1. Homeostasis

2. A.Homeostasis-maintaining of a constant internal environment -constants are maintained between narrow limits despite changing external conditions -maintained by nervous, endocrine and excretory systems -Ex: Body temperature, blood pH, blood glucose, etc.

3. Homeostasis depends on negative feed back circuits A.Negative feedback circuits have 3 components 1. receptor – detects change in organism (example: body temperature) 2. control center – processes info it receives from receptor and directs a response to the effector 3. effector- performs the correct response

4. B. Non-living example 1. receptor- thermometer (detects change in temperature) 2. control center- thermostat (receives info from the thermometer and directs the effector to switch on and heat or cool the room 3. effector-heater or cooler (turns on or off according to instructions from control center) Homeostasis depends on negative feed back circuits

5. C. Negative feedback prevents small changes from becoming too large D. The variables will drift slightly above and below the set points Homeostasis depends on negative feed back circuits

6. Example of negative feedback in humans A.Body temperature is pre-set at about 37°C. B.Sweating 1.Negative feedback system used to dispose of metabolic heat and to cool the body 2.If body temp rises, nerve impulses will be sent to the brain 3.Skin arterioles dilate and more blood flows through the skin 4.Blood transfers heat from the body’s core to the skin 5.Skin temp increases and heat is lost to the environment

7. B. Sweating (continued) 6. Sweat glands secrete large amounts of water making the skin surface damp 7. Water evaporates from the skin causing evaporative cooling 8. When the body’s temp drops below the set point, the brain stops sending signals to the sweat glands Example of negative feedback in humans

8. Body temperature regulation A.Thermoregulation-regulation of body temperature 1.Bodies of birds/mammals have thermoreceptors on the skin and in the heat center of the brain 2.Thermoreceptors monitor changes in environment and body

9. B. If an organism is too hot... 1. Vasodilation occurs-blood vessels widen and increase blood flow to the skin 2. Convection and radiation are increased 3. Convection= transfer of heat by movement of air or liquid 4. Radiation= emission of electromagnetic waves (heat) by objects warmer than absolute zero -when heat radiates from our bodies into the atmosphere Body temperature regulation

10. B. If an organism is too hot... 5. Sweating occurs (evaporation of fluid from the skin) 6. Metabolism decreases because most reactions produce heat as a byproduct 7. Behavioral adaptations Examples: -birds bathing -dogs panting and digging holes (to lay in cool dirt) -rodents go in burrows Body temperature regulation

11. C. If an organism is too cold... 1. Vasoconstriction -blood vessels of the body constrict -blood flow to skin is decreased -skin becomes cooler -heat loss to environment is reduced -convection and radiation are decreased Body temperature regulation

12. C. If an organism is too cold... 2. Shivering-this reaction produces heat as a byproduct (muscular contractions produce heat) 3. Increased metabolism (increased heat production) 4. Birds-fluffing of feathers -traps a layer of air that acts as extra insulation Body temperature regulation

13. C. If an organism is too cold... 5. Layer of fat or blubber -acts as insulation -reduces convection and radiation 6. Special hair structure of polar bears -clear fur functions like optical fibers that transmit UV radiation to their black skin -energy is absorbed and converted to body heat Body temperature regulation

14. D. Conduction-direct transfer of thermal heat between molecules of the environment and those of the body surface Ex: Humans swimming -the heat moves from an area of higher temp (the body) to an area of lower temp (the water) Body temperature regulation

15. Homeostasis and the endocrine system A.Endocrine system (glands) 1.Made of glands that secrete hormones that are transported by the blood 2.Endocrine glands-ductless glands -secrete hormones directly into blood -as the hormones are moved around the body, only cells with specific receptors will react to the hormone (these are target cells)

16. Assignment 1. Explain thermoregulation in the human body. 2. p. 904-905. Explain how blood glucose is regulated. 3. Distinguish between type I and type II diabetes.

17. Blood glucose control A.Pancreas cells monitor blood glucose levels and compare them to the set point B.Normal set point- between 70 and 140 mg/dl C.Negative feedback-the pancreas sends messages to target organs to make them respond and bring glucose levels back to normal 1. The messages are carried by hormones

18. D. Pancreas-has two types of glands 1. exocrine gland-with ducts -produces digestive enzymes that are released into the small intestine (not related to blood glucose levels) 2. endocrine gland-no ducts -clustered in small groups called the Islets of Langerhans -produce hormones that regulate blood glucose -make up 1-2% of the pancreatic weight Blood glucose control

19. E. Islets of Langerhans-have chemoreceptors that are sensitive to blood glucose levels -two types 1. alpha cells-secrete a hormone called glucagon 2. beta cells-secrete hormone called insulin Blood glucose control

20. F. Glucose levels -glucose is absorbed via cellular respiration after digestion -glucose levels increase after a meal -glucose levels decrease after exercise -glucose can by converted into glycogen and stored in the liver and muscles (this is equivalent to starch in a plant) Blood glucose control

21. G. If blood glucose levels increase 1. Beta cell in the islets of Langerhans produce insulin and secrete it into blood a. Insulin-a protein hormone that regulates carbohydrate metabolism -lowers blood glucose levels 2. Insulin stimulates the liver and muscle cells to absorb glucose from the blood and convert it to glycogen *Glycogen = 10% of the liver’s weight Blood glucose control

22. G. If blood glucose levels increase 3. Liver glycogen is more readily available for energy and blood glucose maintenance than muscle glycogen 4. Muscle glycogen is used primarily for muscle energy 5. When blood glucose levels return to normal, insulin is not secreted **Also, adipose tissue converts blood glucose into fat when blood glucose is high Blood glucose control

23. H. If blood glucose is too low... 1. alpha cells of the Islets of Langerhans produce glucagon 2. Glucagon stimulates the liver to breakdown glycogen (convert it back to glucose) *the liver is targeted because it is where most glycogen is stored 3. Once blood glucose is raised glucagon is no longer secreted Blood glucose control

24. Homeostasis and the nervous system A.The nervous system controls thermoregulation B.Nervous system has two parts 1.Central nervous system (brain and spinal cord) 2.Peripheral nervous system (neurons)

25. C. Neurons -nerve cells that have structures and properties that allow them to conduct signals by taking advantage of electrical charges across their membranes -transfer signals very quickly by depolarizations of their cell membranes Homeostasis and the nervous system