Anatomy and Physiology: Structures and Functions of the Body

Anatomy and physiology sit at the foundation of every biological and medical science — anatomy mapping where structures are, physiology explaining what those structures do. Together they form a discipline that spans the 206 bones of the adult human skeleton, the 37 trillion cells estimated by researchers at the Bianconi et al. (2013) study published in Annals of Human Biology, and every chemical signal passing between them. This page covers the core definitions, the mechanisms that link structure to function, the practical scenarios where that knowledge matters, and the boundaries that define where anatomy and physiology end and other disciplines begin.

Definition and scope

Anatomy is the study of biological structure — the physical arrangement of tissues, organs, and systems. Physiology is the study of function — how those structures operate, regulate, and communicate. The two are inseparable in practice: the bicuspid shape of the mitral valve is anatomy; the way that shape prevents backflow of blood from the left ventricle into the left atrium during systole is physiology.

The field divides into gross anatomy (structures visible to the unaided eye), histology (tissue-level structure under microscopy), and cytology (cell-level organization). Physiology mirrors this hierarchy, addressing whole-organ function, tissue-level processes like gas exchange across alveolar membranes, and cellular mechanisms like the sodium-potassium pump that maintains a resting membrane potential of approximately −70 millivolts in neurons.

Human anatomy is organized across 11 organ systems, as catalogued by OpenStax Anatomy and Physiology — a peer-reviewed, openly licensed reference used by universities across the United States. Those systems range from the integumentary system (skin, hair, nails) to the nervous, endocrine, cardiovascular, lymphatic, respiratory, digestive, urinary, and reproductive systems, plus the skeletal and muscular systems that together account for roughly 70 percent of body mass.

Understanding how the discipline organizes itself is part of what the broader Biology Authority index treats as foundational biological literacy.

How it works

The organizing principle of anatomy and physiology is the structural-functional relationship: form follows function, and function is constrained by form. A textbook example is the nephron — the functional unit of the kidney. Its looping architecture (the loop of Henle) creates a concentration gradient in the renal medulla that allows the collecting duct to reabsorb water without expending additional ATP. The structure is the mechanism.

At the cellular level, physiology depends on four categories of biological molecules — proteins, lipids, carbohydrates, and nucleic acids — each performing specific structural or signaling roles. Integral membrane proteins embedded in the phospholipid bilayer act as ion channels, receptors, and pumps. The sodium-potassium ATPase, for instance, moves 3 sodium ions out and 2 potassium ions in per cycle, consuming 1 ATP molecule. That stoichiometry — 3 out, 2 in, 1 ATP — is not incidental; it maintains the electrochemical gradient that neurons use to propagate action potentials.

Homeostasis is the central operational concept of physiology. The body maintains core temperature within approximately 36.1–37.2°C (97–99°F), blood glucose between 70–100 mg/dL in a fasted state (NIH MedlinePlus), and blood pH between 7.35 and 7.45 (American Association for Clinical Chemistry, via MedlinePlus). Each of these parameters is regulated by negative feedback loops — the same conceptual logic that governs a thermostat, though the biological implementation involves hormones, neural signals, and receptor cascades rather than a bimetallic strip.

This kind of mechanistic thinking — tracing a physiological outcome back to its structural and molecular causes — is also the subject of the broader how-science-works-conceptual-overview resource, which situates anatomy and physiology within scientific methodology.

Common scenarios

Anatomy and physiology knowledge surfaces in four major real-world contexts:

Clinical medicine and diagnostics — A physician interpreting an electrocardiogram is reading the electrical physiology of the heart: the P wave represents atrial depolarization, the QRS complex ventricular depolarization, the T wave ventricular repolarization. Misreading the anatomy of the conduction system leads to misdiagnosis.
Physical rehabilitation — Understanding the origin and insertion points of the rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) determines which exercises address which injury patterns. The supraspinatus, the most commonly torn of the four, initiates the first 15 degrees of shoulder abduction.
Pharmacology — Drug targets are anatomical and physiological structures. Beta-blockers act on β1 adrenergic receptors in cardiac muscle to reduce heart rate and contractility. The receptor's location in the myocardium — not the lung or liver — defines the drug's primary therapeutic window.
Medical imaging interpretation — CT, MRI, and ultrasound require working anatomical knowledge to read correctly. A radiologist identifying a structure on a cross-sectional CT image is navigating the body in planes — axial, coronal, sagittal — defined entirely by anatomical convention.

Decision boundaries

Anatomy and physiology are distinct from adjacent fields in ways that matter for research and practice.

Anatomy vs. pathology: Anatomy describes normal structure; pathology describes structural deviation from that norm. A hypertrophied left ventricle with a wall thickness exceeding 12 mm (American Heart Association, Circulation) is no longer anatomy — it is a pathological finding.

Physiology vs. biochemistry: Physiology operates at the organ-and-system level; biochemistry operates at the molecular level. The two overlap in cell physiology, but a physiologist studying renal filtration is asking different questions than a biochemist characterizing aquaporin-2 channel kinetics.

Gross anatomy vs. histology: Gross anatomy resolves structures at the scale of centimeters; histology resolves at the scale of micrometers. The transition point is roughly the resolution limit of unaided human vision — approximately 0.1 millimeters. Below that threshold, light microscopy and electron microscopy take over.

These distinctions matter practically: a researcher designing an experiment about cardiac output is working in physiology; one mapping the ultrastructure of cardiac sarcomeres is working at the histological or ultrastructural boundary.