The Composition of Blood

 

I.                     Blood Plasma – the fluid portion of blood discounting the cells (formed elements)

A.      Composition – water containing man dissolved substances

B.       Amount of blood – varies with size, sex, and age.  Average is around 5 liters.  7% to 9% of body weight.

C.       Slightly alkaline (pH greater than 7 – averages 7.35 to 7.45)

II.                   Formed Elements

A.      Kinds:

1.        Erythrocytes (Red Blood Cells) – function is to transport oxygen (4.5 to 5 million per cubic millimeter)

2.        Leukocytes (White Blood Cells) – function is defense of the body (5,000 to 10,000 per cubic millimeter)

3.        Platelets (thrombocytes) – function is formation of clots (300,000 per cubic millimeter)

B.       Formation of blood cells occurs in red bone marrow.  Some lymphocytes and monocytes are formed by lymphatic tissue in the lymph nodes, thymus, and spleen.

III.                 Mechanisms of blood disease

A.      Most blood disorders result from failure of blood producing tissues

B.       Diseased bone marrow can sometimes be replaced by tissue transplanted from a donor

IV.                 Red Blood Cells

A.      Disk shaped – increases surface area for exchange of oxygen and carbon dioxide

B.       Functions – transport oxygen and carbon dioxide

V.                   Red Blood Cell disorders

A.      Anemia – inability of blood to carry adequate oxygen to tissues, characterized by:

1.        Abnormal red blood cell numbers

2.        Deficiency of hemoglobin

B.       Changes in RBC Numbers

1.        Hematocrit – test in which a centrifuge is used to separate whole blood into formed elements and liquid fraction; normal RBC volume is about 45% of total

2.        RBC Count – hemocytometer or automatic counter is used to calculate actual number of red blood cells (4.5 to 5.5 million per cubic millimeter is normal)

3.        Aplastic anemia – low RBC number caused by bone marrow destruction

4.        Pernicious anemia – low RBC number caused by lack of available vitamin B12.

5.        Folate-deficiency anemia – low RBC number caused by lack of vitamin B9 (folic acid)

C.       Changes in hemoglobin

1.        Both amount and quality of hemoglobin is important

2.        Hemoglobin concentration is often measured with optical devices

3.        Normal Ranges:

a         Female – 12-14 grams per deciliter

b         Male – 14-16 grams per deciliter

4.        Iron deficiency anemia – low hemoglobin caused by lack of iron

5.        Hemolytic anemia – abnormal hemoglobin that causes deformation and fragility of red blood cells

6.        Abnormal types of hemoglobin can be separated with electrophoresis for further study.

7.        Sickle Cell Anemia – inherited disorder in which abnormal hemoglobin causes characteristic RBC deformities.

8.        Thalassemia – inherited disorder in which a small amount of abnormal hemoglobin is produced

VI.                 White Blood Cells

A.      General function – defense

B.       Neutrophils and monocytes carry out phagocytosis

C.       Lymphocytes produce antibodies (B-Lymphocytes) or directly attack foreign cells (T-Lymphocytes)

D.      Eosinophils protect against parasites and irritants that cause allergies.

E.       Basophils produce heparin, which inhibits clotting.

F.       White Blood Cell Disorders

1.        Leukopenia – abnormally low WBC count

2.        Leukocytosis – abnormally high WBC count

3.        Leukemia – cancer; elevated WBC count; cells do not function properly

VII.               Platelets and blood clotting

A.      Platelets play an essential role in blood clotting

B.       Blood clot formation

1.        Clotting factors released at injury site produce prothrombin activator

2.        Prothrombin activator and calcium convert prothrombin to thrombin

3.        Thrombin triggers formation of fibrin, which traps RBC’s to form clot.

C.       Clotting Disorders

1.        Thrombosis – formation of an inappropriate stationary clot (thrombus)

2.        Embolism – dislodged blood clot (embolus)

3.        Hemophilia – X-linked inheritance of inability to form essential clotting factors

4.        Thrombocytopenia – Abnormally small number of platelets