Download B4 - Homeostasis

B4 Homeostasis
What you should know….
What is homeostasis?
• 1 minute - write a definition of
homeostasis
• Homeostasis means
keeping a constant internal
environment
Why do we need it?
• If there was not a constant internal
environment, our enzymes would not work
properly. That would mean that nothing
would operate correctly and we would die.
What needs to be
controlled?
• 1. Carbon dioxide Extra carbon dioxide
must be removed, otherwise the body
becomes too acidic. It is lost mainly in the air
we breathe out, but a small amount is lost in
the urine.
• 2. Urea This is the waste chemical produced
when we digest amino acids in the liver. It is
poisonous and so must be removed. This is
done mainly through the urine, although
some is lost through our sweat.
• 3. Ions If the right balance of ions is
not kept, our cells can become
shriveled, swollen or even burst!
Important ions include sodium,
potassium, hydrogen and phosphate.
These are controlled through our urine
and the amount of water we drink. We
also lose some, like sodium ions,
through our faeces and our sweat.
• 4. Sugar Having enough glucose for
respiration plus adequate stores of
glycogen is critical. If the blood glucose level
falls too low we will die.
• 5. Water Seventy percent of our body mass
is water. Without keeping the right amount of
water we would die. The kidney is the key
means of this control
• 6. Temperature The enzymes that control
every chemical reaction in our body work best
at their optimum temperature of 37 degrees
Centigrade. If our body cells get too hot or
too cold they would die. So would we!
• A way to remember these 6 things
is by learning this...
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When (Water)
Shall (Sugar)
I
(Ions)
Clean (CO2)
The
(Temperature)
Utensils (Urea)
Which organs are involved?
• The hypothalamus (in the brain) monitors
water, temperature and carbon dioxide
content of blood.
• The pituitary gland secretes a number of
hormones, a key one is ADH (anti-diuretic
hormone) which is important in regulating the
water content of the body.
• The liver helps to control glucose content of
the body by storing it as glycogen. It is also
involved in temperature regulation, acting as
the body's furnace by increasing the rate of
respiration when we are cold.
• The lungs are involved by getting rid of
carbon dioxide from the body.
• The pancreas is involved in maintaining a
constant amount of glucose in the body
through the actions of glucagon and
insulin.
• The muscles of the body can help to
maintain a stable body temperature as
muscular activity and shivering help to
generate heat.
• The kidneys are involved in
controlling the amount of water in the
body.
• The skin is the largest organ and has
a central role in maintaining a
constant temperature
What if we get too hot?
• The hypothalamus sends impulses to the
skin which cause 3 things to happen:
• 1. Our hairs lie flat: so letting more heat out.
• 2. We sweat: the evaporation of this cools us
down.
• 3. More blood goes through the skin: this
acts like a radiator to radiate out heat.
What if we get too cold?
• If we get too cold the hypothalamus sends
other impulses so that the reverse
happens:
• 1. Our hairs stand up: this traps a layer of air
which acts like an insulator.
• 2. We stop sweating: this stops the heat loss
by evaporation.
• 3. Less blood goes through the skin: the
skin will appear paler and colder.
The kidney - what does it
do?
• One job that they are involved in is
reabsorbing excess water so that we don't dry
out.
• Blood enters the kidney through the renal
artery. It is filtered and the 'clean' blood leaves
via the renal vein. Any waste material leaves
through the ureter, then to the bladder and the
world outside!
If nothing else happens then the
materials, such as water and urea, will
end up going all the way through the
nephron, down the ureter, through the
bladder and into the toilet!
However, sometimes the body needs to
grab back chemicals such as water and
glucose which are still useful. This
happens when they move out of the
fluid in the nephron back into the
capillary network that twists around
the nephron.
This process is called reabsorption.
If there isn’t enough water
in the body?
• When there is too little water in the
body the following sequence of
events occurs:
• Flowchart
If there’s too much water in
the body?
• Draw a flow chart similar to the
previous one for if there was too
much water in the body.
Negative feedback
• These are examples of negative
feedback.
• Receptors in the body identify a
change. The body then carries out
any necessary processes to return
the body to its normal state.
What happens if the kidneys
don’t work properly?
• DIALYSIS
Blood is taken out of a vein and pumped
through a machine that cleans it. This
cleaning is done by getting the waste
materials like urea to diffuse across a
selectively permeable membrane into a
plasma-like fluid.The 'clean' blood is then
returned to the patient.
• A better way is to have a kidney transplant.
Here, a healthy kidney is taken from a donor,
usually someone who has sadly been killed in
an accident or illness.The kidney is then sewn
into place with all of the blood vessels and
tubes connected.
• The success rate is about 80% if the tissue
types are found to be the same between
donor and patient.However the patient must
take antibiotics and anti-rejection drugs for the
rest of their life! Quite a daunting prospect but
at least they can lead a normal life otherwise.
Revision key points:
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What is homeostasis?
Why do we need it?
What has to be controlled?
Which organs are involved?
Controlling temperature
Controlling body water
Dealing with kidney failure
Diffusion
• Movement of particle from an area of
high conc to a low conc.
Osmosis
• Movement of water particles from an
area of high conc to a low conc,
through a partially permeable
membrane
Active Transport
• Molecules that are too big
• Molecules moving from low to high
concs.
• Involves a carrier protein in the cell
membrane