1200 cm3 of blood flows through a vein in 4 minutes. What is the rate of blood flow in cm3 per second?
- Change the time to seconds: 4 × 60 = 240 s.
- Rate = volume ÷ time = 1200 ÷ 240.
- = 5 cm3 per second.
Answer: 5 cm3 per second.
The heart, blood vessels and blood
Biology · Organisation. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
The idea
The heart is an organ that pumps blood around the body in a double circulatory system. The right ventricle pumps blood to the lungs, where gas exchange takes place. The left ventricle pumps blood around the rest of the body, so its muscle wall is thicker.
Blood enters the atria through veins, passes into the ventricles and leaves through arteries. Valves stop it flowing backwards. The resting heart rate is controlled by a group of cells in the right atrium, the natural pacemaker.
Blood is a tissue. It is made of plasma, a liquid in which red blood cells, white blood cells and platelets are suspended.
Rules to remember
- Body → vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta → body.
- Arteries carry blood away from the heart at high pressure: thick walls of muscle and elastic tissue. Veins carry blood back at low pressure: thinner walls, wide lumen, valves.
- Capillaries have walls one cell thick, so substances diffuse quickly between blood and tissues.
- rate of blood flow = volume of blood ÷ time
- Air path: trachea, bronchi, alveoli. Alveoli have a very large surface area, thin walls and a good blood supply.
- Red blood cells: no nucleus, full of haemoglobin, carry oxygen. White blood cells: defend against pathogens. Platelets: help blood to clot. Plasma: carries dissolved substances such as glucose, urea and carbon dioxide.
- An artificial pacemaker is an electrical device that corrects an irregular heart rate. The coronary arteries supply the heart muscle with blood.
Common mistake
Students think every artery carries oxygenated blood. Arteries are named by direction: the pulmonary artery carries deoxygenated blood away from the heart to the lungs.
Worked example
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