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Components of Blood

1) The main function of blood is to transport oxygen to tissues througout the body and transport carbon dioxide back to the lungs.

2) Blood has other critical roles as well though. It transports nutrients, wastes and hormones. It also transports white blood cells (leukocytes) that are part of the immune system.

3) Blood is technically classified as a connective tissue making it the only fluid connective tissue in the human body.

4) Blood can be centrifuged (spun really fast) to separate out the various components. Erythrocytes (red blood cells) comprise about 41% of the volume of blood. The buffy coat comprises about 4% or less and consists of leukocytes (white blood cells) and platelets. These components all spin to the bottom.

Composition of Blood Hematocrit

5) About 55% of blood is plasma which is the liquid non-cell component of blood. These percentages can vary depending on the person and the time the blood is collected. The plasma is basically water with dissolved nutrients, hormones and proteins.

6) Red blood cells (erythrocytes) are responsible for carrying oxygen throughout the body. They contain a protein called hemoglobin which binds oxygen.

Hemoglobin Figure

7) The hemoglobin protein has an iron containing molecule called heme. Heme is the part of hemoglobin the oxygen binds. Each protein of hemoglobin has 4 heme molecules, thus 4 oxygen binding sites per hemoglobin protein. And- one red blood cell contains 250 million hemoglobin molecules!

8) Remember, hemoglobin is a protein, while heme is a compound that binds to hemoglobin. Iron is an element bound to heme.

Heme Chemical Structure

9) So, oxygen binds to the iron component of heme bound to hemoglobin isnide of red blood cells. Inside the lungs, hemoglobin picks up oxygen in the pulmonary alveoli. The blood is then pumped throughout the body where oxygen is released to cells.

Hemoglobin Oxygen Release Figure

10) There are several types of white blood cells (leukocytes. These can be divided into the granulocytes and agranulocytes (based on whether granules can be observed inside them). The granulocytes are neutrophils, eosinophils and basophils. The agranulocytes are monocytes and lymphocytes.

Labelled Diagram of White Blood Cells

11) Hematopoiesis is process of blood cell formation. All blood cells are derived from hematopoietic stem cells located in bone marrow.

Origin of Blood Cells Diagram

12) Red blood cells have no nucleus (anucleate) and last for about 120 days before being broken down by the spleen.

13) Erythropoietin is the hormone produced by the kidneys which stimulates production of blood cells.

14) Platelets are required for blood clotting. They are derived from cells called megakaryocytes.

Blood Coagulation

15) Anemia is a condition where people have a low number of red blood cells or they have red blood cells with a decreased ability to carry oxygen. Sickle cell anemia is a genetic disease causing red blood cells to have an abnormal shape.

Anemia Diagram