Anatomical Terminology (TM)
Anatomical Terminology
The Biological Hierarchy
Organisms are living things consisting of at least one cell, which is the smallest unit of life that can reproduce on its own. Unicellular organisms, such as the amoeba, are made up of only one cell, while multicellular organisms are comprised of many cells. In a multicellular organism, the cells are grouped together into tissues, and these tissues are grouped into organs, which perform a specific function. The heart, for example, is the organ that pumps blood throughout the body. Organs are further grouped into organ systems, such as the digestive or respiratory systems.
A system is a collection of interconnected parts that make up a complex whole with defined boundaries. Systems may be closed, meaning nothing passes in or out of them, or open, meaning they have inputs and outputs. Organ systems are open and will have a number of inputs and outputs.
Directional Terms
Learning anatomy requires an understanding of the terminology used to describe the location of a particular structure. Anatomical science uses common terms to describe spatial relationships, often in pairs of opposites. These terms usually refer to the position of a structure in an organism that is upright with respect to its environment (e.g., in its typical orientation while moving forward).
Directional Terms
Term | Meaning | Example |
|---|---|---|
inferior | away from the head | The pelvis is inferior to the head. |
superior | closer to the head | The head is superior to the pelvis. |
anterior | toward the front | The eyes are anterior to the ears. |
posterior | toward the back | The ears are posterior to the eyes. |
ventral | toward the front | The stomach is ventral to the spine. |
dorsal | toward the back | The spine is dorsal to the stomach. |
medial | toward the midline of the body | The heart is medial to the arm. |
lateral | further from the midline of the body | The arm is lateral to the chest. |
proximal | closer to the trunk | The knee is proximal to the ankle. |
distal | away from the trunk | The ankle is distal to the knee. |
Body Cavities
The internal structure of the human body is organized into compartments called cavities, which are separated by membranes. There are two main cavities in the human body: the dorsal cavity and the ventral cavity (both named for their relative positions).
The dorsal cavity is further divided into the cranial cavity, which holds the brain, and the spinal cavity, which surrounds the spine. The two sections of the dorsal cavity are continuous with each other. Both sections are lined by the meninges, a three-layered membrane that protects the brain and spinal cord.
The ventral cavity houses the majority of the body’s organs. It also can be further divided into smaller cavities. The thoracic cavity holds the heart and lungs, the abdominal cavity holds the digestive organs and kidneys, and the pelvic cavity holds the bladder and reproductive organs. Both the abdominal and pelvic cavities are enclosed by a membrane called the peritoneum.
