7 Facts About the Heart and Blood

Together with the lymphatic system, the human cardiovascular system makes up the body’s circulatory system. The cardiovascular system is comprised of the heart and lungs, which distribute nutrients, oxygen, hormones and blood cells throughout the body. Renal circulation is the blood supply to the kidneys, which comprises 20% of the heart’s output.

This list provides 7 interesting facts about the heart and blood.

1. An adult’s heart beats about 100,000 times per day

Diagram of the heart.

During the lifetime of the average person, the heart beats well over 2 billion times.

2. Heart muscle is resistant to fatigue

Cardiac muscle.

Muscle fatigue is caused by a build up of lactic acid caused by anaerobic (lacking oxygen) muscle metabolism. The muscles of the heart are very well supplied with oxygen and cardiac muscle contains more mitochondria (these release energy in the muscles) than skeletal muscles so the chance of anaerobic metabolism is reduced significantly.

3. There are an estimated 60,000 miles of blood capillaries in an average adult human

Blood capillary with red blood cell.

It is hard to believe, but if the blood capillaries were removed from an adult they would stretch 2.5 times round the equator! This figure is possible because blood capillaries are tiny, about a tenth of the diameter of a human hair.

4. Red blood cells last for about 4 months

Scanning electron microscope image of red and white blood cell.

When they die or are damaged, the red blood cells in your body collect in the spleen. The red cells are broken down and some products are recycled whilst the rest is excreted.

 5. The three major types of white blood cells are granulocytes, monocytes and lymphocytes

Whits blood cell.

Granulocytes kill invading bacteria, momocytes fight viruses and lymphocytes control your immune system.

6. Blood cells are made in bone marrow

Blood cells made in the bone marrow.

All blood cells have a limited lifetime, most white cells for example live only for a few days, or weeks at most.

7. Your kidneys control how many red blood cells are produced

Kidney diagram.

If the number of red blood cells is low or if your body is short of oxygen, the kidney releases a hormone called erythropoietin which makes the bone marrow produce more red blood cells.

Taught science for 16 years at a secondary school in the East Midlands.