2.  The human body has a set of conditions under which it operates optimally  These conditions are: Temperature: 37 °C Blood Sugar: 0.1% Blood pH: 7.35

3.  We know, however, that our external environment does not always provide the ideal conditions for our body  For example, the temperature in Canada can range from -40°C to 40°C  You may eat food high in sugar  You may consume acidic or basic foods

4. Homeostasis – the process by which a constant internal environment is maintained despite changes in the external environment Homoios – similar Stasis – standing still Homeostasis is achieved through constant monitoring and feedback of body conditions

6.  Three functional components: 1. A monitor (special sensors located in the body) 2. A coordinating centre (Relays information from the monitor to the regulator) 3. A regulator (helps restore the normal balance)

7.  CO 2 levels increase during exercise  Chemical receptors in the brain stem are stimulated (monitors)  Nerve cells (coordinating centre) from the brain carry impulses to muscles (regulator) that increase the rate and depth of breathing  Increased breathing movements help flush excess CO 2 from the body

8. Dynamic Equilibrium – condition that remains stable within fluctuating limits There is a tolerable range for different levels in the body

10. Feedback is a mechanism that makes an adjustment within the body Negative Feedback – process by which a mechanism is activated to restore conditions to their original state Positive Feedback – process by which a small effect is amplified

11. Prevent small changes from becoming too large More common than positive feedback

12. Thermostat You set your thermostat (coordinating centre) to a preferred temperature A thermometer (monitor) inside the thermostat continually reads the room temperature If the temperature drops below the set level, the furnace (regulator) switches on to provide heat Once the room has warmed up to the set point, the furnace switches off

14.  Less common in the body  Reinforces a change  Move the controlled variable even further away from a steady state  Positive feedback allows a physiological event to be accomplished quickly

15. Birth A decrease in progesterone (a hormone) is believed to initiate small contractions of the uterus These contractions bring about the release of another hormone (oxytocin) which causes much stronger contractions As contractions continue, the baby moves down the birth canal This causes even more oxytocin to be released which causes even stronger contractions Once the baby is born, the contractions atop which in turn stops the release of oxytocin

17. Different species of animals are adapted to different temperature ranges, and each animal has an optimal temperature range Thermoregulation – maintenance of body temperature within a range that enables cells to function efficiently

18. Invertebrates and most fish, amphibians, and reptiles are ectotherms These animals depend on air/water temperature to regulate metabolic rates These animals regulate their activity based on the environment (hiding under rocks on a hot day) Some animals such as tuna fish have highly adapted circulatory system designed to conserve heat

19.  Mammals and birds are endotherms  They are able to maintain a constant body temperature regardless of their surroundings  The hypothalamus is the region of the vertebrate’s brain responsible for coordinating many nerve and hormone functions (considered a type of “thermostat”)

20. In humans, body temperature can vary slightly during the day Temperature falls during the night Body temperature can also vary from the core of the body to the extremities Core temperature (chest cavity, abdominal cavity, and CNS) is maintained at 37°C while temperature in the arms and legs may be up to 4°C lower on cold days

21.  How does the body protect itself from over heating?  Sweating (evaporation of perspiration causes cooling on the skin)  Blood vessels in the skin dilate (this blood is cooled and returns to the internal organs to cool them)

22. How does the body protect itself from the cold? Smooth muscles and arterioles constrict, limiting blood flow (reduces heat loss from the skin) Hair stands on end (hairs trap warm air close to the skin to reduce heat loss) Shivering (contraction of muscles generate heat by increasing metabolism)

23.  The body’s response to both heat and cold stress is regulated by the hypothalamus  This is the coordinating centre for the body’s response to heat and cold