What are the components of blood?

Your blood is made up of liquid and solids. The liquid part, called plasma, is made of water, salts, and protein. Over half of your blood is plasma. The solid part of your blood contains red blood cells, white blood cells, and platelets.

See also:

What is the path blood takes through the Circulatory System?

What are the parts of the hearts?

How does the heart work?

red blood cell next to platelet and white blood cell

By Electron Microscopy Facility at The National Cancer Institute at Frederick (NCI-Frederick)-- Red blood cell (red), Platelet (yellow), white blood cell (blue)--From left to right: erythrocyte, thrombocyte, leukocyte

Red Blood Cells

Red blood cells (RBC) also called erythrocytes, deliver oxygen from your lungs to your tissues and organs. Blood cells constantly die and your body makes new ones. Red blood cells live about 120 days. Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen (O2) to the body tissues—via blood flow through the circulatory system. The cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the red color of the cells. Carbon monoxide is so dangerous because it binds much stronger to hemoglobin that oxygen.

White Blood Cells

White blood cells (WBCs), also called leukocytes or leucocytes. They are a component of the immune system that is involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from cells in the bone marrow known as hematopoietic stem cells. Leukocytes are found throughout the body, including the blood and lymphatic system. Some white blood cells live less than a day, but others live much longer. All white blood cells have nuclei, which distinguishes them from the other blood cells, such as red blood cells and platelets.

The two main categories of white blood cells are granulocytes and agranulocytes. Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm.



Neutrophils (a type of granulocyte) are the most abundant of all the WBCs. Neutrophil are the most abundant type of granulocytes and the most abundant (40% to 75%) type of white blood cells in most mammals. They form an essential part of the innate immune system.They are formed from stem cells in the bone marrow. They are short-lived and highly motile, or mobile, as they can enter parts of tissue where other cells/molecules wouldn't be able to enter otherwise.Neutrophils are a type of phagocyte and are normally found in the bloodstream. During the beginning (acute) phase of inflammation, particularly as a result of bacterial infection, environmental exposure, and some cancers, neutrophils are one of the first-responders of inflammatory cells to migrate towards the site of inflammation. They are the predominant cells in pus, accounting for its whitish/yellowish appearance.


Eosinophils are a type of white blood cells and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. Along with mast cells, they also control mechanisms associated with allergy and asthma. They are granulocytes that develop during hematopoiesis in the bone marrow before migrating into blood.

Mast Cell (Mastocyte)

Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing, angiogenesis, immune tolerance, defense against pathogens, and blood–brain barrier function. Mast cells are very similar to basophil granulocytes (a class of white blood cells) in blood. Both are granulated cells that contain histamine and heparin, an anticoagulant. Both cells also release histamine upon binding to immunoglobulin E


A basophil is a type of white blood cell. Basophils are the least common of the granulocytes, representing about 0.5 to 1% of circulating white blood cells. However, they are the largest type of granulocyte. They are responsible for inflammatory reactions during immune response, as well as in the formation of acute and chronic allergic diseases, including anaphylaxis, asthma, atopic dermatitis and hay fever. They can perform phagocytosis (cell eating), produce histamine and serotonin that induce inflammation, and heparin that prevents blood clotting.


Agranulocytes, also known as mononuclear leukocytes, are white blood cells with a one-lobed nucleus. They are characterized by the absence of granules in their cytoplasm, which distinguishes them from granulocytes. The 2 types of agranulocytes in the blood circulation are lymphocytes and monocytes. A third type of agranulocyte, the macrophage, is formed in the tissue when monocytes leave the circulation and differentiate into macrophages.


Lymphocytes include natural killer cells (NK cells) (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic adaptive immunity), and B cells (for humoral, antibody-driven adaptive immunity). They are the main type of cell found in lymph, which prompted the name lymphocyte. T cells are involved in cell-mediated immunity, whereas B cells are primarily responsible for humoral immunity (relating to antibodies). The function of T cells and B cells is to recognize specific “non-self” antigens, during a process known as antigen presentation.


They are the largest type of leukocyte and can differentiate into macrophages or dendritic cells. As a part of the vertebrate innate immune system monocytes also influence the process of adaptive immunity. Monocytes are amoeboid in appearance, and have a granulated cytoplasm.


Macrophages are a type of white blood cell that engulfs and digests cellular debris, foreign substances, microbes, cancer cells, and anything else that does not have the types of proteins specific of healthy body cells on its surface in a process called phagocytosis. These large phagocytes are found in essentially all tissues, where they patrol for potential pathogens by amoeboid movement.


Platelets help blood to clot when you have a cut or wound. Bone marrow, the spongy material inside your bones, makes new blood cells. and platelets live about 6 days. Like red cells, platelets (thrombocytes) have no nucleus. However, unlike red cells that originate in the marrow as nucleated cells and lose their nucleus, platelets are produced by budding off from a giant multinucleated marrow cell called a megakaryocyte.

Blood Plasma

Blood plasma is the pale yellow colored liquid component of blood that normally holds the blood cells in whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the intravascular fluid part of extracellular fluid (all body fluid outside of cells). It is mostly water (up to 95% by volume), and contains dissolved proteins (6–8%) (i.e.—serum albumins, globulins, and fibrinogen), glucose, clotting factors, electrolytes (Na+, Ca2+, Mg2+, HCO3−, Cl−, etc.), hormones, and carbon dioxide . Plasma also serves as the protein reserve of the human body. It plays a vital role in an intravascular osmotic effect that keeps electrolytes in balanced form and protects the body from infection and other blood disorders.

Blood Types

There are four blood types: A, B, AB, or O. Also, blood is either Rh-positive or Rh-negative. So if you have type A blood, it's either A positive or A negative. Which type you are is important if you need a blood transfusion. And your Rh factor could be important if you become pregnant - an incompatibility between your type and the baby's could create problems.

Test your Understanding:

1. The purpose of hemoglobin is:
a) to bind carbon monoxide to prevent poisoning
b) to help the blood to clot
c) to bind and transport oxygen to cells
d) to help fight infection

2. Blood Plasma contains which of the following component
a) water
b) proteins
c) sugar and electrolytes
d) All of the above

3. What statement best describes Macrophages?
a) they are white blood cells that produce antibodies
b) they are cells primarily responsible for allergic responses
c) they are large phagocytes that are found in most parts of the body
d) they are granulocytes that turn into mast cells

4. Which of the following statements in not correct?
a) There are four blood types: A, AB, O and B
b) plasma also serves as the protein reserve for the body
c) platelets like most cells have a nucleus
d) Plasma is mostly water (95%)

5. The cell responsible for humoral, antibody-driven adaptive immunity is
a) T-Cell
b) B- cell
c) Macrophage