AQA A2 Biology Unit 5 3.5.4 Homeostasis

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3.5.4 Homeostasis

Principles

HOMEOSTASIS is the MAINTENANCE OF A CONSTANT INTERNAL ENVIRONMENT.

Homeostatic mechanisms in the body need to monitor both the internal and external environments and respond to
any changes in order to maintain important factors such as pH, temperature, glucose, salt and water concentrations,
within their normal range.…

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Synoptic Questions:

Explain in as much detail as possible the consequences of having too much glucose or ions in the blood.
o Lowers the water potential of the blood.
o Therefore water moves by osmosis from cells into the blood.
o This causes cells to shrink and become dehydrated.
Explain…

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Warm substances leaving the body such as air breathed out or the loss of urine.

In mammals temperature regulation is controlled by the HYPOTHALAMUS.

This is constantly monitoring the temperature of the blood when it flows through it and it also receives information
about the external temperature from receptors in…

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Warming Mechanisms in Endotherms

It is essential for endotherms to be able to respond rapidly to falling external temperatures.

Peripheral cold receptors in the skin detect that the environmental temperature is lower than body temperature and
they send impulses to the heat gain centre in the hypothalamus. This co-ordinates the…

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At a low body temperature, the heat gain centre in the hypothalamus sends impulses to the brown fat cells via
sympathetic nerves.
This increases their rate of respiration which generates more heat.
Hibernating animals use brown fat tissue to generate heat to prevent them from freezing to death.

Hormones:

Adrenaline…

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Diabetes

Symptoms of Diabetes;

Since insulin is not being produced, blood glucose levels may rise to dangerously high levels, HYPERGLYCAEMIA.
The kidneys which normally reabsorb all of the glucose passing into the nephrons, cannot cope and so some
glucose is excreted in the urine, GLYCOSURIA.
Extra water and salt follow…

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