AQA GCSE Biology Unit B2 Chapter 5 (Homeostasis)

lots of stuffs about homeostasis.

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  • Created on: 20-05-10 12:50

Homeostasis

The conditions inside the body must be controlled within narrow limits. This is called homeostasis. These conditions inculde water content, ion content, body temperature and blood glucose concentration.

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Body temperature

The thermoregulatory centre is the part of the brain that monitors and controls body temperature.

Human enzymes wok best at 37 degrees C so the body's temperature needs to be controlled. The thermoregulatory centre gathers information as nerve impulses from temperature receptors in the brain (sensitive to the blood flow there) and the skin (sensitive to skin temperature)

If the core temperature gets too hot sweat glands release more sweat.This evaporates, removing heat energy from the skin. Superficial blood capillaries dilate - allowing moreblood to flow through the skin, and more heat to be lost.

If the core temperature gets too cold muscles contract rapidly (shivering). These contractions require energy from respiration, and some of this released as heat. Superficial blood capillaries constrict letting less heat blood flow through the skin and conserving heat in the body. The hairs on the skin rise, trapping a layer of air near the skin, which helps to insulate the skin against heat loss.

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Controlling blood glucose

The pancreas monitors and controlls the concentration of glucose in the blood. It produces a hormone called insulin when blood glucose levels are high. Insulin causes glucose to move from the blood into cells. This would happen after eating a meal that is rich in carbohydrates. If the blood sugar level falls e.g. after exercise, glucagon is released from the pancreas. The liver also releases glucose from glycogen stores. In emergencies, glucose might even be made from fat or protein.

Diabetes is a disease where the concentration of glucose in the blood isn't conrolled properly. In type 1 diabetes, the pancreas doesn't produce enough insulin which means blood glucose levels can become fatally high. It can be treated by monitoring food intake or injections of insulin 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 concentraion stays normal.

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Banting and Best

Two doctors, Frederick Banting and Charles Best, made an extract from the pancreas in 1921. The extract had anti-diabetic properties and the 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.

You don't really know that off by heart, but should be able to evaluate the data and also comment on the use of animal testing.

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Excretion

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. Wate products that must be removed include carbon dioxide and urea.

Carbon dioxide is produced as a result of aerobbic respiration. It is excreted through the lungs when we breathe out.

Urea 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.

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