Physiology: Homeostasis

Homeostasis

• a condition of equilibrium or balance in the body’s internal environment

• maintained by the body’s regulatory processes

To maintain homeostasis a control system must

• detect deviations from normal in the internal environment that need to be held within limits

• integrate this information with other relevant information

• make appropriate adjustments to restore a factor to its desired value

Set point

the normal range for a given system and will be monitored by the control contre for that particular system (ex: hypothalamus monitoring body temp)

Intrinsic controls

local controls that are inherent in the organ

Extrinsic controls

• regulatory mechanisms initiated outside an organ

• accomplished by nervous and endocrine systems

Feedback loops

responses make after a change

• negative and positive

Feedforward loops

responses made in anticipation of a change

Basic components of a feedback loop

Negative Feedback loop

• primary type of homeostatic control

• opposes initial change

Components of the negative feedback loop

Sensor: monitors magnitude of a controlled variable

Control center: compares sensor’s input with a set point

Effector: makes a response to produce a desired effect

Main goal of the negative feedback loop

keeping internal environment stable

• ex: body temp, nutrients/wastes, O2/CO2 levels, pH, water/electrolytes, blood volume, blood pressure

Example of the negative feedback loop

Negative feedback loop set point and response loop example

Positive feedback loop

• amplifies an initial change and therefore does not truly contribute to homeostasis

• does not occur very often

  • abnormal changes move the body farther away from homeostatic balance and potentially toward death

Example of positive feedback loop

contractions during labour

Homeostatic imbalances

disruptions of homeostasis can lead to disease and death

Disorder

a general term for any derangement of abnormality of function

Disease

a more specific term for an illness characterized by a recognizable set of signs and symptoms

Aging and homeostasis

aging is a normal process characterized by a progressive decline in the body’s ability to restore homeostasis

• ex: blood pressure, diabetes

Feedforward Mechanisms and Anticipation

• although not as commonly used in the body, there are mechanisms which are activated before a change in a variable actually occurs

• these mechanisms attempt to anticipate changes before they occur rather than responding to a change after it has occurred

• ex: saliva production prior to eating (prepare for the breakdown of carbohydrates), central command makes changes prior to exercise