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.