homeostatis

what is homeostasis

state of steady, physical and chemical conditions maintained by living systems.

what is the homeostatic range

acceptable range of variation for a homeostatic variable

factors that are homeostatically regulated

1. [nutrient molecules]
2. [O2 & CO2]
3. [waste products]
4. pH
5. [water], [salts], [other electrolytes]
6. Blood volume and pressure
7. Temperature

coordination of organ systems

1. skin separates the internal and external environment
2.fluids of the internal environment bathe all cells of the organism and differ in composition from the external environment
3. a circulatory system moves materials to and from all parts of the internal environment
4. some organs carry out the exchange of materials between the internal and external environments
5. cells of organs exchange materials with each other via te internal environment

homeostatic control system

functionally interconnected network of body components that operate to maintain a given factor in the internal environment relatively constant around an optimal level

intrinsic control

local controls, inherent compensatory responses of an organ to a change

extrinsic control

responses of an organ that are triggered by factors external to the organ, namely, by the nervous and endocrinesystems

what do both intrinsic and extrinsic control generally operate on the principle of

negative feedback

negative feedback mechanism

The most common homeostatic control mechanism. The net effect is that the output of the system shuts off the original stimulus or reduces its intensity.

negative feedback loop requires

(1) a sensor that can detect a change in the internal environment and (2) set point which is a reference point to compare against (3) an effector that can be activated by the sensor

limitations of negative feedback

control initiated after variable has been disturbed, incomplete correction, over correction (oscillations in controlled variable), disadvantages overcome by multiple regulatory mechanisms

regulation of blood glucose

insulin and glucagon

Thermoregulation

Process of maintaining an internal temperature within a tolerable range.

thermoregulation stimulus

increase in body temperature

thermoregulation physiological response to the stimulus

negative feedback to reduce temperature

thermoregulation multiple regulatory mechanisms

involuntary (paracrine, endocrine, ANS AND CNS), voluntary (CNS)

positive feedback

Feedback that tends to magnify a process or increase its output.

negative feedback error signal

reduce deviation from reference point

positive feedback error signal

increase deviation from reference point (vicious circle)

rising phase of the action potential

depolarization --> opens Na channel--> further depolarisation (+ feedback loop) UNTIL STOP when Na channels inactivate

feedforward mechanism

brings about a compensatory response in antipicipation of a change in a regulated variable

change in renal function

in preparation for changes brought on by food intake which results in changes of conc. of ions in the plasma that will need to be controlled within physiological range