Download Homeostasis

Homeostasis
Keeping things steady...
• Many chemical reactions happen inside
your body.
• Reactions are controlled by enzymes.
• Enzymes work best in certain conditions.
• Therefore it is important to keep certain
things in our body constant:
– Temperature
– pH
– Water content
Controlling conditions
Homeostasis – keeping a constant internal
environment (controlling conditions in the
body within narrow limits)
• These conditions include:
–
–
–
–
Water content
Ion content
Body temperature
Blood glucose concentration
Controlling conditions
• The brain has overall control of our body
processes.
• When blood flows through the brain, it
checks:
– the temperature
– the concentration of chemicals such as carbon
dioxide.
Our blood is providing feedback to our
brain.
Blood gets too
hot
Brain switches
on cooling
mechanisms
Normal body
temp.
Blood gets too
cold
Blood temperature
falls
Normal body
temp.
Brain switches
on warming
mechanisms
Blood
temperature
rises
Removing waste products
• Carbon dioxide
– Produced during cellular respiration.
– Every cell in body respires.
– If it was not removed it would affect the pH
of the cells (make it more acidic). This would
affect the working of the enzymes in cells.
– Carbon dioxide moves out of cells into blood.
– Blood carries it back to lungs.
– Carbon dioxide removed when you breathe out.
Removing waste products
• Urea
– Produced in liver when excess amino acids are
broken down.
– In the liver the amino group is removed and
converted into urea. The rest of the amino
acid used in respiration or to make other
molecules.
– Urea (poisonous) passes from liver into blood.
– If levels build up in blood causes a lot of
damage.
– Urea removed from blood by the kidneys. It is
then removed in urine.
Removing waste products
• Water and ions
– Water is lost through breathing, sweating
and in urine.
– Ions are lost in sweat and urine.
– If the water or ion content is wrong, too
much water may move into or out of your
cells.
Controlling body temperature
Temperature regulation
• Human enzymes work best at 37ºC, so the
body’s temperature is controlled.
• A part of the brain called the
thermoregulatory centre monitors and
controls body temperature.
• It gathers information as nerve impulses from
temperature receptors in:
– the brain - these are sensitive to the temperature
of the blood flowing there
– the skin - these are sensitive to skin temperature
Thermoregulatory centre is found in the
hypothalamus
Temperature regulation
• If you become too hot or too cold,
there are several ways in which your
temperature can be controlled.
– Sweating,
– Shivering,
– Skin capillaries and
– Hairs.
Too cold
• When we get too cold:
– Muscles contract rapidly - we shiver. These contractions
need energy from respiration, and some of this is released as
heat.
– Blood vessels leading to the skin capillaries become narrower
- they constrict - letting less blood flow through the skin and
conserving heat in the body.
– The hairs on the skin also help to control body temperature.
They lie flat when we are warm, and rise when we are cold.
The hairs trap a layer of air above the skin, which helps to
insulate the skin against heat loss.
Too hot
• When we get too hot:
– Sweat glands in the skin release more sweat. This
evaporates, removing heat energy from the skin.
– Blood vessels leading to the skin capillaries become
wider - they dilate - allowing more blood to flow
through the skin, and more heat to be lost.
Too cold
A - Hair muscles pull hairs on end.
B - Erect hairs trap air.
C - Blood flow in capillaries
decreases.
Too hot
D - Hair muscles relax. Hairs lie flat
so heat can escape.
E - Sweat secreted by sweat glands.
Cools skin by evaporation.
F - Blood flow in capillaries
increases.
Controlling blood sugar
The pancreas monitors and controls the concentration of
glucose in the blood.
• What happens when your blood glucose levels get too
high?
–
–
–
–
Pancreas produces a hormone called insulin.
Insulin causes glucose to move from the blood into cells.
Glucose is changed into glycogen in the liver.
So insulin lowers the blood glucose concentration if it has
become too high.
• What happens if your blood glucose levels get too low?
– Pancreas produces a hormone called glucagon.
– Glucagon tells the liver to break the glycogen down to glucose
again.
– Glucose is released into the blood.
– So glucagon raises your blood sugar levels.
Glucose rises
(food intake)
Insulin causes
glucose to
change to
glycogen
Normal blood
glucose level
Glucose falls
(exercise)
Glucose falls
Normal blood
glucose level
Glucagon causes
glycogen to
change to
glucose
Glucose rises
Diabetes
• Diabetes is a disease where the concentration of
glucose in the blood is not controlled properly by
the body.
• In type 1 diabetes, the pancreas does not
produce enough insulin.
– This can lead to high levels of glucose in the blood,
which can be fatal.
– Kidneys produce glucose in urine, produce lots of urine
and always thirsty.
– Glucose cannot get into cells – lack energy and feel
tired.
– Break down fat and protein to use as fuel – lose weight.
Treating diabetes
• Type I
– Inject insulin into
blood (treatment
NOT cure).
• Type II
– Manage diet – avoid
carbohydrate rich
food.
In 2005 scientists produced insulinsecreting cells from stem cells
which cured diabetes in mice. More
research is needed but the
scientists hope that before long
diabetes will be a disease that we
can cure rather than just treat.