Introduction to Anatomy and Physiology

Definitions and Relationships

Anatomy and physiology are foundational sciences in understanding the structure and function of the human body. Their study reveals how the body's form enables its vital processes.

• Anatomy: The study of internal and external structures of the body and the physical relationships among body parts.

• Physiology: The study of how living organisms perform their vital functions.

• Complementarity of Structure and Function: Structure and function are closely linked; the form of a structure determines its function, and vice versa.

Specialties in Anatomy

Gross (Macroscopic) Anatomy

Gross anatomy examines structures visible to the naked eye and can be subdivided into several approaches:

• Surface Anatomy: Study of general form and superficial markings.

• Regional Anatomy: Study of all structures in a specific body region.

• Sectional Anatomy: Study of body structures by examining cross-sections.

• Systemic Anatomy: Study of the anatomy of organ systems.

• Clinical Anatomy: Focus on anatomical features important in medical practice.

• Pathological Anatomy: Study of anatomical changes due to disease.

• Radiologic Anatomy: Study of structures as seen with imaging techniques.

• Surgical Anatomy: Study of anatomical landmarks important for surgery.

Body Planes and Sections

• Frontal (Coronal) Plane: Divides the body into anterior (front) and posterior (back) portions.

• Sagittal Plane: Divides the body into left and right portions.

  • Midsagittal: Divides the body into equal left and right halves.

  • Parasagittal: Divides the body into unequal left and right portions.

• Transverse (Horizontal) Plane: Divides the body into superior (upper) and inferior (lower) portions.

Microscopic Anatomy

Microscopic anatomy examines structures that require magnification.

• Cytology: Study of cell structure.

• Histology: Study of tissue structure.

Specialties in Physiology

• Cell Physiology: Functions of cells and their chemical processes.

• Organ Physiology: Functions of specific organs.

• Systemic Physiology: Functions of organ systems.

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

Levels of Organization

The human body is organized into six hierarchical levels, each increasing in complexity:

1. Chemical Level: Atoms and molecules.

2. Cellular Level: Cells, the smallest living units.

3. Tissue Level: Groups of similar cells performing specific functions.

4. Organ Level: Two or more tissues working together (e.g., heart, stomach).

5. Organ System Level: Groups of organs performing major functions (11 systems in humans).

6. Organism Level: The complete living individual.

Major Organ Systems of the Human Body

The human body contains 11 major organ systems, each with distinct functions:

Medical and Anatomical Terminology

Medical Terminology

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

• Eponyms (names based on discoverers) are sometimes used but are being replaced by more precise terms.

Anatomical Terminology

• Standardized terms describe body regions, sections, and positions.

Anatomical Position

• Standing erect, head level, eyes forward

• Feet parallel and slightly apart

• Arms at sides, palms facing forward

Views: Anterior (front), Posterior (back), Supine (lying face up), Prone (lying face down)

Anatomical Landmarks (Regions)

• Head: Cranial, cephalic, frontal, orbital/ocular, otic, nasal, buccal, oral, mental

• Neck: Cervical

• Trunk: Thoracic, mammary, abdominal, umbilical, pelvic, pubic

• Upper Limb: Axillary, brachial, antecubital, antebrachial, manual, palmar, carpal, digits, pollex

• Lower Limb: Femoral, patellar, crural, tibial, tarsal, pedal, plantar, digits, hallux

• Back: Dorsal, acromial, olecranal, lumbar, gluteal, popliteal, sural, calcaneal

Abdominopelvic Regions and Quadrants

Anatomical Directions

• Superior (Cranial): Toward the head

• Inferior (Caudal): Toward the feet

• Anterior (Ventral): Toward the front

• Posterior (Dorsal): Toward the back

• Medial: Toward the midline

• Lateral: Away from the midline

• Proximal: Closer to the point of attachment

• Distal: Farther from the point of attachment

• Superficial: Toward or on the surface

• Deep: Away from the surface

Body Cavities

Body cavities are closed, fluid-filled spaces that protect and house vital organs. They are lined by serous membranes (serosa).

• Parietal Serosa: Lines the cavity wall

• Visceral Serosa: Covers the organ surface

• Serous Fluid: Lubricates, reducing friction between layers

Major Body Cavities of the Trunk

• Thoracic Cavity: Contains right and left pleural cavities (lungs), pericardial cavity (heart), and mediastinum (central region with heart, vessels, trachea, esophagus)

• Abdominopelvic Cavity: Extends from diaphragm to pelvis

  • Abdominal Cavity: Contains digestive organs, kidneys, spleen

  • Peritoneal Cavity: Space lined by peritoneum, suspending many abdominal organs

  • Retroperitoneal Space: Behind peritoneum; contains kidneys, pancreas

  • Pelvic Cavity: Contains reproductive organs, rectum, bladder

  • Infraperitoneal: Organs below the peritoneal cavity

Homeostasis

Homeostasis is the maintenance of a stable internal environment, essential for survival. Physiological systems regulate variables such as temperature, blood pressure, and pH within narrow limits.

Homeostatic Regulation

• Autoregulation: Local, automatic adjustments by cells, tissues, or organs.

• Extrinsic Regulation: Regulation by nervous (rapid) or endocrine (slower) systems using electrical or chemical signals.

Components of a Homeostatic Regulatory Mechanism

1. Receptor (Sensor): Detects changes in the environment.

2. Control Center (Integrator): Processes information and sends commands.

3. Effector: Carries out the response to restore balance.

Negative and Positive Feedback

• Negative Feedback: Opposes or reverses the original stimulus, maintaining variables within normal ranges.

  • Example: Body temperature regulation—sweating lowers temperature, shivering raises it.

• Positive Feedback: Amplifies the original stimulus, driving a process to completion.

  • Example: Blood clotting—chemicals accelerate clotting until bleeding stops; also, uterine contractions during childbirth.

Systems Integration in Homeostasis

All organ systems interact to maintain homeostasis. Disruption of homeostasis can result in disease or death. The body is in a state of dynamic equilibrium, constantly adapting to internal and external changes.