HomeostasisHomeostasis
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GlossaryGlossary
Maintain – keep up.Maintain – keep up. Constant – the same.Constant – the same. Internal – inside the body.Internal – inside the body. Environment – surroundings of the Environment – surroundings of the
body.body. Feedback - a Feedback - a cyclecycle in which the output in which the output
of a system “feeds back” to modify or of a system “feeds back” to modify or reinforce the actions of the system in reinforce the actions of the system in order to maintain homeostasis.order to maintain homeostasis.
GlossaryGlossary
Negative feedback - a change causes system 1 Negative feedback - a change causes system 1 to send a message to system 2 to restore to send a message to system 2 to restore homeostasis. When system 1 detects that homeostasis. When system 1 detects that system 2 has acted, it stops signaling for system 2 has acted, it stops signaling for action and system 2 stops (turned off). action and system 2 stops (turned off).
Positive feedback - the original stimulus is Positive feedback - the original stimulus is promoted rather than stopped. Positive promoted rather than stopped. Positive feedback is rarely used to maintain feedback is rarely used to maintain homeostasis. An example of positive feedback homeostasis. An example of positive feedback is childbirth.is childbirth.
What is Homeostasis?What is Homeostasis?
Body cells work best if they have the Body cells work best if they have the correctcorrect TemperatureTemperature Water levelsWater levels Glucose concentrationGlucose concentration
Your body has mechanisms to keep Your body has mechanisms to keep the cells in a constant environment.the cells in a constant environment.
What is Homeostasis?What is Homeostasis?
The maintenance The maintenance of a constant of a constant
environment in environment in the body is called the body is called
HomeostasisHomeostasis
Controlling body Controlling body temperaturetemperature
All mammals maintain a constant All mammals maintain a constant body temperature.body temperature.
Human beings have a body Human beings have a body temperature of about 37temperature of about 37ººC.C. E.g. If your body is in a hot environment E.g. If your body is in a hot environment
your body temperature is 37your body temperature is 37ººCC If your body is in a cold environment If your body is in a cold environment
your body temperature is still 37your body temperature is still 37ººCC
Controlling body Controlling body temperaturetemperature
Animals with a large surface area compared Animals with a large surface area compared to their volume will lose heat faster than to their volume will lose heat faster than animals with a small surface area.animals with a small surface area.
Volume = _______
Surface area = ______
Volume : Surface area ratio = ___________
Volume = _______
Surface area = ______
Volume : Surface area ratio = ___________
Controlling body Controlling body temperaturetemperature
Volume : Surface area ratio = 1:6
Volume : Surface area ratio = 1:5
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
Controlling body Controlling body temperaturetemperature
Volume : Surface area ratio = 1:6
Volume : Surface area ratio = 1:5
The bigger the Volume : Surface Area
ratio is, the faster heat will
be lost.
Penguins huddling to Penguins huddling to keep warmkeep warm
What mechanisms are there What mechanisms are there to cool the body down?to cool the body down?
1.1. SweatingSweating When your body is hot, sweat glands When your body is hot, sweat glands
are stimulated to release sweat.are stimulated to release sweat. The liquid sweat turns into a gas (it The liquid sweat turns into a gas (it
evaporates)evaporates) To do this, it needs heat.To do this, it needs heat. It gets that heat from your skin.It gets that heat from your skin. As your skin loses heat, it cools down.As your skin loses heat, it cools down.
Sweating
The skin
What mechanisms are there What mechanisms are there to to coolcool the body down? the body down?
2.2. VasodilationVasodilation Your blood carries most of the heat Your blood carries most of the heat
energy around your body.energy around your body. There are capillaries underneath There are capillaries underneath
your skin that can be filled with your skin that can be filled with blood if you get too hot.blood if you get too hot.
This brings the blood closer to the This brings the blood closer to the surface of the skin so more heat surface of the skin so more heat can be lost.can be lost.
This is why you look red when you are This is why you look red when you are hot!hot!
If the temperature rises, the blood vessel dilates (gets bigger).
This means more heat is lost from the surface of the skin
What mechanisms are there to What mechanisms are there to warmwarm the body up? the body up?
1.1. VasoconstrictionVasoconstriction This is the opposite of vasodilationThis is the opposite of vasodilation The capillaries underneath your The capillaries underneath your
skin get constricted (shut off).skin get constricted (shut off). This takes the blood away from the This takes the blood away from the
surface of the skin so less heat can surface of the skin so less heat can be lost.be lost.
If the temperature falls, the blood vessel constricts (gets shut off).
