Biology 11

By the end of today you should be able to:  Define homeostasis  List the three processes of homeostatic control systems in the body.  Give examples of positive and negative feedback loops and identify which ones are more common.  Understand thermoregulation – the process of maintaining homeostasis in different environments.

Homeostasis  Body Facts – A recipe for body balance  The human body works best at a temperature of 37°C  With a 0.1% blood sugar level  Blood pH level of  Homeostasis Greek: homoios “similar” or “like,” and stasis “standing still” Process in which your body adjusts to environmental conditions to maintain a stable internal environment  This system of balance requires active and constant monitoring about body conditions

Homeostatic control system  All homeostatic control systems have 3 functional components: 1. Monitor: signals coordinating center that an organ has begun to operate outside its normal limits 2. Coordinating center: relays information to appropriate regulator 3. Regulator: acts to restore normal balance

Exercise Example:  Example: increase in carbon dioxide and decrease in oxygen during exercise Monitor: chemical receptors in brain stem are stimulated by increased CO 2, chemical receptors in carotid arteries detect low oxygen levels Coordinating center: receptors go to brain, which sends nerve signals to muscles to increase depth and rate of breathing Regulator: increased breathing movements flush excess carbon dioxide from body and increases oxygen content  Because of the fluctuating nature of the control system, it is often called a dynamic equilibrium

Negative and Positive Feedback  The body maintains homeostasis through 2 feedback mechanisms: Positive feedback Negative feedback  Which do you think is more common?

Positive Feedback  The stimulus causes the reaction from the body to get stronger and stronger until the stimulus is gone  Positive feedback systems move the variable even further away from a steady state.  In short: response increases initial stimulus  Useful for allowing a specific physiological event to be accomplished quickly  Not useful for maintaining homeostasis Example: Uterine contractions during birth release the hormone oxytocin, which stimulates more, stronger uterine contractions. This lasts until the baby is expelled from the uterus.

Negative Feedback  Similar to a thermostat  Body has a pre-determined set of internal conditions  When the body goes outside of those conditions, it will take action to return to its optimal range  In short: response reduces initial stimulus  VERY COMMON IN THE BODY!

Example of negative regulation: thermostat

Thermoregulation Regulation of heat distribution

Thermoregulation  Maintenance of body temperature within a range that enables cells to function efficiently  Two types of animals: Ectotherms:  Invertebrates, and most fish, amphibians, and reptiles  Metabolic activity partially regulated by environment  Adapted behavioural adaptations, such as sunning on rocks or going into the shade  These animals depend on air temperature to regulate metabolic rates; therefore, activity

Thermoregulation Endotherms:  Mammals, birds, “warm- blooded” creatures  Maintain constant body temperature regardless of surroundings  Increase rate of cellular respiration to generate heat  However, in humans, body temperature does vary slightly during the day, and from peripheral to core of body

Hypothalamus – internal thermostat  The hypothalamus is your body’s internal thermostat  Located in the middle of the brain  It controls the pituitary gland, which in turn controls all hormones in your body  Along with controlling temperature, the hypothalamus acts as a relay station between the nervous system and the endocrine (hormone) system

Response to Heat Stress 1. Thermoreceptors in skin detect a rise in body temperature 2. Nervous system in brain sends message to hypothalamus 3. Hypothalamus response:  Sweat glands to initiate sweating – evaporation of sweat cools body  Blood vessels to dilate – more blood goes to skin, which has been cooled by evaporation (VASODILATION)  When blood returns to core, cools internal organs

Response to Cold Stress 1. Thermoreceptors in the skin send a message to the hypothalamus 2. Hypothalamus response: Constricts smooth muscle of arterioles – blood flow is limited, heat loss from skin is reduced (VASODILATION) Constricts smooth muscle around hair follicles, causing hair to stand on end – erect hair traps warm air next to skin Skeletal muscles to initiate rhythmic contractions (10 – 20x per minute) – shivering  If exposure to cold is prolonged: Elevation of metabolism (hormonal response) Deposition of “brown fat,” a special adipose tissue that can convert chemical energy into heat – especially important in newborns, because they are not able to shiver

Thermoregulation Summary

Mammalian diving reflex  If the body’s core temperature falls below the normal range (hypothermia), the individual can fall into a coma and die  Some people can survive sustained exposure to cold, because of the mammalian diving reflex When a mammal is submerged in cold water, heart rate slows Blood is diverted to brain and other vital organs Heat is conserved

Freezing cells – facts and fiction  Remember that water is the universal solvent and that it has 7 specific traits.  Your cells are mostly made of water (cytoplasm).  As water freezes, it expands and forms ice crystals.  These ice crystals completely destroy cells, blood vessels, organs, nerves, etc. – causing death – This is the danger of the cold!  Frostbitten areas appear waxy and swollen, because of the effect of the cold.

Frostbite

First Aid Treatment for Frostbite  Remove the victim from the cold. DO NOT attempt to thaw frostbitten tissues if there is a possibility they could freeze again. DO NOT RUB OR MASSAGE the affected site!  Fill a shallow container with enough water to cover the frostbitten body part. Make sure the water is at room temperature. The water does not have to be cool, but it cannot be too warm. The warmer the water, the worse the pain.  Continue to refresh the water in the container as it cools. Keep the water at the same temperature as consistently as possible. It may take several hours to completely thaw severe frostbite.  As soon as feasible, get the victim to medical assistance - even after thawing frostbite.