Frequently Asked Questions: Circulatory System

Q. Why don't giraffes get dizzy with all that lifting of their necks up and down?
A. There are special valves inside the veins in a giraffe's neck. If the giraffe's head is up, the valves let the blood flow back to the heart. If the giraffe's neck is down, the one-way valves close up.

Q. What are bruises?
A. Bruises are a leakage of blood out of fragile thin capillaries into the surrounding tissues. They heal after white blood cells travel to the area surrounding and digesting any damaged cells, and after the capillary walls have been repaired.

Q. What are 'heart attacks' and 'strokes'?
A. Heart Attacks are also called coronary occlusions. The heart has its own blood supply from the coronary artery to nourish the heart muscle with oxygen and nutrients. When that artery becomes blocked due to a build-up of fat and salt in the diet over time, the blood supply to the heart muscle ceases, and a small part of the heart muscle dies. This is accompanied by considerable pain.
A 'stroke' is very similar to a 'heart attack', but it is an artery in the brain that becomes blocked and part of the brain is damaged. Depending on what part of the brain is damaged and for how long that part of the brain was deprived of oxygen, a person may temporarily or permanently lose control of some muscles or may lose memory or senses. A 'stroke' is usually called a cerebro-vascular accident.

Q. What are varicose veins?
A. The blood vessels that carry blood from the lower areas of the body back to the heart are veins. These have valves to allow the one-way flow of blood to help against the downward pull of gravity. In occupations where a person may be standing for long periods of time (e.g. teachers, shop assistants), these valves may weaken and be damaged, allowing the vein to balloon out into varicose veins.

Q. Why is blood red?
A. In red blood cells, there is a red-coloured chemical called haemoglobin that transports oxygen and carbon dioxide around the body. It is bright red when carrying oxygen and dark red when it is carrying carbon dioxide.

Q. How do you get dark circles under your eyes?
A. Rubbing your eyes releases histamines that cause swelling and darkness of the capillaries of your eyes.