Brent Cornell

    
Our modern understanding of circulatory system is based upon the discoveries of 17^th century English physician, William Harvey

• Harvey’s findings were published in a book commonly called De Motu Cordis – On the Motion of the Heart and Blood

Prior to Harvey’s findings, scientists held to the antiquated views of the Greek philosopher Galen, who believed that:

• Arteries and veins were separate blood networks (except where they connected via invisible pores)
• Veins were thought to pump natural blood (which was believed to be produced by the liver)
• Arteries were thought to pump heat (produced by the heart) via the lungs (for cooling – like bellows)

Based on some simple experiments and observations, Harvey instead proposed that:

• Arteries and veins were part of a single connected blood network (he did not predict the existence of capillaries however)
• Arteries pumped blood from the heart (to the lungs and body tissues)
• Veins returned blood to the heart (from the lungs and body tissues)

Circulation According to William Harvey

    
The human heart is a four chambered organ, consisting of two atria and two ventricles

• The atria act as reserviors, by which blood returning to the heart is collected via veins (and passed on to ventricles)
• The ventricles act as pumps, expelling the blood from the heart at high pressure via arteries

The reason why there are two sets of atria and ventricles is because there are two distinct locations for blood transport

• The left side of the heart pumps oxygenated blood around the body (systemic circulation)
• The right side of the heart pumps deoxygenated blood to the lungs (pulmonary circulation)

There is therefore a separate circulation for the lungs (right side of heart) and for the rest of the body (left side of heart)

• The left side of the heart will have a much thicker muscular wall (myocardium) as it must pump blood much further

Overview of Pulmonary and Systemic Circulation