Homeostasis

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Homeostasis
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Learning objectives

• The human body needs to maintain and regulate a
  steady state in order to function correctly
• Homeostasis involves interactions between various
  systems of the body

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Homeostasis

• the tendency of a system, esp. the physiological
  system of higher animals, to maintain internal
  stability, owing to the coordinated response of
  its parts to any situation or stimulus tending to
  disturb its normal condition or function -
  Dictionary.com Unabridged (v 1.1)
• The ability or tendency of an organism or a cell
  to maintain internal equilibrium by adjusting its
  physiological processes. - American Heritage
  Stedman's Medical Dictionary

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Homeostasis

• There are several examples of homeostasis and the
  processes involved
• We have already looked at the reproductive
  hormones and how oestrogen and LH are linked
  through NEGATIVE FEEDBACK i.e. as one gets more
  it causes the other to get less
• Here are 3 more commonly used examples

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Temperature Control

• Also known as THERMOREGULATION
• The enzymes in our bodies work best at around
  37C
• we need to be able to keep our bodies as close to
  this temperature as possible
• The body will react if it gets too hot or if it
  gets too cold
• It will adjust the temperature back to where it
  should be

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Thermoregulation

• Involves receptors linked to the HYPOTHALAMUS
  located in the brain
• Nerve impulses are sent from here to the SKIN
• Skin reacts to change body temperature

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Too Hot?

• VASODILATION blood vessels near the skin get
  wider
• This allows more warm blood to flow near the
  surface and lose heat, cooling you down
• Muscles controlling the hairs on your skin relax
  causing the hairs to lie flat
• Sweat is secreted from sweat glands as it
  evaporates, this cools you down

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Too Hot?
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Too Cold?

• VASOCONSTRICTION blood vessels near the skin
  get smaller
• Less blood flows near the surface, keeping the
  heat closer to your body core
• Erector muscles contract, pulling your hairs up
  on end
• This traps warm air close to your skin
• Sweat glands no longer secrete sweat
• Shivering also helps to warm you up your
  muscles generate more heat through respiration

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Water Control

• Also known as OSMOREGULATION
• Controlled by the hypothalamus using negative
  feedback
• Involves the pituitary gland and the kidneys

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Osmoregulation

• Water is very important to the body, but it must
  maintain the right amount
• If there is a problem, it is spotted by
  OSMORECEPTORS in the hypothalamus
• A message is sent through nerve impulses to the
  pituitary gland
• This changes the amount of a particular hormone
  it releases
• The change in hormone level causes the kidneys to
  react

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Not Enough Water..?

• Hypothalamus signals the pituitary gland
• Pituitary increases its release of the hormone
  ADH (ANTI-DIURETIC HORMONE)
• More ADH enters kidney, stimulating it to
  reabsorb more water
• Smaller amounts of more concentrated urine are
  produced

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Osmoregulation
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Too Much Water..?

• Hypothalamus signals the pituitary gland
• Pituitary slows down its release of the hormone
  ADH
• Less ADH enters kidney, which then absorbs LESS
  water
• More urine is produced
• Urine is LESS concentrated

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Blood Sugar levels

• When food is digested, sugar glucose is
  produced
• It is important that blood sugar levels do not
  get too high HYPERGLYCEMIA or too low
  HYPOGLYCEMIA
• It involves the hormone INSULIN

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Too much glucose

• Receptors in the blood sense high levels of
  glucose
• Nerve impulses sent to the PANCREAS
• Insulin is released into the blood
• Triggers an increase in glucose being converted
  in glycogen by the LIVER
• Glucose levels drop to normal
• Insulin no longer produced and degrades

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Not Enough Glucose

• Receptors in the blood sense low levels of
  glucose
• Nerve impulses sent to the pancreas
• Insulin stops being released into the blood
• Less glucose is converted in glycogen by the
  liver
• Less glucose absorbed by the cells
• Glucose levels return to normal

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Glucose Regulation
Insulin crystals
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Glucose Regulation

• People who cannot naturally control their blood
  sugar levels are called DIABETIC
• They must control their blood sugar manually by
  controlling their diet, and by injecting
  themselves regularly with insulin