Homeostasis Flashcards
What is homeostasis
The maintenance of a constant internal environment within an appropriate range in the body in response to changes in external and internal environ
Why is keeping a constant internal environment vital
For cells to function normally and stop them from being damaged eg if body temp too high enzymes become denatured
Normal concentration of glucose in the blood and why this must be maintained
90mg per 100cm3, cells need a constant energy supply to work
How is water lost from the body
Via urine and sweating
What controls the water content of the blood and urine
The kidneys
What do homeostatic systems involve
Receptors, a communication system and effectors
Process of how negative feedback works
Receptors detect when a level is too high or low and info communicated via nervous system/ hormonal system to effectors
-effectors respond to counteract the change to bring the level back to normal
Does negative feedback work within certain limits
Yes, if change is too big then effectors may not be able to counteract it
What do positive feedback mechanisms do
Amplify the change that triggered it, effectors respond to further increase the level away from the normal level
Explain example of positive feedback
Blood clot after injury
-Platelets become activated and release a chemical which triggers more platelets to be activated
-platelets very quickly form a blood clot at the injury site and process ends with negative feedback when body detects the blood clot has been formed
Is positive feedback involved in homeostasis
No because it doesn’t keep your internal environment stable
Mechanisms used to reduce body temp
-sweating (more sweat secreted from sweat glands when body’s too hot, water in sweat evaporated from the surface of skin and takes heat from the body and skin is cooled)
-hairs lie flat (erector pili muscles relax so hairs lie flat, less air trapped so skin less insulated and heat lost more easily)
-vasodilation (arterioles near surface of skin dilate so more blood flows through the capillaries in the surface layers of the dermis meaning more heat lost from the skin by radiation and temp is lowered)
-no adrenaline or thyroxine released
Mechanisms to increase body temp
-shivering (muscles contract in spasms which makes body shiver and more heat produced from increased respiration)
-much less sweat secreted from sweat glands, reduces amount of heat loss
-hairs stand up, erector pili muscles contract making hairs stand up which traps more air and prevents heat loss
-vasoconstriction (arterioles near the surface of the skin constrict so less blood flows through the capillaries in surface layers of the dermis which reduces heat loss)
-body releases adrenaline and thyroxine which increase metabolism so more heat produced
Why can hairs on surface of skin increase body temp
When erect trap layer of air which is a poor conductor of heat
Which part of the brain maintains body temp in mammals at constant level
Hypothalamus
Process of homeostasis to maintain constant body temp
-hypothalamus receives info about temp from thermoreceptors which sends impulses along sensory neurones
-hypothalamus sends impulses along motor neurones to effectors
-effectors respond to restore body temp back to normal
What is the control of body temp called and what does this
Thermoregulation, heat loss and heat gain centre in hypothalamus
What happens when rise in body temp
Thermoreceptors detect temp is too high, send impulse along sensory neurone to hypothalamus
-hypothalamus sends signals to effectors along motor neurones
-responses brought about
-more heat lost and less heat produced by the body
What happens when fall in body temp
-thermoreceptors detect temp is too low, send impulse along sensory neurones to hypothalamus
-hypothalamus sends signals to effectors along motor neurone
-responses brought about
-more heats produced and conserved by the body
What can affect the activity of transcription factors and how do they do this
Hormones, cross the cell membrane, enter nucleus and bind to transcription factors to alter gene transcription/work from the cell membrane
At normal body temp what does thyroid hormone receptor do
It is a transcription factor that binds to DNA at the start of a gene which decreases transcription of a gene coding for a protein that increases metabolic rate
What happens at cold temps in terms of thyroxine
Thyroxine released which binds to the thyroid hormone receptor causing thyroid hormone receptor and thyroxine to act as an activator, transcription rate increases producing more protein which increases the metabolic rate causing an increase in body temp
Why can’t protein hormones easily pass cell membrane
Unlike steroid and thyroid hormones they aren’t lipid soluble
How can some hormones work from the cell membrane
Bind to receptors in cell membrane which activate messenger molecules in cytoplasm of cell, these messenger molecules activate protein kinases (enzymes) which trigger a cascade of reactions inside cell in which TFs can be activated which can then affect the transcription of genes in cell nucleus
How is rate of glycolysis controlled by negative feedback
When level of ATP increases it inhibits enzymes involved in early stages of glycolysis by binding to enzyme and changing the shape of its active site meaning ATP production decreases
What are peptide hormones
Made of AAs eg HGH and insulin, small and charged so cannot pass across membrane so must bind to receptor on surface to activate TFs
Where does transcription factor bind
Promoter region on gene
What are steroid hormones
Made from lipids, non-polar so can pass across cell surface membrane and bind to TFs eg oestrogen and testosterone are hormones
