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
what are the main factors that contribute to blood glucose levels
-diet - glucose is released from carb digestion
-exercise
-action of hormones - insulin reduces blood glucose whilst glucagon and adrenelin increase it
what action does the body take if blood glucose raises to high - steps
1- beta cells in the islet of langherns detect an increase in blood glucose
2- insulin binds to its receptor - due to comp shape - in the CSM - mainly on liver,muscles and adipose(fat) cells
3- this sends a chemical signal to vesicles in the cytoplasm which contain glucose channel/transport proteins
4-vesicles move to the CSM and fuse with it
5- increased number of glucose channel proteins increases the rate of gluocse uptake by the cell and teritary structure of transport protien changes allowing more glucose to enter into the cell
6- enzymes activated which leads to
-increased rate of respiration
-increased conversion of glucose to fat in the adipose cells
-increased conversion of glucose to glycogen - known as glycogenesis
7- blood glucose is lowered, causing beta cells to decrease secretion of insulin - negative feedback
what actions does the body take if the blood glucose levels go below the norm - steps - second messenger model
1- alpha cells in the islets of langherns detect low blood sugar and relase glucagon
2-glucagon is the first messenger, it binds to a receptor site on a transmembrane protein
3- this causes the protein to change shape, activating adenyl cyclase enzyme
4- Adenyl cyclase converts ATP to cAMP
5- cAMP acts as the 2nd messenger starting a series of reactions
6- cAMP activates the protein kinase eznmye which goes onto activate phosphorylase enzymes
7- phosphorylase catalyses the conversion of glycogen to glucose - known as glycoenolysis
8- glucagon also activates enzymes to convert AAl and glycerol to glucose - known as gluconeogenesis
which other hormone increase blood glucose conc by the second messenger model
-adrenelin - switch glucagon for adreneline
-casues breakdown of glycogen in the liver boosts blood glucose conc
-inactivating an enzyme which causes glucose to be converted to glycogen
how does cortisol affect blood glucose
-secreted by the adrenal glands when glycogen stores in the liver become exhausted
-causes the liver to convert AA and glycerol to gluocse and rasing blood glucose conc
what organs are involved in maintaing blood glucose
-pancreas and liver
what are the two types of diabetes
-type 1 - juvenile-onset or insulin dependent
-type 2 - late-onset or insulin independent
what are the symptoms of diabetes
-after a meal blood glucose levels rise as insulin is not being produced - so may go to dangerously high levels = hyperglycaemia
-in the kidneys - if blood sugar is too high - they cannot cope and some glucose is excreted in the urine = glycosuria
-extra water and salt then follows and the person then urinates a lot and feels thirsty
-feel tired as uptake is too slow
-cells start metabolising fat and proteins which leads to the build-up of ketones in the blood - leads to pear-drop-smelling breath
-combo of dehydration, salt loss and low ph can lead to coma and death
how can diabetes lead to a coma
-no glycogen stores to mobilise glucose levels so the blood glucose level drops significantly - and no glucose for respiration = coma
do type 1 diabetics produce insulin
no
do type 2 diabetics produce insulin
yes but body does respond to it
describe the blood glucose level diabetes graph
-diabetic blood glucose is always higher
-immediately after glucose is ingested blood glucose increases for both diabetic and non-diabetic at the same time
-diabetic increases more quickly
-non-diabetic more quickly as insulin reduces blood glucose to normal
-diabetic is slow to return to normal as it is used up by the cells
how to describe insulin level diabetes graph
-non-diabetic
-after glucose is swallowed insulin levels increase sharply immediately after
-beta cells release insulin to respond to increase in blood glucose
-falls back to normal level of the pre-glucose stage
-diabetic
-remains steady
-no increase after glucose is swallowed
-non-diabetic line is always higher than the diabetic line
when to symptoms of type 1 diabetes occur and why
-below the age of 20
-pancreas fails to produce insulin
-thought to be linked to an autoimmune disease where there is damage to the b-cell
-or mutation in the gene coding for insulin
how is type 1 diabetes treated
-insulin injection
-need to monitor diet and blood glucose levels carefully and inject the right amount of insulin
why can insulin not be taken orally
-hormone so it is a protein and would be digested by protease in the stomach before it could be absorbed
what is hypoglycaemia
-where the blood glucose drops too low
-symptoms are shaking, sweating, blurred vision and loss of concentration
-need to eat sugars quickly to bring their blood glucose back up
-could fall into a coma if not as cells do not have enough glucose for resp
what is hyperglycaemia
-blood sugar rises too high
-eaten sugary foods or have not had enough insulin
-can lead to coma because of dehydration, salt loss and low blood pH
why is type 2 diabetes diagnosed and what are the causes
-over 40/later in life
-gradual loss of the responsiveness of the cells to insulin although it can be due to an insulin definceny
-associated with obesity and lack of exercise and poor diet
-symptoms similar to that of type 1
what are the treatment options for type 2
-primarily - diet and exercise management
-once these measures become inadequate then drugs can be taken which are designed to
-increase insulin output by pancreas
-decrease amount of glucose released from the liver
-increase sensitivity/responsiveness of cells to insulin
-decrease absorption of carbs from intestine
-slow emptying of the stomach to delay the presentation of carbs for digestion and absorption into small intestine
-when this doesn’t work then have to take injections
