Most of today’s medical terms are formed from Greek and Latin roots, few have Arabic origins. All terms used in medicine to describe human body are standardized in an international reference guide, Terminologia Anatomica. These terms are the foundation of medical terminology and it is important that doctors and scientists throughout the world use the same name for each structure. Even though different nations elaborate and use their own set of medical terms, based on standard Latin terms, the communication and progress in the medical field are possible thanks to the common and precise scientific language. Hence, you should always rely on this resource guide, which lists the proper anatomical terms and organizes them for all body systems. Similar resources are available for histological and embryological terminology.
The general rule of the Terminologia Anatomica system is that there should be one term for each structure and that the term should have some informative and descriptive value. The eponyms, i.e., terms derived from the name of a real or mythical individual, are often used in medicine, but are not recommended, because they do not provide anatomical context and often are not standardized.
Take these three terms as an example: Bertin’s bone, Bertin’s column, Bertin’s ligament. The first one is not actually a bone, but a part of the sphenoid bone, called sphenoidal concha. The second term refers to the structure located in the kidney (renal column), while the third term indicates a ligament strengthening the coxofemoral joint, properly called iliofemoral ligament. Hence, these eponyms give no indication as to the type or localization of the structure. Another problem with eponyms is that, in some cases, the name given to a certain structure is not actually that of the researcher who described it first. Also, the correct pronounciation of such terms requires the knowledge of person’s nationality. All in all, it is best to avoid eponyms while describing human anatomy.
Description of the body, with its parts, regions, and organs, requires an initial point of reference and the use of common descriptors. Hence, in anatomy, and in medical practice, it is assumed that the body is in an anatomical position.
In the anatomical position, an individual stands upright in front of an examiner, with the lower limbs close together, the feet parallel and slightly separated, and the toes directed anteriorly; the head is leveled and the eyes look forward; the upper limbs run down at the sides of the body with the palms facing forward.
All the anatomical descriptors refer to the body in the anatomical position, even if only parts or sections of the body are being considered. In practice, anatomists identify and locate body structures, while health-care professionals observe and locate any change to them, using descriptive terms based on the premise that the body is the anatomical position. Hence, you should always keep that position in mind, in order to be able to do the same throughout your anatomy studies.
Anatomists typically study and describe human body and organs in dissection, often referring to slices or sections, performed along different planes; similarly, radiologists examine human body by means of diagnostic imaging techniques in different planes.
A horizontal plane (also called transverse plane) cuts perpendicularly across the long axis of the body, hence it separates the body into superior (upper) and inferior (lower) parts. The horizontal planes lie at right angle to the coronal and sagittal planes. It is the most common plane used in computed tomography and magnetic resonance imaging; radiologists often call it an axial plane and use it obtain transverse sectional images (scans) of the body for study.
A coronal plane, also called a frontal plane, is a vertical plane passing through the body from side to side, thus dividing it into anterior and posterior parts. The coronal planes lie perpendicular to sagittal planes.
A sagittal plane, is a vertical plane passing through the body from the front to the back and divides the structures into left and right parts. The sagittal planes lie perpendicular to coronal planes. The sagittal plane that divides the body into right and left halves (equal parts) is referred to as the median plane.
Sections may be obtained by anatomical sectioning or medical imaging techniques. The three anatomical sections used for displaying internal structures are the longitudinal, transverse and oblique sections.
Regardless of the position of the body, a longitudinal section runs lenghtwise or parallel to the long axis, while a transverse section (cross section) runs perpendicular to the long axis of the whole body or body part, hence crossing it at right angle. Finally, an oblique section does not run along any standard anatomical plane.
It is worth noting that a transverse section of the foot is made in the coronal plane of the body (the long axis of the foot runs horizontally and the transverse section must be perpendicular to it), while the same section of the trunk runs along the horizontal plane of the body (the transverse section is done perpendicularly to the long axis of the trunk, which runs vertically). Importantly, a longitudinal section can be actually obtained in any plane, as long as it runs along the long axis of the body or its part, and not only in two standard anatomical vertical planes, i.e. coronal and sagittal planes.
