HOMEOSTASIS >
The conditions inside the body must be controlled within narrow limits. This is called homeostasis. These conditions include water content, ion content, body temperature and blood glucose concentration.
The thermoregulatory centre is the part of the brain that monitors and controls body temperature. The pancreas meanwhile monitors and controls blood glucose concentration. It produces a hormone called insulin that reduces blood glucose levels. Diabetes is a disease which can be caused by insufficient insulin.
Removing waste products
Waste products must be removed from the body. If they are not, they will increase in concentration and may interfere with chemical reactions or damage cells. Waste products that must be removed include carbon dioxide and urea.
Production and removal of waste products
Waste product Why is it produced? How is it removed?
carbon dioxide it is a product of aerobic respiration through the lungs when we breathe out
urea it is produced in the liver when excess amino acids are broken down the kidneys remove it from the blood and make urine, which is stored in the bladder temporarily
Water enters the body through food and drink. It is also a product of aerobic respiration in cells. If the amount of water in the body is wrong, cells can be damaged because too much water enters or leaves them. The animation shows how the amount of water lost as urine is controlled. Note that you do not need to know any details of this for the examination.
The pancreas and insulin
The pancreas monitors and controls the concentration of glucose in the blood. It produces a hormone called insulin. Insulin causes glucose to move from the blood into cells. It lowers the blood glucose concentration if has become too high. This can happen after eating a meal that is rich in carbohydrates (for example, sweets, potatoes, bread, rice or pasta).
The animation shows how this works.
Diabetes
Diabetes is a disease where the concentration of glucose in the blood is not controlled properly by the body. In type 1 diabetes, the pancreas does not produce enough insulin. This can lead to high levels of glucose in the blood, which can be fatal.
Banting and Best
You should be able to evaluate experimental data from Banting and Best’s experiments which led to insulin being discovered.
Two doctors, Frederick Banting and Charles Best, made an extract from the pancreas in 1921. The extract had anti-diabetic properties, and they tested it successfully on diabetic dogs. The first tests in humans were carried out in 1922, and were a success too. Some patients who were in a diabetic coma even recovered. The extract contained the hormone insulin.
Diabetes
There are two types of treatment for diabetes:
• Careful monitoring of food intake, with particular care taken over carbohydrates - which are digested into glucose.
• Injecting insulin into the blood before meals. The extra insulin causes glucose to be taken up by the liver and other tissues. Cells get the glucose they need for respiration, and the blood glucose concentration stays normal.
Temperature regulation
Human enzymes work best at 37ºC, so the body’s temperature is controlled. A part of the brain called the thermoregulatory centre monitors and controls body temperature. It gathers information as nerve impulses from temperature receptors in:
• the brain - these are sensitive to the temperature of the blood flowing there
• the skin - these are sensitive to skin temperature
Sweating
Sweating is one way to help cool the body. We sweat more in hot conditions, so more water is lost from the body. This water must be replaced through food or drink to maintain the balance of water in the body.
Ions such as sodium ions and chloride ions are also lost when we sweat. They must be replaced through food and drink. If the body’s ion content is wrong, cells can be damaged.
Temperature regulation - higher
If you become too hot or too cold, there are several ways in which your temperature can be controlled. They involve sweating, shivering, skin capillaries and hairs.
Too hot
When we get too hot:
• Sweat glands in the skin release more sweat. This evaporates, removing heat energy from the skin.
• Blood vessels leading to the skin capillaries become wider - they dilate - allowing more blood to flow through the skin, and more heat to be lost.
Too cold
When we get too cold:
• Muscles contract rapidly - we shiver. These contractions need energy from respiration, and some of this is released as heat.
• Blood vessels leading to the skin capillaries become narrower - they constrict - letting less blood flow through the skin and conserving heat in the body.
The hairs on the skin also help to control body temperature. They lie flat when we are warm, and rise when we are cold. The hairs trap a layer of air above the skin, which helps to insulate the skin against heat loss.
Controlling temperature
Too cold Too hot
A - Hair muscles pull hais on end.
B - Erect hairs trap air.
C - Blood flow in capillaries decreases. D - Hair muscles relax. Hairs lie flat so heat can escape.
E - Sweat secreted by sweat glands. Cools skin by evaporation.
F - Blood flow in capillaries increases.
Remember: Capillaries do not move up and down inside the skin. Temperature is regulated by controlling the amount of blood which flows through the capillaries.
