01 Foundations of Human Anatomy and Physiology
Learn the language used to describe body structures, how the body is organized, where its cavities are located, and how structure supports function.
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describes body structures and how they are arranged, while explains how those structures work. The two are closely connected because a structure’s form helps determine what it can do.
Standard anatomical language makes it possible to describe locations precisely regardless of how a person is positioned. Anatomical descriptions use a shared reference position and directional terms.
Anatomical language and planes
Descriptions use the as their reference: standing upright and facing forward, with the arms at the sides, palms facing forward, and feet directed forward. Directional terms locate one structure in relation to another.
Superior and inferior: toward the head and toward the feet, respectively. The chest is superior to the abdomen.
Anterior (ventral) and posterior (dorsal): toward the front and toward the back, respectively. The sternum is anterior to the heart.
Medial and lateral: toward the midline and away from the midline, respectively. The nose is medial to the eyes.
Proximal and distal: nearer to and farther from a limb’s attachment to the trunk, respectively. The elbow is proximal to the wrist.
Superficial and deep: nearer to and farther from the body surface, respectively. The skin is superficial to the muscles.
Body planes
Body planes are imaginary sections used to describe views or cuts. A divides the body into left and right portions; the frontal, or coronal, plane divides it into front and back portions; and the transverse plane divides it into upper and lower portions. A midsagittal plane divides the body into equal left and right halves.
Levels of body organization
The body’s progress from simpler components to increasingly complex structures:
Chemical level: atoms and molecules, such as water and proteins.
Cellular level: cells, the smallest living units of the body.
Tissue level: groups of cells and their surrounding materials working together, such as muscle tissue.
Organ level: structures made of two or more tissue types that perform particular functions, such as the heart.
Organ-system level: organs that cooperate in major body functions, such as the cardiovascular system.
Organismal level: the whole person, whose organ systems work together.
These levels are interdependent. Molecules form cell structures; cardiac muscle cells form heart tissue; tissues make up the heart; and the heart works with blood vessels to circulate blood.
protect internal organs and provide spaces in which organs can move and change size. The two major cavities are the dorsal (posterior) cavity and the ventral (anterior) cavity.
Dorsal cavity: The cranial cavity contains the brain. The continuous vertebral, or spinal, cavity surrounds the spinal cord.
Ventral cavity: The thoracic cavity contains the lungs and heart. The diaphragm separates it from the abdominopelvic cavity, which includes the abdominal and pelvic regions. The abdominal region contains many digestive organs; the pelvic region contains the urinary bladder, internal reproductive organs, and part of the large intestine.
Within the thoracic cavity, each lung is enclosed by a pleural cavity, and the heart is enclosed by a pericardial cavity. These cavities are lined by serous membranes that produce a small amount of fluid, helping reduce friction as organs move. The abdominal and pelvic regions are continuous rather than separated by a solid wall.
How structure supports function
are linked throughout the body: the form of a body part helps explain what it does. The thin walls of lung alveoli allow gases to diffuse between air and blood. Folds and projections in the small intestine increase its surface area for absorbing nutrients. The heart’s muscular walls contract to pump blood, while its valves help keep blood moving in one direction.
This relationship also connects organ systems. Oxygen enters the blood in the lungs, and the cardiovascular system transports it to tissues, where cells use it to release energy from nutrients. The respiratory, cardiovascular, digestive, and other systems contribute to the needs of the whole organism.