Blood is composed of red blood cells, various kinds of white blood cells, blood platelets, and plasma. Each of these constituents serves a different purpose.

The red blood cells transport oxygen and carbon dioxide through your body.

The white blood cells can recognize and eliminate harmful substances and pathogens that can make you sick.

Blood platelets are pieces of cell that form the crust on a wound.

The plasma transports nutrients from your small intestine to tissue and organs, and urea from your liver to the kidneys. It also takes care of spreading hormones through your body.

Blood also plays an important role in conserving a steady internal environment, regulating things such as body temperature and acidity levels (also known as pH).

Red blood cells

Red blood cells or erythrocytes are cells without a nucleus. These cells transport oxygen from the lungs to all over your body, while also taking care of discharging carbon dioxide to your lungs.

Blood that contains a lot of oxygen has a bright red color. Low-oxygen blood, on the other hand, is dark red. In our figures, we have given the low-oxygen blood a blue color to clearly show the difference.
Erythrocytes contain a red pigment that is called hemoglobin (also known as HbA1).
Hemoglobin is composed of four protein chains with an iron atom that can bind oxygen.

A low red blood cell count leads to anemia.

White blood cells

White blood cells or leukocytes protect your body against harmful substances and pathogens such as bacteria and mold.

There are five different types of white blood cells. How much of these white blood cells you have in your blood differs per type.

Neutrophil granulocytes

The largest portion, between 40% and 75%, of white blood cells in your blood are neutrophil granulocytes (the so-called neutros).

Neutros are involved in immune responses and phagocytosis (which is the absorbing, eating up) of micro-organisms such as bacteria and mold.

Eosinophil granulocytes

Eosinophil granulocytes (or eos) make up only a small portion, 1% to 2%, of all white blood cells.

Eosinophil granulocytes are involved in the destruction of parasites and allergic reactions.

Basophil granulocytes

Under 1% of all white blood cells are basophil granulocytes (the so-called basos).

These cells have an S-shaped nucleus and a large number of purple-blue granules in the cytoplasm. These granules contain, among other things, histamine.

These cells are responsible for anti-inflammatory responses.

Lymphocytes

Roughly one third of all white blood cells, between 20% and 40%, are lymphocytes (a.k.a. lymphos).

Lymphocytes are involved in immune responses and recognize foreign substances (so-called antigens).

Monocytes

2% to 10% of all white blood cells are monocytes (a.k.a. monos).

Monocytes are large round or oval-shaped cells. They have an irregularly shaped cell nucleus with 1 or 2 dents and blue-gray cytoplasm, which looks like it is covered in small granules.

Monocytes differentiate into macrophages and engulf all kinds of foreign substances through phagocytosis. They can kill infected cells, and clear up dead or damaged tissue.

Blood platelets

Blood platelets or thrombocytes are pieces of cell that make sure that blood clots when necessary.

Blood plasma

The blood plasma fulfills an important transport function and helps keep your body’s internal environment steady, such as by regulating your body temperature.