Cardiovascular System

Introduction

The cardiovascular system is essential for transporting blood, nutrients, gases, and waste products throughout the body. It consists of the heart, blood vessels, and associated structures, and is regulated by complex physiological mechanisms to maintain homeostasis.

Key Vocabulary

• Arrhythmias: Abnormal heart rhythms that can affect cardiac output and overall heart function.

• Atherosclerosis: The buildup of fatty deposits (plaques) in arterial walls, leading to reduced blood flow and increased risk of cardiovascular events.

• AV Node: The atrioventricular node, which coordinates the electrical signals between the atria and ventricles.

• Bicuspid Valve: Also known as the mitral valve, located between the left atrium and left ventricle.

• Cardiac Output: The volume of blood pumped by the heart per minute.

• Endocardium: The inner lining of the heart chambers.

• Hypertension: Chronically elevated blood pressure, a major risk factor for heart disease and stroke.

• Left Atrium: Receives oxygenated blood from the lungs.

• Left Ventricle: Pumps oxygenated blood to the systemic circulation; has the thickest wall due to high pressure.

• Myocardium: The muscular layer of the heart responsible for contraction.

• Pericardium: The protective sac surrounding the heart.

• Right Atrium: Receives deoxygenated blood from the body.

• Right Ventricle: Pumps deoxygenated blood to the lungs.

• SA Node: The sinoatrial node, the heart's natural pacemaker.

• Tricuspid Valve: Located between the right atrium and right ventricle.

• Vena Cava: Large veins (superior and inferior) that return deoxygenated blood to the right atrium.

Heart Structure and Function

Membranes Around the Heart

The heart is surrounded by the pericardium, a double-walled sac that provides protection, reduces friction, and anchors the heart within the thoracic cavity.

• Fibrous Pericardium: Outer layer, tough and inelastic.

• Serous Pericardium: Inner layer, consists of parietal and visceral layers with pericardial fluid in between.

Pathway of Blood Through the Heart

Blood flows through the heart in a specific sequence, ensuring oxygenation and circulation throughout the body.

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

2. Passes through the tricuspid valve into 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 bicuspid (mitral) valve into the left ventricle.

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

Heart Valves and Chamber Regulation

Heart valves ensure unidirectional blood flow and prevent backflow between chambers.

• Tricuspid Valve: Right atrium to right ventricle.

• Pulmonary Valve: Right ventricle to pulmonary artery.

• Bicuspid (Mitral) Valve: Left atrium to left ventricle.

• Aortic Valve: Left ventricle to aorta.

Valves open and close in response to pressure changes during the cardiac cycle.

Heart Chambers: Structure and Function

• Left Ventricle: Thickest wall due to high pressure needed to pump blood throughout the body.

• Right Ventricle: Thinner wall, pumps blood to the lungs at lower pressure.

Cardiac Physiology

Cardiac Output

Cardiac output is the amount of blood the heart pumps per minute, determined by stroke volume and heart rate.

• Stroke Volume: Amount of blood ejected per beat.

• Heart Rate: Number of beats per minute.

Pacemaker Regulation

The SA node initiates electrical impulses, setting the pace for heart contractions. The AV node delays the impulse, allowing atrial contraction before ventricular contraction. These signals can be detected on an ECG (electrocardiogram).

Arrhythmias

• Benign Arrhythmias: Some irregular rhythms (e.g., occasional premature beats) may be tolerated.

• Fatal Arrhythmias: Ventricular fibrillation or sustained tachycardia can be life-threatening due to loss of effective cardiac output.

Blood Pressure Regulation

The brain monitors blood pressure via baroreceptors in the aorta and carotid arteries, adjusting heart rate and vessel diameter through autonomic nervous system responses.

Cardiovascular Pathology

Hypertension

Hypertension is persistently high blood pressure, increasing the risk of heart disease, stroke, and kidney damage.

• Treatment: Lifestyle changes (diet, exercise), medications (ACE inhibitors, beta-blockers).

Atherosclerosis

Atherosclerosis involves the accumulation of plaques in arterial walls, narrowing vessels and impeding blood flow.

• Risk Factors: High cholesterol, hypertension, smoking, diabetes.

• Statins: Medications that lower cholesterol and stabilize plaques, reducing cardiovascular risk.

Summary Table: Heart Structures and Functions

Additional info:

• ECG (Electrocardiogram) is a diagnostic tool for assessing heart rhythm and conduction abnormalities.

• Cardiac output is a key determinant of tissue perfusion and blood pressure.