Chapter 12: The Heart – Anatomy, Physiology, and Circulation

Chapter 12: The Heart

Learning Outcomes

• Describe the anatomy of the heart, including blood supply and pericardium structure.

• Trace the flow of blood through the heart, identifying major blood vessels, chambers, and heart valves.

• Explain the events of an action potential in cardiac muscle and describe the conducting system of the heart.

• Identify the electrical events recorded in a normal electrocardiogram.

• Explain the events of the cardiac cycle and relate heart sounds to specific events in this cycle.

• Define and calculate cardiac output.

• Describe factors influencing heart rate and stroke volume, and explain coordination of adjustments during physical activity.

The Heart's Role in the Cardiovascular System

General Function

• The heart beats about 100,000 times/day for approximately 80 years.

• Pumps about 7500 L of blood/day through three types of blood vessels:

  • Arteries: Carry blood away from the heart.

  • Veins: Return blood to the heart.

  • Capillaries: Small, thin-walled vessels between smallest arteries and veins.

• Two major circuits of blood flow:

  • Pulmonary circuit: Carries blood to/from lungs.

  • Systemic circuit: Carries blood to/from the rest of the body.

The Circulatory System

Overview

• The heart is the central pump of the circulatory system, maintaining the flow of blood through pulmonary and systemic circuits.

• Blood exchanges gases (O2 and CO2) in lung and tissue capillaries.

Chambers of the Heart

Structure and Function

• The heart contains four muscular chambers:

  1. Right atrium: Receives blood from systemic circuit.

  2. Right ventricle: Pumps blood into the pulmonary circuit.

  3. Left atrium: Receives blood from pulmonary circuit.

  4. Left ventricle: Pumps blood into systemic circuit.

• Both atria contract together; both ventricles contract together.

Heart Characteristics

Size, Location, and Orientation

• Size: About the size of a fist; weighs less than 1 lb.

• Location: Lies between lungs in the mediastinum within the thoracic cavity.

• Orientation: Apex (bottom) rests on diaphragm; base formed by atria.

Pericardium

Structure and Function

• Fibrous pericardium: Outer layer, tough, inelastic, dense irregular connective tissue. Prevents overstretching, provides protection, anchors heart.

• Serous pericardium: Inner, thinner, delicate membrane. Two parts:

  • Parietal pericardium: Fused to fibrous pericardium.

  • Visceral pericardium (epicardium): Covers heart muscle tissue.

• Pericardial fluid: Found between layers, reduces friction.

The Location of the Heart

Pericardial Cavity

• The pericardial cavity surrounds the heart, formed by the visceral and parietal pericardium.

• Relationship can be visualized as a fist pushed into a balloon.

The Surface Anatomy of the Heart

Major Features

• Auricle: Expandable extension of an atrium; increases capacity.

• Sulci (grooves):

  • Coronary sulcus: Marks border between atria and ventricles.

  • Anterior and posterior interventricular sulcus: Mark boundary between left and right ventricles.

• Ligamentum arteriosum: Connects aortic arch to pulmonary trunk.

• Base: Superior end, connection for great vessels.

• Apex: Inferior end, pointed tip.

Major Vessels

• Superior and Inferior Vena Cavae: Carry blood from systemic circulation back to right atrium.

• Aorta: Arises from left ventricle, carries blood out to body.

• Pulmonary trunk: Arises from right ventricle, splits into right and left pulmonary arteries (to lungs).

• Pulmonary veins: Return blood to left atrium.

Coronary Circulation

Blood Supply to the Heart

• Supplies blood to cardiac muscle tissue.

• Arteries originate at aortic sinuses (base of aorta):

  • Right coronary artery: Supplies right atrium and parts of both ventricles; branches into marginal and posterior interventricular arteries.

  • Left coronary artery: Supplies left atrium, left ventricle, interventricular septum; branches into circumflex and anterior interventricular arteries.

