Cardiovascular System: Structure, Function, and Pathology

Cardiovascular System

Introduction

The cardiovascular system is essential for transporting blood, nutrients, gases, and wastes throughout the body. Understanding its structure and function is fundamental in Anatomy & Physiology.

Key Vocabulary

• Arrhythmias: Abnormal heart rhythms that can affect the efficiency of the heart's pumping action.

• Atherosclerosis: The buildup of fatty deposits (plaques) in the arterial walls, leading to narrowed and stiffened arteries.

• AV Node: The atrioventricular node, a key part of the heart's electrical conduction system that coordinates the top and bottom chambers.

• Bicuspid Valve: Also known as the mitral valve; it separates the left atrium and left ventricle.

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

• Endocardium: The inner lining of the heart chambers.

• Hypertension: High blood pressure, a chronic condition that increases the risk of heart disease and stroke.

• Inferior Vena Cava: The large vein that carries deoxygenated blood from the lower body to the right atrium.

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

• Pericardium: The double-walled sac that encloses the heart, providing protection and reducing friction.

• Right Atrium: The chamber that receives deoxygenated blood from the body.

• Right Ventricle: The chamber that pumps deoxygenated blood to the lungs.

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

• Tricuspid Valve: The valve between the right atrium and right ventricle.

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

Structure and Function of the Heart

Membranes Around the Heart

The heart is surrounded by protective membranes that serve to cushion and reduce friction during heartbeats.

• Pericardium: A double-layered sac with an outer fibrous layer and an inner serous layer.

• Function: Protects the heart, anchors it within the thorax, and prevents overfilling with blood.

• Layers: Fibrous pericardium (outer), serous pericardium (parietal and visceral layers).

Pathway of Blood Through the Heart

Blood flows through the heart in a specific sequence, ensuring oxygenation and distribution to 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 into the pulmonary arteries to the lungs.

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

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

6. Pumped through the aortic valve into the aorta and out to the body.

Heart Valves and Flow Regulation

Valves ensure unidirectional blood flow and prevent backflow between chambers.

• Tricuspid Valve: Between right atrium and right ventricle.

• Pulmonary Valve: Between right ventricle and pulmonary artery.

• Bicuspid (Mitral) Valve: Between left atrium and left ventricle.

• Aortic Valve: Between left ventricle and aorta.

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

Heart Wall Structure

The heart wall consists of three layers, each with distinct functions.

• Epicardium: Outer layer (visceral pericardium).

• Myocardium: Thick muscular middle layer responsible for contraction; thickest in the left ventricle due to high pressure needed to pump blood throughout the body.

• Endocardium: Inner lining of the heart chambers.

Cardiac Output

Cardiac output is a measure of the heart's efficiency in pumping blood.

• Definition: The volume of blood pumped by each ventricle per minute.

• Formula:

$\text{Cardiac Output (CO)} = \text{Stroke Volume (SV)} \times \text{Heart Rate (HR)}$

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

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

• Example: If SV = 70 mL/beat and HR = 70 beats/min, CO = 4900 mL/min.

Electrical Regulation of the Heart

The heart's rhythm is controlled by specialized cells and can be monitored using an ECG.

• SA Node: Initiates the electrical impulse (pacemaker).

• AV Node: Delays the impulse, allowing atria to contract before ventricles.

• Bundle of His and Purkinje Fibers: Distribute the impulse through the ventricles.

• ECG: Records the electrical activity; P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).

Arrhythmias

Arrhythmias are disturbances in the heart's rhythm, with varying degrees of severity.

• Benign Arrhythmias: Some, like occasional premature beats, may be harmless.

• Fatal Arrhythmias: Ventricular fibrillation or sustained tachycardia can be life-threatening.

• Recognition: Detected via ECG and clinical symptoms.

Blood Pressure Regulation

The brain monitors and regulates blood pressure to maintain homeostasis.

• Baroreceptors: Specialized sensors in the carotid sinus and aortic arch detect changes in blood pressure.

• Medulla Oblongata: Integrates signals and adjusts heart rate and vessel diameter accordingly.

Hypertension

Hypertension is a chronic elevation of blood pressure, increasing cardiovascular risk.

• Definition: Blood pressure consistently above 140/90 mmHg.

• Causes: Genetics, obesity, high salt intake, stress, lack of exercise.

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

Atherosclerosis

Atherosclerosis is a major cause of cardiovascular disease, characterized by plaque buildup in arteries.

• Pathophysiology: Accumulation of lipids, cholesterol, and inflammatory cells in arterial walls.

• Consequences: Reduced blood flow, risk of heart attack or stroke.

• Statins: Medications that lower cholesterol and stabilize plaques.

Summary Table: Heart Chambers and Valves

Chamber	Valve	Function
Right Atrium	Tricuspid Valve	Receives deoxygenated blood from body
Right Ventricle	Pulmonary Valve	Pumps blood to lungs
Left Atrium	Bicuspid (Mitral) Valve	Receives oxygenated blood from lungs
Left Ventricle	Aortic Valve	Pumps blood to body

Additional info:

• Understanding the structure and function of the heart is foundational for diagnosing and treating cardiovascular diseases.

• Regular monitoring of blood pressure and cholesterol can help prevent complications such as hypertension and atherosclerosis.