Erythrocytes and Blood

BLOOD

Blood is a red viscous fluid that is composed of 55% plasma and 45% cellular elements. The plasma is comprised of approximately 92% water, 7% proteins, and the remainder of minerals, vitamins, oxygen, electrolytes, carbohydrates, lipids, and carbon dioxide. The cellular elements of the blood are leukocytes, erythrocytes, and platelets. The leukocytes are divided into neutrophils, eosinophils, basophils, lymphocytes, and monocytes.

THE IMPORTANCE OF THE ANALYSIS OF BLOOD IN HEALTH CARE DELIVERY

Blood is the most often tested tissue in hospitalized patients or when visiting the clinic or physician’s office. Blood will reflect pathologic changes that take place in the internal organs of the body. The blood becomes a quick way to provide information about the functions of the body and the general overall of the body.

BONE MARROW

Bone marrow is a “soft”, hematopoietic tissue that is located in the flat bones of the adult skeleton. In young children, the entire skeleton contains hematopoietic marrow. Marrow consists of veins, venous sinuses, connective tissue, fat cells, adventia cells and blood forming cells. Marrow is of two types, red and yellow. Yellow marrow is inactive, containing fat cells and a vascular network of vessels. The Red marrow is the site of cell formation and maturation. The erythromyeloid line of cells are formed in the bone marrow. The lymphoid line of cells is formed in the lymphatic organs of the body.

BLOOD IN THE VASCULAR SYSTEM

The blood in the vascular system and heart will make up about 7% to 8% of the total body weight. The average adult male (about 155 pounds), contains from 5.5 to 6.0 liters (10 to 12 pints) of blood. A large person will contain more blood than a smaller person and males contain more blood than a female. There is approximately 32 mls of blood per pound of body weight.

FORMATION OF RED BLOOD CELLS

Erythrocytes develop from a pluripotent hematopoietic stem cell that under the stimulus of certain cytokines will develop into a progenitor cell line designated by the general term, erythromyeloid stem cell. With proper cell chemical stimulus, the cell will then maturate into a cell designated as a burst forming unit-erythrocyte (bfu-e) which can form 1000 like cells.


The next maturation step yields a colony-forming unit-erythrocyte (cfu-e), which can divide into 64 cells. The rubriblast rises from the cfu-e cell and is the first visually recognized cell in the erythrocyte series. The order of maturation proceed to the prorubricyte, rubricyte, metarubricyte, reticulocyte, and finally the mature erythrocyte. The mature erythrocytes will live up to 120 days and is then replaced.

HEMOGLOBIN MOLECULE AND ITS ROLE IN THE BODY

Hemoglobin synthesis begins in the rubriblast and continues through the development of the reticulocyte. Normal hemoglobin synthesis begins with the cell joining glycine and succinylCoA in a process that synthesizes a non-protein molecule, a pyrrole ring, when combined with iron forms heme. Four polypeptide molecules (two designated as alpha chains and two designated as beta chains to form hemoglobin A) molecule combine with four heme structures to form the hemoglobin molecules. It takes 300 million hemoglobin molecules to fill an erythrocyte. A hemoglobin molecule can combine with four oxygen molecules to form oxyhemoglobin. If hemoglobin is not combined with oxygen, it is called reduced hemoglobin.


The adult male will contain about 14 to 18 grams of hemoglobin per 100 mLs. The adult female will contain 12 to 16 grams in the same volume. Hemoglobin can combine with carbon dioxide to form carbaminohemoglobin, which is transported from the tissues to the lungs.Other normal globin molecules are the delta chains (that combine with alpha chains) to form A2 type of hemoglobin (normally about 3% of the hemoglobin in the adult). Gamma chains combine with alpha chains to form fetal (F) hemoglobin. Fetal hemoglobin is replaced during the first year of life with normal adult hemoglobin, designated as hemoglobin A. Any deviation in the hemoglobin chains produces an abnormal hemoglobin.

AGING AND FATE OF ERYTHROCYTES

The red blood cells circulates through the body over the course of 120 days and is subjected to mechanical stresses as it passes through capillaries and the spleen. The membrane of the RBC that undergoes mechanical damage is removed from circulation by the macrophages that are found in the spleen. The heme and globin are released back into circulation where the iron and protein components are re-utilized. Heme is converted to biliverden, then to bilirubin. Bilirubin is excreted by the liver into the bile duct and eventually discharged into the intestine.

THE EFFECTS OF SMOKING ON BLOOD

Cigarette smoking induces erythrocytosis and an oxygen debt. Carbon monoxide, a by-product of smoking, binds to hemoglobin 200 times stronger than oxygen, forming carboxyhemoglobin which can make up to 8% of the total hemoglobin. There will be a resultant increased risk of coronary heart disease, impaired circulation in the lower legs, and decreased night vision.

THE IMPORTANCE OF INDICES CALCULATIONS IN BLOOD TESTING

The RBC indices is a mathematical calculation to yield three clinical parameters useful in diagnosing anemia. The first indices is the Mean Corpuscular Volume (MCV) average RBC volume is calculated by dividing the hematocrit value by the RBC count value. Normal values are 80 to 100 femtoliters (fL). If the value is below 80 fL, then this indicates microcytic anemia. A value greater than 100 would suggest macrocytic anemia. The second indices is the Mean Corpuscular Hemoglobin (MCH).

This describes the hemoglobin content of each RBC and is obtained by dividing the hemoglobin value by the RBC count value. The normal value ranges from 27 to 32 picograms (pg). Values below 27 pg are suggestive of hypochromic anemia. The third indices is the Mean Corpuscular Hemoglobin Concentration (MCHC), describing the hemoglobin concentration in RBC’s. Normal values range from 31 to 36 g/dL. Low value suggest hypochromic anemias. Note: Indices normal values may vary slightly from region to region or lab to lab.