While there is only one median plane, the number of horizontal, coronal and sagittal planes sectioning the body is unlimited. For this reason, it is important to specify the location or level of every described section (e.g. transverse section through the forth thoracic vertebra).
Anatomical terms of position and movements
Terms of position and relationship
Directional terms are used to describe the location of one body part with respect to another. They can be arranged as pairs of opposites.
Two ipsilateral structures lie on the same side of the body, while those on the opposite sides (left and right) are called contralateral. Superior refers to a structure located above another structure in the body in the anatomical position, hence nearer the head; inferior refers to a structure that is below another structure, or closer to the feet. Anterior means in front of another structure, or closer to the front surface of the body, while posterior means behind another structure or toward the back. Medial is used to indicate that a structure lies closer to the median plane of the body; lateral denotes that a structure is further away from the median plane than another structure. Proximal refers to a part that is closer to, while distal is further away from, the origin or attachment point of a structure.
Terms of movements - flexion and extension
Movements occur in anatomical planes and around axes. Flexion and extension occur in a sagittal plane, around a transverse axis. Flexion, generally, is a reduction in the angle between two body parts and a movement in an anterior direction, while extension is related to a straightening or an increase in the angle between two body parts, caused by a movement in a posterior direction.
Two exceptions are evident in humans, i.e. the knee and ankle joints, which acquired particular orientation related to the upright position. Flexion of the knee involves posterior movement and extension involves anterior movement of the leg. An upward movement at the ankle joint, lifting only the front of the foot and toes off the ground, is a dorsiflexion, while plantarflexion is a downward movement of the foot.
Terms of movements - abduction and adduction
Abduction and adduction occur in a frontal plane, around a sagittal (anteroposterior) axis. Abduction, generally, is a movement away from the median plane of the body, while adduction moves a body part toward it.
When movements of the digits are considered, the reference plane is the median plane of the hand or foot and it is assumed that it runs through the 3rd (middle) finger or the 2nd toe. For instance, abduction of fingers means spreading them apart away from, while adduction means bringing the fingers together toward, the middle finger.
Terms of movement - rotation
Rotation of a body part occurs around its long axis. Medial rotation, also called internal rotation, brings the anterior surface of the limb closer to the median plane of the body. Movement in the opposite direction, which brings the anterior surface of the limb away from the median plane, is called lateral or external rotation. When the head rotates around the longitudinal axis to face sideways, the movement is simply called lateral, left or right, rotation of the head and neck.
Terms of movement - rotation of hand and feet
Specific terms are used to describe rotational movements of the distal upper limb and feet. Rotational movements of the forearm and hand are called pronation and supination. Pronation moves the hand so that the palm faces posteriorly, when starting from the anatomical position, or inferiorly, when the elbow is flexed. Supination is the opposite movement, directing the palm of the hand, respectively, anteriorly or superiorly. If you find it difficult to associate these two terms with the movements they describe, remember that you can hold a coffee cup in the supinated hand, but it is prone to fall if you pronate your hand.
Rotational movements of the feet are called eversion and inversion. Eversion moves the feet so that the sole turns outwards, i.e. away from the body median plane, raising the lateral margin of the foot. Eversion is not an isolated movement of the foot, as it is associated with dorsiflexion and abduction of the foot; this combined movement is called pronation of the foot. Inversion is the opposite movement, which rotates the sole inwards, i.e. toward the median plane, raising the medial margin of the foot. When the foot inverts, it also adducts and plantarflexes; this combined movement produces supination of the foot.
Movements of thumb
Movements of the thumb occur in the planes different from that of other digits, since the thumb is medially rotated by 90o at its carpometacarpal joint in the anatomical position. Hence, flexion and extension occur in a coronal plane, while abduction and adduction occur in a sagittal plane. Opposition is a particular and complex movement that brings the tip of the thumb in contact with the pads of other fingers.
