Body planes and sections
A plane is an imaginary flat surface passed through the body, and a section is what that plane exposes. This chapter names the three standard planes, shows why the same plane meets different organs at different levels, and teaches you to read the direction letters printed on any image.
By the end of this chapter you can
- Name the three standard planes, give the synonyms transverse and frontal, and state which body portions each plane separates.
- Tell a midsagittal plane from a parasagittal plane and name organs that only one of them can cross.
- Explain why two sections in the same plane can show different organs, and name what an axial plane meets at the nipples, the navel, and the hips.
- Explain what a single section can and cannot show, and why neighboring sections are needed to follow a tube-shaped structure such as the aorta.
- Read the letters R, L, A, P, S, and I on an image as the patient's own directions, recognize an oblique plane, and tell a long-axis view of an organ from a short-axis view.
Three planes, three ways to cut
A is an imaginary flat surface passed through the body, like a pane of glass. Anatomy names three standard planes, and each one cuts through the body in a different direction.
An plane, also called a plane, cuts straight across the long axis of the body. In a person standing in anatomical position it lies parallel to the floor. It divides the body into superior and inferior parts, like a cut across a loaf of bread.
A plane, also called a plane, stands upright and runs from side to side, passing from one ear to the other like a crown. It divides the body into anterior and posterior parts.
A plane also stands upright, but it runs from front to back, like an arrow passing through the nose and out the back of the head. It divides the body into right and left parts. Sagitta is the Latin word for arrow.
Each plane separates exactly one pair of directions: axial separates superior from inferior, coronal separates anterior from posterior, and sagittal separates right from left. The other two pairs lie within the plane, so it cannot separate them.
Like directions, planes travel with the body. When a patient rolls from to , the coronal plane through the chest still separates anterior from posterior.
In the figure below, choose Axial, Coronal, or Sagittal to see that plane on its own.
Interactive model
Three planes through one body
All three planes meet in the chest. Pick one to see the section it makes, then move it.
Three planes at right angles. Each one separates one pair of directions. The dashed lines show where the other two planes cross each section.
Body location map
Midsagittal and parasagittal
Only one sagittal plane passes exactly through the and splits the body into equal right and left halves. This is the plane, also called the median plane.
Every other sagittal plane runs parallel to the midsagittal plane but lies to one side of it. These are planes, and para means beside. A plane only two centimeters from the midline is parasagittal, and so is a plane through the shoulder.
The midsagittal plane passes through structures that sit on the midline, such as the sternum (the breastbone), the vertebral column (the spine), and the urinary bladder. It misses every paired organ, since the two eyes, the two lungs, and the two kidneys lie lateral to the midline, one on each side.
Slide the plane six centimeters toward the patient's right and it becomes parasagittal. It now cuts through the right lung, the liver, and the right kidney, and it passes lateral to the spine.
In many places the two sides of the body are near mirror images, so a parasagittal section through the right side can look much like one through the left. The letters printed on the image always refer to the patient, which makes them the surest way to tell the two sides apart.
Same plane, different level
Every slice of a loaf faces the same way, yet each shows a different part of the loaf. The same is true of body planes: the type of plane gives the direction, and the gives the position along the body. A level is named by a the plane passes through, such as axial at the kidneys or coronal through the hip joints.
At the level of the nipples, an axial plane passes through the chest and cuts the heart with a lung lateral to it on each side. Moved inferiorly to the upper abdomen, the same plane meets the liver on the patient's right and the stomach on the patient's left.
A hand's width further inferiorly, at the level of the navel (the belly button), the plane meets the kidneys. It also crosses the and , the body's largest artery and vein, which lie anterior to the spine. At the level of the hips, inside the pelvis, it meets the urinary bladder anteriorly and the rectum (the last part of the bowel) posteriorly.
Parallel axial planes are stacked from superior to inferior, parallel coronal planes from anterior to posterior, and parallel sagittal planes side by side from right to left. Move the plane through the transparent body below and watch which organs light up at each level.
Interactive model
Move the plane through the organs
Slide the plane or jump to a landmark and watch the section change. Then try the three tasks.
lies flat, like slicing a loaf of bread. It separates upper from lower.
Body location map
What this slice shows
Seen from the feet, the way axial images are shown, so the patient's right is on your left.
Axial through the heart
Try it
0 of 3 done
What one section can and cannot show
A is the flat surface a plane exposes at one position. It shows only the structures the plane touches there, so a structure that is missing from one section may simply lie superior or inferior to it.
