Skip to main content
Back

The Cardiovascular System: Structure, Function, and Disorders

NotesPracticeVideo lessons

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Cardiovascular System Overview

Introduction to the Cardiovascular System

The cardiovascular system, also known as the circulatory system, is essential for maintaining homeostasis in the human body. It consists of the heart (the pump), blood vessels (the distribution network), and is regulated by the nervous system, which manages heart rate and blood distribution.

  • Heart: Pumps blood throughout the body.

  • Blood vessels: Network for blood transport (arteries, capillaries, veins).

  • Nervous system: Controls heart rate and vessel distribution.

Blood Vessels: Structure and Function

Types of Blood Vessels

  • Arteries: Carry blood away from the heart under high pressure; thick-walled.

  • Capillaries: Microscopic vessels for exchange of solutes and water with body cells; thin-walled and porous.

  • Veins: Return blood to the heart; thin-walled and highly distensible.

Arteries

  • Structure: Three layers—endothelium (innermost), smooth muscle with elastic fibers (middle), connective tissue (outer).

  • Function: Carry blood away from the heart under pressure.

  • Aneurysm: Defect in arterial wall causing ballooning; can be fatal if ruptured.

Arterioles and Precapillary Sphincters

  • Arterioles: Smallest arteries, regulate blood flow into capillaries.

  • Precapillary sphincters: Control blood flow into capillaries.

  • Vasodilation: Relaxation increases blood flow.

  • Vasoconstriction: Contraction decreases blood flow.

Capillaries

  • Structure: One cell layer thick, forming extensive networks (capillary beds).

  • Function: Selective exchange of substances with interstitial fluid.

  • Fluid movement: Driven by blood pressure (filtration) and plasma proteins (reabsorption).

Lymphatic System

  • Function: Maintains blood volume, returns excess interstitial fluid, transports large substances, and plays a role in immunity.

  • Structure: Blind-ended capillaries, lymphatic vessels, and lymph (fluid derived from interstitial fluid).

Veins

  • Structure: Three layers, thin-walled, larger lumen than arteries, highly distensible.

  • Function: Return blood to the heart and serve as a blood reservoir.

  • Blood return mechanisms:

    • Contraction of skeletal muscles

    • One-way valves

    • Pressure changes from breathing

The Heart: Structure and Function

Heart Anatomy

  • Composed of: Cardiac muscle tissue (myocardium), pericardium (protective sac), epicardium (outer layer), endocardium (inner layer).

  • Chambers: Four (two atria, two ventricles) separated by a septum.

  • Valves: Four (tricuspid, bicuspid/mitral, pulmonary, aortic) prevent backflow.

Pattern of Blood Flow

  • Pulmonary circuit: Right side of heart pumps deoxygenated blood to lungs; returns oxygenated blood to left atrium.

  • Systemic circuit: Left side pumps oxygenated blood to body; returns deoxygenated blood to right atrium.

  • Blood passes through the heart twice per body circuit; deoxygenated and oxygenated blood do not mix.

Major Arteries and Veins

  • Coronary arteries: Supply the heart muscle (myocardium); susceptible to blockage (atherosclerosis).

  • Coronary veins: Return blood from myocardium to right atrium.

The Cardiac Cycle

  • Atrial systole (0.1 s): Atria contract, ventricles fill.

  • Ventricular systole (0.3 s): Ventricles contract, blood ejected to arteries.

  • Diastole (0.4 s): Both atria and ventricles relax.

Heart Sounds

  • "Lub-dub" sound: Lub = AV valves close; Dub = semilunar valves close.

  • Heart murmurs: Abnormal sounds due to disturbed blood flow, often from defective valves.

Cardiac Conduction System

  • Sinoatrial (SA) node: Pacemaker, initiates heartbeat.

  • Atrioventricular (AV) node: Relays impulse to ventricles.

  • AV bundle and Purkinje fibers: Distribute impulse through ventricles.

