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 and Scope

• 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 rather than static images.

Terminology in Anatomy & Physiology

• Medical terms often use 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

Hierarchy of Organization

• Chemical level: Atoms combine to form molecules.

• Cellular level: Cells are made up of molecules; the cell is the basic unit of life.

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

• Organ level: Contains two or more types of tissues working together to perform specific functions.

• Organ system level: Organs that work closely together to accomplish a common purpose.

• Organismal level: The sum total of all organ systems working together to maintain life in the whole organism.

Example

• The cardiovascular system includes the heart (organ), which is made of muscle tissue, connective tissue, etc., and is composed of cells and molecules.

Body Functions Necessary for Life

Essential Life Functions

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

• Movement: Includes movement of the body, organs, and cells (e.g., muscle contraction, movement of blood).

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

• Digestion: Breakdown of ingested foodstuffs to simple molecules that can be absorbed.

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

• Excretion: Removal of wastes produced by 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 as a whole.

Major Divisions of the Body

Axial and Appendicular Divisions

• Axial division: Includes the head, neck, and trunk.

• Appendicular division: Includes the limbs (arms and legs).

Body Systems and Their General Functions

The Eleven Organ Systems

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

• Skeletal system: Provides support and protection, stores minerals, and forms blood cells.

• Muscular system: Produces movement, maintains posture, and generates heat.

• Nervous system: Directs immediate responses to stimuli, coordinates activities of other organ systems.

• Endocrine system: Directs long-term changes in activities of other organ systems via hormones.

• Cardiovascular system: Distributes blood, nutrients, gases, and waste products.

• Lymphatic system: Defends against infection and disease, returns tissue fluids to the bloodstream.

• Respiratory system: Delivers air to alveoli, provides oxygen to blood, removes carbon dioxide.

• Digestive system: Processes food, absorbs nutrients, and eliminates waste.

• Urinary system: Eliminates waste from the body, regulates water, electrolyte, and acid-base balance.

• Reproductive system: Produces sex cells and hormones, supports embryonic development (female).

Organs and Organ Systems

Definitions

• 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 Role in Maintaining Life

Definition and Importance

• Homeostasis: The maintenance of a relatively stable internal environment despite continuous external changes.

• It is a dynamic state of equilibrium, constantly adjusting as needed.

• Maintained by contributions of all organ systems, especially the nervous and endocrine systems.

Components of Homeostatic Control

• Receptor: Detects changes (stimuli) and sends information to the control center.

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

• Effector: Carries out the response to restore balance.

Feedback Mechanisms

• Negative feedback: Most common; response reduces or shuts off the original stimulus (e.g., regulation of body temperature, blood glucose).

• Positive feedback: Response enhances or exaggerates the original stimulus (e.g., blood clotting, labor contractions).

Homeostatic Imbalance

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

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

Directional Terms in Anatomy

Standard Anatomical Position

• Body erect, facing forward, arms at sides with palms facing forward, feet slightly apart.

• Directional terms are always based on this standard position.

• Right and left refer to the body being viewed, not the observer.

Common Directional Terms

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

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

• 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.

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

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

• Superficial: Toward or at the body surface.

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

Body Planes and Sections

Three Major Planes

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

  • Midsagittal (median) plane: Lies exactly in the midline.

  • Parasagittal plane: Not on the midline.

• 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

Major Body Cavities

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

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

Ventral Body Cavity Subdivisions

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

• Abdominopelvic cavity: Subdivided into:

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

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

Membranes in 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).

• Examples: Pericardium (heart), Pleura (lungs), Peritoneum (abdominopelvic cavity).

Abdominal Regions and Quadrants

Four Abdominal Quadrants

• Used primarily by clinicians to describe location of pain or injury.

Nine Abdominal Regions

• Used primarily by anatomists for more precise identification of organ locations.

Summary Table: Levels of Structural Organization

Additional info: These notes provide foundational knowledge for understanding human anatomy and physiology, essential for further study in health sciences and clinical practice.