Complete Blood Cell Count Lab

Complete Blood Cell Count

Background

Blood appears to be just a red fluid, but is actually made up of many different types of cells, molecules, and liquids.  The liquid portion of blood is called plasma and is 90% water.  Plasma is also made up of dissolved minerals such as potassium, sodium, and calcium.  Proteins, such as hormones and antibodies also travel through the blood.  The most common cellular components of blood include platelets, red blood cells, and white blood cells.  Blood cells are created within the bone marrow and then differentiate to perform different functions throughout the body.

Platelets

Platelets, or thrombocytes, are irregularly-shaped cells circulating in the blood.  Platelets are responsible for preventing excess blood loss by forming a “scab.”  When platelets are exposed to the air, they begin to break apart and react with fibrinogen, that then creates fibrin, which are tiny thread-like fibers.  Fibrin forms a web-like layer that prevents blood cells from passing through, and as this layer dries it hardens to form the scab that we see on the surface of a wound.

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Red Blood Cells

Red blood cells (RBCs), or erythrocytes, are primarily responsible for delivering oxygen throughout the body.  They are the most common type of blood cell, with approximately 20-30 trillion of them circulating within the blood vessels of an adult.  A single red blood cell will live for about 120 days, and completely circulates the body more than 75,000 times within its lifetime.

Mature red blood cells appear to be oval biconcave discs, and they do not have a nucleus in order to make room for hemoglobin. Hemoglobin is a large, iron-containing protein that is able to transport oxygen molecules and is also what gives red blood cells their red color. 

Capillaries surround the alveoli in the lungs.  As oxygen is brought into the alveoli, it will diffuse through the capillaries and bind to the hemoglobin on the red blood cells that are circulating.  The red blood cells with bound oxygen travel back to the heart and through larger blood vessels to eventually reach capillaries in body tissues.  The oxygen is released from hemoglobin to diffuse through the capillaries into the tissues that need it to survive.

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White Blood Cells

White blood cells (WBCs), or leukocytes, are responsible for immunity.  They have a much shorter life cycle than red blood cells, ranging from a few days to a few weeks.  The number of white blood cells in the blood varies greatly depending on whether they are fighting an infection.  They only make up approximately 1% of the blood volume in a healthy adult.

There are many different types of white blood cells based on their structure and function.  A major feature used to categorize white blood cells is the presence of granules within the cytoplasm.  White blood cells with granules are called granulocytes and without granules are agranulocytes.  These groups can be further broken down.  The table below summarizes the five most common types of white blood cells.  The granulocytes include neutrophils, eosinophils, and basophils, while the agranulocytes include lymphocytes and monocytes.

Types of White Blood Cells
Type	Percent of WBCs	Target	Diagram	Actual Appearance
Neutrophil	50 - 70%	Bacteria, fungi
Eosinophil	1 - 3%	Large parasites, allergic response, inflammatory response
Basophil	0.4 - 1%	Release histamine
Lymphocyte	25 - 35%	B cells, T cells, natural killer cells
Monocyte	4 - 6%	Differentiate into macrophages or dendritic cells

Blood Cell Count

A healthy adult has about 4.5 to 5 million red blood cells and approximately 8,000 white blood cells in each drop of blood.  Determining the number of red and white blood cells can assist a healthcare specialist in the diagnosis of disease.  A decrease in the number of red blood cells may indicate a condition known as anemia.  A lack of red blood cells means a lack of oxygen, which can lead to symptoms such as fatigue, headache, paleness, shortness of breath, and even fainting.  The presence of anemia can help direct a physician to a specific diagnosis.  A decrease or increase in the number of white blood cells can also indicate a problem.  For example, a large increase in white blood cells is commonly indicative of an infection. 

A complete blood cell count (CBC) is a common procedure performed to determine the number of red and white blood cells in an individual.  A hemocytometer is a specialized counting chamber used for blood cell counts.  Blood is diluted and added to the surface of the hemocytometer that contains a grid.  The number and types of cells located within each square of the grid are counted using a microscope, and are used to estimate the total amounts in blood.  In the following activity, you will use a simulated hemocytometer sample to estimate the red and white blood cell count for your patients.

The Franklin Institute.  2013.  Blood.  The Human Heart, The Franklin Institute, www.fi.edu.

Gartner, L. and Hiatt, J.  2007.  Leukocytes.  Color Textbook of Histology, Saunders Elsevier.