T3 and T4

Hashimoto's Disease

*A cause of primary hypothyroidism *An autoimmune disorder in which the thyroid gland is attacked

Cretinism

*A cause of primary hypothyroidism *Can be caused by: -Iodine deficiency during pregnancy -Infant iodine deficiency -Congenital errors in T₄and T₃synthesis (has nothing to do with iodine deficiency)

Primary Hypothyroidism

*Accounts for ~ 90% of hypothyroidism cases *The inability to produce T₄and T₃ *Can be caused by BOTH Hashimoto's Disease and Cretinism *Is "primary" because the thyroid gland is the problem

Grave's Disease

*Cause of Hypersecretion *Autoimmune disease *Autoantibodies (agonists) are produced that mimic Thyroid Stimulating Hormone (TSH)

Thyroid Tumor

*Cause of Hypersecretion *Sometimes causes hyposecretion (but rare)

Thyroid Storm

*Cause of Hypersecretion *Sudden release of large amounts of T₄and T₃ *Exact cause is unknown but the leading theories are: -Stress -Infections -Idiopathic

Pituitary Tumor

*Cause of Hypersecretion *Tumor in the anterior pituitary *Causes increased Thyroid Stimulating Hormone (TSH) production

Secondary Hypothyroidism

*Caused by either decreased: -Thyroid Stimulating Hormone (TSH)/Thyrotropin -Decreased Thyrotropin Releasing Hormone (TRH) *Causes thyroid gland to atrophy

Triiodothyronine: Structure and Abundance

*Contains three iodine molecules as part of its structure -~40% of triiodothyronine is created by the de-iodization of thyronine *More physiologically effective the thyronine - 5 times more potent *Produced in the follicular cell of the thyroid *Stored in the colloid -Enough stored to last ~ three months

T₄ and T₃: Inhibition of Release

*Decreased levels of Thyroid Stimulating Hormone (TSH)/Thyrotropin -Inhibited by decreased Thyrotropin Releasing Hormone (TRH) and increased T₄ and T₃ *Decreased blood iodine *Hyperglycemia

Goiter

*Enlarged thyroid gland *Can be cause by BOTH hypersecretion and hyposecretion of the thyroid gland

T₄ and T₃: Hypersecretion

*Grave's Disease *Thyroid Storm *Pituitary Tumor *Thyroid Tumor

Symptoms of Thyroid Hyersecretion

*High body temperature (copious sweating) *Heat intolerance *Weight loss *Increased heart rate *Hypertension *Hyperexcitable (due to central nervous system stimulation) *Diarrhea due to stimulation of the digestive tract *Exophthalmos (protruding of the eyes) *Goiter (enlarged thyroid gland)

T₄ and T₃: Functions

*Increase metabolism -Increases heat production (which helps maintain body temperature) *Increase protein synthesis *Increase blood glucose -Increase glyconeogenesis and glycogenolysis) *Decrease plasma cholesterol *Increase heart rate and heart contractility -Permissive effect on β-1 receptors of the heart *Increase respiratory rate *Stimulate growth hormone

Symptoms of Hypothyroidism

*Low body temperature (cold, dry skin) *Cold intolerance *Decreased heart rate *Low blood pressure *Lethargy due to depression of central nervous system *Constipation due to inhibition of digestive tract *Increased plasma cholesterol *Myxedema (thickening of soft tissue) *Goiter -Only if caused by primary hypothyroidism

T₄ and T₃: Hyposecretion

*Primary Hypothyroidism -Hashimoto's Disease -Cretinism *Secondary Hypothyroidism

T₄ and T₃: Where Produced

*Produced in the follicular cell of the thyroid *Stored in the colloid -Enough stored to last ~ three months

Exophthalmos

*Symptom of thyroid hypersecretion *Protruding of the eyes caused by: -Mucoprotein and fluid deposition behind the eyes -Inflammation of extraocular muscles

Myxedema

*Thickening of soft tissue *Non-pitting edema (tissue feels hard) *Edema NOT caused by excess interstitial fluid

T₄ and T₃: Stimulation of Release

*Thyroid Stimulating Hormone (TSH)/Thyrotropin -Also causes thyroid to enlarge *Increased blood iodine -Iodine required to make T4 and T3 *Hypoglycemia *Cold -Increases Thyrotropin Releasing Hormone (TRH) *Stress -Increases Thyrotropin Releasing Hormone (TRH)

T₄ and T₃- full names

T₄ is Thyroxine T₃is Triiodothyronine

Thyroxine: Structure and Abundance

-Contains four iodine molecules as part of its structure -Most abundant circulating thyroid hormone ~90% *Produced in the follicular cell of the thyroid *Stored in the colloid -Enough stored to last ~ three months