—condition in which cardiac muscle fibers

are “out of step,” producing no effective pumping action

Chronic diseases of the heart

Coronary Circulation and Coronary Heart Disease

Blood, which supplies oxygen and nutrients to the myocardium of the heart, flows through the right and left coronary arteries

Blockage of blood flow through the coronary arteries can cause myocardial infarction

CHD

Atherosclerosis (type of “hardening of arteries” in which lipids build up on the inside wall of blood vessels) can partially or totally block coronary blood flow

Angina pectoris—chest pain caused by inadequate oxygen to the heart

Heart Failure

Heart failure—inability to pump enough returned blood to sustain life; it can be caused by many different heart diseases

Right-sided heart failure—failure of the right side of the heart to pump blood, usually because the left side of the heart is not pumping effectively

Heart Failure

Left-sided heart failure (congestive heart failure)—inability of the left ventricle to pump effectively, resulting in congestion of the systemic and pulmonary circulations

Diseased hearts can be replaced by donated living hearts (transplants) or by artificial hearts (implants), although both procedures have yet to be perfected