endocrine system - eastern mediterranean university
TRANSCRIPT
ENDOCRINE SYSTEM
THYROID HORMONES
ASST. PROF. DR. EMRE HAMURTEKIN EMU FACULTY OF PHARMACY
CHAPTER III
THYROID HORMONES
HYPOTHALAMIC-PITUITARY-THYROID AXIS
Hypothalamus secrete thyroid-releasing hormone
(TRH) and somatostatin.
TRH stimulates TSH synthesis and release.
Thyroid glands are composed of numerous follicles.
HYPOTHALAMIC-PITUITARY-THYROID AXIS
FOLLICLES and COLLOID
FOLLICLES and COLLOID
Follicular cells are supported by an extensive
basolateral vasculature.
Follicular cells synthesize and secrete thyroid
hormone.
TSH increases expression of cellular components
needed for hormone synthesis.
TSH also increases the production of colloid.
THYROID HORMONE SYNTHESIS
T3/T4 = 1:10
T4 has a longer half-life, but lower biological activity.
Conversion of T4 to T3 occurs primarily in target tissues.
Steps in synthesis:
1. Iodide uptake
2. Apical secretion
3. Oxidation
4. Iodination
5. Conjugation
6. Endocytosis
7. Proteolysis
8. Secretion
IODIDE UPTAKE and APICAL SECRETION
OXIDATION and IODINATION
IODINATION
IODINATION (organification) and
CONJUGATION
T3 and T4
ENDOCYTOSIS
TSH
Megalin receptors
PROTEOLYSIS and SECRETION
THYROID HORMONE SYNTHESIS
EFFECTS (Thyroid Hormone)
1. Growth & Development Especially nervous tissue and bone development
Development of stretch reflexes (ankle jerk reflex)
Increases ossification (linear growth in children and adolescents)
Thyroid hormone deficiencies can result with mental impairments and short stature in children
2. Macronutrient metabolism Effect the carbohydrate, lipid and protein metabolism
3. Basal Metabolic Rate
Low thyroid hormone leves are associated with, Low basal O2 consumption
Weight gain
Cold intolerance
High thyroid hormone leves are associated with, High basal O2 consumption
Weight loss
Elevated body temperatures
4. Catecholamine Synergy
When T3 & T4 and norepinephrine (sympathetic nervous system) are released in concert, physiological functions of both are heightened.