Anatomical Terms, Body Planes, and Body Cavities: An Orientation to Human Anatomy

Anatomical Terms and Body Orientation

Anatomical Position and Directional Terms

Understanding the standard anatomical position and directional terms is essential for accurately describing locations and relationships of body parts.

• Standard anatomical position: The body stands erect, feet slightly apart, arms at the sides with palms facing forward and thumbs pointing away from the body.

• Directional terms: Used to describe the location of one body structure relative to another. Always based on the standard anatomical position.

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

Regional Terms

Regional terms specify particular areas within the body's main divisions.

• Major divisions:

  • Axial: Head, neck, and trunk

  • Appendicular: Limbs (arms and legs)

• Regional terms designate specific body areas within these divisions.

Body Planes and Sections

Body Planes

Body planes are imaginary flat surfaces that divide the body or organs for anatomical study.

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

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

  • Parasagittal plane: Offset from the midline.

• Frontal (coronal) plane: Divides the body into anterior (front) and posterior (back) parts.

• Transverse (horizontal) plane: Divides the body into superior (upper) and inferior (lower) parts; produces a cross section.

• Oblique section: Cuts made at angles other than 90° to a vertical plane.

Sections

A section is a cut along a plane. Named after the plane, e.g., a sagittal section is a cut along the sagittal plane.

Body Cavities and Membranes

Body Cavities

The body contains internal cavities that protect organs and allow for organ movement and growth. These cavities are classified as dorsal or ventral.

• Dorsal body cavity: Protects the nervous system.

  • Cranial cavity: Encases the brain.

  • Vertebral cavity: Encases the spinal cord.

• Ventral body cavity: Houses internal organs (viscera).

  • Thoracic cavity: Surrounded by ribs and chest muscles.

    • Pleural cavities: Each surrounds a lung.

    • Mediastinum: Contains the pericardial cavity (encloses the heart) and surrounds other thoracic organs (esophagus, trachea, etc.).

    • Pericardial cavity: Encloses the heart.

  • Abdominopelvic cavity:

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

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

Clinical Note: Homeostatic Imbalance

The pelvic cavity is less protected by bone, making organs in the abdominopelvic cavity more vulnerable to trauma.

Membranes in the Ventral Body Cavity

Serous membranes (serosa) line the ventral body cavity and cover organs within it.

• Parietal serosa: Lines the cavity walls.

• Visceral serosa: Covers the organs (viscera).

• Serous fluid is secreted between the layers, reducing friction.

Clinical Note: Homeostatic Imbalance

Inflammation of serous membranes (e.g., pleurisy, peritonitis) can cause pain and organ dysfunction due to friction between layers.

Abdominopelvic Quadrants and Regions

Quadrants

The abdominopelvic cavity is divided into four quadrants for clinical and anatomical reference:

• Right upper quadrant (RUQ)

• Left upper quadrant (LUQ)

• Right lower quadrant (RLQ)

• Left lower quadrant (LLQ)

Regions

Nine regions, resembling a tic-tac-toe grid, provide more precise localization:

• 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

Other Body Cavities

In addition to the main dorsal and ventral cavities, the body contains several smaller cavities:

• Oral and digestive cavities: Mouth and digestive tract

• Nasal cavity: Within and posterior to the nose

• Orbital cavities: House the eyes

• Middle ear cavities: Contain bones transmitting sound vibrations

• Synovial cavities: Joint cavities, not exposed to the environment