homeostasis Flashcards
what does homeostasis mean
keeping a steady state
what does homeostasis mean in bio
maintenience of a constant internal enviroment
what things have to be kept constant in the body
-constant pH
-temp
-glucose
-salt and water conc
what stages/ things does the homeostatic system involve
stimulus - change from the norm or set point
receptor - detects the change from the norm
co-ordinator - compares actual values with the norm
effector - bring about the corrective norm
response - restoring norm values
what systems does the homeostatic mechanims involve
-endocrine
-nervous
what are feedback systems
changes in the body that are constantly monitored by receptors which detect stimuli and send signals to effectors via a co-ordinator
what are the 2 types of feedback systems
-positive feedback
-negative feedback
what are psotive feedback systems
-enhances the effect of the stimulus - a greater deviation from the norm causes an even greater deviation from the norm in a cycle
what are negative feedback systems
reverses the effect of the stimulus - a deviation from the norm is corrected
what factors are involved in feedback systems
-set point - the normal level
-receptor - detects deviations from the set point
-controller - co-ordiantes information from various receptors
-effector - brings about corrective measures in order to restore the set point
-feedback loop - informs the recpetors of the changes brought about by the effectors - this is important to ensure that the receptor does not continue to stimulate the effectors which would result in over correction
how does negative feedback loop reverse the stimulus
The factor/stimulus is continuously monitored
If there is an increase in the factor, the body responds to make the factor decrease
If there is a decrease in the factor, the body responds to make the factor increase
The system is restored to its original level
eg body temp and blood glucose
how do receptors control the negative feedback loop
Receptors detect any deviations from the normal range (stimuli) which results in a corrective mechanism to return the factor back to its normal range
In a negative feedback loop there are usually two corrective mechanisms:
One for when the factor becomes too low
One for when the factor becomes too high
The corrective mechanisms may involve the nervous system or the endocrine system
The magnitude of the correction required to bring a factor back within its normal range is monitored and regulated by negative feedback
As the factor gets closer to its normal value the level of correction reduces
how does postive feedback enhance the effect of the stimulus
-corrective action remains on
-norm becomes even greater
eg oxytocin in childbirth - contractions result int he production of more hormone so contractions get stronger - ends in child being born
nerve impulse - small influx of Na+ to the neurone
alters permeability of the membrane resulting in the futher influx of Na+
why is homeostasis important in chnages in temp and pH
-enzymes very sensitive to temp and pH
how can low temp effect enzymes
Lower temperatures either prevent reactions from proceeding or slow them down:
Molecules move relatively slow
Lower frequency of successful collisions between substrate molecules and active site of enzyme
Less frequent enzyme-substrate complex formation occurs
Substrate and enzyme collide with less energy, making it less likely for bonds to be formed or broken (stopping the reaction from occurring)
how can high temp affect enzymes in extreme
However, as temperatures continue to increase, the rate at which an enzyme catalyses a reaction drops sharply, as the enzyme begins to denature:
Bonds (eg. hydrogen bonds) holding the enzyme molecule in its precise shape start to break
This causes the tertiary structure of the protein (ie. the enzyme) to change
This permanently damages the active site, preventing the substrate from binding
Denaturation has occurred if the substrate can no longer bind
Very few human enzymes can function at temperatures above 50°C
This is because humans maintain a body temperature of about 37°C, therefore even temperatures exceeding 40°C will cause the denaturation of enzymes
High temperatures cause the hydrogen bonds between amino acids to break, changing the conformation of the enzyme
how does high temp effect enzymes not extreme
Molecules move more quickly
Higher frequency successful collisions between substrate molecules and active site of enzyme
More frequent enzyme-substrate complex formation
Substrate and enzyme collide with more energy, making it more likely for bonds to be formed or broken (allowing the reaction to occur)
how does changes in pH affect enzymes
All enzymes have an optimum pH or a pH at which they operate best
Enzymes are denatured at extremes of pH
Hydrogen and ionic bonds hold the tertiary structure of the protein (ie. the enzyme) together
Below and above the optimum pH of an enzyme, solutions with an excess of H+ ions (acidic solutions) and OH– ions (alkaline solutions) can cause these bonds to break
This alters the shape of the active site, which means enzyme-substrate complexes form less easily
Eventually, enzyme-substrate complexes can no longer form at all
At this point, complete denaturation of the enzyme has occurred
what are the consequences of having too much glucose or ions in the blood
-hypertonic
-water moves out of the cells
-down WP gradient
-cell shrinks
what are the consequences of the blood becoming too dilute
-hypotonic
-water moves into cell by osmosis
-down WP gradient
-cell bursts
what happens if the blood glucose is too low
-glucose needed for respiration
-less energy avliable for active transport
-and other metabolic reactions
how much glucose do brain cells use and why must glucose be in the bloodstream
25% and brain cells cannot store glucose so needs to be readily avaliable in the blood
what happens to the water potential if the blood glucose is too high
-make water potential of blood more negative and body cells will begin to lose water by osmosis and may become severly dehydrated
what happens if the blood glucose falls below the norm
-insufficent energy for cells to function
