Chapter 2: The Body's Physical Systems

Using cystic fibrosis as an illustrative case study, the material demonstrates how dysfunction in one system creates cascading effects throughout the body and influences psychological well-being and social functioning. The nervous system serves as the body's primary communication network, with billions of neurons transmitting electrochemical signals through dendrites, axons, and synaptic connections facilitated by neurotransmitters and glial support. The central nervous system, comprising the brain and spinal cord, coordinates complex mental processes, emotional regulation, and vital autonomic functions through specialized regions including the cerebrum, limbic system, cerebellum, and brainstem. The peripheral nervous system extends this control through somatic pathways governing voluntary movement and autonomic pathways regulating involuntary organ function via sympathetic and parasympathetic divisions. Complementing neural communication, the endocrine system employs hormones secreted by glands including the pituitary, adrenal, thyroid, and pancreas to regulate growth, stress responses, and metabolic processes. The digestive system breaks down food through mechanical and enzymatic action, absorbing nutrients across the small intestinal epithelium for cellular metabolism and energy production. Respiratory function exchanges oxygen and carbon dioxide across alveolar membranes, while the cardiovascular system distributes oxygenated blood and nutrients throughout the body via the heart's four chambers and complex vessel networks, with dysfunction contributing to hypertension and atherosclerosis. Blood composition includes plasma and cellular elements responsible for oxygen transport, immune defense, and hemostasis. The immune system provides multilayered protection through physical barriers, nonspecific phagocytic responses, and targeted lymphocyte-mediated immunity via T cells and antibody-producing B cells. System compromise through stress, malnutrition, or disease such as AIDS or autoimmune conditions reduces defensive capacity and overall physiological resilience.