Lesson · A.1.1
Anatomical terms, planes and directions
The anatomical position, the three body planes, and the directional term pairs the HESI A2 expects you to apply to a diagram, not just define.
By the end of this lesson you can
- Describe the standard anatomical position and explain why every directional term assumes it.
- Name the three main body planes and say what each one separates.
- Apply the paired directional terms (superior/inferior, proximal/distal, and so on) to a labelled figure or a clinical description.
The HESI A2 Anatomy and Physiology subtest opens this unit with terminology because the rest of the exam assumes you already have it. A question about the kidneys or the heart will casually use "posterior" or "proximal" without pausing to define it, so if the vocabulary is not automatic, you lose time translating rather than answering.
The anatomical position
Every directional term in anatomy is defined relative to one fixed reference posture: the anatomical position. The body stands upright and faces forward, the feet are flat on the floor and a little apart, the arms rest at the sides, and the palms turn forward so the thumbs point away from the body.
That last detail matters more than it looks. Palms forward rotates the forearm so the radius and ulna lie side by side rather than crossed, which is the reason "anterior" on the forearm reliably means the palm side in every textbook diagram and every HESI figure.
The three body planes
A plane is an imaginary flat surface used to section the body for description or imaging. The HESI A2 expects you to know three.
| Plane | Also called | What it separates |
|---|---|---|
| Sagittal | (midsagittal if exactly midline) | Right side from left side |
| Frontal | Coronal | Front (anterior) from back (posterior) |
| Transverse | Cross-sectional, axial | Upper (superior) from lower (inferior) |
A sagittal plane runs front to back and divides the body into right and left portions. Only one specific sagittal plane, the one running exactly down the midline, produces equal right and left halves. Any other sagittal cut still separates right from left, just not into two identical pieces.
A frontal or coronal plane runs side to side and top to bottom, dividing the body into a front section and a back section, the way a door standing in its frame separates what is in front of it from what is behind it.
A transverse plane runs horizontally, dividing the body into an upper portion and a lower portion. This is the plane a CT scanner uses to generate the stacked cross-sectional slices radiology reports call axial images.
Oblique plane. Any cut that is not purely vertical or purely horizontal, made at an angle between the three standard planes. Less tested than the main three, but recognise the term if it appears.
Directional term pairs
The HESI A2 tests these as opposites, so learn them in pairs rather than as an isolated list.
- Superior / inferior: toward the head versus toward the feet. The heart is superior to the stomach.
- Anterior (ventral) / posterior (dorsal): toward the front of the body versus toward the back. The sternum is anterior to the heart.
- Medial / lateral: toward the midline of the body versus away from it. The nose is medial to the ears.
- Proximal / distal: closer to the point where a limb attaches to the trunk versus farther from it. The elbow is proximal to the wrist.
- Superficial / deep: closer to the body surface versus further into the body. A graze is superficial; a stab wound that reaches muscle is deep.
- Cranial / caudal: toward the head versus toward the tailbone end of the body, used mainly along the spine.
- Ipsilateral / contralateral: on the same side of the body versus on the opposite side.
Proximal and distal cause the most missed HESI items because they feel like they should mean "up" and "down." They do not. They are measured along a limb from its point of attachment to the trunk, so on the leg, the hip is proximal and the toes are distal, and on the arm, the shoulder is proximal and the fingertips are distal, regardless of whether the limb is raised, lowered, or bent.
Directional terms describe a fixed relationship in anatomical position, not the orientation of the patient in front of you.
Quick self-check. If a term still feels ambiguous, ask which of the three planes would show it best. Right versus left is a sagittal question, front versus back is a frontal question, and top versus bottom is a transverse question.
Redraw the figure, not just the label, whenever a question stacks two or three of these terms together ("the structure lateral and superior to the umbilicus"). The terms are simple individually. The exam earns its difficulty by combining them, so practise applying pairs together before you move to the next lesson on body cavities and regions.
- Every directional term is relative to the anatomical position, not to however the patient happens to be lying.
- The three planes are sagittal (left/right), frontal or coronal (front/back), and transverse (upper/lower).
- Proximal and distal describe distance from the trunk along a limb, not up or down in space.
- Ipsilateral means same side, contralateral means opposite side, and both are common on HESI wording and in charting.
- Ambiguous HESI items usually resolve if you redraw the figure in anatomical position before you answer.
Check yourself
0 / 51Which description matches the standard anatomical position that every directional term is based on?
2In anatomical position, why does 'anterior' reliably mean the palm side of the forearm on anatomy diagrams?
3A colleague says, 'Since this patient is curled on their side, we should call whichever part is currently facing the ceiling superior.' What is the mistake in this reasoning?
4A cut is made through the body running front to back, but well to the right of the midline rather than exactly down the centre. Which statement about this cut is accurate?
5Which pair of body sections does a frontal, or coronal, plane divide the body into?