Hormones That Affect
Metabolism
Glands & Metabolism
• Metabolism is the sum of the chemical reactions
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required to live.
Metabolism (metabolic rate) is affected by the
thyroid, parathyroids and anterior pituitary gland.
The thyroid gland is situated just below the
larynx.
The parathyroid glands sit on the thyroid.
The pituitary gland is situated just below the
hypothalamus.
The Thyroid Gland
• The thyroid is located just below the larynx and it
secretes the hormone thyroxine.
• Thyroxine aids in the oxidation (breakdown) of
sugar and nutrients in the body.
• People that produce ample amounts of thyroxine
usually can eat a lot of food without gaining any
weight because it is broken down very quickly.
• People that have hypothyroidism are the
opposite…they have low levels of thyroxine and
because of this they do not oxidize nutrients fast
enough and they gain weight quickly.
Controlling the Thyroid
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The thyroid is brought into action by a negative feedback system
which involves the hypothalamus and pituitary gland.
• Low Metabolic Rate…
• Detected by the hypothalamus – it releases thyroidreleasing hormone (TRH) which goes to the
pituitary.
• Pituitary receives TRH and produces thyroidstimulating hormone (TSH) which goes into blood to
get to thyroid gland.
• Upon receiving TSH, the thyroid gland secretes
thyroxine which raises metabolic rate.
The Parathyroid Glands
• The parathyroids are four smaller glands found
within the thyroid gland.
• Their control/action is not under the influence of
the nervous or endocrine systems – the
parathyroids respond directly to changes in their
immediate surroundings.
• The parathyroids produce parathyroid
hormone (PTH) which raises the levels of
calcium in the blood.
Growth Hormone
• Growth hormone (somatotropin) is made and released
by the anterior pituitary.
• Growth hormone…
– Growth hormone causes tissues to increase in number and/or
size. In muscles, the cells increase in size by promoting protein
synthesis and inhibiting protein breakdown. In bones, the cells
elongate and the skeleton lengthens.
– The growth hormone also promotes the breakdown of fats into
fatty acids which can actually replace glucose as the primary
fuel. Glucose builds up in the blood – good for the brain – while
the fatty acids provide a ton of energy for growth. (This is why
you often see a loss of fat accompanying a growth spurt.)
• Too much or too little during childhood can result in
dwarfism or gigantism.
FIN