Anatomy

The heart is a muscle that pumps blood throughout the body’s systems. The left side of the heart pumps oxygenated blood from the lungs to all body systems via the arterial supply. Blood then returns to the right side of the heart via the venous system, where waste products are excreted by various organs. The right side then pumps deoxygenated blood into the lungs, where carbon dioxide (CO2) is released, and oxygen is absorbed. This cycle repeats with each heartbeat.

The heart consists of:

• External walls
• Blood-filled chambers
• Valves that allow blood to flow through the chambers
• Blood vessels that carry blood to the other structures
• Electrical signaling conduction system

The three walls of the heart are:

• Endocardium; innermost layer
• Myocardium: muscular middle layer
• Epicardium: outermost layer

Chambers of the heart:

• Right atrium
• Right ventricle
• Left atrium
• Left ventricle

Valves of the heart:

• Atrioventricular valves:
  • Tricuspid valve: lies between the right atrium and the right ventricle
  • Mitral valve: lies between the left atrium and left ventricle
• Semilunar valves:
  • Aortic valve: oxygenated blood flows from the left ventricle to the aorta
  • Pulmonary valve: deoxygenated blood

Blood vessels:

• Arteries: carry oxygenated blood
• Veins: carry deoxygenated blood
• Capillaries: small blood vessels for the exchange of deoxygenated and oxygenated blood

Chambers of the heart

The heart is separated into four chambers that work to ensure blood flow occurs in the right direction. The left and right sides of the heart work separately to ensure blood reaches either the lungs or the body system. The left side of the heart pumps blood directly to the lungs, providing oxygen to the blood, while the right side of the heart receives blood that has been pumped throughout the entire body and is deoxygenated.

Definitions

Aorta

Transports oxygenated blood from the heart to the peripheral systems

Right atrium

Receives deoxygenated blood from the body system and then pumps it to the right ventricle

Right ventricle

Receives blood from the right atrium and pumps deoxygenated blood to the lungs via the pulmonary arteries

Left atrium

Receives oxygenated blood from the lungs via four pulmonary veins

Left ventricle

Receives oxygenated blood from the left atrium and pumps oxygenated blood into the aorta, distributing it to the brain, organs, and tissues.

Superior vena cava

Large vein that carries deoxygenated blood from the head, chest, arm, and neck

Inferior vena cava:

Large vein that carries deoxygenated blood from the feet, legs, and abdomen

Blood flow through the heart: step-by-step

1. Deoxygenated blood returns to the heart:
   • Blood lacking oxygen returns from the body to the heart through two large veins:
     • Superior vena cava: brings blood from the upper body.
     • Inferior vena cava: brings blood from the lower body.
2. Right atrium
   • The deoxygenated blood enters the right atrium, the heart’s upper right chamber.
3. Right ventricle
   • Blood flows from the right atrium into the right ventricle, the lower right chamber.
4. Pulmonary arteries to the lungs
   • The right ventricle pumps the blood through the pulmonary arteries to the lungs.
   • (Note: Despite being called arteries, these carry deoxygenated blood.)
5. Lungs oxygenate the blood
   • In the lungs, carbon dioxide is exchanged for oxygen. The now oxygen-rich blood is ready to return to the heart.
6. Left atrium
   • Oxygenated blood returns to the heart via the pulmonary veins into the left atrium, the upper left chamber.
7. Left ventricle
   • Blood moves from the left atrium into the left ventricle, the lower left chamber.
8. Aorta to the body
   • The left ventricle pumps the oxygen-rich blood into the aorta, the body’s main artery, which distributes it throughout the body.

Electrical signals in the heart

Electrical signals within the heart act as a pacemaker to the heart by assisting with controlling heart rate, coordinating the heart chambers (atria and ventricles), adapting to the changing needs of the body, and ensuring appropriate circulation.

Definitions

Sinoatrial node

The sinoatrial (SA) node initiates the normal heart rhythm sending blood from the atria into the ventricles

Atrioventricular Bundle

A bundle of electrically charged cardiomyocytes that causes blood to move from the atrium to the ventricle

Bundle of His

Electrically charged fibers that carry signals through the central components of the heart to assist with maintaining consistent contractility of the heart by sending signals from the AV node to the Purkinje fibers

Purkinje fibers

Specialized electrically charged fibers that work with greater efficiency to cause contraction of the right and left ventricles

Crucial factors of cardiac function

The amount of blood pumped with each heartbeat is crucial to maintaining the vitality of the lungs and the peripheral system. The principles that are important in this process are and preload. If there is dysfunction in either of these components, then the individual may experience stroke, myocardial infarction, or death.

Definitions

Preload

Amount of blood in ventricles at the end of diastole

Afterload

The pressure that the heart must overcome to pump blood to the lungs and the peripheral system

Stroke volume

Amount of blood pumped out by the ventricle at the end of each contraction

Cardiac output

Heart rate multiplied by stroke volume to determine how much blood is pumped from the ventricles in liters per minute

Diastole

Relaxation of atrium and ventricles

Systole

Contraction of the atrium and ventricle