• Anastomoses: Interconnections between arteries, provide alternate pathways for blood supply.

• Great and middle cardiac veins: Drain blood from coronary capillaries into the coronary sinus.

Myocardial Infarction (MI)

Pathology

• Commonly called a "heart attack".

• Area of dead tissue is called an infarct.

• Caused by interruption in blood flow to cardiac muscle, often due to coronary artery disease (CAD).

• CAD is caused by buildup of fatty deposits on artery walls.

• Most common cause of death worldwide.

The Three Layers of the Heart Wall

Layer	Location	Function
Epicardium	Outer surface (visceral pericardium)	Protection, composed of epithelium & connective tissue
Myocardium	Middle layer	Cardiac muscle cells, contraction, forms spiral/band patterns
Endocardium	Inner layer	Lines chambers, covers valves, reduces friction

Heart Wall and Cardiac Muscle Tissue

Muscle Arrangement

• Atrial musculature forms bands wrapping around atria in a figure-eight pattern.

• Ventricular musculature forms spiral bands around ventricles.

• Concentric layers increase efficiency of contraction.

Heart Wall--Cardiac Muscle Cells

Cellular Features

• Smaller than typical skeletal muscle cells.

• Contain a single nucleus.

• Myofibrils organized into sarcomeres.

• Large amount of mitochondria for energy.

• Cells joined at intercalated discs (linked by desmosomes and gap junctions).

• Gap junctions allow action potentials to conduct from cell to cell, increasing contraction efficiency.

Connective Tissue in the Heart

Support and Structure

• Collagen and elastic fibers wrap around muscle cells, providing support, strength, and preventing overexpansion.

• Helps heart return to normal shape after contraction.

• Forms cardiac skeleton:

  • Encircles bases of large vessels and each heart valve.

  • Stabilizes valve position.

  • Physically isolates atrial muscle from ventricular muscle (electrical insulation).

Chambers of the Heart: Functional Differences

Chamber	Wall Thickness	Pressure	Main Function
Right Ventricle	Thinner	Lower	Propels blood to pulmonary circuit
Left Ventricle	Thicker	Higher (4-6x)	Propels blood to systemic circuit

Internal Anatomy of the Heart

Partitions and Valves

• Interatrial septum: Separates atria; contains fossa ovalis (remnant of foramen ovale).

• Interventricular septum: Separates ventricles.

• Atrioventricular (AV) valves: Tricuspid (right), Bicuspid/Mitral (left); one-way valves from atrium to ventricle.

• Semilunar (SL) valves: Pulmonary & Aortic; one-way valves from ventricles to arteries.

Circulation Within the Heart

Blood Flow Pathway

• Right atrium receives deoxygenated blood via superior/inferior vena cava and coronary sinus.

• Blood moves through tricuspid (AV) valve into right ventricle.

• Right ventricle pumps blood through pulmonary (SL) valve into pulmonary trunk, which divides into right/left pulmonary arteries (to lungs).

• Left atrium receives oxygenated blood via four pulmonary veins.

• Blood moves through bicuspid (AV) valve into left ventricle.

• Left ventricle pumps blood through aortic (SL) valve into ascending aorta (to body).

Summary Table: Blood Flow Through the Heart

Step	Chamber/Valve	Direction
1	Right atrium	Receives deoxygenated blood
2	Tricuspid valve	To right ventricle
3	Right ventricle	To pulmonary trunk
4	Pulmonary valve	To pulmonary arteries
5	Lungs	Gas exchange
6	Pulmonary veins	To left atrium
7	Bicuspid valve	To left ventricle
8	Left ventricle	To aorta
9	Aortic valve	To systemic circulation

Additional info: These notes cover the anatomical and physiological foundations of the heart, including its structure, blood supply, and the pathway of blood through its chambers and valves. For further study, students should review the mechanisms of cardiac muscle contraction, the conducting system, and the regulation of cardiac output and heart rate.