Structural Levels of Organization and Major Divisions of the Body

Learning Objectives

• Define key terms related to anatomy and physiology.

• Discuss the levels of organization of the body.

• Discuss the body functions necessary for life.

• Discuss the eleven body systems and the general function of each.

• Define organ and organ system.

• Discuss homeostasis and its function in maintaining life.

• Discuss the directional terms of the body.

• Identify the three planes of division of the body.

• Identify the two major cavities and the subdivisions of each.

• Identify the nine abdominal regions and the four abdominal quadrants.

Key Terms Related to Anatomy & Physiology

Definitions and Importance

Anatomy and physiology are foundational sciences for understanding the human body. Mastery of their terminology is essential for effective communication in healthcare.

• Anatomy: The study of the structure of body parts and their relationships to one another.

• Physiology: The study of the function of body parts; how they work to carry out life-sustaining activities.

Subdivisions of Anatomy

• Gross (macroscopic) anatomy: Study of large, visible structures.

• Regional anatomy: Examines all structures in a particular area of the body.

• Systemic anatomy: Focuses on one system (e.g., cardiovascular, nervous, muscular).

• Surface anatomy: Studies internal structures as they relate to the overlying skin (e.g., muscles or veins seen on surface).

• Microscopic anatomy: Deals with structures too small to be seen by the naked eye (e.g., cells, tissues).

• Developmental anatomy: Studies anatomical and physiological development throughout life (from baby to adult).

Subdivisions of Physiology

• Renal physiology: Concerns the function of the kidney and urine production.

• Neurophysiology: Describes how the nervous system works to provide function.

• Physiology is dynamic and fluid, involving continuous processes and interactions.

Medical Terminology

Medical terms often use roots, prefixes, and suffixes from Greek and Latin to describe body sections or regions.

• Lingua (root word): tongue

• Sublingual: under the tongue

• Cardio (root word): heart

• Pericarditis: inflammation of the pericardium (membrane around the heart)

• Leuko (root word): white; leukocyte: white blood cell

Levels of Organization in the Human Body

Hierarchical Structure

The human body is highly organized, from the smallest chemical units to the complete organism.

1. Chemical Level: Atoms, molecules, and organelles.

2. Cellular Level: Single cell; the basic unit of life.

3. Tissue Level: Groups of similar cells performing a common function.

4. Organ Level: Contains two or more types of tissues working together.

5. Organ System Level: Organs that work closely together to accomplish a common purpose.

6. Organismal Level: All organ systems combined to form the whole organism.

Major Divisions of the Body

Body Regions

• Head, neck, and trunk: Central axis of the body.

• Appendicular region: Limbs (arms and legs).

Directional Terms

Directional terms are used to describe the locations of structures relative to other structures or locations in the body.

• Superior (cranial): Toward the head or upper part of a structure.

• Inferior (caudal): Away from the head or toward the lower part of a structure.

• Anterior (ventral): Toward the front of the body.

• Posterior (dorsal): Toward the back of the body.

• Medial: Toward the midline of the body.

• Lateral: Away from the midline of the body.

• Proximal: Closer to the origin of the body part or point of attachment.

• Distal: Farther from the origin of the body part or point of attachment.

Body Planes

• Frontal (coronal) plane: Divides the body into anterior and posterior parts.

• Transverse (horizontal) plane: Divides the body into superior and inferior parts.

• Sagittal plane: Divides the body into right and left parts.

Body Cavities

The body contains two major cavities, each with subdivisions:

• Dorsal body cavity: Protects the nervous system organs.

  • Cranial cavity: Encloses the brain.

  • Vertebral (spinal) cavity: Encloses the spinal cord.

• Ventral body cavity: Houses internal organs (viscera).

  • Thoracic cavity: Contains the heart and lungs.

    • Pleural cavities: Each surrounds a lung.

    • Pericardial cavity: Encloses the heart.

    • Mediastinum: Contains other thoracic organs (e.g., esophagus, trachea).

  • Abdominopelvic cavity:

    • Abdominal cavity: Contains stomach, intestines, spleen, and liver.

    • Pelvic cavity: Contains urinary bladder, reproductive organs, and rectum.

Abdominal Regions and Quadrants

For clinical and anatomical reference, the abdomen is divided into regions and quadrants.

• Four Quadrants:

  • Right Upper Quadrant (RUQ)

  • Left Upper Quadrant (LUQ)

  • Right Lower Quadrant (RLQ)

  • Left Lower Quadrant (LLQ)

• Nine Regions:

  • Right hypochondriac region

  • Epigastric region

  • Left hypochondriac region

  • Right lumbar region

  • Umbilical region

  • Left lumbar region

  • Right iliac (inguinal) region

  • Hypogastric (pubic) region

  • Left iliac (inguinal) region

Functions Necessary for Life

Basic Life Functions

• Maintaining boundaries: Separation between internal and external environments.

• Movement: Activities promoted by the muscular system.

• Responsiveness: Ability to sense and respond to stimuli.

• Digestion: Breakdown of ingested foodstuffs.

• Metabolism: All chemical reactions that occur in body cells.

• Excretion: Removal of wastes from metabolism and digestion.

• Reproduction: Cellular division for growth or repair; production of offspring.

• Growth: Increase in size of a body part or of organism.

Homeostasis and Its Function in Maintaining Life

Definition and Mechanisms

Homeostasis is the maintenance of a relatively stable internal environment despite continuous changes in the outside environment. It is a dynamic state of equilibrium, maintained by contributions of all organ systems.

• Involves regulation of variables such as temperature, blood volume, and pH.

• Maintained primarily by the nervous and endocrine systems.

• Homeostatic control mechanisms involve three components:

  • Receptor: Senses changes in the environment.

  • Control center: Determines the set point and appropriate response.

  • Effector: Carries out the response.

Feedback Mechanisms

• Negative feedback: Reduces or shuts off the original stimulus. Example: Regulation of body temperature, blood glucose by insulin.

• Positive feedback: Enhances or exaggerates the original stimulus. Example: Enhancement of labor contractions by oxytocin, platelet plug formation and blood clotting.

Homeostatic Imbalance

• Disturbance of homeostasis increases risk of disease.

• With aging, control systems become less efficient.

• Negative feedback mechanisms may become overwhelmed, allowing destructive positive feedback mechanisms to take over (e.g., heart failure).

Summary Table: Levels of Organization

Summary Table: Body Cavities

Summary Table: Abdominal Quadrants

Example: Application of Anatomical Terminology

Understanding anatomical terminology allows healthcare professionals to communicate accurately about patient conditions and procedures. For example, describing a laceration in the right lumbar region or a contusion to the posterior of the head provides precise information for diagnosis and treatment.

Additional info: Some content was inferred and expanded for completeness and clarity, including the summary tables and detailed explanations of feedback mechanisms and body regions.