Terms in this set (8)
Why is homeostasis important
- Homeostasis involves control systems that keep you internal environment roughly constant in a state of dynamic equilibrium.
- Keeping internal environment constant is vital for cells to function normally and to stop them being damaged.
- If body temperature is too high enzymes become denatures, active sites change no longer works metabolic reactions are less efficient.
How do homeostatic systems detect changes
- Homeostatic systems involve receptors, a communication system and effectors
- Receptors detect when a level of (e.g. temperature) is too high or too low and the informations communicated via the nervous system or the hormonal system to effectors.
- The effectors respond to counteract the change bringing the level back to normal.
Define negative feedback mechanism
- The mechanism that restores the level to normal.
- Negative feedback keeps levels around the normal level (e.g. temperature around 37 degrees)
- Negative feedback only works within certain limits if the change is too big then the effectors may not be able to counteract it.
How do these homeostatic mechanisms reduce body temperature
1. Sweating - more sweat is secreted from sweat glands when the bodys too hot. The water in the sweat then evaporates from the surface of the skin and takes heat from the body which cools the skin.
2. Hairs lie flat - erector pili muscles relax so the hairs lie flat so less air is trapped, so the skin is less insulated and heat can be lost more easily.
3. Vasodilation - arterioles near the surface of the skin dilate. More blood flows through the capillaries in the surface layers of the dermis. This means more heat is lost from the skin by radiation lowering the temperature
How do these homeostatic mechanisms increase body temperature
1. Shivering - muscles contract in spasms making the body shiver and more heat is produced from increased respiration.
2. Hormones released - Body releases adrenaline and thyroxine which increase metabolism so more heats produced
3. Less sweat is secreted reducing heat loss.
4. Hairs stand up - erector pili muscles contract when its cold which makes the hairs stand up to trap more air and so prevents heat loss.
5. Vasoconstriction - arterioles near the surface of the skin constrict so less blood flows through capillaries in the surface layers of the dermis reducing heat loss
How is body temperature maintained
- Body temperature in mammals is maintained at a constant level by the hypothalamus in the brain.
- The hypothalamus receives information about temperature from thermoreceptors.
- Thermoreceptors send impulses along sensory neurones to the hypothalamus, which sends impulses along motor neurones to effectors (muscles and glands)
- The effectors respond to restore the body temperature back to normal.
- Control of body temperature is called thermoregulation
Genes :Transcription factors
- In a cell there are proteins called transcription factors that control the transcription of genes.
- Transcription factors bind to DNA sites near the start of genes and increase or decrease the rate of transcription
- Factors that increase the rate are called activators
- Those that decrease the rate are called repressors
How hormones bind to transcription factors
- Hormones can bind to some transcription factors to change body temperature.
1. At normal body temperature, the thyroid hormone receptor (transcription factor) binds to DNA at start of a gene.
- This decreases the transcription of a gene coding for a protein that increases metabolic rate.
2. At cold temperatures thyroxine is released, which binds to the thyroid hormone receptor, causing it to act as an activator
- The transcription rate increases, producing more protein.
- The protein increases the metabolic rate, causing an increase in body temperature.
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