Electrocardiogram (ECG/EKG)

  • P wave: Atrial depolarization.

  • QRS complex: Ventricular depolarization.

  • T wave: Ventricular repolarization.

  • Used to detect arrhythmias and other heart conditions.

Blood Pressure and Its Regulation

Blood Pressure

  • Systolic pressure: Highest pressure during ventricular contraction.

  • Diastolic pressure: Lowest pressure during ventricular relaxation.

  • Measured in mm Hg using a sphygmomanometer.

  • Normal: Systolic < 120 mm Hg, Diastolic < 80 mm Hg.

Hypertension and Hypotension

  • Hypertension: Chronic high blood pressure; risk factor for cardiovascular disease.

  • Hypotension: Abnormally low blood pressure; may cause dizziness or fainting.

Table: Blood Pressure Categories

Category

Systolic (mm Hg)

Diastolic (mm Hg)

Normal

<120

<80

Elevated

120–129

<80

Hypertension Stage 1

130–139

80–89

Hypertension Stage 2

≥140

≥90

Hypertensive Crisis

>180

>120

Regulation of Blood Pressure

  • Homeostasis: Maintained by regulating cardiac output and arteriole diameter.

  • Baroreceptors: Pressure sensors in aorta and carotid arteries; initiate negative feedback to adjust heart rate and vessel diameter.

  • Hormonal control: Epinephrine, norepinephrine, ADH, aldosterone, renin-angiotensin, and ANH influence blood pressure.

  • Local control: Precapillary sphincters adjust local blood flow based on tissue needs.

Equation: Blood Pressure

  • Blood pressure is determined by cardiac output and peripheral resistance:

Cardiovascular Disorders

Major Disorders

  • Hypertension: Chronic high blood pressure.

  • Aneurysm: Weakening and ballooning of arterial wall.

  • Atherosclerosis: Cholesterol deposits in arteries; risk factors include high cholesterol, obesity, sedentary lifestyle, smoking, diabetes, hypertension, and family history.

  • Angina: Chest pain from reduced blood flow to heart muscle.

  • Heart attack (myocardial infarction): Death of heart tissue due to blocked blood flow.

  • Heart failure: Weakened heart muscle, leading to fluid accumulation (congestive heart failure).

  • Embolism: Blockage of a blood vessel by material (clot, fat, air, etc.).

  • Stroke: Brain damage from interrupted blood supply (embolism or vessel rupture).

Table: Risk Factors for Hypertension

Risk Factor

Description

Genetics

Family history of hypertension

Age

Risk increases with age

Obesity

Excess body weight increases risk

Physical inactivity

Lack of exercise

High salt intake

Increases blood pressure

Alcohol

Excessive consumption

Chronic stress

Long-term stress response

Treatments and Prevention

  • Angina: Medications, balloon angioplasty, coronary artery bypass graft (CABG).

  • Heart attack: Immediate medical attention, ECG diagnosis, clot-dissolving drugs, CABG.

  • Heart failure: Medications (diuretics, drugs to increase contractility), lifestyle changes.

  • Embolism and stroke: Clot-dissolving drugs, surgical repair, rehabilitation.

  • Heart replacement: Transplant, artificial heart, xenotransplantation.

Reducing Cardiovascular Risk

  • Do not smoke (smoking doubles risk).

  • Monitor and manage cholesterol and blood pressure.

  • Engage in regular exercise.

  • Maintain healthy weight and control diabetes.

  • Avoid chronic stress.

Summary Table: Key Blood Vessel Differences

Vessel Type

Wall Thickness

Pressure

Direction of Blood Flow

Artery

Thick

High

Away from heart

Capillary

Very thin (one cell layer)

Low

Exchange with tissues

Vein

Thin

Lowest

Toward heart

Additional info:

  • Some table entries and details were inferred based on standard cardiovascular physiology.

  • Equations and normal values are based on current clinical guidelines.

Pearson Logo

Study Prep