Regulation

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?