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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 7.35.
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 CO2, 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 Stress1. Thermoreceptors in skin detect a rise in
body temperature2. Nervous system in brain sends message to
hypothalamus3. 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 Stress1. Thermoreceptors in the skin send a message to
the hypothalamus2. 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.