Regions of the human body are named areas used to describe where structures lie and how they relate to one another. The body is divided into axial and appendicular parts, then into smaller regions such as the head, neck, trunk and limbs. The abdomen also has regional and quadrant maps.
What are the axial and appendicular parts of the body?
The axial part forms the central portion of the body: the head, neck and trunk. The appendicular part comprises the upper limbs and lower limbs, together with the girdles that connect them to the trunk. A girdle is a supporting arrangement of bones through which a limb attaches to the axial skeleton, the bones of the central body.
These are divisions of the whole body, not just its skeleton. Each region contains several kinds of structure, including skin, muscles, vessels and nerves. A region is therefore a location rather than a single organ or tissue type.
Regional descriptions assume the anatomical position: standing upright, facing forwards, with the arms at the sides and the palms facing forwards. Right and left always refer to the person being described, not to the observer. Anterior means towards the front, and posterior means towards the back.
What belongs to the head and neck?
The head includes the cranial region, which surrounds the brain, and the facial region, which includes the face. Smaller named areas include the forehead, temple, cheek and chin. These surface regions help locate structures without requiring a description of the entire head.
The neck connects the head to the trunk. It contains the cervical vertebrae, the neck portion of the vertebral column or spine, as well as muscles, vessels, nerves and passages for air and food. Its upper boundary lies beneath the head, while its base meets the upper thorax and shoulder regions.
The head and neck are often studied together because many structures continue between them. Nevertheless, they remain distinct regions: a vessel passing through the neck does not become a different kind of structure when it enters the head.
How is the trunk divided into thorax, abdomen, pelvis and back?
The trunk is the central body below the neck, excluding the limbs. Its principal regional descriptions include the thorax, abdomen, pelvis and back. These names describe connected areas rather than completely separate boxes.
- Thorax: the chest region, enclosed by the ribs, breastbone and thoracic vertebrae, the vertebrae of the chest. Its cavity, or internal space, contains the lungs and heart. The diaphragm, a muscular partition, separates the thoracic cavity from the abdominal cavity.
- Abdomen: the region between the thorax and pelvis. Its walls surround the abdominal cavity, which contains much of the digestive tract and other organs. Unlike the thorax, much of its front and sides are supported by muscle rather than a bony cage.
- Pelvis: the lower part of the trunk associated with the pelvic girdle, the two hip bones linking the lower limbs to the axial skeleton. Together with the sacrum, these bones form the bony pelvis. The pelvic cavity continues below the abdominal cavity without a complete partition between them.
- Back: the posterior region of the trunk. It extends across levels corresponding to the thorax, abdomen and pelvis and includes the vertebral column and its overlying tissues.
A body region and a body cavity are not interchangeable terms. The thoracic region includes its wall as well as its internal space, and the back is not a separate cavity. Similarly, an organ may extend across more than one surface region.
What are the subdivisions of the upper limb?
The upper limb includes the shoulder region and the free upper limb, meaning the portion extending from the shoulder towards the fingers. In precise anatomical usage, the arm is only one part of the upper limb.
- Arm: the region between the shoulder and elbow.
- Forearm: the region between the elbow and wrist.
- Hand: the distal part of the upper limb, including the wrist, palm and fingers.
The elbow and wrist are useful boundaries between these regions. The hand also has a dorsal surface, meaning its back surface; the left hand has the same regional organisation as the right hand.
Two additional terms describe position along a limb. Proximal means nearer its attachment to the trunk, while distal means farther from that attachment. The elbow is proximal to the wrist, and the fingers are distal to the wrist.
What are the subdivisions of the lower limb?
The lower limb includes the hip and gluteal regions and the free limb extending towards the toes. The gluteal region is the buttock area behind the hip. As with the arm, the anatomical meaning of leg is narrower than its everyday meaning.
- Thigh: the region between the hip and knee.
- Leg: the region between the knee and ankle.
- Foot: the distal part of the lower limb, including the ankle region, sole and toes.
The knee separates the thigh from the leg, while the ankle marks the transition to the foot. The foot has a plantar surface, meaning the sole, and a dorsal surface, meaning its upper surface.
The groin is the junction between the lower abdominal wall and the upper thigh. It is a boundary region rather than another name for the whole hip or pelvis. Naming the thigh, leg or foot makes a location more exact than simply naming the lower limb.
What are the nine abdominal regions and four quadrants?
The abdomen can be mapped using either nine regions or four quadrants. Both are surface-description systems: they indicate where a structure projects onto the abdominal wall, not a set of internal compartments. Their right and left labels follow the anatomical position.
The nine-region scheme uses two vertical and two horizontal reference lines. The vertical lines descend from the midpoints of the clavicles, or collarbones. A common arrangement uses an upper horizontal plane near the lower costal margins, the lower borders of the rib cage, and a lower plane through prominent points on the upper borders of the hip bones.
| Level | Person's right | Centre | Person's left |
|---|---|---|---|
| Upper | Right hypochondriac region | Epigastric region | Left hypochondriac region |
| Middle | Right lumbar region | Umbilical region | Left lumbar region |
| Lower | Right iliac region | Hypogastric region | Left iliac region |
Hypochondriac means beneath the rib cartilages; epigastric identifies the upper central area. Lumbar refers here to the lateral abdominal areas, and umbilical means around the umbilicus, or navel. The iliac regions are also called inguinal regions, while the hypogastric region is also called the pubic region.
The four-quadrant scheme uses a vertical midline and a horizontal line through the umbilicus. It gives:
- Right upper quadrant.
- Left upper quadrant.
- Right lower quadrant.
- Left lower quadrant.
Quadrants provide a broader location than the nine regions. Neither scheme confines an organ to one labelled area: the stomach, liver and intestines can occupy or cross several areas.
How do regional and systemic anatomy differ?
Regional anatomy studies all the structures within a particular area and their relationships. Studying the forearm region, for example, brings together its bones, muscles, vessels, nerves and skin. This approach emphasises what lies beside, superficial to or deep to another structure; superficial means nearer the body surface, and deep means farther from it.
Systemic anatomy studies structures grouped by a shared role, such as the skeletal, muscular or nervous system. It follows those structures across regional boundaries. A nerve can therefore be studied both as part of the nervous system and as a structure passing through a particular limb region.
These approaches organise the same anatomy in different ways. In the 3D model next to this article, you can rotate the body and switch layers on and off to compare regional position with the arrangement of different structures.