B3.3 Homeostasis

  • Created by: Fiona S
  • Created on: 10-04-15 21:50

Removal of waste and water control

Homeostasis is maintaining a constant internal environment

Carbon Dioxide

Produced by Respiration

Problem: could dissolve in our blood plasma forming Carbonic Acid (drop in pH.) so we will end up with denatured enzymes.

Removed? CO2 travels in blood to the alveoli = exhaled


Produced from the break down of excess amino acids in the liver

Problem: becomes toxic (poison)

Removed? The kidney filters urea from the blood - helps to form urine. Excreted via the bladder as urine.

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Removal of waste and water control

The water and ions in our bodies come from our food and drink. If there is too much water in the bloodstream osmosis will take place so water will move into our cells and burst (lysis).

The ions are essential to life and are absorbed into the bloodstream in the gut from digested food. The kidney maintains the ion concentration in the blood.

We are taking in water in food and drinks and losing it in sweat (evaporation from skin) and when we breathe out.

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Physiology of Kidneys

Kidney cells are called nephrons.


Stage 1 Ultrafiltration: Water, Urea, Salts and Glucose are forced into the Bowman's Capsule. Blood cells and large proteins cannot pass through.

Stage 2 Selective Reabsorbtion: In the first tube 2/3rds of the salts and water and all the glucose moves out of the nephron by active transport. These substances are reabsorbed back into the blood capillary. NO urea get reabsorbed.

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Physiology of Kidneys

Stage 3 Loop of Henle: This part of the loop is permeable to water but not salt. Water passively osmosis out of the nephron because of low water potential of the medulla tissue fluid.

Stage 4 Loop of Henle: This part is permeable to salts not water

Stage 5 Collecting Duct: Remaining substances move through the second convoluted tube into the collecting duct.

Or simply...

A healthy kidney produces urine by:

  • first filtering the blood
  • reabsorbing all the sugar
  • reabsorbing the dissolved ions needed by the body
  • reabsorbing as much water as the body needs
  • releasing urea, excess ions and water as urine
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How is Urea made?

1. Protein is eaten (protein is made up of amino acids)

2. Protein is split up by digestion.

3. Amino acids are used by the cells to make new proteins

4. Some amino acids are left over.

5. Waste amino acids are changed into UREA in the LIVER.

6. Urea carried in bloodstream to KIDNEYS where filtered out into URINE.

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Maintaining Body Balance

Water and mineral ions enter your body when you eat or drink. The water and ion content of your body are carefully controlled to prevent damage to your cells.

Water is lost through:

  • Breathing
  • Sweating
  • Urination

Ions are lost through:

  • Sweating 
  • Urination

If the water or ion content of your body is wrong, too much water may move in or out of your cells. That's why control is vital.

It is also very important to control:

  • Body Temperature
  • Level of Glucose in Blood
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Maintaining Body Balance

Homeostasis plays an important role in controlling the levels of:

  • Water
  • Ions
  • Temperature
  • Blood Sugar
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The Kidney

A kidney transplant involves: replacing the damaged kidney with a healthy kidney form a donor. Healthy Organs can come from a living or recently deceased person. Living donor are often close friends or relatives of the patients.

Organ rejection is: when the recipients body sees the transplanted tissue as foreign causing an immune response. This happens because the recipient's T cells do not recognise the antigens on the cells of the donated kidney as 'self'. To reduce this risk:

  • The recipient can be given drugs to suppress their immune system. This make the body less able to fight infections
  • A donor with a similar tissue type to that of the recipient should be found e.g. an identical twin
  • The recipient can be kept in a sterile area to avoid risk of infection

Dialysis: involves diverting the blood through an 'artificial kidney' machine that cleans it and returns it to the body.

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The Dialysis machine

  • In a dialysis machine a person's blood flows between partially permeable membranes
  • Waste urea passes out from the blood into the dialysis fluid
  • Treatment by dialysis restores the concentrations of dissolved substances (e.g. glucose, mineral ions such as sodium) in the blood to normal levels
  • Dialysis has to be carried out at regular intervals
  • During dialysis it is important that useful substances in the blood, such as glucose and mineral ions, are not lost. To prevent this the dialysis fluid contains the same concentrations of these substances as blood plasma. This means only waste products and excess ions and water diffuses into the dialysis solution.
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Kidney Dialysis - Features of the Treatment

1) Partially Permeable Membrane between blood and Dialysis Fluid

  • So blood cells and large proteins cannot pass through
  • Dialysis - no urea, concentration of sugar and mineral ions

2) Counter current flow of Blood and Dialysis Fluid

  • Maintain the diffusion gradient

3) Constant circulation of Dialysis Fluid

  • Same concentration gradient of substances, avoid equilibrium

4) Blood Thinner

  • To avoid blood clots

5) Bubble Trap

  • Get rid of air bubbles which can pop blood vessels
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How does a dialysis machine work?

It is trying to maintain a equilibrium of water, salt and glucose and get rid of urea.

1) Dialysis fluid has no urea in it to encourage all urea to leave by diffusion.

2) Dialysis fluid will be balanced in salt, sugar and water, so only excess salt and water is lost.

3) Dialysis fluid contains the same concentration of glucose, so glucose won't diffuse into the fluid.

