Thyroid disorders

made up of a series of follicles, an outer layer of follicle cells surrounding a lumen of gelatinous colloid, including thyroglobulin, and associated parafollicular cells (C cells).

•Thyroid hormones, thyroxine (T4) and triiodothyronine (T3) are produced and secreted by the follicles.

•Thyrotropin-releasing hormone (TRH) is produced by the hypothalamus to signal to the anterior pituitary to produce thyroid stimulating hormone (TSH).
•Thyroid-stimulating hormone released then binds to its receptor on thyroid follicle cells to stimulate the production and release of thyroid hormones, iodinated amine hormones, T3 (tri-iodo-thyronine) and T4 (tetra-iodo-thyronine).
•The thyroid gland also produces the peptide hormone, calcitonin in response to increased blood calcium levels.

•Tyrosine-rich thyroglobulin synthesized and released into the lumen.
•Iodide is actively taken up from the blood transported into the lumen.
•Enzyme thyroid peroxidase converts iodide to free iodine.
•Oxidised iodine atoms iodinate tyrosine in thyroglobulin (1 or 2 iodines per tyrosine).
•Mono- or di-iodotyrosines couple together to form thyroxine (T4) or Tri-iodothyronine (T3).
•Taken up by follicular cell, lysosomal enzymes break down thyroglobulin, which allows T4 and T3 to diffuse into bloodstream.

T3

T3 and T4 circulate as a bound inactive form, binding to thyroxine-binding globulin or albumin to improve solubility and preventing urinary excretion

dissociating from transport proteins

•peripheral target tissues (especially liver and kidneys) through the removal of one iodine

intracellular thyroid hormone receptor

- deficient in iodine, you cannot make enough thyroid hormone
- Negative feedback mechanism would be suppressed due to deficiency of thyroid hormone.
- As a result, TRH and TSH would continue to increase prompting the thyroid gland to produce more thyroid hormone.
Subsequently, the thyroid gland swells in size result in a condition called goitre.

underactivity of the thyroid gland

•Tiredness, sensitivity to cold, weight gain, slow movements and thoughts, slow heart rate, muscle aches and weakness, dry thickened skin, brittle hair and nails, loss of sex drive, depression, confusion and memory loss, irregular or heavy periods, growth and mental retardation in children.

•Hormone replacement with levothyroxine (identical to endogenous T4).
- has a long half life
• can give iodine supplement

excessive activity of the thyroid gland

•Sensitivity to heat, weight loss, anxiety, rapid heart rate, atrial fibrillation, bulging eyes, hair loss, longer period cycles, hand tremor, thirst, hunger.

•Inhibitors of thyroid synthesis e.g. carbinazole and propylthiouracil inhibit thyroid peroxidase and prevent iodination of thyroglobulin
•Surgical resection of the thyroid
•Thyroid ablation with radioactive iodine.