The Human Heart

The heart is a strong, powerful organ, consisting of cardiac muscle. The heart pumps continuously, without resting and without becoming fatigued. Its function is to pump blood to the lungs and around the body. The heart is one of the key organs in the Circulatory System.


Anatomy of the heart

The heart consists of four chambers and is divided into left and right by a wall of muscle called the septum. By convention, the heart is often illustrated with the left side on the right as you look at it. In other words, imagine you are looking at someone’s heart; your right is their left!

Atria & Ventricles

The right side of the heart consists of an atrium that receives blood returning from the body, and the right ventricle, which then pumps blood out to the lungs, via the pulmonary artery.

The left side again contains an atrium and a ventricle. The left atrium receives the oxygenated blood returning from the lungs and the ventricle then pumps this blood around the body.

Atrioventricular Valves

The atria and ventricles are separated by valves known as Atrioventricular, or AV valves. The purpose of these valves is to prevent blood from flowing in the wrong direction. Following the movement of blood from the atrium, into the ventricle, the AV valve snaps shut which causes the first heart sound of the heartbeat (often described as “lub dub”, with the closing of the AV valves being the “lub”)

Due to the distance in which the blood being pumped from the left ventricle has to travel, a more forceful contraction is required. For this reason, the muscular wall of the left side is thicker than that of the right side.

Semilunar Valves

The “dub” sound is caused by the closing of two other valves, known as the Semilunar or SL valves. These are located between each ventricle and the artery leaving the heart and again prevent the blood from flowing backward.

The way in which the cardiac muscle contracts in order to force blood around the body is highly specialised and is described on the heartbeat page.

Box diagram of the heart

A box diagram is a great way to learn and remember the passage of blood through the heart. The chambers are simplified into boxes with arrows indicating the passage of oxygenated and deoxygenated blood.

The heart conduction system

The conduction system of the heart refers to how the heart contracts. The heart is unique in that it never tires and is able to generate its own electrical impulses without the need for stimulation from the central nervous system. On average the heart beats approximately 70 beats per minute. Read more on the conduction system of the heart here.

Facts about the human heart

Here are 7 fascinating facts about the Human Heart that everyone would like to know!

  • It takes 20 seconds for blood to circulate through the entire body. Oxygenated blood leaves the aorta about 1 mile an hour.
  • The power output of the heart ranges from 1-5 watts per minute. Which is equivalent to the usage of a 60-watt bulb. It has been said that enough energy is produced a day to drive a truck 20 miles.
  • “Ventricle” means “little belly” in Latin whereas “Atrium” is Latin for “entrance hall”.
  • Red blood cells live for up to 4 months and make approximately 250,000 round trips around the body before returning to the bone marrow, where they were born, to die. Between 2.5 and 3 million red blood cells (erythrocytes) are lost and replaced every second.
  • Human blood is colourless, it is the hemoglobin that makes it red.
  • Due to the heart having its own electrical impulse, it will continue to beat even when removed from the body as long as it has an adequate supply of oxygen.
  • On average, the human body has about 5 liters (almost 9 pints) of blood continually traveling through it by way of the circulatory system. A kitchen tap would need to be turned on all the way for at least 45 years to equal the amount of blood pumped by the heart in an average lifetime.

Human heart quizzes

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