the thyroid (greek thyreos, shield, plus eidos, form) consists of two lobes connected by isthmus ...
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Disorders of the
Thyroid Gland
By Amir Ashkan Ashrafian M.D
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Disorders of the Thyroid Gland: Introduction
The thyroid gland ⇨ T3 & T4⇨Thyroid hormone receptors ell differentiation + Thermogenic & metabolic homeostasis
Autoimmune disorders: overproduction of thyroid hormones
(thyrotoxicosis) OR Glandular destruction and hormone
deficiency (hypothyroidism) Benign nodules and various forms of
thyroid cancer
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Thyroid Anatomy The thyroid (Greek thyreos, shield, plus
eidos, form) consists of two lobes connected by isthmus
Anterior to the trachea between the cricoid cartilage and the suprasternal notch
Normal thyroid is 12–20 g , vascular, soft
Four parathyroid glands,producing parathyroid hormone , are located posterior to each pole of the thyroid
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Thyroid Histology
The thyroid gland consists of numerous spherical follicles composed of thyroid follicular cells that surround secreted colloid, a proteinaceous fluid containing large amounts of thyroglobulin, the protein precursor of thyroid hormones
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Regulation of the Thyroid Axis
TSH, secreted by the thyrotrope cells of the anterior pituitary, pivotal role in controling thyroid axis
The most useful physiologic marker of thyroid hormone action
The thyroid axis is a classic example of an endocrine feedback loop. Hypothalamic TRH stimulates pituitary production of TSH, which, in turn, stimulates thyroid hormone synthesis and secretion. Thyroid hormones feed back to inhibit TRH and TSH production
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Iodine Metabolism and Transport
Iodide uptake is a critical first step in thyroid hormone synthesis. Ingested iodine is bound to serum proteins, particularly albumin. Unbound iodine is excreted in the urine. The thyroid gland extracts iodine from the circulation in a highly efficient manner
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Cretinism
Cretinism : mental & growth retardation Children in iodine-deficient regions who not treated
with iodine or thyroid hormone (early life). These children are often born to mothers with iodine deficiency
∼Maternal T3,T4 deficiency worsens the condition Concomitant selenium def. ⤳ neurologic
manifestations of Cretinism Iodine supplement of salt, bread etc. ⇨⬇Cretinism. Iodine deficiency the most common cause of
preventable mental deficiency Mild iodine deficiency ⟾ subtle reduction of IQ Oversupply of iodine ⤳ ⬆Autoimmune thyroid
disease
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Hypothyroidism
Iodine deficiency remains the most common cause of hypothyroidism worldwide. In areas of iodine sufficiency, autoimmune disease (Hashimoto's thyroiditis) and iatrogenic causes (treatment of hyperthyroidism) are most common
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Classification Congenital Hypothyroidism
Iatrogenic hypothyroidism
Autoimmune Hypothyroidism ⥥ Hashimoto's ( Goitrous thyroiditis ) ⬇ Atrophic thyroiditis
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Clinical Manifestations Insidious onset : may become aware of
symptoms only after euthyroidism Hashimoto's thyroiditis ⤳ irregular firm
goiter rather than symptoms of HypoT Dry skin, decreased sweating Puffy face, edematous eyelids Nonpitting pretibial edema Constipation & weight gain (despite
poor appetite) Due to fluid retention in the
myxedematous tissues
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Clinical Manifestations
There is pallor, & often yellow tinge to the skin due to carotene accumulation
Nail growth is retarded Hair is dry, brittle, difficult to manage,
and falls out easily ( diffuse alopecia ) Thinning of the outer third of the
eyebrows (Also in Leprosy) Cool extremities Impaired Memory & concentration
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Associated Autoimmune diseases
Vitiligo
Pernicious anemia
Addison's disease
Alopecia areata
Type 1 diabetes mellitus
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Treatment: Hypothyroidism
Daily replacement dose of levothyroxine
Radiation
Early studies of the pathogenesis of thyroid cancer focused on the role of external radiation, which predisposes to chromosomal breaks, leading to genetic rearrangements and loss of tumor-suppressor genes.
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Thyrotoxicosis Thyroid hormone excess ⤷HyperthyroidismCauses of Thyrotoxicosis: Primary hyperthyroidism Graves' disease(Genetic + Iodine
intake) Toxic multinodular goiter Toxic adenoma Drugs: iodine excess (Jod-Basedow
phenomenon)
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Symptoms of Thyrotoxicosis Hyperactivity, irritability, dysphoria
Heat intolerance and sweating
Palpitations
Fatigue and weakness
Weight loss with increased appetite
Diarrhea
Polyuria
Oligomenorrhea, loss of libido
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Signs of Thyrotoxicosis Tachycardia; atrial fibrillation in the elderly
Tremor
Goiter
Warm, moist skin
Muscle weakness, proximal myopathy
Lid retraction or lag
Gynecomastia
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Treatment: Graves' Disease
By reducing thyroid hormone synthesis
Using antithyroid drugs
Reducing the amount of thyroid tissue with radioiodine (131I) treatment
Thyroidectomy
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