Reference lines - vertical lines of the thorax
It is important to know the location of body organs and their projection on the body surface, so that an examiner knows where to auscultate, percuss, or palpate them and can document precisely the location of pathological findings during a physical examination. To that scope, several imaginary lines on the anterior or posterior trunk wall are often used as reference.
Vertical lines of the thorax:
- anterior median line – lies in the median plane over the sternum; the apex beat of the heart is typically felt in the 5th left intercostal space, 9 cm laterally from the anterior midline;
- sternal line – runs next to the lateral margin of the sternum;
- midclavicular line – runs from the midpoint of the clavicle;
- parasternal line – lies midway between the sternal and midclavicular lines;
- anterior axillary line – runs from the anterior axillary fold, formed by the margin of the pectoralis major muscle;
- midaxillary line – runs from the apex of the axillary fossa;
- posterior axillary line – runs from the posterior axillary fold, formed by the margin of the lattissimus dorsi muscle;
- scapular line – passes through the inferior angle of the scapula;
- paraverterbal line – typically used in radiology, runs along the tips of the transverse processes;
- posterior median line – along the tips of the spinous processes of the vertebrae.
Reference lines - transverse planes of the trunk
Transverse planes of the trunk:
- transverse thoracic plane – runs horizontally across the sternal angle (at the junction between the manubrium and body of the sternum) and the intervertebral disc between the 4th and 5th thoracic vertebrae; the trachea bifurcates at this level;
- transpyloric plane – runs horizontally midway between the superior border of the manubrium of the sternum and the superior border of the pubic symphysis, typically crossing the 1st lumbar vertebra; it is termed so, because it commonly crosses the pylorus (the distal end of the stomach) when a patient is lying down;
- subcostal plane – passes through the lowermost palpable points of the costal arch, which correspond to the costal cartilages of the 10th ribs;
- transumbililcal plane - passes through the umbilicus and generally marks the level of the disc between the 3rd and 4th lumbar vertebrae;
- supracristal plane – passes through the uppermost palpable points of the iliac crest, typically crossing the 4th lumbar vertebra;
- intertubercular plane – passes through the iliac tubercles, which can be palpated approximately 5 cm posterior to the anterior superior iliac spine on each side, typically crossing the 5th lumbar vertebra;
- interspinous plane – passes through the easily palpated left and right anterior superior iliac spines.
For general descriptions, clinicians usually divide the abdomen into for quadrants, using the vertical anterior median line and horizontal transumbilical line. These lines, intersecting at a right angle, create 4 quadrants (right and left upper and lower).
For more accurate descriptive and diagnostic purposes, two vertical lines and two horizontal lines can be drawn in order to create nine abdominal regions. The vertical lines are the right and left midclavicular lines, while the horizontal lines run along the subcostal (or, alternatively, transpyloric) and intertubercular (or interspinous) planes. The abdominal regions are, on either side, right and left hypochondrium, flank or lateral region, and groin or inguinal region; centrally located regions are called epigastric region or epigastrium, umbilical region, and pubic region or hypogastrium.
Correct use of these descriptive quadrants and regions is essential in clinical practice, as each area overlies the parts of abdominopelvic cavity containing different organs. The knowledge of their location allows examination of single organs and correlation of pain to specific structures (in the referred pain, though, the pain and the organ where the pathology occurred may lie in different regions).
Anatomical terms are descriptive terms standardized in an international reference guide, Terminologia Anatomica, and should be used worldwide. Colloquial terminology can be used to communicate with patients.
Anatomical directional terms refer to the body in the anatomical position. Three standard anatomical planes (transverse, frontal, and sagittal) divide the body to obtain sections. Other anatomical terms describe relationships of body parts, compare the position of structures, or describe movement.
And now, on a lighter note, you can enjoy this interactive tutorial about medical terms.
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