Human Physiology: 6.2 Blood System Flashcards
What was Galen’s theory about the blood system?
Galen was an ancient Greek philosopher and surgeon who developed the following theories
Blood is formed in the liver from ingested food
Blood is pumped backwards and forwards between the liver and the right ventricle in the heart
Some blood moves into the left ventricle through invisible pores and mixes with air from the lungs
This mixing of air with blood produces spirits which are distributed to the body via the brain
Blood is consumed by the tissues so that new blood must be continuously made”
“Galen’s theories were overturned by English physician William Harvey through a series of experiments and observations. What theories were proposed by William Harvey?
Blood is pumped to the brain and body by the heart
Blood circulates through the pulmonary and systemic circulation systems
Capillaries exist which link arteries to veins
Blood flow is too fast for blood to be consumed by the tissues; it would run out too quickly to be replaced. Instead, blood returns to the heart and re-circulates”
How did Harvey investigate the heart as a pump and circulation mechanism of blood?
Harvey used a series of experiments to show that blood flow is unidirectional and that the presence of valves prevents backflow in veins
Harvey attached a tourniquet to a person’s upper arm and instructed them to grip tightly onto a pole
A tourniquet is a band applied to a limb to limit blood flow to the lower part of that limb
Once the veins became visible, Harvey proceeded to apply pressure to the veins systematically to show how blood flow was affected
He used this method to demonstrate how blood moves unidirectionally through the veins in the arm
He then demonstrated how the heart acts as a pump which forces blood out through the arteries; it then circulates around the body before it returns to the heart through the veins
He also showed that the blood being pumped out of the heart was travelling too quickly to be constantly used up by the tissues, as described by Galen
Despite not having powerful enough microscopes to see the capillaries, Harvey predicted their presence as small vessels which link the arteries to the veins
Explain the human body having a double circulatory system
A double circulatory system passes through the heart twice for every one complete circuit of the body, with blood passing through two separate circuits known as pulmonary and systemic circulation
In the pulmonary circulatory system
The right side of the heart pumps deoxygenated blood to the lungs for gas exchange
Blood pressure is lower in the pulmonary system; this prevents damage to the lungs
In the systemic circulatory system
Oxygenated blood returns to the left side of the heart from the lungs
The left ventricle then pumps the oxygenated blood at high pressure around the body”
