The circulatory system is as important as the other systems are for all living beings. And in our body, the blood circulatory system plays a very important role, which keeps all the organisms going. Any change in the amount of blood in our body can cause weakness, various diseases, or even death! This shows the immense importance of blood in the lives of all organisms. Blood has no formula or equation; it is just a fluid containing liquid and solid particles. 

What is blood?

Blood is a body fluid that is made of several components (which are both solids and liquids), and they are red blood cells (RBCs), white blood cells (WBCs), plasma, and platelets. Blood is alkaline and has a pH of about 7.35 to 7.45. If there is any change in the pH of the blood due to some problems, it can cause us irritation or other problems too. All the components have specialized features, which makes their presence in the blood very important. This body fluid has many important roles, each of which is responsible for organisms' survival. 

Types of blood

There are 4 types of blood: A, B, AB, and O. They can be negative or positive, but it depends on the blood groups of our parents. If we add both negative and positive blood groups, there are 8 blood groups in total, but the main types are 4. The blood group of an offspring is inherited from their parents; hence, it is genetic. The rarest blood groups and their percentages are 

• O positive, available at about 35%, is pretty common.
• O negative, which is available at about 13%
• A positive, available at about 30%, is not very rare either.
• A negative which is available at about 8%
• B positive, which is available at about 8%
• B negative, which is available at about 2%
• AB positive, which is available at about 2%
• AB negative, which is available at about 1%, and between these, the rarest one is AB negative.

The function of blood

Blood is an essential fluid for our body, and the reasons are:

• It transports oxygen, carbon dioxide, and nutrients to all the cells in our body, which are very important for all organisms.
• It forms blood clots that stop excessive blood loss (which is very harmful to our health.)
• This specialized body fluid carries various hormones responsible for how we act or behave.
• It fights infections.
• Blood regulates our body temperature.
• It carries all the waste materials or fluids in our bodies and transports them to the kidneys and livers. They then clean/ purify the blood and transport back to the body by the blood.

Blood cells

There are a lot of cells that are present in the blood. They all have different and important features, like preventing blood loss, engulfing foreign particles, or fighting infections or other diseases. The names of the blood cells are white blood cells which are monocytes, lymphocytes, neutrophils, eosinophil, basophils, and macrophages, and also red blood cells, that is, erythrocytes and platelets. They work and protect us from various problems as they regulate through the entire body by the blood vessels (arteries, veins, and capillaries).

White blood cells

Monocytes, lymphocytes, neutrophils, eosinophil, basophils, and macrophages are the types of white blood cells available. Monocytes destroy germs or pathogens like viruses, bacteria, fungi, and protozoa. Lymphocytes help our bodies fight infections and other problems. Eosinophil fight diseases to save our bodies. Basophils defend our bodies from pathogens like viruses, bacteria, fungi, and protozoa. Macrophages kill microorganisms and keep dead cells away from our bodies. 

Red blood cells

Erythrocytes are red blood cells containing a red pigment called hemoglobin, responsible for the red color of our blood. Lizards have no hemoglobin in their blood, which is white. The other organisms have hemoglobin in their blood, so our blood looks red. Red blood cells do not contain any nucleus, so they can carry more oxygen and nutrients. As there is no nucleus and the shape is like a biconcave disk, the surface area and capacity to carry any substance are more.

There are a lot of other facts about blood and cells: 

• Firstly, Blood is essential to life, without which one cannot survive and may even face death.
• Not every animal contains red blood in their body; some have white, e.g., Lizards.
• There is no substitute for blood discovered till now.
• There is a total of 150 billion red blood cells.
• There are approximately 1.2-1.5 gallons of blood in our bodies.
• Blood mostly contains plasma which is the liquid part of the blood. Blood is generally liquid, even if many solid particles are present.
• Scientists have discovered that red blood cells can be stored in refrigerators at a temperature of 6ºC or even less for about 42 days/ more than a month.