ANATOMICAL TERMINOLOGIES

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 Navigating Anatomy with Language

Directional terms provide precise descriptions of a structure's location. They allow a description of anatomical position by comparing location relative to other structures or within the rest of the body. Standard anatomical terms for direction include:


1. Superior and inferior (cranial and caudal) are used when referring to parts of the body which are toward an end of the body. Superior structures are toward the head (cranial) while inferior (caudal) structures are toward the feet. Examples include the superior and inferior vena cava, which carry deoxygenated blood away from the head (superior) and from the lower body (inferior) to the heart.

2. Anterior and posterior are sometimes used in place of superior and inferior, respectively. These words are used more often for animal anatomy and rarely and only with very specific meaning in human anatomy. Anterior refers to the side of the structure facing up in the standard anatomical position while posterior refers to the bottom side. For example, the pituitary gland has an anterior and posterior side, each of which secretes different types of hormones.

3. Dorsal and ventral are sometimes used in place of anterior and posterior, respectively. Dorsal means the back side or upper side, while ventral means the frontal or lower side. These are mostly used with animal anatomy, but can be used in human anatomy as long as they are describing the side of an appendage. One example is the dorsal fin in fish, found on the upper side of the fish's body.

4. Lateral is used to describe anything closer to the sides of the body (toward the arms, in the standard anatomical position), while medial is used to describe anything toward the middle of the body. In general, many structures of the human body are bilateral and symmetrical with the middle of the body, such as the lungs or the arms.

5. Deep refers to structures closer to the interior center of the body. For example, bones in an appendage are located deeper than the muscles. Superficial is used to describe structures that are closer to the exterior surface of the body. For example, the outer layers of skin are superficial to deeper layers of skin.

6. Proximal and Distal describe one point relative to another. Proximal refers to a point closer to the reference point while distal refers to a point farther away. When describing appendages, the proximal end of the appendage connects the appendage to the body, while the distal end is away from the body.


Diagram of anatomical termterms




Directional axes in a tetrapod.


This image uses a drawing of a horse to demonstrate the terms cranial, caudal, proximal, distal, dorsal, and ventral.



Regional terms describe anatomy by dividing the parts of the body into different regions that contain structures that are involved in similar functions. Two primary terms are used to describe the main regions of the body:


1. The Axial Region makes up the main axis of the human body and includes the head, neck, chest, and trunk.

2. The Appendicular Region makes up the parts of the human body that connect to the axial region. This includes the limbs and appendages.

These are the two basic categories of regional terms; however, many other terms are used to describe smaller regions within the axial and appendicular regions. For example, the brachial region consists of the arm as a part of the appendicular region, while the abdominal region consists of the abdomen as a smaller part of the axial region. 


  The abdominal region is subdivided into even smaller regions based on different functions of groups of organs and tissues in that region. If a person is experiencing pain in one part of the abdominal region, then the smaller regional divisions can help determine the organs involved in the problem to better treat symptoms.


Axes Describe Relative Positions

Another method for describing region An axis uses a straight line between two parts of the body to describe a region of the body with linear direction. For example, blood can be said to flow in a proximal or distal direction through a region marked by that axis. The X, Y, and Z axes of the Cartesian coordinate system are used describe the specific location of an axis in standard anatomical position. 


Many types of axes can give regional direction. Any pair of corresponding directional terms can be combined to form an axis (such as proximal-distal for an appendage).


i. The Dorsoventral axis (DV axis) is formed by the connection of the dorsal and ventral points of a region. The region between the belly (ventral) and back (dorsal) is often described by a DV axis.

ii.  The Anterioposterior axis (AP axis) is the axis formed by the connection of the anterior (top) and posterior (bottom) ends of a region. The AP axis of a region is by definition perpendicular to the DV axis and vice-versa.

iii. The Left-to-right axis is the axis connecting the left and right hand sides of a region. It is used to describe the lateral sides of a region, which in humans are often symmetrical around the center of the body. It is perpendicular to both the DV and AP axes.




Different Directional AP Axes in Three Body Segments of a Horse

Axis (A) (in red) shows the AP axis of the tail, (B) shows the AP axis of the neck, and (C) shows the AP axis of the head.


In this image, a horse is labeled with directional terms including anterior, posterior, distal, ventral, dorsal, and proximal. In addition, three red arrows indicate potential axes: one the length of the horse's tail, one the length of the neck, and one the length of the head.

Axes give more clarity and detail for describing the location of an anatomical region. They are commonly used in both zoology and human anatomy, and can be paired with body planes to give even more detail to anatomical direction, region, and location.

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