Because a section is flat, it can mislead you about shape. A sausage sliced across shows a small circle, and the same sausage sliced lengthwise shows a long strip. The aorta is a long tube, and sections show it the same way. On an axial section it is a small circle anterior to the spine, and on a coronal or sagittal section it is a long stripe running along the trunk. A circle in one section can therefore be a long tube passing through the plane.
For this reason, never judge a structure from a single . Follow it through the neighboring sections, where a tube stays a circle at level after level and a solid organ grows, shifts, and shrinks. On axial sections the kidney is a small oval near its superior end, widens through its middle, and narrows again toward its inferior end. Scrolling through the sections in this way rebuilds the three-dimensional organ in your mind.
Sagittal: the aorta as one long stripe
Axial: five neighbors, top to bottom
A ring in front of the spine at every level. Same size, same place: a tube passing through each plane.
Reading the letters on an image
Images carry small letters at their edges, and each letter names a direction on the patient, never on the viewer. R and L are the patient's right and left, A and P are anterior and posterior, and S and I are superior and inferior. Some systems print H and F, for head and feet, in place of S and I.
An axial image is displayed as if you were standing at the patient's feet and looking toward the head. The patient's right therefore appears on the left side of the picture, and the R marker sits at the left edge. This is why the liver, which lies on the patient's right, appears on the left of an axial image.
The letters also tell you which plane you are looking at. An axial image has R and L on its sides, with A at the top and P at the bottom. A coronal image has R and L on its sides, with S at the top and I at the bottom. It is displayed as if you were facing the patient, so the patient's right again appears on the left of the picture. A sagittal image has A and P on its sides, with S at the top and I at the bottom. Read the letters before you name any structure, because an image can be flipped or turned while the letters stay attached to the patient.
Oblique planes
An plane is a plane tilted away from all three standard planes. Oblique planes are useful because many organs sit at an angle inside the body, and the standard planes cut them crookedly.
The heart lies tilted, with its tip pointing inferiorly and to the patient's left. Each kidney leans so that its superior end is more medial than its inferior end. The spine curves, and the discs between its bones, the vertebrae, follow that curve. A plane angled to match one of these structures shows it in one clean piece, while the standard planes scatter it across several sections.
Oblique planes are described with the same words as the standard planes. Each one is tilted from axial, coronal, or sagittal, and its level is named by a landmark it passes through.
Sliding a plane and tilting it are different moves. Sliding keeps the plane's direction and changes only its level, so an axial plane stays axial. Tilting changes the direction itself, and that change is what makes a plane oblique.
Long axis and short axis
An organ that sits at an angle has its own axis, the line that runs along its length. A plane lined up with that axis gives a long-axis view, and a plane at a right angle to the axis gives a short-axis view. A banana shows the difference: a lengthwise cut gives one long strip, and a cut across gives a round coin. Both are oblique planes, named for the organ's own axis.
The heart lies tilted in the chest, with its tip pointing inferiorly, anteriorly, and to the patient's left, so the standard planes cut it at awkward angles. A long-axis view follows the heart from its base to its tip and shows its chambers end to end. The heart's two main pumping chambers are the left and right . A short-axis view cuts straight across both ventricles: the thick wall of the left ventricle shows as a ring, with the thinner right ventricle curved against it like a crescent.
The uterus (the womb) usually tips anteriorly and rests on the bladder, so its long axis is tilted too. Like the heart, it is viewed both along its length and across it.
Optional: a look ahead to MRI
A first look at MRI
Four MRI examples to browse: each shows its plane and the anatomy it crosses.
sagittal plane
Brain (midline)
The brain in profile. The face points to the viewer's left, the cerebellum tucks under the back of the brain, and the brainstem runs down toward the spinal cord. Anterior to posterior and superior to inferior are both in the picture, so this is sagittal.
Midline sagittal slice; anterior (face) is to the left.
Practice
Read a section
Six quick questions on sections cut from the model: tap an organ, name a plane from its letters, or name the level. Practice only, nothing is graded.
Key ideas to remember
- (transverse) separates superior from inferior, (frontal) separates anterior from posterior, and separates right from left.
- Only the plane splits the body into equal halves. Every other sagittal plane is and can cross paired organs such as a lung or a kidney.
- The plane gives the direction and the level gives the location, so an axial plane at the nipples meets the heart while the same plane at the hips meets the bladder.
- A section shows only what the plane touches, so follow a structure through neighboring sections. Read the R, L, A, P, S, and I letters as the patient's own directions.
Check what you learned
Twenty-five questions from this chapter, two of them illustrated, each with the answer, the reasoning, and a memory aid.
1 of 4: The patient lies supine. Seen from above with the head at the top. The patient's right hand is on your left, and so is the liver.
1 of 5: Axial. The plane lies flat, parallel to the floor.