Structural Levels of Organization and Major Divisions of the Human Body

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 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: Focuses on just one system (e.g., cardiovascular, nervous, muscular).

• Surface anatomy: Examines 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 involves understanding processes, not just static images.

Medical Terminology

• 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

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 to perform specific functions.

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

• 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 and anabolism.

• Excretion: Removal of wastes from metabolism and digestion.

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

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

Organs and Organ Systems

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

• Organ system: A group of organs that work together to accomplish a common purpose.

The Eleven Body Systems and Their General Functions

• 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: Allows movement, maintains posture, and produces 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 cells, water, and dissolved materials; distributes heat.

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

• Respiratory System: Delivers air to alveoli, provides oxygen to bloodstream, removes carbon dioxide.

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

• Urinary System: Excretes waste products from the blood, controls water balance, stores urine.

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

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, blood pressure, and glucose levels.

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

Feedback Mechanisms

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

• Positive feedback: The response enhances or exaggerates the original stimulus (e.g., enhancement of labor contractions by oxytocin).

Directional Terms and Body Planes

Directional Terms

• Used to explain where one body structure is in relation to another.

• Based on standard anatomical position (body erect, feet slightly apart, palms facing forward).

• Terms include: superior/inferior, anterior/posterior, medial/lateral, proximal/distal, superficial/deep.

Major Divisions of the Body

• Axial: Head, neck, and trunk.

• Appendicular: Limbs (arms and legs).

Body Planes

• 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 Subdivisions

• Dorsal body cavity: Protects the nervous system; includes cranial and vertebral cavities.

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

• Thoracic cavity: Contains pleural cavities (each surrounds a lung) and the pericardial cavity (encloses the heart).

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

Membranes

• Serous membranes: Thin, double-layered membranes that cover surfaces in the ventral body cavity.

• Parietal serosa: Lines internal body cavity walls.

• Visceral serosa: Covers internal organs.

Abdominal Regions and Quadrants

Abdominal Quadrants

• Four quadrants used by clinicians:

  • Right Upper Quadrant (RUQ)

  • Left Upper Quadrant (LUQ)

  • Right Lower Quadrant (RLQ)

  • Left Lower Quadrant (LLQ)

Abdominal Regions

• Nine regions used primarily by anatomists:

  • 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

Level	Description	Example
Chemical	Atoms combine to form molecules	Water, proteins
Cellular	Cells are made up of molecules	Muscle cell
Tissue	Groups of similar cells	Muscle tissue
Organ	Contains two or more types of tissues	Heart
Organ System	Organs that work closely together	Cardiovascular system
Organismal	All organ systems combined	Human being

Additional info: This guide expands on the provided notes with definitions, examples, and a summary table to ensure a comprehensive understanding suitable for college-level Anatomy & Physiology students.