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Introducing the Human Body
1.1 Anatomy and Physiology
Anatomy - Anatomy is the study of the structure of body parts. It is also the study of the relationship among these parts. The heart, for example, consists of chambers, valves, and associated blood vessels.
Physiology - Physiology is the study of the function of body parts. The parts of the heart, for example, work together to pump the blood throughout the body.
There is a close association between anatomy and physiology. Structure complements function. The four chambers of the heart have muscular walls that contract to pump the blood. The makeup of the valves prevents the backflow of blood.
1.2 Levels of Organization
The anatomy of the human body is composed of different levels of organization. These levels represent a series of steps. Each level is a building step for the next level. These levels are:
Atom - All matter consists of elements. These simple substances exist as discrete, submicroscopic particles called atoms. The four most common elements of the human body are carbon, hydrogen, oxygen, and nitrogen.
Molecule - Atoms bond into molecules. About 65 percent of human body weight consists of water molecules. Smaller molecules bond into larger molecules that have biological functions. Monosaccharides (e.g., glucose), for example, bond into polysaccharides (e.g., starch). These carbohydrates are an energy source.
Organelle - Molecules compose the parts of the cell called organelles. Each of these parts carries out a specific function. The ribosome, for example, is the site of protein synthesis.
Cell - The cell is the smallest unit displaying the properties of life. Cells tend to specialize. There are about 200 different kinds of specialized cells in the human body. Neurons (nerve cells) send signals. Leukocytes (white blood cells) fight infection.
Tissue - Similar cells function together in a tissue. Muscle cells work together in skeletal muscle tissue. These cells contract, producing body movement.
Organ - Two or more tissues work together in an organ. The heart is an organ that consists of several tissue types.
Organ Systems - Organs with related functions are part of the same organ system. The heart and blood vessels are organs of the circulatory system. They function to circulate the blood throughout the body.
Organism - All organ systems make up the organism. The organ systems of the human body include the nervous, circulatory, respiratory, and digestive systems.
1.3 Anatomical Terms
Anatomical terms are used to describe the makeup of the body accurately and concisely. All of these terms are used with reference to anatomical position. In this position the subject studied is facing forward and standing erect. The arms are hanging at the sides. The palms and toes are pointed forward.
1.3.1 Directional Terms
Directional terms compare the relative position of one body part to another body part. These terms occur in pairs. The members of each pair have opposite meanings.
Superior/Inferior - Superior means closer to the head. Inferior means closer to the feet. The neck is superior when compared to the chest, which is inferior. When compared to the abdomen, the chest is superior and the abdomen is inferior.
Anterior/Posterior - Anterior (ventral) refers to a part that is closer to the front of the body. Posterior (dorsal) refers to a part that is closer to the back. The heart is anterior when compared to the vertebral column, which is posterior. When compared to the sternum (breastbone), the heart is posterior and the sternum is anterior.
Medial/Lateral - Medial refers to a part that is closer to an imaginary midline passing vertically through the body. Lateral refers to a part that is farther from this midline. The nose is medial when compared to the eyes (lateral). When compared to the ears, the eyes are medial. The ears are lateral.
Proximal/Distal - Proximal refers to a part of a limb that is closer to the trunk (torso) of the body. Distal refers to a limb part that is farther from the trunk. The forearm is proximal when compared to the wrist (distal). The wrist is proximal when compared to the fingers (distal).
Other directional terms include:
Superficial - Closer to the surface of the body
Deep - Farther away from the surface of the body
Parietal - Referring to the wall of a body cavity
Visceral - Referring to an organ within the body cavity
1.3.2 Planes and Sections of the Body
Imaginary incisions can be made through the body to study the internal anatomy. These sections represent imaginary planes.
Sagittal Plane - A sagittal plane passes through the body longitudinally, dividing it into left and right regions. A midsagittal section passes through the midline of the body.
Coronal (Frontal) Plane - A coronal plane passes through the body longitudinally, dividing it into anterior and posterior regions.
Transverse Plane - A transverse plane passes through the body horizontally, dividing it into superior and inferior regions. These sections can also pertain to organs of the body. Sagittal, coronal, and transverse planes all pass through the heart.
1.3.3 Body Cavities
There are two main cavities of the human body, the dorsal cavity and ventral cavity. Each cavity is divided into subcavities.
Dorsal Cavity - The dorsal cavity consists of the cranial cavity and spinal cavity. The cranial cavity is formed by the superior bones of the skull. It contains the brain. The spinal cavity is formed by a series of vertebrae. It contains the spinal cord.
Ventral Cavity - The ventral cavity consists of thoracic and abdominopelvic subcavities.
The thoracic cavity is superior to the diaphragm. It is subdivided into a left and right pleural cavity. The pleural cavities contain the lungs. The mediastinum is the space between the pleural cavities. It contains the trachea (windpipe), esophagus, thymus gland, and heart. The heart is contained within a separate cavity of the mediastinum, the pericardial cavity.
The abdominopelvic cavity is inferior to the diaphragm. The larger abdominal portion contains the liver, gallbladder, stomach, small intestine, and most of the large intestine. The smaller pelvic portion contains the rest of the large intestine, bladder, and reproductive organs.
