Peripheral blood is the fluid that circulates throughout the body’s vessels, including arteries, capillaries, and veins. It serves as a transport system, delivering oxygen and nutrients to tissues and cells while simultaneously removing carbon dioxide and other waste products. Beyond its role in transport, peripheral blood also participates in the body’s immune responses and helps regulate body temperature. It is the blood that can be readily sampled from a vein, typically in the arm, for various medical assessments.
Components of Peripheral Blood
Peripheral blood is a complex fluid with distinct elements. It consists of liquid plasma, suspending cellular components like red blood cells, white blood cells, and platelets.
Red blood cells, also known as erythrocytes, are the most abundant cellular component, making up about 40% of the blood’s volume in adults. These tiny biconcave disks lack a nucleus and are primarily responsible for oxygen transport. They contain hemoglobin, an iron-rich protein that binds to oxygen in the lungs and delivers it to body tissues, while also carrying carbon dioxide back to the lungs for expulsion.
White blood cells, or leukocytes, are larger than red blood cells but less numerous. Their main function is to provide immune defense against infections and foreign invaders. These cells include types like neutrophils, which ingest bacteria, and lymphocytes, which are involved in specific immune responses. Monocytes can also become macrophages, removing foreign materials.
Platelets, also called thrombocytes, are small cell fragments derived from megakaryocytes in the bone marrow. Their primary role is in blood clotting, a process known as hemostasis. When a blood vessel is damaged, platelets gather at the injury site and clump together to form a plug, helping to seal the vessel and initiate further clot formation.
Plasma is the liquid portion of blood, accounting for approximately 55% of the total blood volume. It is primarily composed of water, about 90%, and contains dissolved proteins, salts (electrolytes), hormones, and nutrients. Key proteins include albumin, which helps maintain fluid balance, and antibodies, which fight infections. Plasma also contains clotting factors, essential for blood coagulation.
Role in Health and Diagnostics
Peripheral blood plays an important role in assessing health and diagnosing medical conditions. Healthcare providers frequently use blood samples for diagnostic tests, offering a minimally invasive way to gather information about circulating cells and reveal insights into overall health or disease.
One common diagnostic test that utilizes peripheral blood is the Complete Blood Count (CBC). A CBC measures the number and size of red blood cells, white blood cells, and platelets, along with hemoglobin and hematocrit levels. Abnormalities in these counts can indicate various conditions; for instance, low red blood cell levels may suggest anemia, while elevated white blood cell counts can point to an infection or inflammation.
Often, a healthcare provider may order a peripheral blood smear (PBS) in conjunction with or after a CBC, especially if the CBC results show abnormalities. In a PBS, a small drop of blood is spread thinly on a glass slide, stained, and then examined under a microscope by a trained technician or pathologist. This microscopic examination allows for a detailed assessment of the morphology (shape, size, and structure) of individual blood cells.
Examining the peripheral blood smear can reveal specific cellular abnormalities not detected by automated CBC machines. For example, abnormally shaped red blood cells might suggest nutritional deficiencies, certain inherited disorders like sickle cell disease, or chronic diseases. The presence of immature white blood cells or changes in their appearance can indicate conditions such as leukemia, other bone marrow disorders, or parasitic infections. This detailed visual analysis provides specific insights into blood cell health, aiding in the diagnosis and monitoring of a wide range of blood-related conditions.