Peripheral Blood Lab

Introduction

Blood provides a mechanism by which nutrients, gases, and wastes can be transported throughout the body. It consists of a number of cells suspended in a fluid medium known as plasma. The cells of the blood consist of erythrocytes, platelets, and leukocytes or white blood cells. Erythrocytes are responsible for transporting gases,

The cells of the blood are important because they are a readily accessible population whose morphology, biochemistry, and ecology may give indications of a patient's general state or clues to the diagnosis of disease. For this reason, the complete blood count (CBC) and the differential white cell count are routinely used in clinical medicine. It is very important to be able to recognize normal blood cells and to distinguish pathological cells from the normal variants.

The identification of blood cells is based primarily on observations of the presence or absence of a nucleus and cytoplasmic granules. Other helpful features are cell size, nuclear size and shape, chromatin appearance, and cytoplasmic staining. The chart at the end of this section explains what to look for in the effort to identify the component cells of a blood smear.

Erythrocytes

Erythrocytes, or red blood cells, are by far the predominant cell type in the blood smear. They appear as biconcave discs of uniform shape and size (7.2 microns) that lack organelles and granules. Red blood cells have a characteristic pink appearance due to their high content of hemoglobin. The central pale area of each red blood cell is due to the concavity of the disc. Also visible in this slide are several platelets, which play a crucial role in the blood clotting cascade.

Neutrophils

Neutrophils are by far the most numerous of the leukocytes. They are characterized by a nucleus that is segmented into three to five lobes that are joined by slender strands. The cytoplasm of neutrophils stains a pale pink. Its primary (larger) granules contain acid hydrolases and cationic proteins, and its secondary (smaller) granules contain a variety of antimicrobial substances used to destroy bacteria that they phagocytose during the acute inflammatory response.

Eosinophils

Eosinophils are larger than neutrophils and are distinguished by bilobed nucleus and large red or orange granules of uniform size. These granules contain major basic protein, which is released to kill organisms too large to phagocytose, such as parasites and helminthes (worms). Eosinophils make up between 1 and 3% of the total white blood cells in the human blood.

Basophils

Basophils are intermediate in size between neutrophils and eosinophils and have simple or bilobed nuclei. They contain many coarse purple granules that can vary in size or shape. These granules contain histamine, which is released to cause a vasoactive response in hypersensitivy reactions, and heparin, which is an anticoagulant. Basophils are not phagocytic.

Lymphocytes

Lymphocytes can appear either small or large. The small lymphocyte is about the same size as an erythrocyte and contains a dark nucleus with a thin rim of surrounding cytoplasm. Lymphocytes do not contain visible granules. Small lymphocytes are inactive. Large lymphocytes (10 - 15 microns) contain more cytoplasm than small lymphocytes, and the cytoplasm remains basophilic. Large lymphocytes are active B or T cells. It is not possible to distinguish B- and T-lymphocytes at this level of magnification.

Monocytes

Monocytes are larger than lymphocytes and granulocytes and contain nuclei that often contain an indentation on one side. The cytoplasm contains small granules with lysosomal enzymes and peroxidase. Monocytes are phagocytic cells that are important in the inflammatory response.

Lab Quiz

1. Identify the blood cell.

Answer: Monocyte
2. Identify the blood cell.

Answer: Eosinophil
3. Identify the blood cell.

Answer: Neutrophil
4. Identify the blood cell in the middle.

Answer: Basophil
5. Identify the blood cell.

Answer: Lymphocyte