Regulation

Homeostasis

Homeostasis “steady state” Keeping constant (or close to it!) conditions in an

organism’s internal environment, even when the external environment changes

37C body temperature, 7.4pH of blood The interstitial fluid (ISF), which fills the

spaces between our cells, is primarily responsible for maintaining homeostasis Why?

Homeostatic Control Systems

Every homeostatic control system has 3 major components: 1. Receptor

Detects a change in some variable of the animal’s internal environment

2. Control Center Processes information it receives from the receptor

and directs an appropriate response by the effector 3. Effector

Performs the appropriate response, as dictated by the control center

Homeostatic Control Systems

CHANGE HAPPENS

RECEPTOR

CONTROL CENTER

EFFECTOR

Negative Feedback

Overall Idea: Change happens Then, the response (by the EFFECTOR) is in the

OPPOSITE direction of the original change Most common feedback system in animals Often HORMONES or NERVES are the

messengers (receptors and effectors)

Negative Feedback

Thermostat Example: Thermostat is set at 70˚ Temperature DROPS to

67˚

Thermostat “tells” heater to turn on to RAISE temperature back to 70˚

OPPOSITE DIRECTIONS Checks and balances!

Negative Feedback Examples

Blood Glucose Levels If blood sugar level is too LOW, glucagon

(hormone) tells liver to release glycogen (stored sugar)

If blood sugar level is too HIGH, insulin (hormone) tells liver to take glucose out of the blood and store it in the liver as glycogen

Blood Sugar Regulation

Negative Feedback Examples

Blood Calcium Levels If the blood calcium level is too LOW, parathyroid

hormone (made in parathyroid glands) causes calcium to be released into the blood (from the bones)

If the blood calcium level is too HIGH, calcitonin (made in the thyroid gland) will cause calcium to be absorbed from the blood (into the bones)

Negative Feedback Examples

Body Temperature If the body temperature

gets too LOW, the hypothalamus (a gland in the brain – the “master gland”) tells the body to SHIVER to generate heat

If the body temperature gets too HIGH, the hypothalamus tells the body to release heat as sweat

Positive Feedback

Overall Idea: Change happens Then, the response is in the SAME direction as

the original change The change is AMPLIFIED, not reversed

Positive Feedback Examples

Childbirth Oxytocin (hormone) is released, causing the

cervix to dilate and starting contractions The dilation of the cervix and the contractions

cause MORE oxytocin to be released, therefore intensifying the contractions

Positive Feedback Examples

Blood Clotting Platelets accumulate at the site of a blood vessel

break or tear This causes MORE platelets to come, therefore

causing blood to clot Also causes fibrin (inactive) to be converted to

fibrinogen (active) Signal Transduction Pathway

Thermoregulation

Endotherms “warm-blooded” Maintain a stable internal body temperature Not as affected by external changes

Ectotherms “cold-blooded” Body temperature fluctuates with the external

environment Very affected by external changes

AP Lab 10 Connection…

Daphnia Taxonomy? Expose Daphnia to

increasingly-warm temperatures

What is the relationship between metabolism (think enzyme reactions!) and heart rate? What should happen? Why?