Principles of Anatomy and Physiology

1. Anatomy and Physiology: The Foundation of Understanding

Because structure and function are so closely related, you will learn about the human body by studying its anatomy and physiology together.

Structure and Function. Anatomy, the study of body structures, and physiology, the study of body functions, are intertwined. The structure of a body part often reflects its function, like the thin walls of lung air sacs facilitating rapid oxygen transfer.

Branches of Study. Both anatomy and physiology have diverse branches. Anatomy includes embryology, histology, and gross anatomy, while physiology encompasses neurophysiology, endocrinology, and cardiovascular physiology. These specialized areas allow for in-depth exploration of specific aspects of the human body.

Interdependence. Understanding both anatomy and physiology is crucial for comprehending how the body works. For example, to understand how the respiratory system functions, one must know the structure of the lungs, air passages, and the mechanics of breathing.

2. Levels of Organization: Building the Human Body

All the parts of the human body functioning together constitute the total organism.

Hierarchical Structure. The human body is organized in a hierarchy: chemical (atoms and molecules), cellular (cells), tissue (groups of cells), organ (different tissues), system (related organs), and organismal (the whole person). Each level builds upon the previous one, creating increasing complexity.

System Integration. The body systems, such as the digestive, nervous, and cardiovascular systems, are composed of related organs with common functions. These systems work together to maintain health and allow for reproduction of the human species.

Example: The Stomach. The stomach exemplifies the organ level, comprising epithelial, connective, and smooth muscle tissues. These tissues work together to churn food, secrete digestive fluids, and protect the stomach lining.

3. Life Processes: Defining the Living Organism

When any one of the life processes ceases to occur properly, the result is death of cells and tissues, which may lead to death of the organism.

Key Characteristics. Living organisms exhibit specific life processes, including metabolism (chemical reactions), responsiveness (detecting and reacting to changes), movement (internal and external), growth (increase in size), differentiation (specialization of cells), and reproduction (new cells or individuals).

Metabolism's Two Phases. Metabolism encompasses catabolism (breaking down complex substances) and anabolism (building complex substances). For example, digestion catabolizes proteins into amino acids, which are then used to anabolize new proteins for body structures.

Interdependence of Processes. These life processes are interconnected and essential for survival. Failure in any one process can lead to cellular and tissue death, ultimately threatening the organism's life.

4. Homeostasis: Maintaining Internal Balance

Homeostasis is a dynamic condition.

Dynamic Equilibrium. Homeostasis is the maintenance of a stable internal environment through regulatory systems. It's a dynamic process, not a static one, with parameters like blood glucose fluctuating within a narrow range.

Body Fluids. Maintaining the volume and composition of body fluids, both intracellular (ICF) and extracellular (ECF), is crucial for homeostasis. Interstitial fluid, a type of ECF, surrounds body cells and serves as the internal environment.

Feedback Systems. The body regulates homeostasis through feedback systems involving receptors, control centers, and effectors. Negative feedback reverses changes, while positive feedback reinforces them until an external mechanism intervenes.

5. Chemical Building Blocks: Atoms, Molecules, and Bonds

Each element is a substance that cannot be split into a simpler substance by ordinary chemical means.

Elements of Life. The human body comprises 26 chemical elements, with oxygen, carbon, hydrogen, and nitrogen being the major elements. These elements combine to form atoms, the smallest units of matter.

Atomic Structure. Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in electron shells. The number of protons determines the atomic number, while the sum of protons and neutrons determines the mass number.

Ions and Bonds. Atoms can gain or lose electrons to become ions, forming ionic bonds through electrostatic attraction. Atoms can also share electrons to form covalent bonds, which can be polar (unequal sharing) or nonpolar (equal sharing).

6. Chemical Reactions: Energy and Metabolism

A chemical reaction occurs when new bonds form or old bonds break between atoms.

Energy Dynamics. Chemical reactions involve energy changes, either releasing energy (exergonic) or absorbing energy (endergonic). Chemical energy, stored in molecular bonds, is converted into kinetic energy for various bodily functions.

Activation Energy and Catalysts. Chemical reactions require activation energy to break bonds. Catalysts, such as enzymes, speed up reactions by lowering activation energy without being consumed in the process.

