METABOLISM

1
METABOLISM

• Thyroid Gland is located in front of the trachea.
• It produces hormones
• Thyroxine (T4)?
• Triiodothyronine (T3)?
• T4 and T3 regulate
• body metabolism and
• growth and differentiation
  of tissues

2
T4 and T3

• Tyrosine based hormones, dependent on iodine for
  production.
• Lipophilic, travel through blood bound to a
  protein, thyroxine binding globulin (TBG) and
  cross the cell membrane easily to interact with
  nuclear receptors, thyroid hormone receptor.
• T4 has a longer half-life than T3 and outnumbers
  T3 by 201 in the bloodstream, but T3 is 4 times
  as potent (more active).
• Circulating T4 is converted to T3 by the removal
  of iodine. T4 is considered a precursor to T3.

3
Effects of T4 and T3

• T4 and T3 help our body oxidize sugars and
  nutrients (proteins, fats) at a faster rate.
• All the energy of glucose is transferred to heat
  and ATP, (no storing of glucose) and ATP is
  consumed during activity, therefore there is no
  weight gain.
• Also increase cardiac output, heart rate,
  breathing rate, and production of RNA polymerases
  (so increased protein synthesis as well as
  metabolism)

4
REGULATION of METABOLISM
Metabolic rate decreases Hypothalamus
TRH Pituitary TSH Thyroid
Thyroxine Increase metabolism
inhibits
5
REGULATION of METABOLISM

• Metabolic rate decreases
• hypothalamus sends thyroid releasing hormone
  (TRH) to the anterior pituitary
• Anterior pituitary releases thyroid stimulating
  hormone (TSH)
• TSH acts on thyroid to stimulate release of
  thyroxine.
• thyroxine raises metabolism by increasing sugar
  usage by body tissues
• thyroxine levels feedback on hypothalamus and
  pituitary to inhibit further release of TRH /TSH

6
Thryoid Disorders

• Hypothyroidism low thyroid secretions
• glucose is not oxidized as quickly, and excess
  glucose is converted to glycogen and stored.
• once glycogen stores are filled, excess sugar is
  stored as fat.

http//www.holisticprimarycare.net/topics/topics-h
-n/healthy-aging/94-the-clinical-picture-of-hypoth
yroidism
7
Thyroid Disorders Goiter

• Goiter
• Lack of iodine for producing T4 and T3
• TSH produced continuously in effort to increase
  levels of T4 and T3
• NO Feedback because functional T4 and T3 not
  formed
• Overstimulated thyroid enlarges

• Metabolic rate decreases
• Hypothalamus
• TRH
• Pituitary
• TSH
• Thyroid

8
Other Hormones of the Thyroid Gland

• Thyroid Gland also produces calcitonin
• Decrease calcium in blood by absorption from
  blood to bones

http//ncwcbio101.wordpress.com/
9

• Parathyroid Glands (on the thyroid) produce
  Parathyroid hormone (PTH)
• increase Calcium in blood by calcium release from
  bones, and reabsorption at kidneys, intestines)
• Also increases production of active Vitamin D
• Normal blood levels of calcium are important for
  proper functioning of (for ex.) the nervous
  system and blood clotting.

10
Other Metabolic Hormones

• In addition to TSH, the Pituitary Gland also
  produces Growth hormone (somatotropin)
• Increase Protein synthesis, Breakdown of fats
• Abnomal levels lead to dwarfism, gigantism,
  acromegaly
• Homework p 387 2-7