Cardiovascular System Disorders: Structure, Function, and Pathology

Cardiovascular System: Structure and Function

Overview of the Circulatory System

The circulatory system is responsible for transporting blood, nutrients, gases, and wastes throughout the body. It consists of the heart (the pump), blood vessels (arteries, veins, capillaries), and blood (the fluid).

• Systemic circulation: Delivers oxygenated blood from the heart to the body and returns deoxygenated blood back to the heart.

• Pulmonary circulation: Carries deoxygenated blood from the heart to the lungs and returns oxygenated blood to the heart.

Heart Anatomy

The heart is a muscular organ located in the mediastinum, within the pericardial sac. It is composed of several layers and contains four chambers separated by valves to ensure unidirectional blood flow.

• Layers: Parietal pericardium, epicardium (visceral pericardium), myocardium, endocardium

• Valves: Atrioventricular (tricuspid and mitral) and semilunar (aortic and pulmonary)

• Septum: Divides the right and left sides of the heart

Heart Conduction System

The heart's rhythmic contractions are coordinated by its conduction system, which generates and transmits electrical impulses.

• Sinoatrial (SA) node: Pacemaker, initiates sinus rhythm

• Atrioventricular (AV) node: Delays impulse, located in the right atrium

• AV bundle (bundle of His): Transmits impulses to ventricles

• Purkinje fibers: Distribute impulse through ventricles

• Electrocardiogram (ECG): Records electrical activity (P wave: atrial depolarization, QRS: ventricular depolarization, T wave: ventricular repolarization)

Coronary Circulation

The coronary arteries supply oxygenated blood to the myocardium. The right and left coronary arteries branch from the aorta and further divide to supply the heart muscle.

• Left coronary artery: Divides into left anterior descending and circumflex arteries

• Right coronary artery: Branches into right marginal and posterior interventricular arteries

• Collateral circulation is limited, making blockages dangerous

Cardiac Cycle

The cardiac cycle describes the sequence of events in one heartbeat, including periods of relaxation (diastole) and contraction (systole).

• Diastole: Myocardium relaxes, chambers fill with blood

• Systole: Myocardium contracts, blood is ejected

• Valves open and close to direct blood flow

Cardiac Output and Regulation

Cardiac output (CO) is the volume of blood ejected by a ventricle per minute. It is determined by heart rate (HR) and stroke volume (SV):

• CO = HR × SV

• Preload: Volume of blood returning to the heart

• Afterload: Resistance the heart must overcome to eject blood

Factors affecting cardiac output include sympathetic stimulation, venous return, and peripheral resistance.

Cardiovascular Pathology

Selected Cardiovascular Drugs

Various drugs are used to manage cardiovascular disorders, each with specific actions and adverse effects.

Name	Use	Action	Adverse Effects
Nitroglycerin	Angina attacks and prophylaxis	Reduces cardiac workload, peripheral and coronary vasodilator	Dizziness, headache
Metoprolol	Hypertension, angina, antidysrhythmic	Beta blocker, slows heart rate	Dizziness, fatigue
Nifedipine	Angina, hypertension, peripheral vasodilator, antianginal	Calcium blocker, vasodilator	Dizziness, fainting, headache
Digoxin	Congestive heart failure and atrial dysrhythmias	Slows AV node conduction, increases force of contraction	Nausea, fatigue, headache
Enalapril	Hypertension	ACE inhibitor, blocks formation of angiotensin II	Headache, dizziness
Furosemide	Edema with CHF, hypertension	Diuretic, increases excretion of sodium and water	Nausea, diarrhea, dizziness
Simvastatin	Hypercholesterolemia (CHD)	Decreases cholesterol and LDL	Digestive discomfort
Warfarin	Prophylaxis and treatment of thromboemboli	Anticoagulant, interferes with vitamin K	Excessive bleeding
ASA (aspirin)	Prophylaxis of thromboemboli, anti-inflammatory	Prevents platelet adhesion, anti-inflammatory	Gastric irritation, allergy

Arteriosclerosis and Atherosclerosis

Arteriosclerosis is a general term for arterial wall thickening and loss of elasticity, leading to narrowed lumens and increased blood pressure. Atherosclerosis is a specific type involving the formation of atheromas (plaques) composed of lipids, calcium, and clots in large arteries.

• Major risk factors: Age, gender, genetics, obesity, sedentary lifestyle, smoking, diabetes, hypertension

• Complications: Ischemic heart disease, myocardial infarction, stroke, peripheral vascular disease

Lipid Transport

Lipids are transported in the blood as lipoproteins:

• Low-density lipoprotein (LDL): Transports cholesterol from liver to cells; contributes to atheroma formation

• High-density lipoprotein (HDL): Transports cholesterol from cells to liver for excretion; considered "good" cholesterol

Atherosclerosis: Diagnosis and Treatment

Diagnosis is based on serum lipid levels and imaging studies. Treatment includes lifestyle modifications, medications, and surgical interventions such as coronary artery bypass grafting.

Angina Pectoris and Myocardial Infarction

Angina pectoris is chest pain due to myocardial ischemia (oxygen supply-demand imbalance). Myocardial infarction (MI) occurs when a coronary artery is totally obstructed, leading to tissue necrosis.

