Blood is fascinating. Many people learn in school that its role is to transport oxygen and nutrients around the body and remove waste products. But blood has many functions, including protecting us from pathogens, regulating our temperature, and keeping our internal chemicals and nutrients in balance.
Here are some other things you may not know about blood.
- Blood is liquid and solid
Blood is the body’s connective tissue. It has many cellular components (consisting of red blood cells, white blood cells, and platelets) and an extracellular fluid matrix.
Unlike other connective tissues in the body, blood is a liquid. The extracellular matrix, plasma, is a fluid that suspends cells in the blood. But when the tissue is damaged, for example by a cut, blood, like other connective tissues, becomes stiff. This is called a blood clot.
A blood clot is activated when it comes into contact with something other than the smooth inner surface of a blood vessel, and it begins to clog the wound. Platelets adhere to the open wound and then convert soluble fibrinogen, a type of plasma protein, into insoluble fibrin, which forms a “net” around the plug and prevents further bleeding. Over time, as it heals, the mesh and plug can break down (or pull out if you have scabs).
Most people’s blood is about 45% cells – mainly red blood cells, only 1% white cells, and 55% plasma. Too much or too little of any of these can cause diseases like anemia.
Blood cells are constantly being produced and recycled. The body makes about 2 million red blood cells per second, but this increases dramatically during times of stress, such as at low-oxygen altitudes.
On average, men have 4.7-6.1 million cells per microliter, and women have 4.2-5.4 million cells per microliter. There are 1000 microliters in one milliliter.
- Volume is always changing
The amount of blood in the human body changes within 24 hours. As the body absorbs fluids, it is at its peak before lunch.
During pregnancy, the blood volume of a pregnant woman increases up to 50%. It is designed to support the uterus with the placenta and developing fetus.
But on average, men have 5-6 liters of blood and women have 4-5 liters of blood.
- There are four types of blood
We inherit our blood type from our parents. We have blood type A, B, AB and O. These groups determine which antigens you have, which means that you cannot receive a blood transfusion from a person with a group that does not match your blood type.
But another basic blood group is Rhesus (Rh). People are either Rh+ or Rh- because the Rh+ has an extra antigen and cannot give blood to a person with Rh because it causes an immune response.
- We always make more blood cells
We are constantly recycling blood cells and can make more blood cells when we bleed. This means that we can donate approximately 470 milliliters of blood at one time. It takes 12 weeks for the human body and 16 weeks for women to completely replace all the donated blood cells.
However, if we lose more than 40% of our blood volume (a process called extravasation), we die. If we lose 10-20% of blood, the body goes into shock. In shock, the body will try to correct the situation by increasing heart rate and breathing, and the body will sweat and lose skin color.
- Blood has a “use by” period
Previously, “whole” blood had to be used at once. But now blood is separated into different blood components such as red blood cells, white blood cells, platelets and plasma to be used as effectively as possible, because a patient only needs one blood component.