Anatomy, Physiology, and Pathophysiology
This domain tests structure-function relationships and the mechanisms that produce disease signs and symptoms. Strong answers connect an anatomical change to a physiologic consequence and then to the clinical finding, rather than listing facts in isolation.
Organization and homeostasis
The body is organized from chemical, cellular, and tissue levels through organs, systems, and the whole organism. Homeostasis depends on negative feedback loops that oppose change and positive feedback loops that amplify a process until an endpoint. Compensation is the body's attempt to preserve a critical variable, such as perfusion or pH, and it often produces the earliest abnormal findings.
Language and core physiology
Use anatomical position consistently: proximal means closer to the trunk, distal farther away; medial toward the midline, lateral away. The thoracic cavity contains the mediastinum, pleural spaces, and pericardium; the abdominopelvic cavity is separated by the diaphragm. Perfusion requires adequate cardiac output, vascular tone, and oxygen-carrying capacity. Ventilation moves air; oxygenation loads hemoglobin; they can fail independently.
Pathophysiology as mechanism
Cell injury becomes irreversible when ATP depletion, membrane damage, and calcium influx overwhelm repair. Hypoxia is low oxygen availability; ischemia is reduced blood flow and is more injurious because it also impairs delivery of glucose and removal of waste. Inflammation produces vasodilation, increased capillary permeability, and leukocyte migration, giving redness, heat, swelling, pain, and loss of function. Edema forms from increased hydrostatic pressure, decreased oncotic pressure, lymphatic obstruction, or sodium and water retention. Fever is a hypothalamic set-point change, not simply overheating.
Worked example
A patient with right ventricular failure develops ankle swelling. Reasoning: failing right ventricle raises right atrial and systemic venous pressure, which raises capillary hydrostatic pressure and pushes fluid into dependent tissue. Expect jugular venous distention and hepatomegaly. This differs from hypoalbuminemia, where low oncotic pressure causes generalized edema, and from lymphatic obstruction, where edema is usually unilateral and firm.
Traps that cost marks
- Confusing anatomy (structure) with physiology (function).
- Reversing proximal and distal or medial and lateral.
- Calling every edema "fluid overload."
- Ignoring compensation, which may normalize one value while another deteriorates.
- Saying "decreased oxygen" when the mechanism is hypoperfusion.