Functions and Properties of Blood

Hematology is the study of blood, blood-forming tissues, as well as disorders associated with blood.

Functions - Blood serves 3 basic functions:

Transportation - Blood brings oxygen from the lungs to cells throughout the body, while taking carbon dioxide to the lungs. It also sends nutrients broken down in the gastrointestinal tract and hormones throughout the body. Finally, blood sends heat and waste products to the lungs, kidneys and and skin.

Regulation - Blood supports homeostasis for all bodily fluids. Since it is also mostly water, it helps to maintain body temperature, given the heat absorbing and cooling properties of water. Water content is influenced by blood osmotic pressure according to dissolved ions and proteins.

Protection - Blood clotting prevents excess blood loss due to injury. White blood cells, antibodies and other blood proteins protect against disease.

Physical characteristics

Viscosity 4.5 - 5.5 (where H₂O = 1.0)

Temperature 100.4F

pH 7.35 - 7.45

Salinity .85% - .90%

Volume 5 - 6 liters in males
4 - 5 liters in females

Physical Characteristics of Blood - Due to its many properties, blood is slightly more viscous than water. Normal blood temperature is slightly greater than normal body temperature at 100.4F. Also, pH is slightly alkaline at 7.35-7.45. Extracellular fluid is 20% blood, and makes up around 8% total body mass. The average adult male has a blood volume between 5 and 6 liters, while the average adult female has a blood volume between 4 and 5 liters. Blood volume and osmotic pressure are regulated by several negative feedback mechanisms. Those mechanisms of specific interest involve aldosterone, ADH and atrial natriuretic peptide.

Components of Blood
- Whole blood has 2 basic components:
Blood Plasma - Representing 55% of whole blood, plasma is an aqueous matrix of dissolved substances. Of plasma, water makes up 91.5%, while 7.5% makes up proteins. The remaining 1% is a mix of other solutes including electrolytes, enzymes, hormones and waste products. Though some proteins may also be found elsewhere in the body, plasma proteins are exclusively found in the blood to assist in maintaining osmotic pressure as one means of diffusion across capillary walls. There are 3 basic types of plasma proteins synthsized by hepatocytes (liver cells):

Albumins (54%)

Globulins (38%)

Fibrinogen (7%)

Gamma globulins are also known as immunoglobulins or antibodies. bacterial or viral invasion prompts the production of millions of antibodies, which bind to an antigen (invader).

Formed Elements - Representing 45% of whole blood, formed elements are almost entirely red blood cells (99%), while WBCs and platelets make up less than 1%. When run through a centrifuge RBCs tend to rest at the bottom of a test tube while plasma rises to the top. In between, a thin coat of WBCs and platelets form a thin layer. Platelets are actually cell fragments. WBCs have a wider variety of roles. WBCs have 5 distinct types:

Neutrophils

Lymphocytes

Monocytes

Eosinophils

Basophils

Hematocrit - The hematocrit represents the percentage (%) of total blood volume comprised of RBCs. For females the average is 42% (38-46%), while for males the average is slightly higher at 47% (40-54%) due to higher levels of testosterone in males. Testosterone promotes synthesis of EPO (erythropoietin), which contributes to a higher RBC count.
Anemia is a greatly reduced hematocrit level

Polycythemia is an increase in hematocrit of at least 65%, which may result from tissue hypoxia, accelerated RBC production, dehydration and induced polycythemia (blood doping) abuse by athletes. Because RBCs are a principle transporter of oxygen to muscles, athletes often seek to enhance their endurance with drugs like Procrit or Epogen by increasing the oxygen-carrying capacity of blood. These drugs are normally used to treat anemia. Athletic training at high altitudes also induces a natural rise in hematocrit as a decrease in oxygen promotes EPO production, which in turn stimulates RBC production. The primary disadvantage of polycythemia is the increased viscosity of blood also increases resistance of bloodflow, thereby placing greater burdon on the heart, as well as an increase in blood pressure and risk of stroke. Though its use is banned in most major athletic competitions Epoetin alfa (procrit/epogen) is virtually undetectable, due to the fact that it is virtually identical to naturally occurring EPO.

Summary of Formed Elements:

Name

Concentration

Characteristics

Functions

Erythrocytes (RBCs)
4.8 Million/microliter in females
5.4 Million/microliter in males Biconcave disc
no nucleus
120 day lifespan Transports oxygen and carbon dioxide

Neutrophils
60% - 70% WBC concentration Has 2-5 lobes joined by chromatin with a fine, pale granular cytoplasm Phagocytosis. Uses lysozyme, super oxides and peroxides to destroy antigens.

Eosinophils
2% - 4% WBC concentration has 2 - 3 lobes with large red/orange granules. Responds to histamine in allergic reactions. Phagocytosis. destroys parasitic worms.

Basophils
0.5% - 1% WBC concentration 2 lobes with large, deep blue/purple granules Intensify inflammatory response by liberating heparin, histamine and seratonin

Lymphocytes
20% - 25% WBC concentration T/B cells. Cytoplasm forms ring around nucleus Mediates immune response. B cells become plasma cells that form antibodies. T cells attack viruses, cancer cells and transplanted tissue cells.

Monocytes
3% - 8% WBC concentration kidney-shaped nucleus with blue/gray cytoplasm Becomes machrophage before phagocytosis

Thrombocytes (Platelets)
150,000 - 400,000/microliter cells fragments, no nucleus Forms platelet plug in hemostasis, and releases chemicals to promote vascular spasms and blood clotting.

	Physical characteristics
Viscosity	4.5 - 5.5 (where H₂O = 1.0)
Temperature	100.4F
pH	7.35 - 7.45
Salinity	.85% - .90%
Volume	5 - 6 liters in males 4 - 5 liters in females

Name	Concentration	Characteristics	Functions
Erythrocytes (RBCs)	4.8 Million/microliter in females 5.4 Million/microliter in males	Biconcave disc no nucleus 120 day lifespan	Transports oxygen and carbon dioxide
Neutrophils	60% - 70% WBC concentration	Has 2-5 lobes joined by chromatin with a fine, pale granular cytoplasm	Phagocytosis. Uses lysozyme, super oxides and peroxides to destroy antigens.
Eosinophils	2% - 4% WBC concentration	has 2 - 3 lobes with large red/orange granules.	Responds to histamine in allergic reactions. Phagocytosis. destroys parasitic worms.
Basophils	0.5% - 1% WBC concentration	2 lobes with large, deep blue/purple granules	Intensify inflammatory response by liberating heparin, histamine and seratonin
Lymphocytes	20% - 25% WBC concentration	T/B cells. Cytoplasm forms ring around nucleus	Mediates immune response. B cells become plasma cells that form antibodies. T cells attack viruses, cancer cells and transplanted tissue cells.
Monocytes	3% - 8% WBC concentration	kidney-shaped nucleus with blue/gray cytoplasm	Becomes machrophage before phagocytosis
Thrombocytes (Platelets)	150,000 - 400,000/microliter	cells fragments, no nucleus	Forms platelet plug in hemostasis, and releases chemicals to promote vascular spasms and blood clotting.