The Heart

The Cardiovascular System

Overview of the Heart

• Function: Pumps over 1 million gallons of blood annually.
• Blood Vessels: Comprises over 60,000 miles of blood vessels.

Cardiovascular Circuits

• Pulmonary Circuit: Carries CO2-rich (O2-poor) blood to the lungs for oxygenation.
• Systemic Circuit: Distributes O2-rich (CO2-poor) blood to the body.

Anatomy of the Heart

• Location: Situated in the mediastinum, between the lungs.
• Size & Shape: Approximately 3.5 inches wide at the base, 5 inches from base to apex, and weighs around 10 ounces. The apex is oriented to the left and tapers to a point.
• Orientation: Has anterior and inferior surfaces, and right and left borders.

Pericardium

• Fibrous Pericardium: Dense connective tissue that protects the heart and prevents overstretching.
• Serous Pericardium: Contains a parietal layer, pericardial cavity with fluid, and a visceral layer (epicardium).

Heart Wall Structure

• Epicardium: Outermost layer, also known as visceral pericardium.
• Myocardium: Thick muscular layer responsible for contraction; contains a fibrous skeleton that supports cardiac muscle and valves.
• Endocardium: Smooth inner lining that reduces friction within the heart chambers.

Myocardial Structure

• Cardiac muscle fibers arranged in interlacing bundles to ensure efficient contraction.

Chambers and Sulci

• Chambers: 4 chambers - 2 atria (above) and 2 ventricles (below).
• Sulci: Grooves that contain coronary blood vessels and fat; separate the atria from the ventricles.

Chamber Functions

• Right Atrium: Receives blood from three sources (superior vena cava, inferior vena cava, and coronary sinus).
• Right Ventricle: Fills from the right atrium and pumps blood to the pulmonary trunk via the pulmonary semilunar valve.
• Left Atrium: Receives oxygenated blood from the lungs via pulmonary veins.
• Left Ventricle: Pumps oxygen-rich blood into the aorta, the main artery supplying the body.

Heart Valves

• Atrioventricular (AV) Valves: Prevent backflow; include tricuspid valve (right) and bicuspid (mitral) valve (left).
• Semilunar Valves: Control blood flow into arteries; include aortic and pulmonary semilunar valves.

Valve Mechanics

• AV valves open when ventricles relax; close when ventricles contract, aided by chordae tendineae.
• Semilunar valves open during ventricular contraction and close during relaxation.

Blood Flow Through the Heart

• Blood travels from the body to the right atrium, through the right AV valve to the right ventricle, then to the lungs via the pulmonary trunk. Oxygenated blood returns to the left atrium and passes to the left ventricle which ejects it into the aorta.

Cardiac Cycle

• Phases: Includes atrial systole, ventricular systole, and quiescent periods. Normal cycle lasts about 0.8 seconds at a heart rate of 75 bpm.
• EDV and ESV: End Diastolic Volume (EDV) is about 130ml; End Systolic Volume (ESV) is around 60ml; Stroke Volume (SV) = EDV - ESV.

Coronary Circulation

• Importance: Supplies blood to the heart muscle, with high oxygen demand.
• Anastomoses: Provide alternate routes for blood flow in case of vessel occlusion.

Myocardial Infarction (MI)

• Sudden death of heart tissue due to ischemia; diagnosed via ECG and cardiac enzymes.

Cardiac Output (CO)

• Defined as the volume of blood ejected by each ventricle per minute; calculated as CO = Heart Rate (HR) x Stroke Volume (SV).
• At rest, typical CO is about 4-6 L/min but can increase significantly during exertion.

Risk Factors for Heart Disease

• Includes high blood pressure, high cholesterol, smoking, obesity, and genetic predispositions.

Heart Rate Regulation

• Chronotropic Agents: Positive agents increase HR (like exercise, stress), while negative agents decrease HR (like parasympathetic stimulation).
• Baroreceptors and Chemoreceptors: Monitor blood pressure and chemical levels, providing feedback to the cardiovascular center in the brain, affecting heart rate accordingly.

ECG Interpretation

• Essential for diagnosing irregularities in heart rhythm, myocardial infarctions, and other cardiac conditions.
• Main components include P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization).

Atherosclerosis and Treatment Options

• Atherosclerosis can lead to coronary artery disease and myocardial infarctions; treatment includes lifestyle changes and medical interventions like angioplasty and bypass grafting.

Exercise and Cardiac Health

• Regular aerobic exercise strengthens the heart muscle and improves overall cardiovascular health.