HOMEOSTASIS

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HOMEOSTASIS

• Maintaining a Stable Environment

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What is homeostasis?

• To work well a living organism needs the right
  conditions to function properly.
• Homeostasis is the means by which these internal
  conditions are kept constant.

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Internal conditions which are controlled include

• Temperature
• 1. To maintain the temperature at which
  enzymes work best
• The Water Content of a Body
• 1. Water leaves the body via the lungs when we
  breathe out
• 2. Via the skin when we sweat
• 3.Excess water at lost via the kidneys in urine

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Internal conditions which are controlled include

• The ion content of the body
• 1. Ions are lost via the skin when we sweat
• 2. Excess ions are via the kidneys in urine
• Hormone levels in the body
• 1. TSH is increased or decreased to stimulate
  the thyroid gland to release thyroxin into the
  blood stream or to stop releasing it

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How does it work?

• Whether it is 980F outside or 280F, your body
  will still be around 98.60F.
• Whatever happens in the external environment,
  your body still tries to keep its temperature
  within a very narrow range
• Homeostatic control factors only start to work
  when a particular factor strays beyond a certain
  range.

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Negative FEEDBACK

• When a change in an organism tends to make a
  system respond to reduce it.
• Most biological systems involve negative feedback
  to maintain healthy limits.

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Thermoregulation

• Body temperature is controlled by the brain and
  the skin
• Hot sweating
• Cold goose bumps

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What happens when you get too hot?

• Tiny muscles in the skin make hairs lie flat.
• Glands in the skin secrete sweat onto the skin
  surface in order to increase heat loss by
  evaporation.
• Blood vessels supplying blood to the skin can
  swell or dilate so that more heat is carried to
  the skin where heat can be lost to the air.

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What happens when you get too cold?

• Tiny muscles in the skin make your hair stand
  straight up. This helps to trap a small layer of
  air against the skin as insulation.
• Blood vessels in the skin constrict so less heat
  is carried by the blood to the skin where it can
  be lost.
• Muscles contract and relax causing shivering to
  generate heat.
• Sweat gland close