Introduction to Anatomy & Physiology

Definition and Scope

Anatomy and physiology are foundational sciences in understanding the structure and function of the human body. Anatomy is the study of internal and external body structures and their physical relationships, while physiology focuses on how living organisms perform vital functions. These disciplines are closely integrated, as the principle of complementarity of structure and function states that specific functions are performed by specific structures, and the form of a structure relates to its function.

• Human anatomy: Study of the structure of the human body.

• Human physiology: Study of the function of the human body.

Specialties of Anatomy

• Gross (macroscopic) anatomy: Examines large structures visible to the naked eye.

• Microscopic anatomy: Examines structures only visible with magnification, such as cells and molecules.

Types of Gross Anatomy

• Surface anatomy: Study of body surface features.

• Regional anatomy: Study of specific body areas.

• Sectional anatomy: Understanding relationships by examining cross sections.

• Systemic anatomy: Study of organ systems.

• Clinical anatomy: Application of anatomy in clinical practice (includes pathological, radiologic, and surgical anatomy).

• Developmental anatomy: Anatomical changes from fertilization to adulthood (includes embryology).

Types of Microscopic Anatomy

• Cytology: Study of cell structure.

• Histology: Study of tissue structure.

Specialties of Physiology

• Cell physiology: Function of cells and their chemical processes.

• Organ physiology: Function of specific organs.

• Systemic physiology: Function of organ systems.

• Pathological physiology: Effects of diseases on organs or systems.

Clinical Application

• Physicians use anatomical, physiological, chemical, and psychological information to evaluate patients.

• Signs: Objective disease indications (e.g., fever).

• Symptoms: Subjective disease indications (e.g., tiredness).

• Diagnosis is reached using the scientific method: observation, hypothesis, and experimentation.

Levels of Organization in the Human Body

Hierarchy of Structural Organization

The human body is organized into six major levels, from simplest to most complex:

• Chemical level: Atoms and molecules (e.g., water, proteins).

• Cellular level: Cells, the smallest living units.

• Tissue level: Groups of cells working together for specific functions.

• Organ level: Two or more tissues working together (e.g., heart).

• Organ system level: Groups of organs interacting for a particular function (11 organ systems in humans).

• Organism level: The individual life form.

Overview of Organ Systems

The human body contains 11 organ systems, each with specific major organs and functions.

Medical and Anatomical Terminology

Medical Terminology

• Medical terms are built from word roots, prefixes, suffixes, and combining forms.

• Learning these components aids in understanding anatomy and physiology.

• Commemorative names (eponyms) are often replaced by precise terms, though both may be used.

Anatomical Terminology

• Surface anatomy: Locating structures on or near the body surface using anatomical landmarks.

• Anatomical position: Standard reference position—standing, hands at sides, palms forward, feet together.

• Other positions: Supine (lying face up), Prone (lying face down).

Anatomical Regions and Directions

• Abdominopelvic quadrants: Four regions (RUQ, LUQ, RLQ, LLQ) used in clinical settings.

• Abdominopelvic regions: Nine regions for more precise localization.

• Anatomical directions: Terms describing relative positions (e.g., superior, inferior, anterior, posterior).

Sectional Anatomy and Planes

• Section: A slice through a three-dimensional object, used to visualize internal organization.

• Sectional planes:

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

  • Sagittal plane: Divides body into left and right portions (midsagittal = equal halves, parasagittal = unequal).

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

Body Cavities

Major Body Cavities and Their Functions

• Body cavities: Closed, fluid-filled spaces lined by serous membranes, containing vital organs (viscera).

• Functions:

  1. Protect delicate organs from shocks and impacts.

  2. Permit significant changes in size and shape of internal organs.

Serous Membranes

• Consist of parietal (lines cavity) and visceral (covers organ) layers.

• Serous fluid reduces friction between layers.

Thoracic and Abdominopelvic Cavities

• Thoracic cavity: Contains right and left pleural cavities (lungs), pericardial cavity (heart), and mediastinum (connective tissue stabilizing organs).

• Abdominopelvic cavity: Contains abdominal (digestive organs) and pelvic (reproductive, rectum, bladder) cavities, and the peritoneal cavity (lined by peritoneum).

• Retroperitoneal space: Area behind the peritoneum (e.g., kidneys, pancreas).

• Infraperitoneal: Organs extending below the peritoneal cavity (e.g., bladder).

Homeostasis

Definition and Importance

Homeostasis refers to the continuous physiological processes that maintain a relatively stable internal environment. Physiological systems respond to internal and external changes to keep variables (e.g., temperature, blood pressure) within normal ranges.

Mechanisms of Homeostatic Regulation

• Autoregulation: Automatic, local response to environmental change in a cell, tissue, or organ.

• Extrinsic regulation: Responses controlled by the nervous (rapid, short-term) or endocrine (slower, long-term) systems.

Components of a Homeostatic Regulatory Mechanism

1. Receptor: Detects the stimulus or change.

2. Control center: Receives and processes information, sends commands.

3. Effector: Carries out the commands to adjust the condition.

Negative and Positive Feedback

Negative Feedback

• Regulation that opposes variation from normal; the effector negates the original stimulus.

• Helps maintain variables within a normal range.

Positive Feedback

• Regulation that enhances variation from normal; the response amplifies the original change.

• Used when a rapid, self-amplifying process is needed (e.g., blood clotting).

Systems Integration and Equilibrium

• Physiological systems work together to maintain homeostasis (systems integration).

• Homeostasis is a state of dynamic equilibrium—systems continually adapt to changing conditions.

• Failure to maintain homeostasis leads to disease or death.

Roles of Organ Systems in Homeostatic Regulation

The following table summarizes the primary organ systems involved in regulating key internal variables:

Example: When body temperature rises, the nervous system signals sweat glands (integumentary) to increase sweat production, and blood vessels dilate to release heat, restoring normal temperature.

Additional info: Understanding these foundational concepts is essential for further study in all areas of anatomy and physiology, as they provide the framework for how the body is organized, how it functions, and how it maintains stability in the face of internal and external changes.