Brief+Pathophysiology+Overview

==="Hypothyroidism results from insufficient circulating thyroid hormone as a result of a variety of abnormalities," (Lewis, Dirksen, Heitkemper, Bucher & Camera, 2011, p. 1269). It is classified as either //primary// or //secondary// depending on its cause//. Primary hypothyroidism // occurs when the thyroid tissue is either destroyed or the creation of hormones is defective. //Secondary hypothyroidism// is "related to pituitary disease with decreased TSH secretion or hypothalamic dysfunction with decreased thyrotropin-releasing hormone [TRH] secretion," (Lewis et al., 2011, p. 1269). Also, thyroiditis or discontinuing of hormone therapy could be a cause of transient hypothyroidism. (Lewis et al., 2011, p. 1269).===

=== Most cases of hypothyroidism are of primary origin and thus result from disease in the thyroid gland. 95% of adult patients with hypothyroidism are the result of primary hypothyroidism (Carson, 2009, p. 51) The loss of thyroid tissue causes decreased production of thyroid hormones. “In primary hypothyroidism, insufficient T4 is produced by the thyroid gland. Serum T4 is low and levels of TSH are high. The onset is slow and insidious and, because the affected individual is often an older person, it might be accepted as a normal part of ageing and it can therefore be some time before a medical opinion is sought.” (Carson, 2009, p. 51). Primary hypothyroidism is frequently autoimmune, but it can also be the result of significant iodine deficiency. (Sommers, 2011, p.544). Secondary hypothyroidism is less common and is due to a “failure of the pituitary gland to stimulate the thyroid gland or a failure of the target tissues to respond to the thyroid hormones."(Sommers, 2011, pp. 544-545).===

===Hypothyroidism can also occur in infants, and is termed **cretinism**. It develops due to thyroid hormone deficits during fetal development or early on in the neonates life.To check for this, all infants in the United States are screened at birth (Lewis et al., 2011, p.1269).===