The Cardiovascular System: The Heart

Structure and Organization Structure & Organization Location Between the lungs in the thoracic cavity 2/3 of mass to the left of midline Size: about the same as your closed fist Pointed end (apex) rests on diaphragm Wide end (base) is superior to the apex

Figure 15.01 Position of the Heart and Associated Blood Vessels in Thoracic Cavity

Cardiac Muscle Tissue Cardiac Muscle Unique features Properties Intercalated disks – thick connections between fibers Properties Forms 2 networks: atrial and ventricular Each network works as a single functional unit Long contraction (10-15x longer than skeletal muscle) Long refractory period – no tetanus

Figure 15.02 Pericardium and Heart Wall

Chambers Chambers Left and Right Atria – 2 superior “receiving” chambers Interatrial septum – tissue between the atria Auricles – wrinkled structure on anterior side of atria; increase atrial capacity. Left and Right Ventricles – 2 larger inferior chambers Interventricular septum – tissue between the ventricles

Major Vessels Major Blood Vessels Veins – carry blood to the heart Superior vena cava – carries deoxygenated blood from above the heart Inferior vena cava – carries deoxygenated blood from below the heart Coronary sinus – carries deoxygenated blood from the heart itself Pulmonary veins – carries oxygenated blood from the lungs Arteries – carry blood away from the heart Pulmonary trunk – splits into right & left pulmonary arteries; carries deoxygenated blood to the lungs Aorta – carries oxygenated blood to the rest of the body. Coronary arteries – carry blood to the heart itself

Figure 15.03a Structure of the Heart – Anterior External View

Figure 15.03b Structure of the Heart – Posterior External View

AV Valves Valves (one-way) Atrioventricular (AV) valves Atria to Ventricles Tricuspid valve – 3 cusps; right atrium to right ventricle Bicuspid (mitral) valve – 2 cusps; left atrium to left ventricle Papillary muscles contract to keep valves from blowing out under pressure.

Cow Heart – Internal Anatomy

Semilunar Valves Semilunar valves  ventricles to Lungs/Aorta Pulmonary valve – right ventricle to the lungs Aortic valve – left ventricle to the aorta Pressure of the ventricular contraction open valves Blood flowing back towards the heart fills cup-like cusps, closing valves. Valve order: Tricuspid, Pulmonary, Bicuspid, Aortic “Try Pulmonary before you Buy Aoric”

Figure 15.03c Structure of the Heart – Anterior View

Figure 15.04 Atrioventricular (AV) Valves

Blood Flow Blood flow through the heart From high to low pressure R. Atrium → R. Ventricle → Pulmonary trunk → Lungs → Pulmonary veins → L. Atrium →L. Ventricle → Aorta

Figure 15.05 Blood Flow Through the Heart

The Cardiac Cycle Cardiac Cycle All of the events associated with 1 heart beat Systole: Contraction Diastole: Relaxation 1 Cardiac cycle = 1 atrial systole & diastole + 1 ventricular systole & diastole

Figure 15.08 Cardiac Cycle

Sounds Heart sounds “Lubb” “Dupp” Normal beat: Lubb-Dupp-Pause First, longer sound AV valves closing during ventricular systole “Dupp” Second, shorter, sharper sound Semilunar valves closing at the end of ventricular systole Normal beat: Lubb-Dupp-Pause Heart murmur – abnormal rushing/gurgling heart noise, usually indicates a valve disorder

http://www.smm.org/heart/heart/in-out.htm

AP Conduction Action Potential Conduction Pacemaker: about 1% of cardiac muscle cells initiate APs, setting the heart rhythm. Conduction system: the route for sending APs throughout the heart.

Conduction System Steps The sinoatrial (SA) node initiates the AP and spreads it through the atria, causing them to contract together. The AP reaches the atrioventricular (AV) node, which slows the AP down. The AP travels to the AV bundle (bundle of His) and is conducted to the ventricles. The AP travels through the right and left bundle branches toward the apex. AP travels quickly through Purkinje fibers from the apex through the ventricles; the ventricles then contract together.

Figure 15.06 conduction System of the Heart

Electrical Conduction System

Variations Pacemaker variations Normally the SA node Capable of up to 100 beats/min (bpm) Usually about 75 bpm at rest Diseased/damaged SA node… AV node takes over (40-60 bpm) AV bundle or bundle branch (20-35 bpm) can take over for AV node…but aren’t fast enough Ectopic pacemakers – other cardiac muscle becomes the pacemaker, disrupting heart beat. Artificial pacemaker is then needed.

Electrocardiogram Electrocardiogram (ECG or EKG) A recording of the electrical changes accompanying a heart beat. 3 waves P wave: atrial depolarization QRS complex: ventricular depolarization T wave: ventricular repolarization Depolarization occurs just before contraction; atrial repolarization is masked by the QRS complex.

Figure 15.07 Normal ECG of a Single Heartbeat

Phases of the Cardiac Cycle Relaxation All 4 chambers in diastole Repolarization of the ventricles (T wave) AV valves open; 75% of ventricle filling occurs Atrial systole AP from SA node causes atrial depolarization (P wave) Last 25% of blood enters ventricles AV valves open; semilunar valves closed Ventricular systole: ventricles contract Ventricular depolarization (QRS complex) & contraction AV valves close; semilunar valves open

Cardiac Output Cardiac Output (CO) A measure of cardiac efficiency CO = stroke volume x heart rate Stroke volume (SV) = amount of blood pumped into the aorta during contraction Example CO = 75 mL/beat x 70 beats/min CO = 5250 mL/min CO = 5.25 L/min

Disorders Heart Disorders Coronary Artery Disease Atherosclerosis – blockage of arteries Myocardial ischemia – insufficient blood supply to the myocardium Angina pectoris – pain caused by myocardial ischemia Myocardial infarction (heart attack) – blockage of coronary arteries leading to myocardial cell death

Disorders Congenital Defects Arrhythmias Atrial septal defect (ASD) – foramen ovale fails to close Ventricular septal defect (VSD) – incomplete closure of septum Valvular stenosus – narrowing of a valve Arrhythmias Atrial fibrillation – uncoordinated atrial contraction Ventricular fibrillation – uncoordinated ventricular contraction; may result in death