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 in Anatomy & 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: 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., 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 to provide function.

• Physiology is dynamic and fluid, focusing on processes and mechanisms.

Medical Terminology

• Uses roots, prefixes, and suffixes from Greek and Latin to describe sections or regions of the body.

• 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 Structural 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; the basic unit of life.

• 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, liver).

• Organ system level: Organs that work closely together to accomplish a common purpose (e.g., digestive system).

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

Body Functions Necessary for Life

To maintain life, the body must perform several essential functions:

• 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 (breakdown) and anabolism (synthesis).

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

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

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

Major Divisions of the Body

• Axial division: Head, neck, and trunk.

• Appendicular division: Limbs (arms and legs).

Directional Terms

Directional terms help 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.

Body Planes

Body planes are imaginary lines used to divide the body for anatomical study:

• 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.

Body Cavities and Their Subdivisions

The body contains two major sets of internal cavities:

• Dorsal body cavity:

  • Cranial cavity: Encases the brain.

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

• Ventral body cavity:

  • Thoracic cavity: Contains the heart and lungs.

    • Pleural cavities: Each surrounds a lung.

    • Mediastinum: Contains the pericardial cavity, surrounds other thoracic organs (esophagus, trachea).

    • Pericardial cavity: Encloses the heart.

  • Abdominopelvic cavity:

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

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

Abdominal Quadrants

Abdominal Regions

Homeostasis and Its Role 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 continuous monitoring and regulation of many factors (variables) such as temperature, blood volume, and blood sugar.

• Controlled mainly by the nervous and endocrine systems.

• Homeostatic control mechanisms have three components:

  • Receptor: Senses environmental changes (stimuli).

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

  • Effector: Carries out the response to restore balance.

• Most homeostatic control is via negative feedback (response reduces or shuts off the original stimulus).

• Positive feedback amplifies the original stimulus (e.g., blood clotting, labor contractions).

Consequences of Homeostatic Imbalance

• Increases risk of disease.

• Contributes to changes associated with aging as 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

Additional info:

• Understanding anatomical terminology is essential for clear communication in healthcare settings.

• Examples and clinical scenarios (such as patient case studies) help apply anatomical and physiological concepts to real-world situations.