Homeostasis

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Homeostasis
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Glossary

• Maintain keep up.
• Constant the same.
• Internal inside the body.
• Environment surroundings of the body.
• Feedback - a cycle in which the output of a
  system feeds back to modify or reinforce the
  actions of the system in order to maintain
  homeostasis.

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Glossary

• Negative feedback - a change causes system 1 to
  send a message to system 2 to restore
  homeostasis. When system 1 detects that system 2
  has acted, it stops signaling for action and
  system 2 stops (turned off).
• Positive feedback - the original stimulus is
  promoted rather than stopped. Positive feedback
  is rarely used to maintain homeostasis. An
  example of positive feedback is childbirth.

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What is Homeostasis?

• Body cells work best if they have the correct
• Temperature
• Water levels
• Glucose concentration
• Your body has mechanisms to keep the cells in a
  constant environment.

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What is Homeostasis?

• The maintenance of a constant environment in the
  body is called Homeostasis

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Controlling body temperature

• All mammals maintain a constant body temperature.
• Human beings have a body temperature of about
  37ºC.
• E.g. If your body is in a hot environment your
  body temperature is 37ºC
• If your body is in a cold environment your body
  temperature is still 37ºC

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Controlling body temperature

• Animals with a large surface area compared to
  their volume will lose heat faster than animals
  with a small surface area.

Volume _______ Surface area ______ Volume
Surface area ratio ___________
Volume _______ Surface area ______ Volume
Surface area ratio ___________
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Controlling body temperature
Volume Surface area ratio 16
Volume Surface area ratio 15
For every 1 unit of heat made, heat is lost out
of 6 sides
For every 1 unit of heat made, heat is lost out
of 5 sides
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Controlling body temperature
Volume Surface area ratio 16
Volume Surface area ratio 15
The bigger the Volume Surface Area ratio is,
the faster heat will be lost.
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Penguins huddling to keep warm
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What mechanisms are there to cool the body down?

• Sweating
• When your body is hot, sweat glands are
  stimulated to release sweat.
• The liquid sweat turns into a gas (it evaporates)
• To do this, it needs heat.
• It gets that heat from your skin.
• As your skin loses heat, it cools down.

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Sweating
The skin
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What mechanisms are there to cool the body down?

• Vasodilation
• Your blood carries most of the heat energy around
  your body.
• There are capillaries underneath your skin that
  can be filled with blood if you get too hot.
• This brings the blood closer to the surface of
  the skin so more heat can be lost.
• This is why you look red when you are hot!

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This means more heat is lost from the surface of
the skin
If the temperature rises, the blood vessel
dilates (gets bigger).
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What mechanisms are there to warm the body up?

• Vasoconstriction
• This is the opposite of vasodilation
• The capillaries underneath your skin get
  constricted (shut off).
• This takes the blood away from the surface of the
  skin so less heat can be lost.

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This means less heat is lost from the surface of
the skin
If the temperature falls, the blood vessel
constricts (gets shut off).
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What mechanisms are there to warm the body up?

• Piloerection
• This is when the hairs on your skin stand up .
• It is sometimes called goose bumps or chicken
  skin!
• The hairs trap a layer of air next to the skin
  which is then warmed by the body heat
• The air becomes an insulating layer.

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Controlling Glucose levels

• Your cells also need an exact level of glucose in
  the blood.
• Glucose moves into the cells for cellular
  respiration
• Excess glucose gets turned into glycogen in the
  liver
• This is regulated by 2 hormones (chemicals) from
  the pancreas called
• Insulin
• Glucagon

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If there is too much glucose in the blood,
Insulin converts some of it to glycogen the rest
moves into the cells for use in cellular
respiration.
Glycogen
Insulin
Glucose in the blood
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Glycogen
If there is not enough glucose in the blood,
Glucagon converts some glycogen into glucose.
Glucagon
Glucose in the blood
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Diabetes

• Some people do not produce enough insulin.
• When they eat food, the glucose levels in their
  blood cannot be reduced.
• This condition is known as DIABETES.
• Diabetics sometimes have to inject insulin into
  their blood. They have to be careful of their
  diet.

