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Notes on Blood

Blood is composed of cells (corpuscles) and a liquid intercellular ground substance called

plasma.

The average blood volume is 5 to 6 liters (7% of body weight).

Blood volume components:

55% plasma

45% cellular elements

Plasma

Over 90% of plasma is water. The balance is made up of plasma proteins and dissolved

electrolytes, hormones, antibodies, nutrients, and waste products.

Plasma is isotonic (0.85% NaCl).

Plasma proteins (albumin, globulin, and fibrinogen) are responsible for the viscosity of blood,

for carrying immune material, and for controlling osmotic pressure. Fibrinogen, in bleeding, is

transformed into fibrin and helps form a clot. Plasma defibrinated by clotting is known as blood

serum.

Blood Cells

There are two types of blood cells:

(1) red blood cells (RBC) erythrocytes

(2) white blood cells (WBC) leukocytes

I. Red Blood Cells (Erythrocytes)

Mature RBCs lack a nucleus and the cells are biconcave disks roughly 7.7 micrometers in

diameter.

The normal RBC hematocrit is about 36 to 45.

The normal RBC counts are:

(1) 5.2 X 106/mm3 for males

(2) 4.5 X 10

6

/mm

3

for females

Hemoglobin is a complex molecule of iron and protein and is present in the RBC. RBCs carry

oxygen from the lungs to the tissues (in the form ofoxyhemoglobin) and transport carbon

dioxide from the tissues to the lungs.

Typical RBC lifetime ~ 3 months.

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RBCs are removed from circulation by the spleen and replaced by new RBCs formed in bone

marrow. In the breakdown of hemoglobin, bilirubin is excreted and iron is retained.

II. White Blood Cells (Leukocytes)

As opposed to RBCs, WBCs have nuclei and exhibit ameboid movement.

The normal WBC count in circulating blood is about 5 X 103/mm3 to 9 X 103/mm3.

WBCs contain phosphatases, liberate proteolytic enzymes, and function mainly in phagocytosis,

proteolysis, and antibody formation.

Leukocytosis an increase in the number of leukocytes.

Leukopenia a decrease in the number of leukocytes.

There are two main types of leukocytes: nongranular and granular.

Nongranular leukocytes include lymphocytes and monocytes.

1. Lymphocytes make up between 20% and 25% of total leukocytes and are seldom phagocytic.

Lymphocytes:

1. Originate from lymphoid tissue and bone marrow

2. Function in immunologic responses and the detoxification of noxious substances

3. Are prevalent at sites of chronic inflammation

Some lymphocytes live several years.

2. Monocytes make up between 3% and 8% of total WBC. They are sometimes phagocytic andhelp in debridement.

Granular leukocytes include neutrophils, eosinophils, andbasophils.

1. Neutrophils make up 65% to 75% of leukocytes. They are twice as large as a RBC and

possess a lobulated nucleus.

Neutrophils are the most active and phagocytic (as they provide the first line of defense against

invading organisms).

Dead neutrophils become pus.

2. Eosinophils make up about 2% to 5% of WBCs.

Eosinophils possess large red acidophilic granules and a bilobed nucleus.

Eosinophils are found at the sites of parasitic infections and allergic reactions (particularly in the

GI and respiratory tract) and function in the destruction of antigen-antibody complexes.

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3. Basophils make up 0.5% or less of the total WBC count.

Basophils are rarely phagocytic and contain large quantities of basophilic granules.

Basophils are involved in immune phenomena, and produce heparin, which prevents the clotting

of blood.

Blood platelets are cytoplasmic structures which are not true cells but are cell fragments

characteristic of mammalian blood.

Typical platelet count is about 250,000/mm3 to 350,000/mm3 and are typically about 3 microns

in diameter.

Platelet structures arise by the fragmentation of cytoplasmic processes of giant bone marrow

cells. Platelets agglutinate and adhere to regions of injured vessels. They help physically in

clotting and form thromboplastin (thrombokinase), an integral component of clot formation.

Blood Clotting

Platelets contribute thromboplastin (thrombokinase). The thromboplastic interacts with calcium

ions and prothrombin (a plasma protein). Prothrombin is an inactive precursor of the catalyst

thrombin. In the presence of these components, prothrombin is converted to thrombin.

Subsequently thrombin reacts with the plasma protein fibrinogen, forming fibrin.

Fibrin is an insoluble, coagulated protein which clots.

The clotting reaction can be represented as follows:

platelets thromboplastin

prothrombin + Ca2+ thrombin

fibrinogen fibrin

An anticoagulant is a substance that retards or prevents the coagulation of blood. Examples

include heparin, aspirin, and the drug Dicumarol (bihydrocycoumarin).

Blood Pressure

Blood pressure is usually measured by placing a sphygmomanometer cuff around the arm

compressing the brachial artery and vein.

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Maximum blood pressure is obtained during ventricular systole and minimum blood pressure

indicates ventricular diastole.

The normal blood pressure listed for a young adult is 120 mmHg systolic and 80 mmHg

diastolic.