Homeostasis Introduction to

What is Homeostasis? The body’s attempt to maintain “normal” levels within your body Homeostasis is the mechanism to ensure that all body systems function within an acceptable range to sustain life.

Homeostasis Example: household thermostat Whole control system is called a negative feedback system Monitor- Thermometer Detects decrease in temperature Coordinating centre- Thermostat switches on furnace Regulator- Furnace Thermostat detects temperature increases over “normal” Furnace turns off

Negative feedback Process by which a mechanism is activated to restore conditions to their original state It ensures that small changes don’t become too large. Why is a thermostat a negative feedback system?

Homeostasis Example: household thermostat Room temperature is set to 22 degrees Celsius. When the temperature falls below the “normal” temperature of 22 degrees, the thermostat recognizes change in “normal” temperature and switches on the furnace. When the thermometer detects a temperature above the “normal”, the thermostat switches off the furnace.

Negative Feedback Examples The maintenance of body temperature within a range that enables cells to function efficiently a.Maintaining body temperature b.Operon gene control in bacteria c.Transpirational control in plants (stay tuned for transpiration lab)

Core Temperature Humans have a normal temperature of around 36.2 to 37.2 degrees Celsius Body temperature goes above normal temperature then likely suffering from an infection and your body had to raise its temperature to fight off the infection. If your body goes below this range it indicates hypothermia. Therefore if left untreated it could lead to cell damage and possibly death. _health/diseases/html/sars.stm

Negative Feedback Example: Thermoregulation Heat stress Thermoreceptors detect an increase in body temperature Hypothalamus signals to the sweat glands to initiate sweating. Evaporation of the sweat off the skin causes cooling. inning.html

Negative Feedback Example: Thermoregulation Heat Stress The hypothalamus also sends message to blood vessels in the skin causing them to dilate. Dilation allows for more blood flow to the skin. Heat from the blood is lost to the skin so blood can return to core of your body & cool the internal organs. of-the-dermis.html

Negative Feedback Example: Thermoregulation Heat Stress Monitor: thermoreceptors Coordinating centre: hypothalamus turns on cooling system Regulator: skin blood vessels dilate and sweat glands initiate sweating Result: body temperature decreases; hypothalamus turns off cooling system

Negative Feedback Example: Thermoregulation Cold stress Thermoreceptors message the hypothalamus Hypothalamus sends a message via the nerves to: o Arterioles of the skin cause smooth muscles to contract, constricting arterioles & limiting blood flow =reduced heat loss from the skin and retains heat in the body. o Smooth muscle contract that surrounds the hair follicles in your skin causing the hair to “stand on end” trapping warm air. o Skeletal muscle to contract causing shivering and increasing your metabolism to make heat. ncyclopedia/2/19194.htm

Negative Feedback Example: Thermoregulation Cold stress Monitor: Thermoreceptors Coordinating centre: Hypothalamus Regulator: skin blood vessels constrict and skeletal muscles contract Result: body temperature increases and hypothalamus turns off.

Operons: Another example of negative feedback Bacteria use the operon system to turn genes on and off This is an example of a negative feedback loop

Gene Control in Bacteria promoter: RNA polymerase binding site; begins transcription operator: controls access of RNA polymerase to genes repressor: protein that binds to operator and prevents attachment of RNA polymerase coded from a regulatory gene Repressible (trp operon): tryptophan (a.a.) synthesis transcription is repressed when tryptophan binds to a regulatory protein

Operons Inducible - Usually off but can be turned on or induced by a regulatory protein lactose not present:repressor active, operon off; no transcription for lactose enzymes lactose present: repressor inactive, operon on; inducer molecule inactivates protein repressor (allolactose) Ex: (lac operon): transcription is stimulated when inducer binds to a regulatory protein

Operon Animations content/anisamples/majorsbiolog y/lacoperon.html ations/lacOperon/movie.htm

Positive Feedback Loop Positive feedback is a change in a condition leading to a response which amplifies that change. Births and population growth are good examples of a positive feedback loop.

Childbirth is a positive feedback loop Stretching of uterus causes the secretion of the hormone oxytocin. Oxytocin stimulates uterine contractions which causes more pressure which stumulates more oxytocin production. This continues until the pressure is relieved by the birth of the baby.

Example of positive feedback 1.Damage is done to a blood vessel 2.Clotting fibers accumulate at the site of damage 3.Clot formation triggers release of chemicals 4.Chemicals stimulate the production of more clotting fibers 5.Goes back to step #2

Watch animation of blood clotting bZUeb83uU

When homeostatic mechanisms go awry All disease is caused by a disruption in the homeostatic mechanisms used by the organism Some specific examples are: Grave’s disease (hyperthyroidism) Diabetes Hemophilia

Grave’s Disease Thyroid in the neck produces to much thyroxine and T3 which regulate metabolism Results in enlarged thyroid (goiter), protruding eyes, insomnia, nervousness, and irritability

Diabetes Pancreas does not produce enough insulin Blood gets thick and leads reduced blood flow and lowered glucose available to cells

Hemophilia Clotting factors are not present in high enough concentrations and as a result blood does not clot well Can experience severe bleeding, swelling, or bruising from simple everyday activities