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Kidney Transplant vs. Kidney Dialysis



  • Life could be normal again
  • Infrequent hospital visits
  • No restricted diets


  • Risk of rejection
    • Antigens on cells, could be recognised as a foreign object, it may amount an immune response against it
  • Have to wait for a donor
  • Ethics
  • Have to take immunosupressant drugs - more vulnerable to infections - for the rest of life
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Kidney Transplant vs. Kidney Dialysis



  • No risk of rejection
  • Don't need to take loads of drugs
  • No surgical risk
  • No need to wait for a donor
  • Don't need to worry about ethics


  • Difficult to control the diffusion of substances in the dialysis fluid
  • Have to go on a strict diet
  • Have to go to hospital 3 times a week for 4 hours each time for the rest of your life. Huge impact of a persons life
  • Risk of blood clots
  • Expensive
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Temperature Control

Our core body temperature is 37°C (temperature our blood should be at).

It is important that this temperature is maintained because:

  • Enzymes work at optimum temperature
  • Can denature is temperature is too high
  • Reactions slow if temperature is too low

Our body is constantly monitored and regulated so any fluctuations from the normal are only small.

Body temperatures monitored by the thermoregulatory centre, Hypothalamus, in the brain. It can monitor the body by:

  • Temperature receptors in the skin and brain.
  • If the body temperature deviates from 37°C the hypothalamus and skin receptors send out electrical signals that trigger reactions that increase or decrease heat loss.
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How the skin reduces heat loss

  • When it is cold the skin acts to reduce heat loss.
  • The hair erector muscles contract and make the hairs stand more upright. This traps warm, still air close to the surface of the skin. Less heat is lost by radiation.
  • Sweat glands stop making sweat.
  • Blood vessels near the surface of the skin get narrower so less blood gets near to the surface. this reduces heat loss by radiation.
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How the skin loses heat

  • When it is hot our skin acts to increase heat loss
  • The hair erector muscles relax and make the hairs lie flat against the skin. Less air is trapped near the skin surface. More heat is lost by radiation.
  • Sweat glands make more sweat. This evaporates from the skin surface.
  • Blood vessels near the skin surface widen, so more blood gets near to the surface. his increases heat loss by radiation.
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Regulating Body Temperature

Warming Up

  • Shivering
    • Muscles begin to twitch
    • This rapid contraction and relation of the muscles is called shivering
    • Generates heat, which raises body temperature
  • Goosebumps
    • Involuntarily appear when a person become cold
    • Caused by tiny muscles in the skin
    • Muscles at the hair contract, means that hairs stand up - Piloerection
    • Traps a layer of air - reducing heat loss
  • Vasoconstriction
    • When core body temp falls, blood vessels in the skin get narrower
    • Caused by contraction of the muscular wall of the blood vessels
    • This reduces the volume of blood flowing near the skin surface and reduce the amount of heat loss from the body
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Regulating Body Temperature

Cooling Down

  • Sweating
    • As sweat evaporates it transfers heat away from the body
    • Produced from the sweat glands
  • Arm hair
    • Hairs lie flat
    • Doesn't trap air layer
  • Vasodilation
    • When core body temperature rises, blood vessels in the skin get wider
    • The muscle wall relaxes
    • Allows a larger volume of blood to flow near the skin surface
    • This transfers heat to the environment, cooling the body down
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Sugar Control

What affects our blood sugar levels?

  • Food --> Rise
  • Exercise --> Fall

During the day they can slightly go up or down. Between meals, blood glucose levels are topped up from stored deposits in the liver and muscles. Excess blood glucose levels store the glucose as glycogen.

Excess glucose makes the blood plasma and tissue fluid around cell too concentrated. This can severely damage cells, e.g. causing crenation in red blood cells.

Low blood sugar levels can be equally as dangerous, as it can make cells swell up and burst. This is called lysis.

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The control of blood glucose levels

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The control of blood glucose levels

  • If you have low blood sugar the pancreas promotes glucagon release. The glucagon stimulates the break down of glycogen in the liver which raises blood sugar.
  • If you have high blood sugar the pancreas promtoes insulin release. The insulin stimulates glucose uptake from the blood in the tissue cells which lowers blood sugar in the tissue cells which lower blood sugar and the insulin stimulates glycogen  formation in the liver which also lowers blood sugar levels.
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Controlling Blood Sugar

  • Normal blood sugar range
    • Blood sugar rises after meal
      • Pancreas detects high sugar in blood, pancreas secretes insulin
      • Cells absorb sugar from the blood for respiration
      • Sugar is absorbed by the liver cells and converted to glycogen and stored
    • Blood sugar falls again
  • Normal blood sugar range
    • Blood sugar falls after exercise
      • Pancreas detects low sugar in the blood
      • Pancreas secretes glucagon
      • Liver cells convert stored glucagon back to glucose
    • Blood sugar rises again
  • Normal blood sugar range

Hormones are in bold.

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Diabetes Type 1 vs. Type 2

Type 1

  • Often diagnosed in childhood
  • Not associated with excess body weight
  • Often associated with higher than normal ketone levels at diagnoses
  • Treated with insulin injection or insulin pump
  • Cannot be controlled without taking insulin
  • If your pancreas does not make enough insulin, your blood sugar concentration is not controlled

Type 2

  • Usually diagnosed in over 30 year olds
  • Often associated with excess body weight
  • Often associated with high blood pressure and/or cholesterol levels at diagnosis
  • Usually treated initially without medication or with tablets
  • Sometimes possible to come off diabetes medication
  • Diet-controlled --> people still have insulin, but cells don't respond to it
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