• Types of angina: Classic (exertional), variant (vasospasm), unstable (prolonged, at rest)

• MI warning signs: Chest pressure, shortness of breath, nausea, anxiety, pain radiating to arm/jaw

• Diagnosis: ECG changes, elevated cardiac enzymes (CK, AST, LDH), troponin

Cardiac Dysrhythmias (Arrhythmias)

Dysrhythmias are abnormal heart rhythms caused by conduction disturbances. They can reduce cardiac output and may be life-threatening.

• Sinus node abnormalities: Bradycardia, tachycardia, sick sinus syndrome

• Atrial conduction: Premature atrial contractions, atrial flutter, atrial fibrillation

• AV node: Heart blocks (first, second, third degree)

• Ventricular: Bundle branch block, ventricular tachycardia, ventricular fibrillation, PVCs

Name	Conduction Change	Effect
Bradycardia	Rate regular, slower than 60/min	Stroke volume increased
Tachycardia	Rate regular, fast, 100–160/min	Possibly reduced cardiac output
Atrial flutter	Rate 160–350/min	AV node delays conduction
Fibrillation	Uncoordinated muscle contractions	No filling, output—cardiac standstill
Premature ventricular contractions	Additional ectopic beats	May induce fibrillation
Bundle branch block	Delayed conduction in one bundle branch	Wide QRS wave
Heart Block I	Delays conduction in AV node	Prolongs PR interval
Heart Block II	Delays conduction in AV node, gradually increasing PR until one contraction missed	Periodic decrease in output
Total Heart Block	No conduction in AV node, ventricles slowly contract independent of atrial contraction	Marked decrease in output, causing syncope

Congestive Heart Failure (CHF)

CHF occurs when the heart cannot pump enough blood to meet the body's needs. It may affect the left, right, or both sides of the heart, leading to systemic and pulmonary congestion.

• Left-sided failure: Pulmonary congestion, dyspnea, orthopnea

• Right-sided failure: Systemic congestion, edema in legs, hepatomegaly

• Compensatory mechanisms may worsen the condition

	Left-Sided CHF	Right-Sided CHF
Causes	Infarction of left ventricle, aortic valve stenosis, hypertension, hyperthyroidism	Infarction of right ventricle, pulmonary valve stenosis, pulmonary disease (cor pulmonale)
Basic Effects	Decreased cardiac output, pulmonary congestion	Decreased cardiac output, systemic congestion, edema of legs and abdomen
Signs and Symptoms	Fatigue, weakness, dyspnea, exercise intolerance, cold intolerance, tachycardia, pallor, secondary polycythemia, daytime oliguria, orthopnea, cough, paroxysmal nocturnal dyspnea, hemoptysis	Fatigue, weakness, dyspnea, exercise intolerance, cold intolerance, tachycardia, pallor, secondary polycythemia, daytime oliguria, dependent edema in feet, hepatomegaly, splenomegaly, ascites, distended neck veins, flushed face

Valvular Defects

Valvular defects affect the heart's ability to maintain unidirectional blood flow. They are classified as:

• Stenosis: Narrowed valve opening, impeding blood flow

• Incompetence: Failure to close completely, causing regurgitation

• Mitral valve prolapse: Floppy valve leaflets

• Treatment may involve surgical replacement with mechanical or biological valves

Congenital Heart Disease: Tetralogy of Fallot

Tetralogy of Fallot is the most common cyanotic congenital heart defect, involving four abnormalities:

• Ventricular septal defect (VSD)

• Dextroposition of the aorta

• Right ventricular hypertrophy

• Pulmonary stenosis

It causes right-to-left shunt, cyanosis, and altered blood flow. Diagnosis is by imaging and surgical repair is often required.

Vascular Disorders

Hypertension

Hypertension is persistently elevated blood pressure, classified as primary (essential), secondary, or malignant. It increases the risk of damage to the kidneys, heart, brain, and retina.

• Primary: BP consistently above 140/90 mm Hg

• Secondary: Due to renal or endocrine disease

• Malignant: Severe, rapidly progressive

• Treatment: Lifestyle changes, medications (diuretics, ACE inhibitors)

Aortic Aneurysm

An aortic aneurysm is a localized dilation and weakening of the arterial wall, which may be saccular, fusiform, or dissecting. Risk of rupture and hemorrhage is high.

• Causes: Atherosclerosis, trauma, infection, congenital defects

• Diagnosis: Imaging (ultrasound, CT, MRI)

• Treatment: Blood pressure control, surgical repair

Venous Disorders

Varicose veins are dilated, tortuous superficial veins, often in the legs. Thrombophlebitis and phlebothrombosis involve clot formation in veins, with risk of pulmonary embolism.

• Risk factors: Family history, obesity, pregnancy, prolonged standing

• Treatment: Leg elevation, compression stockings, anticoagulants, surgery

Shock

Shock is a critical condition where blood pressure drops, leading to inadequate tissue perfusion and cellular hypoxia. Types include hypovolemic, cardiogenic, and distributive shock.

• Symptoms: Anxiety, tachycardia, pallor, light-headedness, syncope, sweating, oliguria

• Compensatory mechanisms: Increased heart rate, vasoconstriction, hormone secretion

• Complications: Renal failure, respiratory distress, hepatic failure, DIC, cardiac depression

Additional info: This guide covers the essential structure, function, and pathology of the cardiovascular system, including major diseases, diagnostic methods, and treatments, as relevant to college-level anatomy and physiology.