Feedback Systems In The Body Anatomy & Physiology I Biology 1611 Lecture

Feedback System A Feedback System is a cycle of events in which information about the status of a condition is continually monitored and fed back or reported to a central control region.

A feedback system consists of 3 basic components… The Control Center: Determines the point at which a controlled condition should be maintained. The Receptor: Monitors changes in the controlled condition and then sens the information called the input to the control center. The Effector: Receives information called output from the control center and produces a response called an effect.

Negative Feedback This occurs if a response reverses the original stimulus. Negative Feedback systems tend to maintain conditions that require frequent monitoring and adjustment within physiological limits. Negative Feedback is by far the most common type of feedback in the body.

An Example of Negative Feedback… Homeostasis of Blood Pressure is an example of Negative Feedback. If a stimulus (such as stress) causes blood pressure (controlled condition) to rise, pressure sensitive nerve cells (receptors) in certain arteries send impulses (input) to the brain (control center). The brain sends impulses (output) to the heart (effector) which causes the heart rate to decrease (response) and the return of normal blood pressure and thus, restoration of homeostasis.

Positive Feedback Positive Feedback occurs when a response enhances the original stimulus. Positive Feedback systems tend to regulate conditions that do not occur often and do not require continual fine tuning. Positive Feedback systems only occur in limited and very specific instances in the body. An example is labor and delivery.

An Example of Positive Feedback… Labor and delivery (contractions) is an example of positive feedback. When labor begins, the uterus is stretched (stimulus) and stretch-sensitive nerve cells in the cervix of the uterus (receptors) send nerve impulses (input) to the hypothalamus (control center.) The hypothalamus causes the release of the hormone oxytocin (output) which stimulates the uterus (effector) to contract more forcefully (response).

Positive Feedback Continued… Movement of the baby’s head down the birth canal causes further stretching and the release of more oxytocin. This in turn causes more contractions to occur. This upward cycle of stretching-release of oxytocin-increased contractions is broken (stopped) by the delivery of the baby.

Homeostatic Imbalance Disruptions of homeostasis can lead to disease and death. Disease: any change from a state of health that is characterized by symptoms and signs.

Types of Diseases Local Disease: A disease that affects one part of a limited area of the body. Systemic Disease: A disease that affects either the entire body or several parts.

Symptoms versus Signs… Symptoms: SUBJECTIVE changes in body functions that are not apparent to an observer. Examples: headache, nausea or fatigue. Signs: OBJECTIVE changes that a clinician can observe and measure. Examples: fever, rash, edema or fracture

Diagnosis The ART of distinguishing one disease from another or determining the nature of a disease; a diagnosis is generally arrived at after the taking of a medical history and the administration of a physical examination. To diagnose a patient is as much an ART as it is a SCIENCE…

Other Medical Terms… Autopsy: A medical procedure done to establish a cause of death and to verify previous diagnoses. Autopsies can be done to uncover the existence of diseases not detected during life, to establish the effects of drugs, to reveal congenital conditions and to resolve investigations by law enforcement officials. Necropsy: An autopsy of an animal.