Introduction to Anatomy & Physiology

Overview of Anatomy and Physiology

Anatomy and physiology are foundational sciences in understanding the human body. Anatomy focuses on the structure of body parts, while physiology explores their functions. These disciplines are deeply interconnected, as the structure of an organ determines its function.

• Anatomy: The study of the physical structure of organisms and their parts.

• Physiology: The study of how those parts function and work together.

• Principle of Complementarity: Structure and function are inseparable; what a structure can do depends on its form.

Example: The heart's muscular walls enable it to pump blood efficiently throughout the body.

Branches of Anatomy and Physiology

Subdivisions of Anatomy

• Gross Anatomy: Study of structures visible to the naked eye (e.g., organs, muscles).

• Microscopic Anatomy: Study of structures requiring magnification (e.g., cells, tissues).

• Developmental Anatomy: Study of structural changes throughout the lifespan (e.g., embryology).

• Regional Anatomy: Focuses on specific areas of the body (e.g., head, thorax).

• Systemic Anatomy: Studies body systems (e.g., cardiovascular, respiratory).

• Surface Anatomy: Examines external features and their relation to deeper structures.

• Pathological Anatomy: Compares normal and diseased structures.

• Radiographic Anatomy: Uses imaging techniques (CT, X-ray, MRI) to study structures.

• Molecular Biology: Investigates structures at the molecular and cellular level.

Subdivisions of Physiology

• Systemic Physiology: Examines the function of organ systems (e.g., cardiovascular physiology).

• Cell Physiology: Studies the functions of cells and their organelles.

• Pathophysiology: Investigates functional changes associated with disease or injury.

Example: Pathophysiology explains how increased blood osmotic pressure can lead to edema.

Levels of Organization and Homeostasis

Structural Levels of the Human Body

The human body is organized in a hierarchy from the simplest to the most complex:

1. Atoms

2. Molecules

3. Cells

4. Tissues

5. Organs

6. Organ Systems

7. Organism

Each level builds upon the previous, creating increasing complexity and specialization.

Homeostasis

Homeostasis is the body's ability to maintain a stable internal environment despite external changes. It is a dynamic process, constantly adjusting to maintain equilibrium.

• Dynamic Balance: Homeostasis is not a fixed state; values fluctuate within normal ranges.

• Feedback Mechanisms: The body uses feedback loops to detect and respond to changes.

Types of Feedback

• Negative Feedback: The most common mechanism. The response reduces or eliminates the original stimulus, maintaining balance. Example: Regulation of blood glucose levels by insulin and glucagon.

• Positive Feedback: The response amplifies the original stimulus until a specific event ends the cycle. Examples: Labor contractions, blood clotting, and milk production during breastfeeding.

Aging slows homeostatic responses, but adaptation continues. Disease occurs when values move outside normal ranges (e.g., blood glucose < 60 or > 100 mg/dL).

Anatomical Terminology and Directions

Standard Anatomical Position

The anatomical position is the reference posture for all anatomical descriptions: standing upright, facing forward, arms at sides, palms facing forward.

• All directional terms are based on this position.

• Right and left always refer to the patient's right and left.

Directional Terms

• Anterior (Ventral): Toward the front

• Posterior (Dorsal): Toward the back

• Superior: Above (toward the head)

• Inferior: Below (toward the feet)

• Proximal: Closer to the point of attachment (limbs only)

• Distal: Farther from the point of attachment (limbs only)

• Medial: Toward the midline

• Lateral: Away from the midline

• Superficial: Toward the surface

• Deep: Toward the interior

Key Landmarks: cervical (neck), mental (chin), orbital (eye socket), inguinal (groin), genital (genital area), perineal (between legs), crural (shin), sural (calf).

Mnemonic: "C" (crural) comes before "S" (sural) alphabetically, so crural is in front (shin), sural is in back (calf).

Body Planes and Cavities

Sectional Planes

• Sagittal Plane: Divides the body into right and left parts. Midsagittal (Median): Divides exactly at the midline. Parasagittal: Divides off-center.

• Frontal (Coronal) Plane: Divides the body into anterior and posterior parts.

• Transverse Plane: Divides the body into superior and inferior parts (used in imaging).

• Oblique Plane: Any diagonal cut.

Body Cavities

• Dorsal (Posterior) Cavity:

  • Cranial Cavity: Contains the brain.

  • Spinal (Vertebral) Cavity: Contains the spinal cord.

• Ventral (Anterior) Cavity:

  • Thoracic Cavity: Contains the lungs (pleural cavities), heart (pericardial cavity), and mediastinum (esophagus, trachea, major vessels).

  • Abdominopelvic Cavity: Continuous space below the diaphragm; subdivided for clinical description into abdominal (above hip bones) and pelvic (below hip bones) regions.

Serous Membranes

Structure and Function

Serous membranes are double-layered sacs that surround major organs within body cavities, reducing friction with a lubricating fluid. Each has a parietal layer (lines cavity wall) and a visceral layer (covers the organ), with a fluid-filled cavity between.

Spelling Note: -al endings refer to cavities; -um/-a endings refer to membrane layers.

Inflammation Terms: pericarditis (heart), pleurisy (lungs), peritonitis (abdomen). Excess fluid accumulation is called effusion (pericardial/pleural) or ascites (peritoneal).

Example: Cirrhosis can cause ascites, requiring drainage of peritoneal fluid.

Abdominopelvic Mapping: Quadrants and Regions

Quadrants

The abdomen is divided into four quadrants by a vertical and horizontal line through the umbilicus:

• Right Upper Quadrant (RUQ)

• Left Upper Quadrant (LUQ)

• Right Lower Quadrant (RLQ)

• Left Lower Quadrant (LLQ)

Quadrants are commonly used in clinical settings, especially by nurses, but some organs (e.g., bladder, uterus) may overlap lines.

Regions

For greater precision, the abdomen is divided into nine regions using two vertical (midclavicular) and two horizontal lines (subcostal and transtubercular):

• Central Regions: Epigastric, Umbilical, Hypogastric (pubic)

• Lateral Regions: Right and Left Hypochondriac, Lumbar, and Iliac (inguinal)

Students should practice drawing and memorizing these regions for accurate organ localization.

Action Items for Students

• Memorize the anatomical position and all directional terms (especially crural/sural, proximal/distal).

• Practice drawing the nine abdominopelvic regions by hand.

• Review which organs belong to each body system and their main functions.

• Model serous membranes using the apple/plastic wrap/Ziploc analogy.

• Identify serous layers and cavities on lab specimens.

Additional Info

• Pathological anatomy and embryology will be expanded in future lectures.

• Lab exercises will include identification of cavities and membranes using models and images.