ANATOMY 16
The Human Body in Health and Illness, 8th Edition
Author: Barbara Herlihy, BSN, MA, PhD (Physiology), RN
Copyright: 2026 by Elsevier Inc. All rights reserved.
Chapter 16: Anatomy of the Heart
Lesson Objectives
Describe the location of the heart.
Name the three layers and covering of the heart.
Explain the function of the heart as two separate pumps.
Identify the four chambers and great vessels of the heart.
Explain the functions of the four heart valves.
Describe the physiological basis of the heart sounds.
Describe blood flow through the heart.
List the vessels that supply blood to the heart.
Identify the major components of the heart's conduction system.
Function, Location, and Size of the Heart
Function: The heart is a hollow, muscular organ that pumps and forces blood through the blood vessels, delivering essential nutrients and oxygen to every cell in the body.
Location: The heart is located in the thoracic cavity, specifically within the lower mediastinum, situated between the two lungs and behind the sternum (breastbone).
Size: In adults, the heart is roughly the size of a closed fist and weighs less than 1 pound.
Layers and Covering of the Heart
Endocardium:
Innermost layer of the heart.
Myocardium:
Middle layer composed of cardiac muscle that facilitates contractions.
Epicardium:
Thin, outermost layer of the heart; plays a role in forming the pericardium.
Pericardium:
Protective covering that supports the heart; consists of three layers which protect the heart and anchor it to surrounding structures.
A Double Pump and Two Circulations
The heart functions as two separate pumps:
Right Pump (Pulmonary Circulation)
Pumps blood to the lungs.
Receives deoxygenated blood from the body via the venae cavae.
Left Pump (Systemic Circulation)
Pumps oxygenated blood to the rest of the body.
Receives oxygenated blood from the lungs through the pulmonary veins.
The Heart’s Chambers and Great Vessels
Chambers of the Heart:
Right Atrium
Right Ventricle
Left Atrium
Left Ventricle
Great Vessels of the Heart:
Superior Vena Cava
Inferior Vena Cava
Pulmonary Trunk
Four Pulmonary Vessels
Aorta
Heart Valves
Atrioventricular Valves:
Chordae Tendineae: Cords that anchor these valves to the heart walls.
Tricuspid Valve: Located between the right atrium and right ventricle.
Bicuspid (Mitral) Valve: Located between the left atrium and left ventricle.
Semilunar Valves:
Pulmonic Valve: Located between the right ventricle and pulmonary trunk.
Aortic Valve: Located between the left ventricle and aorta.
Heart Sounds
Normal heart sounds described as "lubb-dupp."
S1: Represents the first heart sound “lubb,” produced by the closure of the atrioventricular valves.
S2: Represents the second heart sound “dupp,” produced by the closure of the semilunar valves.
Abnormal Heart Sounds (Murmurs):
Indicate problematic blood flow and are often described by their timing and pitch.
Extra sounds caused by vibrations:
S3: Third heart sound.
S4: Fourth heart sound.
When both S3 and S4 are present, a “gallop rhythm” is heard.
Pathway of Blood Flow Through the Heart
Right Atrium
Tricuspid Valve
Right Ventricle
Pulmonic Semilunar Valve
Pulmonary Trunk
Pulmonary Arteries
Pulmonary Capillaries
Four Pulmonary Veins
Left Atrium
Bicuspid Valve (Mitral Valve)
Left Ventricle
Aortic Semilunar Valve
Aorta
Blood Supply to the Myocardium
The myocardium is nourished by the coronary arteries:
Right Coronary Artery: Supplies blood to the right side of the heart.
Left Coronary Artery: Supplies blood to the left side of the heart.
Characteristics:
Coronary blood flow can increase during periods of increased cardiac demand.
Greatest coronary blood flow occurs during myocardial relaxation phases (diastole).
Coronary arteries can develop anastomoses, or multiple connections between arterial branches ensuring blood supply continuity.
Cardiac Enzymes and Leaky Cells
When dead myocardial cells leak enzymes into the bloodstream:
Plasma elevations of cardiac enzymes can be detected.
Troponin, a regulatory protein, leaks into the blood and serves as a diagnostic tool for myocardial infarction (heart attack).
Cardiac Conduction System
Components:
Sinoatrial Node: Known as the pacemaker of the heart, initiates electrical impulses.
Atrial Conducting Fibers: Conduct impulses through the atria.
Atrioventricular Node: Relays impulses from atria to ventricles.
