Human body systems and disease mechanisms
Anatomy describes structures and their relationships, while physiology explains their functions. Disease reasoning connects a change in a structure or process with observed consequences. Keep a symptom, a sign, an underlying mechanism and a confirmed diagnosis distinct. A single symptom can arise through several pathways, so an examination question should supply enough context for its intended comparison rather than imply that one common complaint identifies one disease.
Circulation and respiration work together without being the same process. The right side of the heart pumps blood into the pulmonary circulation, and the left side supplies the systemic circulation. Arteries carry blood away from the heart and veins return it; oxygen content is not the definition of either vessel class. Gas exchange depends on surface area, barrier properties and partial-pressure gradients. In a supplied model, cardiac output equals heart rate times stroke volume: 75 beats per minute times 80 millilitres per beat gives 6 litres per minute. This is a calculation from the stated data, not a claim about every healthy or ill person.
The kidney filters plasma and then modifies the filtrate through selective reabsorption and secretion. The nephron includes the filtering unit and tubular structures rather than being another name for the whole urinary tract. Regulation of water, electrolytes and acid-base balance interacts with other organs. Loss of kidney function can therefore affect fluid balance, wastes and several physiological systems. Urinary symptoms require consideration of anatomy, infection, obstruction and other causes rather than immediate treatment from one nonspecific finding.
The nervous system coordinates sensation, movement and autonomic functions. The brain and spinal cord form the central nervous system. Neural signaling depends on membrane properties and coordinated ion-channel activity; the sodium-potassium pump maintains gradients over time rather than directly producing each rapid repolarization event. Muscle function involves cells, neuromuscular communication, circulation and mechanical leverage. Immobilization can reduce muscle size and function, while rehabilitation aims at useful activity rather than simply changing a measurement.
Cellular pathology provides additional vocabulary. Hypertrophy increases cell size; hyperplasia increases cell number. Inflammation can produce redness, warmth, swelling, pain and impaired function through vascular and cellular responses. Ischemia means inadequate tissue blood supply, which can injure cells if sustained. A malignant tumor has invasive potential, but appearance, differentiation and behavior vary and require appropriate diagnostic evidence. These concepts support explanation of a supplied case. They do not replace clinical investigation or establish a universal treatment from a label alone.