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Immunological defense mechanism

Disorders of the thyroid may represent a congential defect in thyroid development or they may develop later in life, with a gradual or a sudden on set. Goiter is an increase in the size of the thyroid gland. It can occur in hypothyroid, euthyroid, and hyperthyroid states. Goiters may be diffuse, involving the entire gland without evidence or nodularity, or they may contain nodules. Diffuse goiters usually become nodular. Goiters may be toxic, producing sings of extreme hyperthyroidism, or thyrotoxicosis, or they may be notoxic. Diffuse nontoxic and multinodular goiters are the result of compensatory hypertophy and hyperplasia of follicular epithelium secondary to some derangement that impaires thyroid hormone output. The degree of thyroid enlargement is usually proportional to the extent and duration of thyroid deficiency. The increased thyroid mass usually achieves a normal, or euthyroid, state eventually. Multinodular goiters produce the largest thyroid enlargements and are often associated with thyrotoxicosis. When sufficiently enlarged they Pathophysiology 172 may compress the esophagus and trachea, causing difficulty in swallowing, a chocking sensation, & respiratory stridor. Such lesions may also compress the superior vena cava, producing distention of the veins of the neck and upper extremities, edema of the eyelids and conjunctiva, and syncope with coughing.