HORMONES THAT AFFECT METABOLISM:
THYROID GLAND
located at base of neck
 two important thyroid hormones (which regulate
body metabolism, growth, and differentiation of
tissues)
 thyroxine (T4)
 triiodothyronine (T3)
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HORMONES THAT AFFECT METABOLISM
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Three different glands affect metabolism
thyroid gland
 helps regulate body metabolism (glucose oxidation
rate)
 produces three hormones
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triiodothyronine, thyroxine, calcitonin
parathyroid gland
 produces parathyroid hormone
 helps regulate calcium levels in blood and lower
phosphate levels
anterior pituitary gland
 produces growth hormones and regulatory
hormones
HORMONES THAT AFFECT METABOLISM
Gland
Hormone
Action
Thyroid
Thyroxine
metabolism
Calcitonin
↓’s calcium levels in blood
Parathyroid
PTH
↑’s calcium levels and ↓’s
phosphate levels
Anterior Pituitary Gland
GH
Growth of bones and
protein synthesis
THYROID GLAND
individuals who secrete higher levels of thyroxine
oxidize sugars and other nutrients at a faster
rate
 When glycogen stores are filled, excess sugar is
converted to fat
 control of thyroid hormones is accomplished by
negative feedback
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FEEDBACK CONTROL LOOPS FOR
THYROID HORMONES
FEEDBACK LOOP...
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receptors in hypothalamus are activated if the
metabolic rate decreases
nerve cells secrete TRH (thyroid releasing hormone)
this stimulates pituitary to release TSH (thyroid
stimulating hormone)
 carried by blood to thyroid gland which then
releases thyroxine which raises metabolism by
stimulating sugar utilization by cells
 high levels of thyroxine cause pathway to be
turned off, inhibiting release of TRH
 VIDEO of thyroxine
Thyroid gland also contains calcitonin
 hormone acting on bone cells to lower level of
calcium found in blood
OH NO!
when inadequate
amounts of iodine are
obtained from the
diet, thyroid enlarges,
producing a goiter.
 If thyroxine levels ↓’s,
TSH ↑’s, and thyroid
is stimulated more
and more
 Thyroid cells continue
to develop and thyroid
enlarges
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PARATHYROID GLANDS
Four parathyroid glands hidden within larger
thyroid gland
 Usually nerves or other hormones regulate the
endocrine glands with the parathyroid glands
being the exception
 These maintain homeostasis by responding
directly to chemical changes in their
immediate surroundings (low calcium levels)
 PTH raises calcium levels in the blood
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PTH (parathyroid hormone) also help activate
vitamin D. (Low levels of vit D cause rickets!)
RICKETS AND GOITERS...
Endocrine System Control
Feedback
REGULATION OF BLOOD CALCIUM
calcitonin
 kidney
reabsorption
of Ca++
thyroid
Ca++ deposited
in bones
high
blood calcium level

uptake
in intestines
Ca++
(10 mg/100mL)
low
activated Vitamin D
bones
release Ca++
 kidney
reabsorption
of Ca++
parathyroid
parathyroid hormone (PTH)
DANGERS OF HIGH CALCIUM LEVELS VIDEO- “THE
DOCTORS”
HUMAN GROWTH HORMONE (AKA
SOMATOTROPIN)
Too little = dwarfism
 Too much = gigantism
 Released by Ant. Pit.
 GH increases cell size
in muscle cell and
connective tissue by
promoting Protein
Synthesis (increasing
Amino Acid uptake)
 Promotes fat burning
 Dec. Levels of GH
with age
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HGH
AND
CONTROVERSY...
Should you take it?
GH affects all body cells BUT mainly bone cells
 Acromegaly- bones of jaw, forehead, fingers and toes
increase in width, once other bones can no longer
increase in length (growth plates fused)
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