The Kidneys and Homeostasis
Kidneys act as filters to 'clean blood'. They perform 3 main roles:
- Removal of Urea: Proteins can't be stored by the body so any excess amino acids are converted into fats and carbs which can be stored. This process occurs in the liver and urea is produced as a waste product from the reactions. Urea is poisonous so released from the blood stream by the liver. The kidneys fliter it out of the blood & into the urine.
- Adjustment of Ion Content: Ions like sodium are taken into the body by food then absorbed by the blood. If the ion content is wrong then too little or too much water could be draw out of the cells via osmosis (damage the cells). Excess ions are removed by the kidneys (after a salty meal). Some ions are also lost in sweat but the kidneys always balance this.
- Adjustment of water content: Water in the body by food & drink, out by urine, sweat and the air we breathe out. Body has to constantly balance water content by: Liquids consumed, amount sweated out & amount excreted by the kidneys in the urine.
On a cold day (no sweat) more urine will be produced thats pale and dilute.
On a hot day (sweat a lot) less urine will be produced thats dark and concentrated
Controlling Blood Sugar
Insulin is a hormone that controls how much sugar there is in the blood. Changes in blood glucose levels are monitored and controlled by the pancreas.
- Eating foods containing carbohydrates puts glucose into the blood from the gut
- Normal metabolism (reactions) of cells removes glucose from the blood. exercise also removes glucose from the blood
Blood Levels too high: insulin added too low: insulin not added
Type 1 Diabetes: disorder where the pancreas doesn't produce enough insulin. The problem,can be controlled in two ways:
- Avoiding foods rich in carbohydrates (i.e. sugars) <-- cause glucose levels to rise rapidly. Exercise after eating to use up extra glucose produced during digestion.
- Injecting Insulin into blood at mealtimes <-- makes liver remove glucose as soon as it enters the blood from the gut when food is being digested. Stops levels of glucose getting too high but they must eat sensibly.
Glucagon & Glycogen
The major effect of glucagon is to stimulate an increase in blood concentration of glucose when blood glucose levels are low.
- Glucagon stimulates breakdown of glycogen stored in the liver.
- When blood glucose levels are high, large amounts of glucose are taken up by the liver.
- Under the influence of insulin, much of this glucose is stored in the form of glycogen.
- Later, when blood glucose levels begin to fall, glucagon is secreted and acts on hepatocytes to activate the enzymes that depolymerize glycogen and release glucose.
Insulin and Diabetes
Insulin was discovered by Banting and Best in the 1920s using this process:
- Tied string around a dog's pancreas so a lot of it wasted away but the bits that made the hormone were left intact
- They removed the pancreas and obtained an extract from it
- Injected this extract into diabetic dogs and observed the effects on their blood sugar levels (BSL)
- After the pancreatic extract was injected the dog's sugar levels fell dramatically, this showed the extract lowed BSL temporarily
- They then went on to isolate the substance in the pancreatic extract
After more experiments Banting and Best injected insulin into a diabetic human, since then it's been mass produce. In the 1980s human insulin made by genetic engineering became available and it didn't cause any adverse reactions which animal insulin often did. Readily disposable syringes are now available as well as slow, intermediate and fast acting insulin's.
Insulin and Diabetes 2
A successful operation means no more insulin injections but your body might reject the tissue. This means costly immunosuppressive drugs must be taken which sometimes have serious side effects.
Advantages: Less travel = saves money, no going to and from hospital. No need to control diet.
Disadvantages: It's dangerous (possibility of death), the kidney might be rejected, initial cost is high & there's a difficulty to find donors.
Another method still in an experimental stage is to transplant just the cells which produce insulin <-- varying success but still problems with rejection.
Modern research into artificial pancreases and stem cell research may mean the elimination of organ rejection but there's still quite a way to go.