His-Purkinje Fibers: Conduct impulses throughout the ventricles.
Automaticity and Rhythmicity:
Automaticity: Cardiac pacemaker cells can generate electrical signals independently.
Rhythmicity: Cardiac tissue fires impulses in a regular, timed manner.
Electrocardiogram (ECG)
Waveforms:
P-wave: Represents atrial depolarization (contraction).
QRS complex: Represents ventricular depolarization (contraction).
T-wave: Represents ventricular repolarization (relaxation).
Intervals:
P-R Interval: Time from the beginning of atrial depolarization to the beginning of ventricular depolarization.
S-T Interval: Time from the end of ventricular depolarization to the beginning of ventricular repolarization.
The Human Body in Health and Illness, 8th Edition
Author: Barbara Herlihy, BSN, MA, PhD (Physiology), RN
Copyright: 2026 by Elsevier Inc. All rights reserved.
Chapter 16: Anatomy of the Heart
Lesson Objectives
Describe the location of the heart, including its anatomical relations.
Name the three layers and covering of the heart, detailing their specific functions and characteristics.
Explain the function of the heart as two separate pumps, including the mechanisms involved in circulation.
Identify the four chambers and great vessels of the heart, emphasizing their roles in the circulatory system.
Explain the functions of the four heart valves and their significance in maintaining unidirectional blood flow.
Describe the physiological basis of the heart sounds, further identifying their clinical relevance.
Describe blood flow through the heart, including details about pressure changes and valve functions during the cardiac cycle.
List the vessels that supply blood to the heart, highlighting the importance of coronary circulation.
Identify the major components of the heart's conduction system, including their functional implications in cardiac rhythm.
Function, Location, and Size of the Heart
Function: The heart is a hollow, muscular organ that serves as the body's vital pump, propelling blood through the extensive network of blood vessels, thereby delivering essential nutrients and oxygen to every cell while removing waste products. Its rhythmic contractions are coordinated to meet the body's fluctuating demands for blood, particularly during physical activity or periods of rest.
Location: The heart is located in the thoracic cavity, specifically within the lower mediastinum. It is anatomically positioned between the two lungs, nestled posterior to the sternum and anterior to the vertebral column. The heart's orientation also features a slight tilt to the left, further affecting its placement within the thoracic cavity.
Size: In adults, the heart typically resembles the size of a closed fist, measuring about 12 cm (5 inches) in length and around 8 to 10 cm (3 to 4 inches) in width. The average weight is approximately 250-350 grams (less than 1 pound). Factors such as age, sex, and physical conditioning can influence heart size and weight.
Layers and Covering of the Heart
Endocardium:
The innermost layer of the heart wall, composed of a smooth layer of endothelial cells that lines the heart chambers and covers the heart valves. This layer helps minimize friction and prevents blood clots.
Myocardium:
The middle layer made up of specialized cardiac muscle tissue responsible for the contractile force of the heart. This layer is thickest in the ventricles, reflecting its critical role in pumping blood out of the heart.
Epicardium:
The thin, outermost layer of the heart which also forms part of the pericardium. It comprises connective tissue and a small amount of fat. It serves to protect the heart and assist in its lubrication.
Pericardium:
A double-layered protective covering that supports the heart. It consists of an outer fibrous layer that anchors the heart to surrounding structures (i.e., diaphragm and sternum) and an inner serous layer containing pericardial fluid that reduces friction during heartbeats.
A Double Pump and Two Circulations
The heart operates as two distinct pumps:
Right Pump (Pulmonary Circulation):
This chamber pumps deoxygenated blood to the lungs for oxygenation. It receives deoxygenated blood from the body via the superior and inferior venae cavae. The right heart includes the right atrium and right ventricle, with the tricuspid valve regulating blood flow into the ventricle.
Left Pump (Systemic Circulation):
This chamber pumps oxygenated blood to the rest of the body. It receives oxygen-rich blood from the lungs through the pulmonary veins and includes the left atrium and left ventricle, equipped with the bicuspid (mitral) valve.
The Heart’s Chambers and Great Vessels
Chambers of the Heart:
Right Atrium: Collects deoxygenated blood from the systemic circulation.
Right Ventricle: Pumps blood to the lungs via the pulmonary trunk.
Left Atrium: Receives oxygenated blood from the lungs.
Left Ventricle: Pumps oxygenated blood into the aorta for distribution to the body.
