Comparison of Traditional Anatomy and Sectional Anatomy

In typical anatomy and physiology courses, the emphasis is on studying body systems. For example, you learn the entire skeletal system before moving on to the muscular system. You study all the organs of the digestive system, their location, structure, and how they relate to each other functionally. In sectional anatomy, you study regions instead of systems, and the focus is on the anatomical relationships of all structures within a given region, such as the thorax or abdomen. The traditional approach to anatomy is to study an entire organ. In sectional anatomy, the anatomy is viewed on what is commonly called a slice of the body. In other words, imagine the body (or organ) as a thinly sliced loaf of raisin bread. Each slice of bread has a different appearance because of the different number and positions of the raisins.

Visualization of an entire organ may require several sequential slices. Returning to the analogy of the raisin bread, finding all the pieces of a single raisin may require looking at several sequential slices, because the raisins have been sliced along with the bread. The same is true for visualizing slices of the body. By studying the anatomical relationships in sequential slices, you develop a more thorough understanding of anatomy. Sophisticated imaging equipment can take the information from the slices and create a three-dimensional (3D) image.

For orientation of a transverse (axial) slice, when viewing either the inferior of a cadaveric slice or a real image, imagine that the patient is supine and you are standing at the person’s feet looking up into the patient’s body. This means that your right is the patient’s left. Fig. 1-1 shows a transverse CT image through the abdomen that illustrates this orientation. The right lobe of the liver, inferior vena cava, and caudate lobe of the liver are on the patient’s right side, but they are on the left side of the image. The left lobe of the liver, the stomach, the spleen, and the left kidney are on the patient’s left side, but they are on the right side of the image. The aorta is slightly to the left of midline. Correct orientation is critical to proper identification of structures.

Now, a couple of cautionary notes for learning sectional anatomy:

1. A given organ varies in appearance at different levels in the same individual. Fig. 1-2 shows images of the liver at three different levels. Notice the changes in appearance at the different levels.

2. Attempting to memorize images likely will lead to mistakes, because no two images are the same. Every individual is different, and even images of the same individual taken at the same level differ because of breathing and involuntary movements. The key is understanding, not memorization.

Before you begin the study of sectional anatomy, it may be profitable to review some of the terminology and concepts you learned in gross anatomy or anatomy and physiology. This can help get you back into the “anatomy” mode and provide a common foundation for the class. The introductory material includes body planes, directional terms, body cavities, membranes of the body cavities, and regional terminology.

Body Planes

To visualize the spatial relationships of internal body parts, the body is sectioned, or cut, along a flat surface, or plane. The ability to interpret sections in various planes is becoming increasingly important in the clinical sciences, especially in the imaging sciences. The three most commonly used planes are the transverse (axial), sagittal, and frontal (coronal) planes, which are at right angles to each other (Fig. 1-3). By analyzing body parts in all three planes, you develop an understanding of the anatomical relationships within the body.

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