Anatomy & Physiology
Anatomy & Physiology is a core content area on the HESI A2. It tests structure–function relationships across organ systems, anatomical terminology, homeostasis, cell transport, histology, and system physiology. Expect questions that ask you to identify a structure, predict a physiological response, or choose the correct sequence in a pathway.
Core rules and concepts
- Anatomical position is standing upright, face forward, palms forward. Directional terms are relative: superior/inferior, anterior/posterior, medial/lateral, proximal/distal, superficial/deep. The three main planes are sagittal, frontal (coronal), and transverse.
- Homeostasis is maintained mainly by negative feedback: a receptor detects a change, a control center compares it with a set point, and an effector reverses it. Examples include baroreceptor control of blood pressure and insulin/glucagon control of glucose. Positive feedback amplifies a change; examples are oxytocin during labor and clotting.
- Cell transport: diffusion and osmosis are passive; facilitated diffusion uses a carrier but no ATP; active transport uses ATP, as in the Na+/K+ pump moving 3 Na+ out and 2 K+ in. Epithelium is avascular and rests on a basement membrane; connective tissue is defined by extracellular matrix; skeletal muscle is striated and voluntary, cardiac is striated with intercalated discs and involuntary, smooth is nonstriated and involuntary.
- Blood flows from the right heart to the lungs and then to the left heart and systemic circulation. The SA node sets the pace; the AV node delays the impulse. Cardiac output = heart rate × stroke volume. In the nephron, glomerular filtration is followed by tubular reabsorption and secretion; ADH increases water reabsorption, and aldosterone increases Na+ reabsorption and K+ secretion.
Worked example
After standing quickly, a patient feels lightheaded and blood pressure falls. Which receptors detect the change, and what is the effector response? Reasoning: baroreceptors in the carotid sinus and aortic arch detect decreased stretch. Afferent signals travel via cranial nerves IX and X to the medulla. The medulla increases sympathetic outflow and decreases parasympathetic outflow. Effectors: heart rate and contractility increase, and arterioles constrict, raising blood pressure. Because the response opposes the initial drop, it is negative feedback.
Traps
Common traps: confusing afferent (toward the CNS) with efferent (away from the CNS); assuming osmosis needs ATP when it is passive through aquaporins; forgetting that pulmonary arteries carry deoxygenated blood; reversing the SA and AV node roles; calling epithelium vascular when it is avascular; and labeling the baroreflex as positive feedback.