Great Vessels of the Heart:
Superior Vena Cava: Drains blood from the upper body.
Inferior Vena Cava: Drains blood from the lower body.
Pulmonary Trunk: Splits into right and left pulmonary arteries leading to the lungs.
Four Pulmonary Veins: Return oxygenated blood from the lungs to the left atrium.
Aorta: The body's main artery, distributing oxygenated blood to all body parts.
Heart Valves
Atrioventricular Valves:
Chordae Tendineae: These fibrous cords anchor the valves to the heart walls, preventing backflow during contraction.
Tricuspid Valve: Located between the right atrium and right ventricle, consisting of three leaflets.
Bicuspid (Mitral) Valve: Located between the left atrium and left ventricle, comprising two leaflets and preventing backflow into the atrium.
Semilunar Valves:
Pulmonic Valve: Located between the right ventricle and pulmonary trunk, facilitating blood flow to the lungs.
Aortic Valve: Located between the left ventricle and aorta, allowing oxygenated blood to enter the systemic circulation.
Heart Sounds
Normal heart sounds are described as "lubb-dupp."
S1 (lubb): Represents the closure of the atrioventricular valves, marking the beginning of ventricular contraction.
S2 (dupp): Represents the closure of the semilunar valves, signaling the end of ventricular contraction.
Abnormal Heart Sounds (Murmurs):
These sounds may indicate problematic blood flow, often described by timing (systolic/diastolic) and pitch variations.
Extra sounds caused by vibrations can indicate issues:
S3: Known as a third heart sound heard in rapid ventricular filling.
S4: Represents the stiffened ventricle, occurring during atrial contraction.
A combination of S3 and S4 may produce a characteristic "gallop rhythm," suggesting heart dysfunction.
Pathway of Blood Flow Through the Heart
Right Atrium
Tricuspid Valve
Right Ventricle
Pulmonic Semilunar Valve
Pulmonary Trunk
Right and Left Pulmonary Arteries
Pulmonary Capillaries
Four Pulmonary Veins
Left Atrium
Bicuspid Valve (Mitral Valve)
Left Ventricle
Aortic Semilunar Valve
Aorta
Blood Supply to the Myocardium
The myocardium, the heart's muscular layer, is nourished by the coronary arteries:
Right Coronary Artery: Supplies blood primarily to the right atrium and right ventricle, and portions of the left ventricle.
Left Coronary Artery: Further branches into the left anterior descending artery and circumflex artery, supplying the left atrium and left ventricle.
Characteristics:
Coronary blood flow increases during heightened cardiac demand, such as exercise.
The greatest coronary blood flow occurs during the diastolic phase when the heart muscles relax.
Coronary arteries can develop anastomoses, providing alternate routes for blood flow to ensure supply continuity, especially during blockages.
Cardiac Enzymes and Leaky Cells
When myocardial cells undergo necrosis, they leak specific enzymes into the bloodstream, which can serve as vital diagnostic markers:
Elevated plasma levels of cardiac enzymes, notably troponin, can indicate myocardial infarction (heart attack).
These biomarkers help in assessing the extent of cardiac damage and the necessary intervention.
Cardiac Conduction System
Components:
Sinoatrial Node: Acts as the heart's natural pacemaker, generating electrical impulses that initiate the heartbeat.
Atrial Conducting Fibers: Transmit impulses through the atria, promoting atrial contraction.
Atrioventricular Node: A critical relay station, it delays impulses before passing them to the ventricles, ensuring efficient heart contraction.
His-Purkinje Fibers: These fibers are responsible for conducting impulses throughout the ventricles, coordinating contraction.
Automaticity and Rhythmicity:
Automaticity: Cardiac pacemaker cells have the ability to spontaneously generate electrical signals, enabling the heart to beat independently.
Rhythmicity: The organized generation and transmission of impulses by cardiac tissue facilitate a regular, timed heartbeat, vital for effective and sustained circulation.
Electrocardiogram (ECG)
Waveforms:
P-wave: Represents atrial depolarization (contraction).
QRS complex: Indicates ventricular depolarization (contraction), a critical aspect of heart function.
T-wave: Reflects ventricular repolarization (relaxation), allowing the heart chambers to prepare for the next beat.
Intervals:
P-R Interval: Measures the time from the onset of atrial depolarization to the onset of ventricular depolarization, indicating conduction duration.
S-T Interval: Measures the duration between ventricular depolarization and repolarization, critical for diagnosing cardiac anomalies.