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Glucose levels rise after a meal.
Insulin is produced and glucose levels fall to
normal again.
Glucose Concentration
Normal
Time
Meal eaten
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Glucose levels rise after a meal.
Glucose Concentration
Diabetic
Insulin is not produced so glucose levels stay
high
Time
Meal eaten
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Glycogen
The glucose in the blood increases.
But there is no insulin to convert it into
glycogen.
Glucose concentration rises to dangerous levels.
Insulin
Glucose in the blood
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Blood Glucose Feedback Mechanism
Pancreas produces Insulin
Glucose into cells Out of blood
Blood glucose increases Homeostasis
Blood glucose decreases (
High )
(Low)
Glucose out of cells
Into blood

Pancreas produces Glucagon
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Controlling water levels

• The control of water levels is carried out by the
  KIDNEYS.
• It is closely linked to the excretion of urea.
• Urea is a waste product that is made when the
  LIVER breaks down proteins that are not needed by
  the body.
• Urea contains the element Nitrogen.

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The kidneys
The kidneys clean the blood of waste products
and control how much water is kept in the body.
The waste products and water make up urine which
is excreted via the ureter.
Dirty blood enters the kidney through the renal
artery. Then, several things happen to clean the
blood...
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1. Filtration
Blood enters the tubule area in a capillary.
The capillary forms a small knot near the
kidney tubule.
The blood is filtered so all the small particles
go into the tubule.
The capillary then carries on to run next to the
tubule.
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The kidney tubule now contains lots of blood
components including Glucose Ions Water Ur
ea
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2. Reabsorb sugar
The body needs to have sugar in the blood for
cells to use in respiration. So all the sugar is
reabsorbed back into the capillary.
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2. Reabsorb sugar
The body needs to have sugar in the blood for
cells to use in respiration. So all the sugar is
reabsorbed back into the capillary.
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3. Reabsorb water
Water and ions are the next to be absorbed. It
depends on how much is needed by the body.
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3. Reabsorb water
Water and ions are the next to be absorbed. It
depends on how much is needed by the body.
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Reabsorbing water
If you have too little water in your blood, you
will produce very concentrated urine. (very
little water in it)
If you have too much water in your blood, you
will produce very dilute urine. (lots of water
in it)
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5. Excrete the waste

• Everything that is left in the kidney tubule is
  waste
• All the urea
• Excess water

This waste is called urine. It is excreted via
the ureter and is stored in the bladder.
The clean blood leaves the kidney in the renal
vein.
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Summary of urine production

• Urea is a waste product made in the LIVER
• Water content of the body is controlled in the
  KIDNEYS
• Urea, water and other waste makes up URINE.
• Urine travels down the URETER and is stored in
  the BLADDER
• Urine is excreted through the URETHRA.

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• Temperature regulation, glucose level control and
  water level control are all examples of NEGATIVE
  FEEDBACK MECHANISMS.

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Homeostasis in Plants

• Control of water levels in the plant is important
  to the survival of the plant.
• This is achieved by a number of methods
• Waxy cuticle on leaves
• Storage of water
• Opening and closing of stomates

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Function of Stomata

• What process involves using CO2 and H2O
  releasing O2 as a waste product?
• Photosynthesis
• What is the plant using this process to make?
• Carbohydrates-glucose
• If the plant needs water for photosynthesis, why
  is water coming out of the stoma?

Guard Cells
Guard Cells
Stoma Closed
Stoma Open
Stoma
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Function of Guard Cells

• These stomata (leaf openings) naturally allow
  water to evaporate out.
• Why would the plant close stomata with guard
  cells?
• Prevent excess water loss through transpiration.
  (conserve water)
• So what is the point of having stomata?
• Allow gas exchange for photosynthesis

Guard Cells
Guard Cells
Stoma Closed
Stoma Open
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• The opening and closing of the stomata maintains
  water balance in the plant and thus maintains
  homeostasis.