My heart

In order to understand the nature of various pathologies this section discusses the structure and function of the heart.

The heart
Is a muscle about the size of your fist which weighs approximately one pound (0.5 kg).
It is located behind and slightly to the left of the breastbone, pumps about 10 pints (4.7 liters) of blood every minute, or 1800 gallons (6768 liters) of blood every day.



Function

The function of the heart is to circulate blood throughout the body.

  • Pumping blood through the lungs removes carbon dioxide and refreshes the blood with oxygen.


  • The oxygenated blood is pumped to the body to provide oxygen and nutrients and to remove waste products.

A healthy heart beats steadily and rhythmically at a rate of about 60 to 100 beats per minute when at rest (normal sinus rhythm). During strenuous exercise, the heart can increase the amount of blood it pumps up to four times the amount it pumps at rest, within only a matter of seconds.

top



Structure
The heart's structure has four chambers with one-way flaps called valves.
The atria are the upper chambers and they receive blood that is being returned to the heart. The right atrium receives blood with little oxygen because the blood has already circulated throughout the body delivering oxygen and nutrients. The left atrium fills with newly oxygenated blood returning from the lungs. When the atria pump (contract), they push the blood through valves (tricuspid and mitral) into the relaxed ventricles. When the ventricles contract, the right ventricle pumps blood through the pulmonary valve into the lungs. The left ventricle pumps blood through the aortic valve to the body, including the heart (through coronary arteries). This continuous cycle of synchronized contractions is driven by the heart's electrical system.

top



The heart's electrical system

  • Causes the heart to beat.


  • Controls the heart rate (the number of beats per minute).


  • Has special pathways (conduction pathways) that carry the electrical signals throughout the lower
    heart chambers (ventricles) for each heartbeat.


When heart cells in the upper heart chambers (atria) receive an electrical signal, they contract (pump) and then relax. The blood from the atria is pumped into the relaxed lower heart chambers (ventricles) and then the ventricles pump blood to the body.
In a healthy heart, each heartbeat begins in the sinus node (the heart's natural pacemaker), which is located in the right atrium. The electrical signal from the sinus node (sinoatrial or SA node) starts an electrical chain reaction that spreads across both atria, much like ripples on the calm surface of a pond. This causes the atria to contract and pump blood into the ventricles.
This electrical chain reaction continues from the atria through an area between the atria and ventricles called the atrioventricular node (AV node or AV junction). The AV node connects to conduction pathways that relay the signal to the ventricles. The AV node acts as an electrical gateway to the ventricles. The conduction pathways deliver the signals to the ventricles and the ventricles pump blood to the body.
An irregularity in the heart's electrical system is called an arrhythmia, or heart rhythm disorder. Rhythm disorders can cause the heart to beat too slowly (bradyarrhythmia) or too fast (tachyarrhythmia).

top | glossary