This means less heat is lost from the surface of the skin
What mechanisms are there to What mechanisms are there to warm the body up?warm the body up?
2.2. PiloerectionPiloerection This is when the hairs on your skin This is when the hairs on your skin
“stand up” .“stand up” . It is sometimes called “goose It is sometimes called “goose
bumps” or “chicken skin”!bumps” or “chicken skin”! The hairs trap a layer of air next to The hairs trap a layer of air next to
the skin which is then warmed by the skin which is then warmed by the body heatthe body heat
The air becomes an insulating The air becomes an insulating layer.layer.
Controlling Glucose Controlling Glucose levelslevels
Your cells also need an exact level of glucose in Your cells also need an exact level of glucose in the blood. the blood.
Glucose moves into the cells for cellular Glucose moves into the cells for cellular respirationrespiration
Excess glucose gets turned into glycogen in the Excess glucose gets turned into glycogen in the liverliver
This is regulated by 2 hormones (chemicals) from This is regulated by 2 hormones (chemicals) from the the pancreaspancreas called: called:
InsulinInsulin
GlucagonGlucagon
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
If there is not enough glucose in the blood, Glucagon converts some glycogen into glucose.
Glycogen
Glucagon
Glucose in the blood
DiabetesDiabetes
Some people do not produce enough Some people do not produce enough insulin.insulin.
When they eat food, the glucose levels When they eat food, the glucose levels in their blood cannot be reduced.in their blood cannot be reduced.
This condition is known as DIABETES.This condition is known as DIABETES. Diabetics sometimes have to inject Diabetics sometimes have to inject
insulin into their blood. They have to insulin into their blood. They have to be careful of their diet.be careful of their diet.
Time
Glucose Concentration
Meal eaten
Insulin is produced and glucose levels fall to normal again.
Glucose levels rise after a meal.
Normal
Time
Glucose Concentration
Meal eaten
Insulin is not produced so glucose levels stay high
Glucose levels rise after a meal.
Diabetic
The glucose in the blood increases.
Glycogen
Insulin
Glucose in the blood
But there is no insulin to convert it into glycogen.
Glucose concentration rises to dangerous levels.
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
Blood Glucose Feedback Mechanism
Controlling water levelsControlling water levels
The control of water levels is carried The control of water levels is carried out by the KIDNEYS.out by the KIDNEYS.
It is closely linked to the excretion of It is closely linked to the excretion of urea.urea.
Urea is a waste product that is made Urea is a waste product that is made when the LIVER breaks down when the LIVER breaks down proteins that are not needed by the proteins that are not needed by the body.body.
Urea contains the element Nitrogen.Urea contains the element Nitrogen.
The kidneysThe 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...
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.
1. Filtration
The kidney tubule now contains lots of blood components including:
Glucose:Ions:Water:Urea:
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.
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.
3. Reabsorb water
Water and ions are the next to be absorbed. It depends on how much is needed by the body.
3. Reabsorb water
Water and ions are the next to be absorbed. It depends on how much is needed by the body.
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)
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.
Renal vein
Ureter
Summary of urine Summary of urine productionproduction
Urea is a waste product made in the Urea is a waste product made in the LIVERLIVER
Water content of the body is controlled in Water content of the body is controlled in the the KIDNEYSKIDNEYS
Urea, water and other waste makes up Urea, water and other waste makes up URINEURINE..
Urine travels down the Urine travels down the URETERURETER and is and is stored in the stored in the BLADDERBLADDER
Urine is excreted through the Urine is excreted through the URETHRAURETHRA..
Temperature regulation, glucose Temperature regulation, glucose level control and water level control level control and water level control are all examples of NEGATIVE are all examples of NEGATIVE FEEDBACK MECHANISMS.FEEDBACK MECHANISMS.
Homeostasis in PlantsHomeostasis in Plants
Control of water levels in the plant is Control of water levels in the plant is important to the survival of the important to the survival of the plant.plant.
This is achieved by a number of This is achieved by a number of methods:methods: Waxy cuticle on leavesWaxy cuticle on leaves Storage of waterStorage of water Opening and closing of stomatesOpening and closing of stomates
Stoma Open Stoma Closed
Guard Cells
Stoma
Function of StomataFunction of StomataGuard Cells
CO2
O2 H2O
What goes in?
What goes out?
•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?
Stoma Open Stoma Closed
Guard Cells
Function of Guard CellsFunction of Guard CellsGuard 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
The opening and closing of the The opening and closing of the stomata maintains water balance in stomata maintains water balance in the plant and thus maintains the plant and thus maintains homeostasis.homeostasis.