Upload
candace-legate
View
218
Download
0
Embed Size (px)
Citation preview
B4: HomeostasisMaintenance of a constant environment within a body
Keeping our cells happy
• Cells work best at certain temperatures and with the right amount of hydration (water present)
• The levels of glucose, salts, urea, oxygen and carbon dioxide must also be controlled
• The control of these factors is automatic and occurs via feedback systems.
Where we are and what we do affect our levels…
Which internal factors are being stressed in each picture?
Feedback loops
The effectors adjust the quantity if the processing centre notices a difference between the sensor reading and the set-point and uses effectors to modify the values Processing
centre
receptor
stimuli
Negative feedback loops
• High “readings” bring about a reduction and low levels result in a rise
Draw a similar flow diagram to show the chain of events if the
car is too slow
Antagonistic effectors
• The use of two effectors which have opposite effects makes the control of systems much more sensitive (a push-pull approach!).
• E.g. blood sugar levels are controlled by two hormones – glucagon (raises sugar levels)– insulin (lowers sugar levels) which we met in C3
(Food Matters)Blood sugar is
too low
Blood sugar isToo high
Glucagon increasesInsulin decreases
Glucagon decreasesInsulin increases
Blood sugar
levels return to the
set point
Another example:
• Body temperature…
temperature is too low
temperature istoo high
shivering increasessweating decreases
shivering decreasessweating increases
temperature returns to the
set point
Some machines use feedback loops too!
• If the incubator gets too hot measured by the thermostat (sensor) then the heater automatically turns off.
• If too cold the heater turns on
• The temperature stays almost constant
Draw a decision chart for the incubator
Temperature control
The core temperature must remain constant (36.8oC in humans) but the extremities (e.g. limbs) can withstand more variationCredit: TONY MCCONNELL/SCIENCE PHOTOLIBRARY
Where is the most heat (i) lost and (ii) retained in the diagram? Use your answers to decide which would be the (iii) warmest and (iv) coolest parts of the body.
What differences in the diagram would you see if the person had a fever?
How is the body temperature maintained?
To maintain the body’s temperature… (a) capillaries of the skin can be opened to lose heat and closed to retain heat(b) shivering due to increased respiration warms up the surrounding tissues(c ) sweating causes cooling as the water evaporates
Set point37oC
Set point37oC
Blood
too hot
Blood
too
cool
Shivering and
vasoconstriction of
capillaries in the
skin
sweating and
vasodilation of
capillaries in the
skin
The hypothalamus of the brain has temperature receptors which detect the blood temperature and automatically trigger the effectors.
Which are the effectors in the diagram?
Can’t take the heat?
If we get too hot the feedback loop does not work as well since we dehydrate and can’t produce as much sweat.
The body will need immediate first aid to lower its’ temperature or else death is possible.
Heat stroke is an uncontrolled increase in body temperature
First aid
Chill out!
• Cold, wet and windy weather can all lower the body temperature of poorly prepared travellers.
• Hypothermia (where heat loss is faster than heat production) occurs if the core temp drops below 35oC
Frostbite damage to hands
Hypothermiafirst aid
•Keep dry and sheltered
•Insulate
•Warm with drinks and food
unless unconscious
•Monitor pulse and breathing
•CPR if necessary
What might happen if a hot water bottle was applied to their limbs?
Why do we have an optimum temperature?
• Most chemical reactions in our body rely on enzymes (biological catalysts made of proteins)
• They need a reasonably high temperature to allow enough collisions with other molecules (substrates) but not too high in case they denature (no longer work)
Enzymes
The substrate fit
perfectly into the
active site of the
enzyme like a key
into a lock!
The shape of the enzyme is due to folding and weak bonding between chains. Too much heating OR a change in pH breaks these weak bonds so the active site changes shape (denatured!)
Active site
On a cellular level
The levels of substrates and other chemicals must be maintained in cells using one of the transport methods below…
• Diffusion e.g. O2, CO2, dissolved food
• Osmosis e.g. water
• Active transport (requires the use of an energy rich molecule) e.g. transport of glucose
Diffusion
Osmosis
Semi-permeable membrane(allows the water through but not the large solute!)
Low solute concentration
High solute concentration
Only the water moves!
Uses of
waterCan you name 3 ways water is gained for our body?
Losses include… •sweating, •breathing,•excretion of urine, •faeces
Controlling our hydration
Our kidneys help to regulate our levels of…– urea ( a waste substance from protein
breakdown)– Water– Salts– Sugars by stopping their loss in urine
kidneysKidneys produce urine ( a mixture of water, urea and occasionally salts)
Bladder stores urine (until a convenient moment!)
Small molecules filtered from the blood and the wanted ones are reabsorbed
Bladder control… it’s all in the mind!
• The pituitary gland uses a hormone called ADH (anti diuretic hormone) to control hydration levels via the bloodstream.
• Uses a negative feedback loop where the blood plasma concentration determines the release of the hormone.
• Hormone makes the kidney more permeable to water allowing it to reabsorb more.
Pituitary gland
Urine: the colour of samples indicate the
level of hydration
High plasma
conc
ADHReleased
by pituitar
y
More water
reabsorbed
lowplasma
conc
ADHnot release
d
less waterReabsorbe
dby kidneys
Dilute urine
Concentrated urine
Which factors may affect your urine colour?
Factors affecting hydration levels:• External temperature• Level of exercise• Water intake• Salt intake• Drug taking…
– Alcohol suppresses ADH so more dilute urine is formed dehydrating the body How might hangovers be explained?
– Ecstasy causes too much ADH to be formed so too much water is absorbed… this can cause the brain to to swell, water intoxication and death as with the case of Leah Betts How might the conditions in the night club have made the effect of ecstasy worse for Leah?