Chapter 01 Part B Notes: The Human Body - An Orientation

Anatomical Position and Directional Terms

  • Standard anatomical position
    • Body erect, feet slightly apart, palms facing forward with thumbs pointing away from body.
    • Used as the reference point for all directional terms.
  • Directional terms describe one body structure in relation to another structure.
  • Direction is always based on the standard anatomical position.
  • Right and left refer to the body being viewed, not the observer's right or left.

Orientation and Directional Terms (Table 1.1-1, 1.1-2, 1.1-3)

  • Superior (cranial)
    • Toward the head end or upper part of a structure or the body; above.
    • Example: The head is superior to the abdomen.
  • Inferior (caudal)
    • Away from the head end or toward the lower part of a structure or the body; below.
    • Example: The navel is inferior to the chin.
  • Anterior (ventral) and Posterior (dorsal)
    • Anterior: Toward or at the front of the body; in front of.
    • Posterior: Toward or at the back of the body; behind.
    • Note: The terms ventral and anterior are synonymous in humans, but this is not the case in four-legged animals. Anterior refers to the leading portion of the body (abdominal surface in humans, head in a cat), but ventral specifically refers to the "belly" of a vertebrate animal, so it is the inferior surface of four-legged animals. Likewise, although the dorsal and posterior surfaces are the same in humans, the term dorsal specifically refers to an animal's back (as in the dorsal fin of a shark). Thus, the dorsal surface of four-legged animals is their superior surface.
  • Medial and Lateral
    • Medial: Toward or at the midline of the body; on the inner side of.
    • Example: The heart is medial to the arm.
    • Lateral: Away from the midline of the body; on the outer side.
    • Example: The arms are lateral to the chest.
  • Intermediate
    • Between a more medial and a more lateral structure.
    • Example: The collarbone is intermediate between the breastbone and shoulder.
  • Proximal and Distal
    • Proximal: Closer to the origin of the body part or the point of attachment of a limb to the body trunk.
    • Example: The elbow is proximal to the wrist.
    • Distal: Farther from the origin of a body part or the point of attachment of a limb to the body trunk.
    • Example: The knee is distal to the thigh.
  • Superficial (external) and Deep (internal)
    • Superficial: Toward or at the body surface.
    • Deep: Away from the body surface; more internal.
    • Example: The skin is superficial to the skeletal muscles.
    • Example: The lungs are deep to the skin.
  • Regional note
    • The same ventral/anterior distinction caveat applies across species as described above.

Regional Terms

  • Two major divisions of the body
    • Axial: Head, neck, and trunk.
    • Appendicular: Limbs (legs and arms).
  • Regional terms designate specific areas within these body divisions.
  • Visual aids mentioned: Figures 1.8a and 1.8b show regional terms used to designate body areas.

Body Planes and Sections (1 of 3)

  • Body planes
    • Surfaces along which the body or structures may be cut for anatomical study.
    • The three most common planes:
    • Sagittal plane
    • Frontal (coronal) plane
    • Transverse (horizontal) plane
  • Sections
    • Cuts or sections made along a body plane.
    • Named after the plane; e.g., a sagittal cut yields a sagittal section.
  • MRI context
    • Figure 1.9 shows planes of the body with corresponding MRI scans.

Body Planes and Sections (2 of 3)

  • Sagittal plane
    • Divides body vertically into right and left parts.
    • A sagittal section results from cutting along this plane.
  • Midsagittal (median) plane
    • Cut was made perfectly on the midline.
  • Parasagittal plane
    • Cut was off-centered, not on the midline.

Body Planes and Sections (3 of 3)

  • Frontal (coronal) plane
    • Divides body vertically into anterior and posterior parts (front and back).
    • Produces a frontal or coronal section.
  • Transverse (horizontal) plane
    • Divides body horizontally (90° to vertical plane) into superior and inferior parts (top and bottom).
    • Produces a cross section.
  • Oblique section
    • Result of cuts at angle other than 90° to the vertical plane.

