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Orientation

Overview of Anatomy and Physiology

1. Anatomy is the study of structure. Observation is used to see the sizes and relationships of body parts.

2. Physiology is the study of how a structure (which may be a cell, an organ, or an organ system) functions or works.

3. Structure determines what functions can occur; therefore, if the structure changes, the function must also change.

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Levels of Structural Organization

There are six levels of structural organization (Figure1.1). Atoms (at the chemical level) combine, forming the unit of life, the cell. Cells are grouped into tissues, which in turn are arranged in specific ways to form organs. A number of organs form an organ system, which performs a specific function for the body (which no other organ system can do). Together, all of the organ systems form the organism, or living body.

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Maintaining Life

1. To sustain life, an organism must be able to maintain its boundaries, move, respond to stimuli, digest nutrients and excrete wastes, carry on metabolism, reproduce itself, and grow.

2. Survival needs include food, oxygen, water, appropriate temperature, and normal atmospheric pressure. Extremes of any of these factors can be harmful.

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Homeostasis

1. Body functions interact to maintain homeostasis or a relatively stable internal environment within the body. Homeostasis is necessary for survival and good health; its loss results in illness or disease.

2. All homeostatic control mechanisms have a receptor that responds to environmental changes, and a control center that assesses those changes and produces a response by activating a third element, the effector (Figure 1.2).

3. Most homeostatic control systems are negative feedback systems, which act to reduce or stop the initial stimulus.

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The Language of Anatomy

Anatomical terminology is relative and assumes that the body is in the anatomical position (erect, palms facing forward (Figure 1.3).

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Directional Terms

1. Superior (cranial, cephalad): above something else, toward the head.

2. Inferior (caudal): below something else, toward the tail.

3. Anterior (ventral): toward the front of the body or structure.

4. Posterior (dorsal): toward the rear or back of the body or structure.

5. Medial: toward the midline of the body.

6. Lateral: away from the midline of the body.

7. Intermediate: between a more medial and a more lateral structure.

8. Proximal: closer to the point of attachment.

9. Distal: farther from the point of attachment.

10. Superficial (external): at or close to the body surface.

11. Deep (internal): below or away from the body surface. (Figure 1.4)

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Body Planes and Sections

1. Medial/saggital section: separates the body longitudinally into right and left parts.

2. Frontal (coronal) section: separates the body on a longitudinal plane into anterior and posterior parts.

3. Transverse (cross) section: separates the body on a horizontal plane into superior and inferior parts. (Figure 1.5)

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Body Cavities

Dorsal: well protected by bone; has two subdivisions.

1. Cranial: contains the brain.

2. Spinal: contains the spinal cord.

Ventral: less protected than dorsal cavity; has two subdivisions.

1. Thoracic: The superior cavity that extends inferiorly to the diaphragm: contains heart and lungs, which are protected by the rib cage.

2. Abdominopelvic: The cavity inferior to the diaphragm that contains the digestive, urinary. and reproductive organs. The abdominal portion is vulnerable because it is protected only by the trunk muscles. There is some protection of the pelvic portion by the bony pelvis. The abdominopelvic cavity is often divided into four quadrants or nine regions. (Figure 1.6)