1. Homeostasis???
DYNAMIC EQUILIBRIUM????

2. Homeostasis is often referred to as a DYNAMIC EQUILIBRIUM – a condition that remains stable within fluctuating limits
Thus, although there are fluctuations in blood glucose levels, body temperature, blood pressure and pH, the homeostatic mechanism ensures that all the body systems function within an acceptable range to sustain life.

3. 1.Negative Feedback
Mechanisms that make adjustments to bring the body back within an acceptable range are referred to as NEGATIVE FEEDBACK
E.g. pH changes
When there is an increase in acids in the body the body will compensate to make things more neutral
Most homeostatic mechanisms in animals operate on this principle

4. Negative Feedback stimulus
(environmental
change)
sensor
(e.g. free nerve ending in the skin)
effector
(a muscle or gland)
response
(system’s output)
integrator
(e.g. brain)
In the negative feedback mechanism, the response of the system cancels or counteracts the effect of the original environmental change

5. Household Thermostat Thermometer: sensor Thermostat: control Centre
Furnace: effector/regulator

8. 2.Positive Feedback Less common in the body Reinforces change
Moves the variable away from the norm
E.g.: birth process
A decrease in progesterone initiates small contractions of the uterus. This signals a release of oxytocin which causes stronger contractions and pushes baby closer to cervix
Once baby is expelled positive feedback stops and negative feedback kick in to get the body back to normal

10. A. Response to Heat Stress
Sensors in brain detect a rise in body temp.
Nerve message is coordinated within the hypothalamus (region in brain) and a signal is sent to the sweat glands to initiate sweating
Evaporation of perspiration from the skin causes cooling and a nerve impulse is sent to the blood vessels of the skin causing them to dilate (allowing more blood flow to skin)
Overall, the skin has been cooled by the evaporation of sweat and the blood loses heat to the skin. When the blood from the skin returns to the core of the body, it cools the internal organs.

12. B.Response To Cold Stress
When the external temperature drops, receptors in the skin send a message to the hypothalamus
The hypothalamus sends a message to the body to increase body temperature
Nerves cause smooth muscles to contract and arterioles to constrict limiting blood flow

13. This reduces heat loss from the skin and retains heat in the core of the body
Nerves messages are also carried to the smooth muscle that surrounds the hair follicles in your skin, causing your hair to stand on end. The small bump made by the contraction is called a “goosebump”
The erect hair traps warm, still air next to the surface of your skin and helps reduce heat loss
The hypothalamus also sends nerve messages to initiate shivering which is a rhythmic contraction of skeletal muscle

17. Hypothermia
A condition in which the body core temperature falls below the normal range
A drop of only a few degrees can lead to coma and even death
Some people have survived sustained exposure to cold temperatures. Their heart rate slows down and the blood is diverted to the brain and other vital organs to conserve heat
This is called the MAMMALIAN DIVING REFLEX

18. Thermoregulation
Different species of animals are adapted to different temperature ranges, each animal has an optimum range
Thermoregulation: is the maintenance of body temperature within a range that enables cells to function properly

20. Ectotherms Invertebrates, most fish, amphibians, and reptiles
Depend on air temperature to regulate metabolic rates
Species have developed behaioural adaptations to overcome these limitations (ex: reptiles sun themselves on rocks or hide in the shade to regulate temperature)

21. Endotherms Mammals including humans, and birds
Able to maintain a constant body temperature regardless of their surroundings
Adjust to decreases in environmental temperatures by increasing the rate of cellular respiration to generate heat

22. Homework
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