Staying in balance

  • Created by: Flo
  • Created on: 04-11-12 11:14


Conditions in the body are controlled to provide a constant internal environment. This is called homeostasis. The conditions that must be controlled include body temperature, water content, carbon dioxide level and blood sugar level.

Hormones are chemicals secreted by glands. They travel through the bloodstream and affect target organs

Maintaining a constant internal environment of the body is called homeostasis, and the nervous system and hormones are responsible for this. Here are some of the other internal conditions that are controlled.

Carbon dioxide is a waste product of respiration. It travels in the bloodstream from cells to the lungs, where it leaves the body when we exhale. Carbon dioxide forms an acidic solution when it dissolves in water. Carbon dioxide levels must be controlled to avoid the blood becoming too acidic or too alkaline.

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Homeostasis cont.

Body temperature

This is controlled to maintain the temperature at which enzymes work best, which is 37 °C. Body temperature can be controlled by:

  • sweating
  • shivering
  • altering blood flow to the skin.

The body’s water content

This is controlled to protect cells by stopping too much water from entering or leaving them. Water content can be controlled by altering water loss from the:

  • lungs when we exhale
  • skin by sweating
  • body, in urine produced by the kidneys.
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Controlling body temperature

Human body temperature can be measured in several places, including the ear, finger, mouth and anus. There are various ways to measure body temperature, including using a clinical thermometer, heat-sensitive strips, digital probes or thermal imaging cameras.

Extremes of body temperature are dangerous because:

  • low temperatures can cause hypothermia and death if untreated
  • high temperatures can cause dehydration, heat stroke and death if untreated.

Control mechanisms

Heat can be gained by respiration, shivering, exercise or by reducing the blood flow to the skin. Clothing also helps to retain heat.

If we get too hot, heat can be lost by reducing the blood flow to the skin or by sweating. Sweating increases heat loss by evaporation.

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Controlling body temperature cont.

Control mechanisms- Higher tier

The body’s temperature is monitored by a part of the brain called the hypothalamus. If you are too hot or too cold, it sends nerve impulses to the skin.

The blood vessels supplying blood to the skin can dilate or swell. This is called vasodilation. It causes more heat to be carried by the blood to the skin, where it can be lost to the surroundings.

Blood vessels can shrink down again. This is called vasoconstriction. It reduces heat loss from the skin once the body’s temperature has returned to normal.

This sort of control is a ‘negative feedback mechanism’. The body’s internal environment is kept almost constant by causing cooling if it gets too hot, and warming if it gets too cold.

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Hormones are chemicals secreted by glands in the body. Different hormones affect different target organs.

The bloodstream transports hormones from the glands to the target organs. Bodily reactions to hormones are usually slower and longer lasting than nervous reactions.

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Controlling blood sugar levels

Glucose is a sugar needed by cells for respiration. It is important that the concentration of glucose in the blood is maintained at a constant level.

Insulin, a hormone secreted by the pancreas, controls blood sugar levels in the body. It travels from the pancreas to the liver in the bloodstream. As with other responses controlled by hormones, the response is slower but longer lasting than if it had been controlled by the nervous system.

glucose leveleffect on pancreaseffect on livereffect on glucose level too high insulin secreted into the blood liver converts glucose into glycogen goes down too low insulin not secreted into the blood liver does not convert glucose into glycogen goes up

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Diabetes is a disorder in which the blood glucose levels remain too high. There are two main types of diabetes:

  • Type 1, which usually develops during childhood
  • Type 2, which usually develops in later life.

Type 1 diabetesType 2 diabetes Who it mainly affects Children and teenagers. Adults under the age of 40. Adults, normally over the age of 40 (there is a greater risk in those who have poor diets and/or are overweight). How it works The pancreas stops making enough insulin. The body no longer responds to its insulin. How it is controlled Injections of insulin for life and an appropriate diet. Exercise and appropriate diet.

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Diabetes cont.

When treating Type 1 diabetes, the dosage of insulin needed by a person depends on their diet and activity.

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