Serous Membranes and Body Cavities (1 of 7) and (2 of 7)

  • Ventral body cavity membranes
    • Serosa (serous membrane): Thin, double-layered membranes that cover surfaces in the ventral body cavity.
    • Parietal serosa: Lines internal body cavity walls.
    • Visceral serosa: Covers internal organs (viscera).
    • The two layers are separated by a slit-like cavity filled with serous fluid.
    • Fluid is secreted by both layers.
  • Names of serosa based on associated cavities/organs:
    • Pericardium: heart
    • Pleurae: lungs
    • Peritoneum: abdominopelvic cavity
  • The serous membrane relationships are illustrated in Figure 1.11 (parietal and visceral layers with serous fluid and the heart).

Dorsal Body Cavity

  • Dorsal body cavity protects the fragile nervous system.
  • Subdivisions:
    • Cranial cavity: encases brain.
    • Vertebral (spinal) cavity: encases spinal cord.

Ventral Body Cavity (1 of 7) and Organization (2 of 7)

  • Ventral body cavity houses the internal organs (viscera).
  • Two major subdivisions separated by the diaphragm:
    • Thoracic cavity
    • Abdominopelvic cavity

Ventral Body Cavity (2 of 7) – Thoracic Cavity

  • Thoracic cavity contains:
    • Two pleural cavities: Each surrounds one lung.
    • Mediastinum: Contains pericardial cavity and surrounds other thoracic organs (e.g., esophagus, trachea).
    • Pericardial cavity: Encloses the heart.

Ventral Body Cavity (3 of 7) – Abdominopelvic Cavity

  • Abdominal cavity: Stomach, intestines, spleen, liver.
  • Pelvic cavity: Urinary bladder, reproductive organs, rectum.

Clinical – Homeostatic Imbalance 1.1

  • Problems occur when structures stray into neighboring cavities.
  • Example: hiatal hernia
    • Part of the stomach protrudes through the diaphragm into the thoracic cavity.
    • Can push stomach acid into the esophagus, causing irritation known as heartburn.
    • Severe cases may require surgical repair.

Serous Membrane Relationships (1 of 2) and (2 of 2)

  • Serous membranes can become inflamed due to infection or other causes.
  • Normally smooth layers can become rough and stick together, causing excruciating pain.
  • Examples: pleurisy (inflammation of pleura) and peritonitis (inflammation of peritoneum).

Ventral Body Cavity (6 of 7) – Abdominopelvic Quadrants and Regions

  • Quadrants (divisions used primarily by medical personnel)
    • Right Upper Quadrant (RUQ)
    • Left Upper Quadrant (LUQ)
    • Right Lower Quadrant (RLQ)
    • Left Lower Quadrant (LLQ)
  • Figure 1.12 shows the four abdominopelvic quadrants.

Ventral Body Cavity (7 of 7) – Abdominopelvic Quadrants and Regions

  • Abdominopelvic regions (nine regions; resemble a tic-tac-toe grid)
    • 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

The Nine Abdominopelvic Regions (Figure 1.13)

  • Figure 1.13 delineates the nine regions and places several organs within them.
  • Example organs displayed in the regions (from the figure caption and labeling):
    • Liver and gallbladder located in the upper right region vicinity.
    • Stomach and spleen located in the upper left regions.
    • Ascending colon located in the right lateral (lumbar) region.
    • Transverse colon located around the umbilical region.
    • Descending colon and initial part of sigmoid colon located in the left lateral and hypogastric regions respectively.
    • Urinary bladder located in the hypogastric region (and portions can extend into the pelvic regions).
  • Figure 1.13(a) shows nine regions delineated by four planes.
  • Figure 1.13(b) shows an anterior view with superficial organs labeled.

Other Body Cavities

  • In addition to the two main body cavities, the body contains several smaller cavities that are exposed to the environment:
    • Oral and digestive cavities
    • Nasal cavity
    • Orbital cavities
    • Middle ear cavities
  • Not exposed to the environment:
    • Synovial cavities: joint cavities