Thyroid Disorder PDF

Physiology of Thyroid Gland (cont...) Department of physiology Dr.Hanan Altaee Applied Physiology –Disorders of Thyroid Gland Hyperthyroidism Hyperthyroidism is caused by: 1. Graves’...

Physiology of Thyroid Gland (cont...) Department of physiology Dr.Hanan Altaee Applied Physiology –Disorders of Thyroid Gland Hyperthyroidism Hyperthyroidism is caused by: 1. Graves’ disease. 2. Thyroid adenoma. In most patients with hyperthyroidism, the thyroid gland is increased to two -three time’s normal size, with tremendous hyperplasia. Also, each cell increases its rate of secretion several folds. 1. Graves’ disease: Graves’ disease is an autoimmune disease and it is the most common cause of hyperthyroidism. In Graves’ disease, the B lymphocytes (plasma cells) produce autoimmune antibodies called thyroid-stimulating auto antibodies or immunoglobulins (TSAbs) (TSI). These antibodies act like TSH by binding with membrane receptors of TSH and activating cAMP system of the thyroid follicular cells. This results in hypersecretion of thyroid hormones. TSAbs act up to 12 hours in contrast to that of TSH, which lasts only for an hour. The high concentration of thyroid hormones caused by the antibodies suppresses the TSH production also. So; the concentration of TSH is low or almost zero in plasma of most of the hyperthyroid patients. 1 Page  2. Thyroid adenoma: A localized tumor develops in the thyroid tissue. It secretes large quantities of thyroid hormones. It is not associated with autoimmunity. As far as this adenoma remains active, the other parts of thyroid gland cannot secrete the hormone. This is because; the hormone secreted from adenoma depresses the production of TSH. Signs and Symptoms of Hyperthyroidism 1. Intolerance to heat as the body produces lot of heat due to increased BMR. 2. Increased sweating due to vasodilatation. 3. Decreased body weight due to fat mobilization. 4. Diarrhea due to increased motility of GI tract. 5. Muscular weakness because of excess protein catabolism. 6. Nervousness, extreme fatigue, inability to sleep, mild tremor in the hands and psychoneurotic symptoms such as hyperexcitability, extreme anxiety or worry. All these symptoms are due to the excess stimulation of neurons in the central nervous system. 7. Toxic goiter (see below) 8. Oligomenorrhea or amenorrhea. 9. Exophthalmos (see below) 2 10. Polycythemia. Page  11. Tachycardia and atrial fibrillation. 12. Systolic hypertension. 13. Cardiac failure. Exophthalmos Protrusion of eye balls is called exophthalmos. Most, but not all hyperthyroid patients develop some degree of protrusion of eyeballs. Exophthalmos is due to the edematous swelling of retro-orbital tissues and degenerative changes in the extraocular muscles. Effect of exophthalmos on vision Severe exophthalmic condition leads to blindness because of two reasons: 1. Protrusion of the eyeball, which stretches and damages the optic nerve, resulting in blindness or 2. Due to the protrusion of eyeballs, the eyelids cannot be closed completely while blinking or during sleep. So, the constant exposure of eyeball to atmosphere causes dryness of the cornea, leading to irritation and infection. It finally results in ulceration of the cornea leading to blindness. Hypothyroidism Decreased secretion of thyroid hormones. Hypothyroidism leads to myxedema in adults and cretinism in children. 3 Page  Myxedema: Myxedema is characterized by generalized edematous appearance. Myxedema occurs due to  Diseases of thyroid gland.  Genetic disorder.  Iodine deficiency.  Deficiency of thyroid-stimulating hormone or thyrotropin-releasing hormone.  Hashimoto’s thyroiditis, which is common in late middle-aged women. The thyroid glands of most of these patients first have autoimmune “thyroiditis,” which means thyroid inflammation. This causes progressive deterioration and finally fibrosis of the gland, with resultant diminished or absent secretion of thyroid hormone. Signs and symptoms of myxedema Typical feature of this disorder is an edematous appearance throughout the body. It is associated with the following symptoms: 1. Swelling of the face. 2. Bagginess under the eyes 3. Non-pitting type of edema, i.e. when pressed, it does not make pits and the edema is hard. It is because of accumulation of proteins with hyaluronic acid and chondroitin sulfate, which form a hard tissue with increased accumulation of fluid. 4. Atherosclerosis: It is the hardening of the walls of arteries because of 4 accumulation of fat deposits and other substances. In myxedema, it occurs because Page  of increased plasma level of cholesterol which leads to deposition of cholesterol on the walls of the arteries. Arteriosclerosis causes hypertension. Other general features of hypothyroidism in adults are: 1. Anemia. 2. Fatigue and muscular sluggishness. 3. Extreme somnolence with sleeping up to 14 to 16 hours per day. 4. Menorrhagia and polymenorrhea. 5. Decreased cardiovascular functions such as reduction in rate and force of contraction of the heart, cardiac output and blood volume. 6. Increase in body weight 7. Constipation. 8. Mental sluggishness. 9. Depressed hair growth. 10. Scaliness of the skin. 11. Frog-like husky voice. 12. Cold intolerance. Cretinism: Cretinism is the hypothyroidism in children, characterized by stunted growth. Causes for cretinism  Congenital absence of thyroid gland.  genetic disorder or  Lack of iodine in the diet. Features of cretinism 5 Page  1. A new born baby with thyroid deficiency may appear normal at the time of birth because thyroxine might have been supplied from mother. But a few weeks after birth, the baby starts developing the signs like sluggish movements and croaking sound while crying. Unless treated immediately, the baby will be mentally retarded permanently. 2. Skeletal growth is more affected than the soft body. The tongue becomes so big that it hangs down with dripping of saliva. The big tongue obstructs swallowing and breathing. Goiter: Goiter means enlargement of the thyroid gland. It occurs both in hypothyroidism and hyperthyroidism. Treatment for thyroid disorders Hyperthyroidism 1. By using Antithyroid Substances: Antithyroid substances are the drugs which suppress the secretion of thyroid hormones. (early stage). Three well-known antithyroid substances are: i. Thiocyanate.(Inhibiting iodide trapping). ii. Thiourylenes.(Inhibit peroxidase enzyme activity + blocking coupling of 6 iodinated tyrosine to form either T3 or T4). Page  iii. High concentration of inorganic iodides. (Iodides in high concentration decrease all phases of thyroid activity). 2. by Surgical Removal In advanced cases of hyperthyroidism, treatment by using antithyroid substances is not possible. Thyroid gland of these patients must be removed by Surgery. (Thyroidectomy). Hypothyroidism The only treatment for hypothyroidism is the administration of thyroid extract or ingestion of pure thyroxine in the form of tablets, orally. 7 Page