Chapter 12 The 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) Apex is on the diaphragm

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 The pericardium and pericarditis Pericardium is a two-layered fibrous sac with a lubricated space between the two layers Inner layer is called visceral pericardium or epicardium Outer layer called parietal pericardium What is the condition for inflammation of the pericardium? Pericarditis Why is this condition serious?

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 Wall of each heart chamber is composed of cardiac muscle tissue called myocardium Endocardium—smooth lining of heart chambers—inflammation of endocardium called endocarditis

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 Pulmonary Veins 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 Semilunar 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 Four valves keep blood flowing through the heart; prevent backflow (two atrioventricular or AV and two semilunar valves) Tricuspid: at the opening of the right atrium into the ventricle Bicuspid (mitral): at the opening of the left atrium into the ventricle Incompetent valves “leak,” allowing some blood back into the chamber from which it came Stenosed valves are narrower that normal, reducing blood flow Rheumatic heart disease—cardiac damage resulting from a delayed inflammatory response to streptococcal infection Mitral valve prolapse (MVP)—incompetence of mitral valve because its edges extend into the left atrium when the left ventricle contracts

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 Venous blood enters the right atrium through the superior and inferior vena cava -- passes from the right atrium through the tricuspid valve to the right ventricle; from the right ventricle through the pulmonary semilunar valve to the pulmonary artery to the lunges – blood from the lungs to the left atrium, passing through the bicuspid (mitral) valve to the left ventricle; blood in the left ventricle is pumped through the aortic semilunar valve into the aorta and is distributed to the body as a whole.

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 What does blood pressure measure? Why is it important to monitor blood pressure? What is an ideal BP?

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? A basic principle of physics states that a decrease in fluid volume in a closed container causes a drop in the pressure with which that fluid is pushing on the sides of that container. Thus, loss of blood (decrease in blood volume) from the blood vessels (a closed network of tubes) decreases the overall pressure of blood in the vessels.

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? This is a positive feedback response because the response, an increase in heart rate and thus an increase in blood flow, actually moves you farther away from the normal range of blood pressure (it amplifies the change rather than reversing the change). A negative feedback response would have restored BP to normal. Does this response (increase in HR) tend to restore homeostatic balance or does it tend to create an imbalance? This response tends not only to create an imbalance, it actually makes an existing imbalance worse (the classic hallmark of a positive feedback response). The BP continues to fall, rather than rise back toward normal.

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