Organization of the Human Body
Organization of the Human Body
Human anatomy and physiology is the study of the structures and functions of the human body.
The following video will provide a review on the Organization of the Human Body.
Levels of Organization and Body Cavities
The body can be studied at seven structural levels: chemical, organelle, cell, tissue, organ, organ system, and organism.
- Chemical: The chemical level involves interactions among atoms and their combination into molecules.
- Organelle: An organelle is a small structure contained within a cell that performs one or more specific functions.
- Cell: Cells are the basic functional units of life. All cells share many characteristics, but they differ in structure and function.
- Tissue: A tissue is a group of cells with similar structures and functions.
- Organ: An organ is composed of two or more tissue types that together perform one or more common function.
- Organ system: An organ system is a group of organs classified as a unit because of a common function or set of functions.
- Organism: An organism is any living thing considered as a whole. Organisms can have anywhere from a single cell to trillions of cells.
Body Cavities
The human body has many cavities, some of which open to the exterior. A cavity is a fluid-filled space in the body that holds and protects internal organs. The ventral cavity (front of the body) contains three major cavities:
- The thoracic cavity is surrounded by the rib cage and separated from the abdominal cavity by the diaphragm. It is divided into right and left halves by a structure called the mediastinum. It contains the esophagus, trachea, thymus gland, heart, and both lungs, along with other structures.
- The abdominal cavity is bounded by the abdominal muscles below the thoracic cavity and contains the stomach, intestines, liver, spleen, pancreas, and kidneys.
- The pelvic cavity is enclosed by the bones of the pelvis and contains the urinary bladder, part of the intestines, and the internal reproductive organs. The abdominal and pelvic cavities are sometimes referred to as the abdominopelvic cavity.
The dorsal cavity is the back of the human body, and it is subdivided into two cavities: cranial and spinal.
- The cranial cavity contains the brain.
- The spinal cavity contains the spinal cord.
Terminology and the Body Planes and Regions
Directional terms refer to the body in the anatomical position, regardless of its actual position. The term anatomical position refers to a person standing erect with the feet forward, arms hanging to the sides, and the palms of the hands facing forward.
Terminology
| Term | Definition |
| Inferior | A structure below another |
| Superior | A structure above another |
| Anterior | Toward the front of the body |
| Posterior | Toward the back of the body |
| Dorsal | Toward the back |
| Ventral | Toward the front |
| Proximal | Closer to the point of attachment to the body than another structure |
| Distal | Farther from the point of attachment to the body |
| Lateral | Away from the midline of the body |
| Medial | Toward the middle or midline of the body |
| Superficial | Toward or on the surface |
| Deep | Away from the surface |
| Anterosuperior | In front or above |
| Midline | A median line |
| Supine position | Lying flat with face and torso facing upward |
| Prone position | Lying face down |
Body Planes
Sectioning the body is a way to look inside and observe the body’s structures. The following are the major planes of the body:
- The sagittal plane runs vertically through the body and separates the body into right and left parts.
- The midsagittal plane divides the body into two equal halves.
- The transverse plane runs parallel to the surface of the ground and divides the body into superior and inferior planes.
- The coronal plane, sometimes called the frontal plane, runs vertically from left to right and divides the body into anterior and posterior parts.
Body Regions
The body is divided into the following four regions:
- Upper limb: The upper limb includes the arm, forearm, wrist, and hand.
- Lower limb: The lower limb is divided into the thigh, leg, ankle, and foot.
- Central region: The central region includes the neck and trunk.
- Head region: The head region includes the entire head.
Human Tissues
A tissue is a group of cells with similar structure and function and similar extracellular substances located between the cells. The table below describes the four primary tissues found in the human body.
| Tissue | Structure | Function | Example |
| Connective | characterized by extracellular material that separate cells from one another | enclosing and separating connecting tissues to one another supportive and moving storing cushioning and insulating transporting protecting | cells of the immune system and blood |
| Epithelial | classified according to the number of cell layers and shapes | protecting underlying structures acting as barriers permitting the passage of substances secreting substances | skin, linings of internal organs |
| Muscle | cells of muscles resemble long threads and are called fibers | providing movement | heart, organs of digestive system |
| Neural | cells are composed of dendrites, cell bodies, and axons | coordinating and controlling many body activities | brain, spinal cord |
Homeostasis and Feedback Mechanisms
Homeostasis is the existence and maintenance of a relatively constant environment within the body. Each cell of the body is surrounded by a small amount of fluid, and the normal functions of each cell depend on the maintenance of its fluid environment within a narrow range of conditions, including temperature, volume, and chemical content. These conditions are known as variables. For example, body temperature is a variable that can increase in a hot environment or decrease in a cold environment.
There are two types of feedback mechanisms in the human body: negative and positive.
Negative Feedback
Most systems of the body are regulated by negative feedback mechanisms, which maintain homeostasis. Negative means that any deviation from the set point is made smaller or is resisted. The maintenance of normal blood pressure is a negative-feedback mechanism. Normal blood pressure is important because it is responsible for moving blood from the heart to tissues.
Positive Feedback
Positive-feedback mechanisms are not homeostatic and are rare in healthy individuals. Positive means that when a deviation from a normal value occurs, the response of the system is to make the deviation even greater. Positive feedback therefore usually creates a cycle leading away from homeostasis and, in some cases, results in death. Inadequate delivery of blood to cardiac muscle is an example of positive feedback.
Let’s Review
- The body can be studied at seven structural levels.
- The human body has multiple body cavities.
- Directional terms refer to the body in the anatomical position.
- Sectioning the body is a way to look inside and observe the body’s structures.
- The four primary tissues found in the human body are connective, epithelial, muscular and nervous.
- Homeostasis is the existence and maintenance of a relatively constant environment within the body.
- The two types of feedback mechanisms in the human body are negative and positive feedback mechanisms.
Organization of the Human Body Flashcards
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