Homeostasis: maintenance of a constant internal environment
What conditions are maintained?
- Temperature: enzymes in body work at 37C
- Water: too much or too little causes more osmosis and can damage cells
- Ions: too few or too many causes more osmosis and can damage cells
- Blood sugar: as above
- CO2 must be removed through exhalation as it's toxic
- Urea is removed in urine as it's toxic
What happens when you get too hot?
- Hairs lie flat so they don't trap insulating layer of air
- Blood vessels dilate allowing more blood to flow so heat transfers to surroundings through radiation
- Sweat glands secrete sweat so evaporation removes heat
What happens when you get too cold?
- No sweat is produced
- Hairs stand up to trap insulating layer of air next to skin, reducing heat loss
- Capillaries near skin constrict to reduce blood flow so less heat is lost through radiation
- Muscles contract causing shivering which involves more respiration so releases heat
What do the kidneys do?
- Filter urea from blood
- Adjust water content
- Adjust ion content
What is urea?
- Proteins can't be stored so they're broken down in the liver into urea.
- Kidneys filter it out of the blood
- It's stored as urine in the bladder and then excreted
Ion and water content
- Excess salts are removed by the liver and some is lost in sweat
- Water is lost in urine, sweat and exhalation
- Cold: less sweat, pale and dilute urine
- Hot: more sweat, dark and concentrated urine
- Blood sugar input: carbohydrates in food put glucose in blood
- Blood sugar output: exercise and reactions in cells remove glucose
The PANCREAS monitors and controls blood glucose
- Pancrease releases insulin
- Insulin tells cells to store glucose as glycogen which is insoluble
- Level returns to normal
- Pancreas releases glucagon
- Glucagon tells cells to convert insoluble glycogen into soluble glucose
- Glucose dissolves in blood and level returns to normal
The person with diabetes is unable to control their blood sugar levels as they have too little insulin
They can help the condition through:
- Avoiding food rich in sugar
- Doing more exercise
- Injecting insulin
The right amount has to be injected to correspond with the person's diet, size and exercise. If not, they risk entering into a coma.
Banting and Best
What did they do?
- Removed the pancreas from a dog
- This resulted in its urine becoming sugary
- They obtained an extract from the pancreas
- Injected the extract into diabetic dogs
- This caused a temporary decrease in blood sugar levels
- They later went on to isolate the insulin gene
- Dogs are quite similar to humans
- It avoided human experimentation
- Animals rights: dogs were harmed
- Dogs are not metabolically the same as humans
- Permanent solution
- No longer have to inject insulin
- Cheaper in the long term
- Body can reject the tissue
- You may need to take expensive immunosuppressive drugs which could have side effects
- Operations always carry the risk of infection