The Pulmonary and Systemic Circuits

Right side of the Heart

Receives oxygen-poor blood from tissues; pumps to lungs to get rid of CO2, picks up O2, via pulmonary circuit

Left side of the Heart

Receives oxygenated blood from lungs; pumps to the body tissues via systemic circuit (comes out of aorta)

Right Atrium

A receiving chamber of the heart; receives blood returning from systemic circuit

Left Atrium

A receiving chamber of the heart; receives blood returning from pulmonary circuit

Right Ventricle

Pumping chamber of the heart; pumps blood through pulmonary circuit

Left Ventricle

Pumping chamber of the heart; pumps blood through systemic circuit

Fossa Ovalis

Remnant of foramen ovale of fetal heart

Interventricular Septum

Separates ventricles and atrium

Pericarditis

Inflammation of pericardium; roughens membrane surfaces causing pericardial friction rub (creaking sound) heard with stethoscope

Cardiac Tamponade

Excess fluid sometimes compresses heart causing limited pumping ability

Heart valves

Ensure unidirectional blood flow through heart; open and close in response to pressure changes

Atrioventricular (AV) Valves

Prevent backflow into atria when ventricles contract

Tricuspid valve: right AV valve

Mitral valve: left AV valve, bicuspid valve

Chordae Tendineae

Anchor cusps to papillary muscles; holds flaps in closed position

Semilunar (SL) Valves

Prevents backflow into ventricles when ventricles relax; open and close in response to pressure changes

Aortic SL valve: left ventricle

Pulmonary SL valve: right ventricle

Incompetent Valve

Condition that severely weakens heart; blood backflows so heart repumps same blood over and over

Valvular Stenosis

Condition that severely weakens heart; stiff flaps that constrict opening causing heart to exert

more force to pump blood

Pulmonary Circuit Blood Pathway

Right atrium → tricuspid valve → right ventricle → pulmonary semilunar valve →pulmonary trunk → pulmonary arteries → lungs → pulmonary veins → left atrium

Systemic Circuit Blood Pathway

Left atrium → mitral valve → left ventricle → aortic semilunar valve → aorta → systemic circulation

Cardiac Cycle

Blood flow through heart during one complete heartbeat; atrial systole (contraction) and diastole (relaxation) followed by ventricular systole and diastole; series of pressure and blood volume changes

Pathway of Blood Through the Heart

Equal volumes of blood pumped to pulmonary and systemic circuits; pulmonary circuit short and low-pressure circulation, systemic circuit long and high-friction circulation; anatomy of ventricles reflects differences, left ventricle walls 3X thicker than right because it pumps with greater pressure

Coronary Circulation

Functional blood supply to heart muscle itself; delivered when heart relaxed; left ventricle receives most blood supply; contains many anastomoses (junctions) which provide additional routes for blood delivery and cannot compensate for coronary artery occlusion; arteries arise from base of aorta

Left Coronary Artery

Branches into anterior interventricular artery and circumflex artery; supplies interventricular septum, anterior ventricular walls, left atrium, and posterior wall of left ventricle

Right Coronary Artery

branches into right marginal artery and posterior interventricular artery; supplies right atrium and most of right ventricle

Angina Pectoris

Thoracic pain caused by fleeting deficiency in blood delivery to myocardium; cells weakened

Ischemia

Heart is deprived of blood due to atherosclerosis

Myocardial Infarction (MI)

Heart attack; prolonged coronary blockage; areas of cell death repaired with noncontractile scar tissue

Hearts Electrical Physiology

Heart depolarizes and contracts without nervous system stimulation; rhythm can be altered by autonomic nervous system

Pacemaker Action Potential

Repolarization closes K+ channels and opens slow

Na+ channels → ion imbalance →

Depolarization Action Potential

Ca2+ channels open → huge influx → rising phase of action potential

Repolarization Action Potential

K+ channels open → efflux of K+

SEQUENCE OF EXCITATION

Sinoatrial (SA) Node

Pacemaker of heart in right atrial wall; depolarizes faster than rest of myocardium; generates impulses about 75X/minute (sinus rhythm); impulse spreads across atria, and to AV node

Electrocardiogram (ECG or EKG)

Composite of all action potentials generated by nodal and contractile cells at given time

P wave - depolarization SA node → atria

QRS complex - ventricular depolarization and atrial repolarization

T wave - ventricular repolarization

Arrhythmias

irregular heart rhythms; uncoordinated atrial and ventricular contractions

Fibrillation

rapid, irregular contractions; useless for pumping blood, circulation ceases, brain death; defibrillation to treat

Extrinsic Innervation of the Heart

Heartbeat modified by ANS via cardiac centers in medulla oblongata

Sympathetic: increases rate and force

Parasympathetic: decreases rate

Cardioacceleratory Center

sympathetic – affects SA, AV nodes, heart muscle, coronary arteries

Cardioinhibitory Center

Parasympathetic – inhibits SA and AV nodes via vagus nerves

Heart Sounds

Two sounds (lub-dup) associated with closing of heart valves; first as AV valves close (beginning of systole); second as SL valves close (beginning of ventricular diastole); pause indicates heart relaxation

Heart Murmurs

Abnormal heart sounds; usually indicate incompetent or stenotic valves

1st Phase of Cardiac Cycle

Ventricular Filling; takes place in mid-to-late diastole; AV valves are open and pressure is low; 80% of blood passively flows into ventricles; atrial systole occurs, delivering remaining 20%

End Diastolic Volume (EDV)

Volume of blood in each ventricle at end of ventricular diastole

2nd Phase of Cardiac Cycle

Ventricular Systole; atria relax and ventricles begin to contract; rising ventricular pressure leads to closing of AV valves; isovolumetric contraction phase; in ejection phase, ventricular pressure exceeds pressure in large arteries, forcing SL valves open

End Systolic Volume (ESV)

Volume of blood remaining in each ventricle after systole

3rd Phase of Cardiac Cycle

Isovolumetric Relaxation happens in early diastole; ventricles relax and atria relaxed and filling; backflow of blood in aorta and pulmonary trunk closes SL valves and causes dicrotic notch (brief rise in aortic pressure as blood rebounds off closed valve); ventricles totally closed chambers; when atrial pressure exceeds that in ventricles, AV valves open and  cycle begins again at step 1

Cardiac Output (CO)

Volume of blood pumped by each ventricle in one minute; CO= heart rate (HR) * stroke volume (SV); SV is calculated by EDV - ESV; HR is number of beats per minute; SV is volume of blood pumped out by one ventricle with each beat; normal is 5.25 L/min