Introduction to Anatomy & Physiology: Characteristics of Living Organisms and Levels of Structural Organization

Introduction to Anatomy & Physiology

Overview

Anatomy and Physiology (A&P) is the study of the structure and function of the human body. This foundational chapter introduces the essential characteristics of living organisms and the hierarchical levels of structural organization that define biological systems.

Characteristics of Living Organisms

Key Properties Shared by All Organisms

• Cellular Composition:

  • Cells are the basic units of life.

  • The smallest unit capable of carrying out all functions of life.

  • All organisms are composed of cells.

• Metabolism:

  • Chemicals are substances with unique molecular composition used in or produced by chemical reactions.

  • Living organisms perform chemical reactions collectively known as metabolism.

  • Metabolic processes either build up (anabolism) or break down (catabolism) substances, depending on the needs of the organism.

• Growth:

  • Occurs when building processes outweigh breaking down processes.

  • Two forms:

    • Increase in size of individual cells.

    • Increase in number of cells.

• Excretion:

  • Elimination of potentially harmful waste products created by metabolic processes.

• Responsiveness or Irritability:

  • Sensing and reacting to changes or stimuli in the environment.

• Movement:

  • Movement of the entire organism, individual cells within the organism, or materials within or between cells.

• Reproduction:

  • Two forms in multicellular organisms:

    • Individual cells reproduce during growth and to replace damaged or old cells.

    • The organism itself reproduces, yielding similar offspring.

Levels of Structural Organization in the Human Body

Hierarchical Organization

The human body is constructed from a series of increasingly larger "building blocks," each representing a structural level of organization. These levels provide the foundation for understanding how complex biological systems function.

Chemical Level

• The smallest level of organization.

• Consists of atoms and molecules (e.g., phospholipid molecules).

• Serves as the foundation for all higher levels.

Cellular Level

• Groups of many different types of molecules combined in specific ways to form cellular structures.

• Example: Squamous epithelial cell with a cell membrane.

Tissue Level

• Two or more cell types cooperate to perform a common function.

• Composed of cells and surrounding extracellular matrix.

• Tissues vary from membrane sheets (covering body cavities) to irregularly shaped cartilage (e.g., in the nose).

• Example: Stratified squamous epithelium.

Additional info:

• Higher levels (not shown in the provided images but inferred from context):

  • Organ Level: Two or more tissue types combined to form organs with recognizable shapes and specialized tasks.

  • Organ System Level: Groups of organs that carry out broad functions (e.g., cardiovascular system).

  • Organism Level: The complete human body, made up of all organ systems working together.

Summary Table: Six Structural Levels of Organization

Level	Description	Example
Chemical	Atoms and molecules	Phospholipid molecule
Cellular	Cells formed from molecules	Squamous epithelial cell
Tissue	Groups of cells and extracellular matrix	Stratified squamous epithelium
Organ	Two or more tissue types forming a structure	Heart, stomach
Organ System	Groups of organs performing broad functions	Cardiovascular system
Organism	Complete living being	Human body

Key Terms and Definitions

• Cell: The smallest unit of life capable of independent function.

• Metabolism: The sum of all chemical reactions in the body, including anabolism (building up) and catabolism (breaking down).

• Extracellular Matrix: Non-cellular material surrounding cells in tissues, providing structural and biochemical support.

• Organ: A structure composed of two or more tissue types that performs a specific function.

Example Application

Understanding the levels of structural organization is essential for studying how diseases affect the body. For instance, cancer may originate at the cellular level but can disrupt tissue, organ, and organ system function as it progresses.