ASCP Phlebotomy Technician (PBT) Exam

Anatomy is the study of body structures and their physical relationships. Physiology is the study of how these structures function. Phlebotomy technicians must understand basic anatomy and physiology to perform specimen collection safely and effectively. Knowledge of body systems helps technicians locate veins, understand how diseases affect laboratory values, and communicate with healthcare providers using proper terminology.

The human body is organized into levels of complexity: atoms, molecules, organelles, cells, tissues, organs, organ systems, and the organism. Cells are the basic structural and functional units of life. Groups of similar cells form tissues. Four primary tissue types exist: epithelial (covering and lining), connective (support and protection), muscle (movement), and nervous (communication and control). Organs are structures composed of two or more tissue types that perform specific functions. Organ systems are groups of organs that work together to accomplish complex functions.

Homeostasis is the maintenance of a stable internal environment despite external changes. The body constantly monitors and adjusts variables such as temperature, pH, glucose levels, and fluid balance. Disruption of homeostasis leads to disease states that phlebotomists help diagnose through specimen collection.

The muscular system comprises approximately 700 muscles accounting for 40–50% of body weight. Primary functions include movement, posture maintenance, heat production, and protection of internal organs. Muscles work with bones as lever systems to produce movement.

Skeletal muscle attaches to bones via tendons and produces voluntary movement. Cells are long, cylindrical, multinucleated fibers with visible striations (alternating light and dark bands). Skeletal muscle is under conscious control through the somatic nervous system. Examples include biceps brachii, quadriceps femoris, and deltoid.

Skeletal muscle fibers contain myofibrils composed of thick (myosin) and thin (actin) filaments arranged in repeating units called sarcomeres. The sarcomere is the functional unit of muscle contraction. During contraction, actin filaments slide over myosin filaments, shortening the sarcomere (sliding filament theory).

Cardiac muscle is found exclusively in the heart wall (myocardium). Cells are branched, striated, and typically uninucleated. Intercalated discs connect adjacent cells and contain gap junctions that allow rapid electrical impulse transmission. Cardiac muscle is involuntary and self-excitable (autorhythmic). The sinoatrial node initiates heartbeats without external stimulation.

Smooth muscle is found in walls of hollow organs including blood vessels, digestive tract, urinary bladder, and uterus. Cells are spindle-shaped, non-striated, and uninucleated. Smooth muscle is involuntary and controlled by the autonomic nervous system and hormones. Contraction is slower but more sustained than skeletal muscle.

Motor neurons communicate with skeletal muscle fibers at the neuromuscular junction. The axon terminal releases acetylcholine (ACh) into the synaptic cleft. ACh binds to receptors on the muscle fiber membrane (sarcolemma), triggering an action potential. The action potential travels along the sarcolemma and into T-tubules, stimulating calcium release from the sarcoplasmic reticulum. Calcium enables actin-myosin interaction and contraction.

Adenosine triphosphate (ATP) provides immediate energy for muscle contraction. ATP stores are limited and must be continuously regenerated. Three systems produce ATP:

Prolonged activity depletes ATP and accumulates metabolic byproducts including lactic acid, inorganic phosphate, and potassium ions. These factors reduce muscle force production. Recovery requires oxygen to clear metabolic waste and replenish energy stores.

Muscle enzymes enter the bloodstream when muscle cells are damaged. Creatine kinase (CK) and lactate dehydrogenase (LDH) are commonly measured to assess muscle injury. Elevated CK levels occur with myocardial infarction, muscular dystrophy, rhabdomyolysis, and strenuous exercise. Intramuscular injections may also elevate CK levels.

Tourniquets cause muscle ischemia during venipuncture. Prolonged tourniquet application (greater than one minute) increases potassium, lactate, and protein concentrations in blood samples. Repeated fist clenching (pumping) during blood draw should be avoided as it raises potassium levels.

Patients with neuromuscular disorders may have fragile veins, limited mobility, or difficulty following instructions during collection. Muscular patients may have deeper veins requiring longer needles or different angle of insertion.