Intro-Homeostasis

The dynamic state in which the body's internal environment remains relatively constant and within physiological limits.

The fluid that surrounds body cells and is the 'internal environment' referred to in the homeostasis definition.

All body structures

• Nervous System- rapid corrections
• Endocrine System- slow corrections

A cycle of events in which a condition in the body is continually monitored, evaluated, changed, re-monitored, reevaluated, and so on.

A monitored variable, such as body temperature or blood pressure.

Any disruption that causes a change in a controlled condition.

• Receptor
• Control center
• Effector

A body structure that monitors changes in a controlled condition and sends information to a control center.

Information sent from a receptor to a control center.

• Structures (i.e., tissues/organs) in the body that:
• Set the range of values within which a controlled condition should be maintained
• Evaluate the input it receives from receptors
• Generates output commands when needed

Information, in the form of nerve impulses or chemical signals, that are relayed from the control center to effectors.

A body structure that receives output from the control center and produces a response that changes the controlled condition.

Nearly every tissue or organ

• 1. Negative feedback system-
• 2. Positive feedback system-

A feedback system in which the effector's output opposes/reverses the change detected in the controlled condition.

A feedback system in which the effector's output strengthens/reinforces the change detected in the controlled condition.

• 1. Higher blood pressure (stimulus, controlled condition) is detected by baroreceptors (receptor) in the walls of certain blood vessels.
• 2. The baroreceptors send nerve impulses (input) to the brain (control center).
• 3. The brain receives, interprets, and responds to these signals by sending nerve impulses (output) to the heart (effector).
• 4. The heart decreases its rate and contractility which causes a decrease in blood pressure--an example of a negative feedback system.

• 1. The first contractions of labor push part of the fetus into the cervix causing it to stretch (stimulus).
• 2. Stretch receptors (receptor) in the cervix send nerve impulses (input) to the brain (control center).
• 3. The brain receives, interprets, and responds to these nerve impulses by releasing oxytocin into the bloodstream (output).
• 4. Muscles (effector) in the wall of the uterus respond to the presence of oxytocin by contracting more forcefully.
• 5. This cycle continues until it is interrupted by the birth of the baby, when cervical stretching (controlled condition) ceases--positive feedback system.

• Disorder
• Disease
• Death

Any abnormality of structure and/or function.

• An illness characterized by a recognizable set of signs and symptoms.
• Specific diseases alter body structure and function in characteristic ways and usually produce a recognizable set of signs and symptoms.

• Objective changes that a clinician can observe and measure.
• E.g.- bleeding, vomiting, diarrhea, fever, etc.

• Subjective changes in body functions experienced by the patient and not apparent to the observer.
• E.g.- headache, anxiety, nausea

The scientific evaluation and identification of a disorder or disease.

• A normal process characterized by progressive decline in the body's ability to restore homeostasis.
• Aging produces observable changes in structure and function that are apparent in all body systems.