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Cardiovascular System: Structure and Function of the Human Heart

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Cardiovascular System

Overview

The cardiovascular system consists of the heart, associated structures, and blood vessels. It is situated in the chest (thorax), posterior to the anterior chest wall.

  • Heart: Muscular organ that pumps blood throughout the body.

  • Blood Vessels: Network for blood circulation.

General Function

The cardiovascular system maintains the circulation of blood, delivering oxygen and nutrients to tissues and removing waste products.

  • Oxygenation: Blood carries oxygen from the lungs to tissues and removes carbon dioxide.

  • Transport: Blood transports hormones, nutrients, and waste products.

  • Homeostasis: Regulates temperature, pH, and fluid balance.

  • Protection: Blood contains cells involved in immune defense.

Human Heart

Location and Size

The heart is located in the mediastinal area of the thoracic cavity, slightly left of the midline, and is protected by the rib cage.

  • Location: Behind the sternum, between the lungs.

  • Size: Approximately the size of a person's fist; average weight is 250-300 grams.

  • Position: The apex points downward and to the left.

Structure of the Heart

Superficial Part

The heart is enclosed by the pericardium, a double-layered sac:

  • Parietal Pericardium: Outer layer attached to the chest wall.

  • Visceral Pericardium (Epicardium): Inner layer covering the heart.

  • Pericardial Space: Space between layers, contains fluid to reduce friction.

Cardiac Muscle Layers

  • Myocardium: Thick muscular layer responsible for contraction.

  • Endocardium: Thin inner lining of the heart chambers.

Chambers of the Heart

The heart has four chambers: two atria and two ventricles.

Chamber

Function

Right Atrium

Receives deoxygenated blood from the body via the superior and inferior vena cava.

Right Ventricle

Pumps deoxygenated blood to the lungs via the pulmonary artery.

Left Atrium

Receives oxygenated blood from the lungs via the pulmonary veins.

Left Ventricle

Pumps oxygenated blood to the body via the aorta; has the thickest wall.

Heart Valves

Types and Functions

Valves ensure unidirectional blood flow and prevent backflow.

  • Atrioventricular (AV) Valves: Separate atria from ventricles.

  • Tricuspid Valve: Between right atrium and right ventricle.

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

  • Semi-lunar Valves: At the exits of the ventricles.

  • Pulmonary Valve: Between right ventricle and pulmonary artery.

  • Aortic Valve: Between left ventricle and aorta.

Valve

Location

Function

Tricuspid

Right AV

Prevents backflow to right atrium

Bicuspid (Mitral)

Left AV

Prevents backflow to left atrium

Pulmonary

Right ventricle exit

Prevents backflow to right ventricle

Aortic

Left ventricle exit

Prevents backflow to left ventricle

Valve Sounds

Valve

Sound Description

Location for Auscultation

AV Valves

Low-pitched, dull "lub" sound

4th ICS, left parasternal border

Semi-lunar Valves

Sharp, high-pitched "dub" sound

2nd ICS, left and right parasternal border

Circulation Pathways

Pulmonary and Systemic Circulation

  • Pulmonary Circulation: Right side of heart pumps deoxygenated blood to lungs for oxygenation.

  • Systemic Circulation: Left side of heart pumps oxygenated blood to the body.

Septum

  • Interatrial Septum: Divides right and left atria.

  • Interventricular Septum: Divides right and left ventricles.

Conduction System of the Heart

Electrical Pathway

The heart's contraction is coordinated by its conduction system, which generates and transmits electrical impulses.

  • Sinoatrial (SA) Node: Pacemaker of the heart, initiates impulse.

  • Atrioventricular (AV) Node: Delays impulse before passing to ventricles.

  • Bundle of His: Conducts impulse from AV node to ventricles.

  • Purkinje Fibers: Distribute impulse throughout ventricles.

Conduction Sequence

  1. Impulse starts at SA node.

  2. Spreads through atria causing contraction.

  3. Delayed at AV node.

  4. Travels down Bundle of His.

  5. Distributed by Purkinje fibers, causing ventricular contraction.

Nervous & Automatic Control

Autonomic Regulation

  • Sympathetic Nervous System: Increases heart rate and contractility.

  • Parasympathetic Nervous System: Decreases heart rate.

  • Automatic Cells: Specialized cells in the SA node initiate heartbeat.

Summary Table: Heart Chambers and Blood Flow

Chamber

Receives Blood From

Sends Blood To

Type of Blood

Right Atrium

Body (via SVC/IVC)

Right Ventricle

Deoxygenated

Right Ventricle

Right Atrium

Lungs (via pulmonary artery)

Deoxygenated

Left Atrium

Lungs (via pulmonary veins)

Left Ventricle

Oxygenated

Left Ventricle

Left Atrium

Body (via aorta)

Oxygenated

Key Terms and Definitions

  • Pericardium: Double-layered sac surrounding the heart.

  • Myocardium: Muscular layer of the heart wall.

  • Endocardium: Inner lining of the heart chambers.

  • Septum: Wall dividing right and left sides of the heart.

  • Valve: Structure that prevents backflow of blood.

  • SA Node: Pacemaker of the heart.

Important Equations

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

  • Stroke Volume: Amount of blood pumped by one ventricle in one contraction.

Additional Info

  • Heart sounds are produced by the closure of valves: "lub" (AV valves) and "dub" (semi-lunar valves).

  • Chordae tendineae and papillary muscles prevent valve prolapse during ventricular contraction.

  • Valvular insufficiency can lead to heart murmurs.

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