Anatomy and Physiology 2e · An Introduction to the Human Body
Overview of Anatomy and Physiology
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Anatomy Study of the structure of body parts and their relationships Full entry → is the study of the structure of the body — the names, shapes, locations, and arrangements of body parts and how they relate. The word comes from the Greek anatome, "to cut apart," a nod to its roots in dissection. Physiology Study of the function of body parts and how they work Full entry → is the study of the function of body parts — what each part does and how. Its name combines the Greek physis ("nature") and logos ("study of"). In short: anatomy asks what and where; physiology asks how and why.
The two are lenses on the same body, joined by the Complementarity of structure and function The principle that a part's structure determines what it can do, and vice versa Full entry →: structure determines function, and function depends on structure. A heart valve is shaped like a flap precisely so it can open and close and keep blood moving one way; change the shape and the function fails. You will use this principle in every chapter of the book.
Each field has subdisciplines. Anatomy splits by scale: Gross anatomy Study of structures visible without a microscope Full entry → studies structures visible without a microscope, by body region (regional), by organ system (systemic), or from the body's surface (surface); microscopic anatomy covers cytology (cells) and histology (tissues); developmental anatomy traces structural change from conception on, with Embryology Study of the first eight weeks of development Full entry → covering the first eight weeks. Physiology splits by system and function: neurophysiology (nervous system), endocrinology (hormones), cardiovascular physiology, immunology, respiratory physiology, renal physiology, exercise physiology, and Pathophysiology Study of how disease changes normal body function Full entry → (how disease alters function). Each returns as its own chapter later in the book.
Why this matters
This topic is the doorway to the course: every later chapter assumes you can tell structure from function and connect the two. For health-care work the payoff is direct — physical assessment is applied Surface anatomy Study of external landmarks that reveal deeper structures Full entry →, and understanding illness starts with the normal structure and function that disease disrupts. Medications work by changing physiology; a drug that relaxes narrowed airways only makes sense if you know what bronchioles are and what they do. On exams, the classic traps are vocabulary-level: confusing a part with its job, or thinking naming a structure is the same as explaining it. Adopt the habit early of asking, "What is this part, and what does its shape let it do?"
The college version
Core Concepts
Anatomy: the science of structure
Regional anatomy organizes the body into areas (head, thorax, upper limb) and studies everything in each area together — the dissection approach. Systemic anatomy follows one system at a time (all bones, then all muscles), the approach of this book. Surface anatomy studies external landmarks — bumps, depressions, contours — that let you locate deeper structures through the skin, the basis of physical examination. Microscopic anatomy requires a microscope: cytology is the study of cells, histology of tissues. Developmental anatomy follows the body from fertilization onward; its early chapter, embryology, covers the first eight weeks, when the body's blueprint is laid down. Modern medical imaging (CT, MRI, ultrasound) adds a non-invasive way to study living anatomy, covered later in this chapter.
Physiology: the science of function
Physiology explains how the body works from molecules up to whole-organism responses. Its subdisciplines line up with the systems you will study: neurophysiology (how neurons send signals), endocrinology (how hormones coordinate long-distance regulation), cardiovascular physiology (how the heart pumps and blood moves), immunology (how the body counters threats), respiratory physiology (gas exchange), renal physiology (filtration and fluid regulation), exercise physiology (responses to activity), and pathophysiology (how disease changes normal function). A good physiology explanation answers how a process happens and why it matters — not just "the lungs exchange gases," but "the thin, moist, richly supplied walls of the alveoli let oxygen diffuse rapidly into the blood."
The principle of complementarity of structure and function
This is the single most useful idea in the book, and it runs both ways. Structure fits function: red blood cells' biconcave disc shape gives a large surface area for gas exchange and lets them bend through narrow capillaries. Function depends on structure: a stiffened heart valve can no longer close completely, and blood leaks backward. Function also shapes structure over a lifetime: heavily loaded bones thicken, and used muscles grow. Whenever you meet a new structure, ask what its shape allows it to do; whenever you meet a function, ask what structure enables it. This habit turns memorization into reasoning — and clinical reasoning needs both halves: anatomy locates a problem (which coronary artery feeds this heart muscle?), physiology explains the symptoms (what happens when its oxygen supply falls?).
