Thyroid gland

One of largest pure endocrine glands in the body ( 20gms).

Its size depends on: 1. age … age size. 2. sex … female > male. 3. physiological condition … (pregnancy, lactation)

Site: Located in the neck just below the larynx, on either side of & anterior to the trachea.

Thyroid gland … (Continued)

Thyroid and para

Thyroid gland secretions

- Secreted by Parafollicular cells.

- Important hormone for Ca2+ metabolism & homeostasis.

● 2 important thyroid hormones: ● Thyroxine (T4) or tetraiodothyronine ● Triiodothyronine (T3)

- Secreted by Follicular cells.

- Can be stored in thyroid gland for couple of months (2-3 months). - Having significant effect on metabolic rate of the body.● Calcitonin

Thyroxine and its precursors: Structure &

Synthesis

Figure 23-8: Thyroid hormones are made from tyrosine and iodine

Thyroid Hormone:Transport

T3 & T4 leave the thyroid gland by diffusion

Both are transported in blood by three transport proteins, Thyroxine binding globulin (TBG), transthyretin and albumin

A majority (70%) of T4 & T3 is bound to TBG

Both enter their target cells by diffusion

Thyroxine and its precursors: Activity

T4 mainly functions as a prohormone. T3 is the main active

thyroid hormone and has the highest binding affinity for thyroid hormone

receptor (TR).Thyroid hormone activity can be

increased in plasma without new synthesis by converting T4 to T3.

If too much thyroid activity is present T4 is converted to the

inactive metabolite rT3 to reduce activity.

T3 & T4 Control Pathways & Diseases from Malfunction

HypothalamusAnterior PituitaryThyroidHypothyroidismGoiter (TSH )Grave's disease

Abnormal thyroid

hormonessecretions

Overview of Thyroid Disease States

Hypothyroidism

Hyperthyroidism

Hypothyroidism

Hypothyroidism is a disorder with multiplecauses

in which the thyroid fails to secrete an adequate amount of thyroid

hormoneThe most common thyroid disorder Usually caused by primary thyroid

gland failureAlso may result from diminished

stimulation of the thyroid gland by TSH

Hypothyroidism

II: Hypothyroidism (myxedema) … cont.

Symptoms of Hypothyroidism:

- Decreased metabolic rate. - Slow heart rate & pulse. - Slow muscle contractions - appetite, weight gain, & constipation. - Prolonged sleep, & dizziness. - Coarse skin. - Slow thinking, lethargy, & mask face. .

Hyperthyroidism

Hyperthyroidism refers to excess synthesis and secretion

of thyroid hormones by the thyroid gland, which results in

accelerated metabolism in peripheral tissues

90% of hyperthyoidism is due to “Grave’s disease

“Grave’s disease

Typical Thyroid Hormone Levels in Thyroid Disease

TSHT4 T3

Hypothyroidism HighLow LowHyperthyroidism LowHigh High

Populations at Risk for Mild Thyroid Failure

WomenPrior history of Graves disease or

postpartum thyroid dysfunctionElderlyOther autoimmune diseaseFamily history of

Thyroid diseasePernicious anemiaType 1 Diabetes mellitus

Caraccio N, et al. J Clin Endocrinol Metab. 2002;87:1533-1538.

Carmel R, et al. Arch Intern Med. 1982;142:1465-1469.

Perros P, et al. Diabetes Med. 1995;12:622-627.

function

A. Stimulates formation of proteins, which exert trophic effects on tissues

B. Is essential for normal brain development

D. Help regulating lipid & CHO metabolism

C. Essential for childhood growthE. important for reproductive functionF. T3 is an important regulator of

skeletal maturation at the growth plate

by

Bader al-onazi