To introduce anatomy, all descriptions begin from the standard anatomical position: a person standing upright with feet together and parallel, arms at the sides with palms facing forward, and the head and eyes directed straight ahead. This reference posture ensures consistency across anatomical descriptions regardless of how a body is actually oriented in life. From this baseline, anatomists describe structures using three principal planes that slice the body into meaningful sections. The sagittal plane divides the body into left and right portions, the coronal plane divides it into anterior and posterior halves, and the transverse plane produces superior and inferior divisions. Together, these planes provide a standardized way to visualize cross-sectional anatomy.
The body is also organized into large fluid-filled compartments called body cavities, which house and protect the internal organs. The dorsal cavity runs along the back and includes the cranial cavity encasing the brain and the spinal cavity enclosing the spinal cord. The ventral cavity, located at the front, is divided by the diaphragm into the thoracic cavity above, containing the heart and lungs, and the abdominopelvic cavity below, containing digestive, urinary, and reproductive organs. Understanding these cavities helps clarify the spatial relationships among organs and informs clinical procedures.
At the microscopic level, all organs are built from four primary tissue types, each with a distinctive role. Epithelial tissue forms the body's coverings and linings, providing barriers on the skin surface and lining the hollow organs and cavities. Connective tissue supports and binds structures together, ranging from the loose tissue that cushions organs to the dense tissue of tendons and the rigid matrix of bone. Muscle tissue is specialized for contraction and exists in three subtypes that will be explored later. Nervous tissue, composed of neurons and supporting glial cells, generates and transmits electrochemical signals for communication and control. These four tissues combine in various proportions to build every organ in the body.