Common Confusions
| Do not confuse | With | Difference |
|---|---|---|
| Anatomy | Physiology | Structure (what/where) versus function (how/why) |
| Gross anatomy | Microscopic anatomy | Visible without a microscope versus requiring one |
| Cytology | Histology | Cells versus tissues (groups of cells) |
| Regional anatomy | Systemic anatomy | Everything in one body area versus one system across the body |
| Knowing a structure's name | Understanding it | Naming is recall; understanding explains what its shape lets it do |
| The shoulder | The knee | Ball-and-socket (wide motion) versus hinge (stable, one-plane motion) |
Eli explains
The same idea, in plain words
Explain it like I’m 10
Your body is like a toy car. Anatomy is studying the pieces — the wheels, the axles, the motor — and where each one goes. Physiology is figuring out what the car does: how the motor makes the wheels turn. The cool part is that the shape of each piece tells you its job: wheels are round so they can roll. If a piece changes shape, the car can't do its job anymore.
Worked example
Structure explains function: the shoulder versus the knee. The shoulder is a ball-and-socket joint: the rounded head of the humerus sits in the shallow glenoid cup, letting the arm swing in nearly every direction — exactly what a reaching limb needs. The knee is built like a hinge: the femur's rounded ends roll against the tibia, guided by collateral and cruciate ligaments, so it mainly bends and straightens in one plane — trading motion for the stability a weight-bearing joint needs. Now use the same example as a diagnostic exercise: if a patient's knee suddenly allows sideways motion it never had, the structure that normally prevents it (the collateral ligaments) has been damaged. The change in structure explains the change in function — the complementarity principle working as a diagnostic tool.
Key takeaways
- Anatomy = structure (what and where); physiology = function (how and why).
- Complementarity of structure and function: structure determines function, and function depends on structure — the book's unifying principle.
- Anatomy subdisciplines: gross (regional, systemic, surface), microscopic (cytology, histology), developmental (embryology).
- Physiology subdisciplines include neurophysiology, endocrinology, cardiovascular physiology, immunology, respiratory physiology, renal physiology, exercise physiology, and pathophysiology.
- Surface anatomy underlies physical assessment.
- A structure's shape is usually the reason it can do its job (valves, red blood cells, alveoli, neurons).
- Embryology = first eight weeks of development; cytology = cells; histology = tissues.
- Reference note: subdivision lists vary slightly between textbooks — match your course's list.
Check yourself
6 review questions from the chapter. Try each one, then open the answer.
What is the difference between anatomy and physiology, and what principle connects them?
Show answer
Anatomy is the study of structure (what and where); physiology is the study of function (how and why). They are connected by the complementarity of structure and function: structure determines function, and function depends on structure.
Name the three broad subdivisions of anatomy and one subdiscipline within each.
Show answer
Gross anatomy (regional, systemic, or surface), microscopic anatomy (cytology or histology), and developmental anatomy (embryology). Any matching example is correct.
Give two examples of how structure enables function in the body.
Show answer
Red blood cells' biconcave disc maximizes surface area for gas exchange and lets them bend through capillaries; heart valves are flap-shaped to open and close and prevent backflow; alveoli's thin, moist walls allow rapid oxygen diffusion; neurons' long processes carry signals over distance.
What does surface anatomy have to do with physical examination?
Show answer
Surface anatomy studies external landmarks that let you locate deeper structures through the skin — exactly the skill used in physical assessment.
Which physiology subdiscipline studies how disease changes normal function?
Show answer
Pathophysiology.
Why is embryology considered part of anatomy?
Show answer
Because embryology traces the structural development of the body during the first eight weeks after fertilization — the study of structure over developmental time.
Study tools & related lessonsKey vocabulary · Related
Key vocabulary
- Anatomy
- Study of the structure of body parts and their relationships
- Physiology
- Study of the function of body parts and how they work
- Complementarity of structure and function
- The principle that a part's structure determines what it can do, and vice versa
- Gross anatomy
- Study of structures visible without a microscope
- Surface anatomy
- Study of external landmarks that reveal deeper structures
- Cytology / Histology
- The study of cells / the study of tissues
- Embryology
- Study of the first eight weeks of development
- Pathophysiology
- Study of how disease changes normal body function
Sources & references
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