Cardiovascular System: Structure, Function, and Regulation

Cardiovascular System: Structure, Function, and Regulation

Heart Anatomy and Circulation

The heart is a muscular organ responsible for pumping blood throughout the body via two main circuits: the pulmonary and systemic circuits. Understanding its structure and function is essential for comprehending cardiovascular physiology.

• Pulmonary vs. Systemic Circuits: The pulmonary circuit carries deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium. The systemic circuit carries oxygenated blood from the left ventricle to the body and returns deoxygenated blood to the right atrium.

• Chambers and Valves: The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle. Valves (tricuspid, pulmonary, mitral, aortic) ensure unidirectional blood flow.

• Blood Flow Pathway:

  1. Deoxygenated blood enters the right atrium via the superior and inferior vena cava.

  2. Passes through the tricuspid valve to the right ventricle.

  3. Pumped through the pulmonary valve to the pulmonary arteries and lungs.

  4. Oxygenated blood returns via pulmonary veins to the left atrium.

  5. Passes through the mitral valve to the left ventricle.

  6. Pumped through the aortic valve to the aorta and systemic circulation.

• Fibrous Pericardium, Pericarditis, Cardiac Tamponade: The fibrous pericardium is the tough outer layer of the pericardial sac. Pericarditis is inflammation of the pericardium. Cardiac tamponade is compression of the heart due to fluid accumulation in the pericardial cavity.

• Heart Wall Layers:

  • Epicardium: Outer layer (visceral pericardium)

  • Myocardium: Middle, muscular layer

  • Endocardium: Inner endothelial lining

• Chordae Tendineae and Papillary Muscles: These structures anchor the atrioventricular (AV) valves, preventing prolapse during ventricular contraction.

• Trabeculae Carneae: Irregular muscular columns on the inner surface of ventricles, aiding contraction.

• Vessels Contributing to Right Atrium: Superior vena cava, inferior vena cava, and coronary sinus.

• Vessels Carrying Oxygenated Blood: Pulmonary veins (to left atrium), aorta (from left ventricle).

• Vessels Carrying Deoxygenated Blood: Pulmonary arteries (from right ventricle), vena cavae (to right atrium).

Coronary Circulation and Cardiac Pathology

The heart receives its own blood supply via the coronary arteries. Disruption of this supply can lead to various cardiac pathologies.

• Coronary Arteries: Branch from the aorta and supply oxygenated blood to the myocardium.

• Cardiac Veins: Drain deoxygenated blood from the myocardium into the coronary sinus, which empties into the right atrium.

• Cardiac Pathologies:

  • CAD (Coronary Artery Disease): Narrowing of coronary arteries due to atherosclerosis.

  • Angina Pectoris: Chest pain due to reduced blood flow to the heart muscle.

  • Myocardial Infarction (Heart Attack): Death of heart muscle tissue due to prolonged ischemia.

  • Balloon Angioplasty: Procedure to open narrowed arteries using a balloon catheter.

  • CABG (Coronary Artery Bypass Grafting): Surgical procedure to bypass blocked coronary arteries.

Cardiac Muscle Physiology

Cardiac muscle cells (cardiomyocytes) have unique properties that enable the heart to contract rhythmically and efficiently.

• Depolarization, Plateau, Repolarization:

  • Depolarization: Rapid influx of Na+ ions.

  • Plateau: Sustained by Ca2+ influx, prolonging contraction.

  • Repolarization: Efflux of K+ ions restores resting potential.

• Cardiac Conduction System:

  1. SA Node (sinoatrial node) – pacemaker, initiates impulse.

  2. AV Node (atrioventricular node)

  3. AV Bundle (Bundle of His)

  4. Right and left bundle branches

  5. Purkinje fibers

• Pacemaker Potential: The gradual depolarization of pacemaker cells in the SA node, leading to spontaneous action potentials and heartbeats.

• ECG (Electrocardiogram) Events:

  • P wave: Atrial depolarization

  • QRS complex: Ventricular depolarization

  • T wave: Ventricular repolarization

• Bradycardia: Slow heart rate (<60 bpm)

• Tachycardia: Fast heart rate (>100 bpm)

• Systole: Contraction phase

• Diastole: Relaxation phase

Cardiac Cycle and Valve Function

The cardiac cycle consists of alternating periods of contraction and relaxation, coordinated with valve opening and closure to ensure efficient blood flow.

• AV Valves: Tricuspid (right), Mitral (left); open during ventricular diastole, closed during systole.

• Semilunar Valves: Pulmonary and aortic; open during ventricular systole, closed during diastole.

• Isovolumetric Contraction: Ventricles contract with all valves closed, pressure rises.

• Isovolumetric Relaxation: Ventricles relax with all valves closed, pressure falls.

• Ventricular Ejection: Semilunar valves open, blood is ejected into arteries.

Cardiac Output and Regulation

Cardiac output is the volume of blood pumped by each ventricle per minute. It is determined by heart rate and stroke volume, and regulated by neural and hormonal factors.

• Definitions:

  • Cardiac Output (CO): Volume of blood pumped per minute.

  • Stroke Volume (SV): Volume of blood pumped per beat.

  • Heart Rate (HR): Number of beats per minute.

• Relationship:

  • $CO = SV \times HR$

• End-Diastolic Volume (EDV): Volume of blood in ventricle at end of diastole.

• End-Systolic Volume (ESV): Volume of blood in ventricle at end of systole.

• Stroke Volume Formula:

  • $SV = EDV - ESV$

• Factors Affecting Cardiac Output:

  • Increased by sympathetic stimulation, increased venous return, exercise.

  • Decreased by parasympathetic stimulation, blood loss, heart disease.

• Regulation by Nervous System:

  • Sympathetic Division: Increases heart rate and contractility.

  • Parasympathetic Division: Decreases heart rate.

  • Cardiac Centers: Located in the medulla oblongata.

Summary Table: Key Cardiac Parameters

Parameter	Definition	Formula
Cardiac Output (CO)	Blood volume pumped per minute	$CO = SV \times HR$
Stroke Volume (SV)	Blood volume pumped per beat	$SV = EDV - ESV$
End-Diastolic Volume (EDV)	Volume in ventricle at end of diastole	--
End-Systolic Volume (ESV)	Volume in ventricle at end of systole	--

Comparison: Sympathetic vs. Parasympathetic Effects on Heart Rate

Division	Effect on Heart Rate	Mechanism
Sympathetic	Increases	Releases norepinephrine, increases SA node firing
Parasympathetic	Decreases	Releases acetylcholine, decreases SA node firing

Additional info:

• Some details, such as the specific order of conduction system structures and the precise locations of valve openings/closures, were inferred based on standard anatomy and physiology knowledge.