Types of Reactions. Common reactions include synthesis (anabolism), decomposition (catabolism), exchange, and reversible reactions. Oxidation-reduction reactions, involving electron transfer, are crucial for energy production.

7. Water, Acids, Bases, and Buffers: Essential for Life

The proper functioning of body cells depends on precise regulation of the composition of their surrounding fluid.

Water's Properties. Water, comprising 55-60% of body mass, is a polar solvent, a reactant in chemical reactions, and has a high heat capacity and heat of vaporization. These properties make it essential for life.

Acids, Bases, and Salts. Acids release hydrogen ions (H+), bases accept H+, and salts dissociate into ions other than H+ or hydroxide ions (OH-). These substances are crucial for maintaining pH balance.

pH and Buffers. The pH scale measures acidity or alkalinity. Buffers, such as the carbonic acid-bicarbonate system, convert strong acids or bases into weak ones to maintain pH homeostasis.

8. Organic Compounds: The Molecules of Life

The way you live your life can either support or interfere with your body’s ability to maintain homeostasis and recover from the inevitable stresses life throws your way.

Carbon's Role. Organic compounds, always containing carbon and usually hydrogen, are held together by covalent bonds. Carbon's ability to form diverse structures makes it essential for life.

Functional Groups. Organic molecules have functional groups attached to their carbon skeletons, conferring specific chemical properties. These groups include hydroxyl, sulfhydryl, carbonyl, carboxyl, phosphate, amino, and ester groups.

Macromolecules. Small organic molecules combine to form macromolecules, including carbohydrates, lipids, proteins, and nucleic acids. These polymers are assembled through dehydration synthesis and broken down by hydrolysis.

9. Cellular Structure: The Basic Unit of Life

Each structure, from the cellular level to the system level, contributes in some way to keeping the internal environment of the body within normal limits.

Three Main Parts. A cell consists of the plasma membrane (outer boundary), cytoplasm (intracellular fluid and organelles), and nucleus (containing DNA). Each component plays a vital role in cellular function.

Plasma Membrane. The plasma membrane is a selective barrier that regulates the flow of materials into and out of the cell. It also plays a key role in communication among cells and between cells and their external environment.

Cytoplasm. The cytoplasm consists of all the cellular contents between the plasma membrane and the nucleus. This compartment has two components: cytosol and organelles.

10. Membrane Transport: Crossing the Cellular Barrier

The body can regulate its internal environment through many feedback systems.

Passive Transport. Passive processes, such as diffusion and osmosis, move substances across the plasma membrane down their concentration gradients without requiring cellular energy.

Active Transport. Active processes, such as active transport, require cellular energy (ATP) to move substances against their concentration gradients. Vesicles are also used to transport substances across the membrane.

Homeostasis. These transport mechanisms are crucial for maintaining homeostasis by regulating the composition of the intracellular environment and facilitating communication between cells.

11. Metabolism: Chemical Reactions in the Body

The body’s ability to maintain homeostasis gives it tremendous healing power and a remarkable resistance to abuse.

Metabolic Reactions. Metabolism is the sum of all chemical processes in the body, including catabolism (breakdown) and anabolism (synthesis). These reactions involve energy transfer, with exergonic reactions releasing energy and endergonic reactions requiring it.

Energy Transfer. ATP (adenosine triphosphate) is the primary energy currency of the cell, capturing energy from exergonic reactions and providing it for endergonic processes. Metabolic pathways, such as carbohydrate, lipid, and protein metabolism, are essential for energy production.

Homeostatic Balance. Metabolic adaptations, including energy balance and regulation of body temperature, are crucial for maintaining homeostasis. Nutrition plays a vital role in providing the necessary building blocks and energy sources for these processes.

12. Tissues: The Fabric of the Body

Tissues are groups of cells and the materials surrounding them that work together to perform a particular function.

Four Basic Types. The human body comprises four basic tissue types: epithelial, connective, muscular, and nervous. Each tissue type has distinct characteristics and functions.

Epithelial Tissue. Epithelial tissue covers body surfaces, lines hollow organs and cavities, and forms glands. It functions in protection, secretion, absorption, and filtration.

Connective Tissue. Connective tissue protects and supports the body and its organs. It binds organs together, stores energy reserves as fat, and helps provide the body with immunity to disease-causing organisms.

Last updated: March 11, 2025