Objective 1: 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 and Physiology

Definitions

• 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: Looks at all structures in a particular area of the body.

• Systemic anatomy: Looks at just one system (e.g., cardiovascular, nervous, muscular).

• Surface anatomy: Looks at internal structures as they relate to the overlying skin (e.g., visible muscles or veins).

• 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.

Subdivisions of Physiology

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

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

• Physiology is a dynamic and fluid process, often studied alongside anatomy for a complete understanding of the human body.

Terminology in Anatomy & Physiology

• Many terms are derived from Greek and Latin roots, prefixes, and suffixes.

• Examples:

  • Sublingual: 'Sub-' (under) + 'lingual' (tongue) = under the tongue.

  • Pericarditis: 'Peri-' (around) + 'card' (heart) + '-itis' (inflammation) = inflammation around the heart.

  • Leukocyte: 'Leuko-' (white) + 'cyte' (cell) = white blood cell.

Levels of Organization in the Human Body

The human body is highly organized, from the smallest chemical level to the whole organism level:

• Chemical level: Atoms, molecules, and organelles.

• Cellular level: Single cell.

• Tissue level: Groups of similar cells performing a common function.

• Organ level: Contains two or more types of tissues working together (e.g., the heart, stomach).

• Organ system level: Organs that work closely together (e.g., digestive system).

• Organismal level: All organ systems combined to make the whole organism.

Body Functions Necessary for Life

All living organisms must perform certain functions to maintain life:

• Maintaining boundaries: Separation between internal and external environments (e.g., skin, cell membranes).

• Movement: Includes movement of the body, organs, and cells.

• Responsiveness: Ability to sense and respond to stimuli (e.g., withdrawal reflex).

• Digestion: Breakdown of ingested foodstuffs to simple molecules.

• Metabolism: All chemical reactions that occur within body cells, including catabolism and anabolism.

• Excretion: Removal of wastes from metabolism and digestion (e.g., urea, carbon dioxide, feces).

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

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

Body Systems and Their General Functions

The human body consists of eleven organ systems, each with specific functions essential for survival:

• Integumentary System: Protects the body, regulates temperature, and provides sensory information.

• Skeletal System: Provides support, protection, and framework for muscles; stores minerals; forms blood cells.

• Muscular System: Allows movement, maintains posture, and produces heat.

• Nervous System: Fast-acting control system; responds to internal and external changes.

• Endocrine System: Glands secrete hormones that regulate growth, reproduction, and metabolism.

• Cardiovascular System: Transports blood, nutrients, gases, and wastes.

• Lymphatic System/Immunity: Returns leaked fluids to blood; defends against pathogens.

• Respiratory System: Supplies blood with oxygen and removes carbon dioxide.

• Digestive System: Breaks down food, absorbs nutrients, and eliminates waste.

• Urinary System: Eliminates nitrogenous wastes; regulates water, electrolytes, and acid-base balance.

• Reproductive System: Produces offspring.

Definition of Organ and Organ System

• Organ: A structure composed of at least two types of tissues that performs a specific function.

• Organ System: A group of organs that work together to perform major functions or meet physiological needs of the body.

Homeostasis and Its Function in Maintaining Life

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

• Involves feedback systems (mainly negative feedback) to regulate variables such as temperature, pH, and blood pressure.

• Disruption of homeostasis increases risk of disease and contributes to changes associated with aging.

• Positive feedback mechanisms are less common and usually control infrequent events (e.g., blood clotting, childbirth).

Directional Terms of the Body

Directional terms are used to describe the locations of structures relative to other structures or locations in the body. They are always based on the standard anatomical position (body erect, facing forward, arms at sides, palms forward).

• 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 the point of attachment.

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

• Superficial: Toward or at the body surface.

• Deep: Away from the body surface; more internal.

Major Divisions of the Body

• Axial region: Head, neck, and trunk.

• Appendicular region: Limbs (arms and legs).

• Regional terms designate specific areas within these major body divisions.

Planes of Division of the Body

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

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

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

Major Body Cavities and Their Subdivisions

• Dorsal body cavity: Protects the nervous system; includes the cranial cavity (encases the brain) and vertebral cavity (encases the spinal cord).

• Ventral body cavity: Houses internal organs (viscera); includes the thoracic cavity and abdominopelvic cavity.

• Thoracic cavity: Contains pleural cavities (each surrounds a lung) and the mediastinum (contains the pericardial cavity, which encloses the heart, and other thoracic organs).

• Abdominopelvic cavity: Contains the abdominal cavity (stomach, intestines, spleen, liver, etc.) and pelvic cavity (urinary bladder, reproductive organs, rectum).

Membranes of the Ventral Body Cavity

• Serosa (serous membrane): Thin, double-layered membrane covering the ventral body cavity and organs.

• Parietal serosa: Lines internal body cavity walls.

• Visceral serosa: Covers internal organs (viscera).

Abdominal Regions and Quadrants

To describe locations in the abdominopelvic cavity, two methods are used:

• 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

Summary Table: Levels of Organization

Example: Clinical Application

Understanding anatomical terminology allows healthcare professionals to communicate accurately about patient conditions, injuries, and procedures. For example, describing a laceration as being in the 'left lumbar region' provides precise information about the injury's location.