Human Anatomy/Terminology and Organization

Anatomy is "the science of the structure of living organisms" so human anatomy is the science of the structure of the human body. This wikibook will hopefully give you a good understanding of what your body is made of and of how it develops. Strictly speaking, how the body functions is physiology. Despite this fact, it is almost impossible to explain anatomy without going into some physiology and vice versa so some physiological concepts will be introduced in this book.

There are two types of anatomy: gross, or macroscopic, and microscopic. Gross anatomy deals with things that can be viewed by the unaided eye. Microscopic anatomy is the study of structures on the cellular level. There are, in turn, 3 fields of study within the topic of gross anatomy. These are surface anatomy, the study of external anatomical forms and markings; regional anatomy, which focuses on a certain region of the body (both internal and external); and systemic anatomy, which focuses on a given organ system. Within microscopic anatomy, there are two topics of study which are of great importance: cytology, the study of cells; and histology, the study of tissue.

Standard Anatomical Position
For positional terminology to make sense, a standard anatomical position has to be established. In human anatomy, the standard anatomical position is supine (lying down face up). The legs are straight and together, or slightly separated. The arms are straight out along the torso with the palms of the hands upward. The arms are separated slightly from the torso. The thumbs point away from the body.

Terminology
In order to talk about anatomy, some terms need to be understood. The terms can be divided into positional terms and descriptive terms. Positional terms help in locating structures by giving precise descriptions of relations (which eliminates the need to specify in what position the subject is). An easy example is superior, which means above or on top of when the subject is upright: The human head is superior to the torso. It cannot be said that the head is above the torso if the person is lying down. Descriptive terms can give varied information.

Descriptions of General Position
Superior and Inferior 

The terms superior and inferior are used when referring to parts of the body which are toward an end of the body. Superior meaning toward the head and inferior meaning toward the feet. Toward an end does not necessarily mean close to the end. For example, the bowels are inferior to the lungs. This does not mean that the bowels are close to the feet nor does it mean the converse (that the lungs are close to the head). It simply means that the lungs are closer to the head than the bowels. Cranial and caudal have the same meaning as superior and inferior, respectively, but are used in reference to animal, rather than human, anatomy.

Anterior and Posterior

Anterior refers to the side of the body facing up in the standard anatomical position. Posterior refers to the bottom side. Like superior and inferior, these do not necessarily mean that the parts they are describing are close to the front or back of the body, they simply explain relative positions. Dorsal and ventral are sometimes used in place of anterior and posterior, respectively. These are mostly used with animal anatomy, but can be used in human anatomy as long as they are describing the side of an appendage.

Lateral and Medial

Lateral is a word used to describe anything which is closer to the outside (toward the arms, in the standard anatomical position) while medial is used to describe anything toward the center of the body.

Superficial and Deep

Superficial is a used to describe structures that are closer to the exterior surface of the body. Deep refers to structures closer to the center of the body region. For example, skin is superficial to bones, and bones are deep to skin.

Proximal and Distal

Proximal and distal are terms that describe one point relative to another. Proximal refers to a point closer to the reference point while distal refers to a point farther away. For example, the metacarpals are distal to the carpus.

Dorsal and Ventral

Dorsal refers to a structure closer to the back of an organism while ventral refers to a point closer to the abdomen; these descriptors are generally used in animal anatomy in place of posterior and anterior, respectively.

Other Directional Terms
Ipsilateral and Contralateral

Ipsilateral refers to two parts that are on the same side of a given reference point. For example, it could be said that the left arm and left leg are ipsilateral to one another with respect to the midsagittal plane. Contralateral is the inverse; the left arm and right leg are contralateral to one another with respect to the midsagittal plane.

Axial and Abaxial

Axial refers to a point close to the midsagittal plane while abaxial refers to a point farther away from the midsagittal plane.

Intermediate

Between two points. For example, the knee is intermediate between the gluteal and the foot.

Visceral

The term visceral refers to any system or point that contacts organs. For example, the visceral peritoneum is in direct contact with the abdominal organs.

Parietal

Conversely, parietal refers to the outer membrane of a system. For example, the parietal pericardium lines the pericardial cavity.