anatomy and physiology

Anatomical Position and Orientation

  • Learning objectives covered: describe the anatomical position; describe directional and regional terms; identify the three main body planes; distinguish dorsal (posterior) and ventral (anterior) cavities and their subdivisions and representative organs; describe serous membranes and their function.

  • Anatomical position definition: the body is standing upright with:

    • feet shoulder-width apart and parallel

    • toes directed forward

    • upper limbs held out to each side

    • palms of the hands facing forward

  • If the body is lying down, it is described as:

    • prone: face-down orientation

    • supine: face-up orientation

  • Understanding of orientation is foundational for describing locations and relations in the body.

Directional Terms

  • Superior (cranial) vs Inferior (caudal):

    • Superior/cranial = toward the head

    • Example: The head is superior to the neck.

    • Inferior/caudal = toward the feet

    • Example: The feet are inferior to the knees.

  • Anterior (ventral) vs Posterior (dorsal):

    • Anterior/ventral = toward the front of the body

    • Example: The sternum is anterior to the heart.

    • Posterior/dorsal = toward the back of the body

    • Example: The vertebral column is posterior to the sternum.

  • Medial vs Lateral:

    • Medial = toward the midline of the body

    • Example: The nose is medial to the ears.

    • Lateral = away from the midline

    • Example: The shoulders are lateral to the neck.

  • Ipsilateral vs Contralateral:

    • Ipsilateral = on the same side of the body

    • Example: The right arm and right leg are ipsilateral.

    • Contralateral = on opposite sides

    • Example: The right arm and left leg are contralateral.

  • Proximal vs Distal:

    • Proximal = closer to the point of attachment to the trunk

    • Example: The elbow is proximal to the wrist.

    • Distal = farther from the point of attachment to the trunk

    • Example: The fingers are distal to the elbow.

  • In anatomical terminology, the trunk refers to the main, central part of the body, distinct from the head and limbs (arms and legs). It is the region to which the upper and lower limbs attach. For example, the terms proximal and distal describe positions relative to the point of attachment to the trunk, where proximal means closer to the trunk and distal means farther from it.

  • Superficial vs Deep:

    • Superficial = closer to the surface

    • Example: The skin is superficial to the muscles.

    • Deep = further from the surface

    • Example: The bones are deep to the muscles.

  • Peripheral:

    • Peripheral refers to the outer regions or edges of an area (as opposed to central).

    • Example: Peripheral nerves extend from the central nervous system to the limbs.

  • Note: The terms are used to describe relative positions and should be interpreted in the context of anatomical position.

  • The paired directional terms are often illustrated in figures (e.g., Figure 1.13).

Body Planes

  • A section is a two-dimensional surface of a three-dimensional structure after it has been cut.

  • Planes of section:

    • Sagittal plane: divides the body into left and right parts

    • Midsagittal (Median) plane: divides equally into left and right halves

    • Parasagittal plane: divides into unequal left and right parts

    • Transverse (Horizontal) plane: divides the body into superior (upper) and inferior (lower) parts

    • Coronal (Frontal) plane: divides the body into anterior (front) and posterior (back) parts

  • For cylindrical organs (e.g., blood vessels, certain ducts):

    • Cross section: perpendicular to the long axis

    • Oblique: at an angle to the long axis

    • Longitudinal: along the long axis

  • The three planes most commonly used in anatomical study and medical imaging are:

    • Sagittal (left-right division)

    • Frontal/Coronal (anterior-posterior division)

    • Transverse (superior-inferior division)

  • Figure references: Figure 1.14 illustrates the Planes of the Body; Figure 1.13 shows directional terms applied to the human body.

Dorsal and Ventral Body Cavities

  • The ventral cavity includes:

    • Thoracic cavity

    • Abdominopelvic cavity and their subdivisions

  • The dorsal cavity includes:

    • Cranial cavity

    • Spinal (vertebral) cavity

  • These cavities house major organs and are lined by serous membranes (serosa) in many regions.

Regions and Quadrants of the Peritoneal Cavity

  • Figure 1.16 presents regions and quadrants within the peritoneal cavity, including:

    • Right lateral region

    • Left lateral region

    • Right inguinal region

    • Pubic region

    • Left inguinal region

  • These regional and quadrant divisions help describe the locations of abdominal organs and pathologies relative to the peritoneal cavity.

Serous Membranes (Serosa) and Their Functions

  • A serous membrane is a thin, double-layered membrane that covers walls and organs within the thoracic and abdominopelvic cavities.

  • Major serous membranes and their associated cavities:

    • Pleura: serous membrane around the lungs in the pleural cavity

    • Pericardium: serous membrane around the heart in the pericardial cavity

    • Peritoneum: serous membrane around several abdominal and pelvic organs in the abdominopelvic cavity

  • Structural concept: the serous membrane forms two layers with a potential space (serous cavity) between them, allowing frictionless movement of organs.

  • Analogy described: the serous membrane lines the pericardial cavity and reflects back to cover the heart, similar to how an underinflated balloon forms two layers surrounding a fist.

Regional Terms and Anatomical Views

  • The human body is shown in anatomical position in both anterior and posterior views to label and identify regional terms.

  • Regions are labeled in boldface in the accompanying figure (Figure 1.12).

  • Understanding regional terminology helps in describing specific areas of the body (e.g., cephalic, thoracic, abdominal, pelvic regions; upper limb and lower limb divisions).

Practical and Foundational Connections

  • Why these terms matter:

    • Essential for clear communication in clinical settings (diagnosis, imaging, surgery, anatomy education).

    • Provide a standardized language for describing locations, injuries, and procedures.

  • Connections to imaging and medical practice:

    • Planes determine how imaging slices are obtained (CT, MRI, ultrasound).

    • Cavities and serous membranes relate to disease processes (e.g., effusions, inflammation) and organ positioning.

  • Ethical and practical implications:

    • Precise terminology reduces miscommunication that could affect patient safety.

    • Proper understanding of anatomy supports accurate diagnosis and effective treatment planning.

Figures Referenced in the Transcript

  • Figure 1.13: Directional terms applied to the human body (paired directional terms).

  • Figure 1.14: Planes of the body (sagittal, frontal/coronal, transverse).

  • Figure 1.15: Dorsal and ventral body cavities (ventral includes thoracic and abdominopelvic cavities; dorsal includes cranial and spinal cavities).

  • Figure 1.16: Regions and quadrants of the peritoneal cavity (right lateral, left lateral, right inguinal, pubic, left inguinal).

  • Figure 1.17: Serous membranes (pleura, pericardium, peritoneum) and their roles in lining cavities and covering organs.

Source Note

  • This content is adapted from an OpenStax ancillary resource (\copyright
    Rice University) under a CC-BY 4.0 International license. Attribution to OpenStax, Rice University; changes and text additions noted where applicable.