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					Thyroid Gland
               Physiologic Anatomy
Thyroid gland is composed, of large
    numbers of closed follicles (100 to 300
    micrometers in diameter) filled with a
    secretory substance called colloid and
    lined with cuboidal epithelial cells that
    secrete into the interior of the follicles.
Major constituent of colloid is glycoprotein
    thyroglobulin
Each molecule of thyroglobulin contains
    about 70 tyrosine amino acids
About 50 mg of ingested iodine
in the form of iodides are required each
    year, or about 1 mg/week
Synthesis of Thyroid Hormones
            Transport of THs
• Approximately 99.98% of T4 is bound to 3
  serum proteins:
Thyroid binding globulin (TBG)
 ~75%; Thyroid binding prealbumin (TBPA)
15-20%; albumin ~5-10%
• Only ~0.02% of the total T4 in blood is
  unbound or free.
• Only ~0.4% of total T3 in blood is free.
General Functions
  SPECIFIC ACTIONS OF THYROID HORMONE:
                METABOLIC
• Regulates of Basal Metabolic
  Rate (BMR).
• Increases oxygen
  consumption in most target
  tissues.
• Permissive actions: TH
  increases sensitivity of target
  tissues to catecholamines,
  thereby elevating lipolysis,
  glycogenolysis, and
  gluconeogenesis.
 SPECIFIC ACTIONS OF THYROID
   HORMONE: DEVELOPMENT
• TH is critical for normal development of the skeletal
  system and musculature.
• TH is also essential for normal brain development
  and regulates synaptogenesis, neuronal integration,
  myelination and cell migration.
• Cretinism is the term for the constellation of defects
  resulting from untreated neonatal hypothyroidism.
       Regulation of Thyroid Glands
TSH, also known as thyrotropin, is an
    anterior pituitary hormone, a
    glycoprotein with a molecular
1. Increased proteolysis of the
    thyroglobulin
2. Increased activity of the iodide
    pump
3. Increased iodination of tyrosine to
    form the thyroid hormones
4. Increased size and increased
    secretory activity of the thyroid
    cells
5. Increased number of thyroid cells
    plus a change from cuboidal to
    columnar cells
                Diseases of the Thyroid
Hyperthyroidism (Toxic Goiter, Thyrotoxicosis, Graves’ Disease), or Thyroid Adenoma
Autoimmune disease (TSI)
The autonomous secretion of thyroid hormone results in diminished or no response of
   TSH to TRH ���� TRH receptors on pituitary thyrotrophs reduced
(1) a high state of excitability,
(2) intolerance to heat,
(3) increased sweating,
(4) mild to extreme weight loss (sometimes as much as 100 pounds),
(5)varying degrees of diarrhea,
(6) muscle weakness,
(7) nervousness or other psychic disorders,
(8) Extreme fatigue but inability to sleep, and
(9) tremor of the hands
               Exophthalmos
• Infiltrative
  Ophthalmopathy
• Protuberance of eyes
• Trapping of extraocular
  muscles in the confined
  space
• may result in paralysis of
  eye movement and
  double vision
              Hypothyroidism
Results from decreased production of thyroid
  hormones
Infancy: cretinism-- growth and mental
  retardation
Later in life-- different set of clinical features
More common in women than men
             Hypothyroidism
Destruction of thyroid
  tissue by prior surgery or
  radioactive iodine
  treatment for
  hyperthyroidism
Endemic iodine deficiency
                 Types of Goiters




Simple Goiter (L) and Nodular (Toxic) Goiter (R)

				
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Description: thyroid Gland.ppt