Homeostasis and Homeostasis and Control SystemsControl Systems

Homeostasis:Homeostasis:

Process that regulates and maintains a Process that regulates and maintains a constant internal environment constant internal environment regardless of the external environment. regardless of the external environment.

Also referred to as Also referred to as Dynamic EquilibriumDynamic Equilibrium (Fluctuation of conditions within an (Fluctuation of conditions within an acceptable range)acceptable range)

For example, regardless of external conditions and substances ingested, the body must maintain:

Temperature 37 degrees Celcius

Blood pH level 7.35

Glucose level (blood sugar level)0.1%

In order to control and In order to control and maintain homeostasis we need maintain homeostasis we need

the following elements:the following elements:

Monitor Monitor (Ex. Sensors throughout the (Ex. Sensors throughout the body that signal the coordinating body that signal the coordinating centre)centre)

Coordinating centreCoordinating centre (Ex. Sends (Ex. Sends information to a specific regulator)information to a specific regulator)

Regulator Regulator (Ex. Will perform a function (Ex. Will perform a function to restore balance)to restore balance)

Examples of regulation: Examples of regulation: Carbon dioxide and Carbon dioxide and

Oxygen levelsOxygen levels

Homeostasis and Homeostasis and FeedbackFeedback

Negative Feedback RegulationNegative Feedback Regulation Counteracts any further actionCounteracts any further action Reverses the original change and brings Reverses the original change and brings

the system back to normal.the system back to normal. The bigger then change the bigger the The bigger then change the bigger the

corrective mechanismcorrective mechanism

In a system controlled by negative feedback the level is never maintained perfectly, but constantly oscillates about the set point. An efficient homeostatic system minimizes the size of the oscillations.

Positive Feedback Positive Feedback RegulationRegulation

o When something small is amplifiedWhen something small is amplified

ThermoregulationThermoregulation

Maintenance of body temperature within a Maintenance of body temperature within a specific range in order for cell function to specific range in order for cell function to occur efficiently.occur efficiently.

EctothermsEctotherms (Fish, amphitibians and reptiles) (Fish, amphitibians and reptiles) depend on air temperature to regulate depend on air temperature to regulate metabolic rates. Thermoregulation is metabolic rates. Thermoregulation is therefore partially dependent on the therefore partially dependent on the environment. Behaviour of these organisms environment. Behaviour of these organisms may help adapt to their environment (Ex. may help adapt to their environment (Ex. Reptiles sun bathing on rocks)Reptiles sun bathing on rocks)

EndothermsEndotherms (Mammals and birds) maintain a (Mammals and birds) maintain a constant body temperature regardless of constant body temperature regardless of environmental conditions. environmental conditions.

Hypothalamus:Hypothalamus: Part of the brain that Part of the brain that controls many nerve and hormone controls many nerve and hormone functions functions (With regards to (With regards to thermoregulation, it can be related to thermoregulation, it can be related to a thermostat where it can turn on toa thermostat where it can turn on to warm the internal environment.)warm the internal environment.)

Effector Response to low temperature Response to high temperature

Smooth muscles in peripheral arterioles in the skin.

Muscles contract causing vasoconstriction. Less heat is carried from the core to the surface of the body, maintaining core temperature. Extremities can turn blue and feel cold and can even be damaged (frostbite).

Muscles relax causing vasodilation. More heat is carried from the core to the surface, where it is lost by radiation. Skin turns red.

Sweat glands No sweat produced.Glands secrete sweat onto surface of skin, where it

evaporates. Water has a high latent heat of evaporation, so it takes heat from the body.

Erector pili muscles in skin (attached to skin hairs)

Muscles contract, raising skin hairs and trapping an insulating layer of still, warm air next to the skin. Not very effective in humans, just causing "goosebumps".

Muscles relax, lowering the skin hairs and allowing air to circulate over the skin, encouraging convection and evaporation.

Skeletal musclesMuscles contract and relax repeatedly, generating heat

by friction and from metabolic reactions.No shivering.

Adrenal and thyroid glands

Glands secrete adrenaline and thyroxine respectively, which increase the metabolic rate in different tissues, especially the liver, so generating heat.

Glands stop releasing adrenaline and thyroxine.

BehaviourCurling up, huddling, finding shelter, putting on more

clothes.Stretching out, finding shade, swimming, removing

clothes.