97. In 13 years old girl a hypotension and polyuria is observed. Preliminary diagnosis – diabetes insipidus. Which hormone deficiency can cause this disease?

Answer. There are several different types of DI, each with a different cause. The most common type in humans is central diabetes insipidus, caused by a deficiency of vasopressin, also known as antidiuretic hormone (ADH). The second common type of diabetes insipidus is nephrogenic diabetes insipidus, which is caused by an insensitivity of the kidneys to ADH. It can also be an iatrogenic artifact of drug use.

98. A 39-year-old female presents to the clinic for a routine health maintenance exam. The patient reports she is feeling nervous and anxious all the time with frequent palpitations. On further questioning she reports having diarrhea and has been losing weight. She has also noticed a change in hair and fingernail growth and frequently feels warm while others are cold or comfortable. She denies any history of depression or anxiety disorder and is not taking any medications. On examination, her heart rate is 110 beats per minute. She has a slight tremor and has increased reflexes in all extremities. A nontender thyroid enlargement is appreciated in the thyroid region. Her TSH level is low at 0.1 mIU/mL. The patient is told that she has an autoimmune antibody process.What is the most likely diagnosis? What is the biochemical mechanism for this disorder?

Answer. This 39-year-old woman has symptoms of hyperthyroidism, thyroid excess.This causes a tachycardia, tremor, nervousness, thin skin, weight loss through the hypermetabolic state, and hyperreflexia. If unchecked, the high levels of thyroid hormone can sometimes even cause adrenergic crisis (so called thyroid storm), which has a high rate of mortality. Normally, the thyroid hormone (thyroxine) is under tight control. The pituitary release of thyroid stimulating hormone is stimulated by insufficient thyroxine, and suppressed by excess thyroxine. In Graves disease, the most common cause of hyperthyroidism an autoimmune immunoglobulin is produced that stimulates the TSH receptor of the pituitary. This is confirmed by either assaying for the thyroidstimulating immunoglobulin, or a radionuclide scan revealing diffuse increased uptake throughout the thyroid gland.

99. The thyroid hormones t3 and t4 are synthesized in the follicular cells of the thyroid gland. From which of the following essential amino acids are the thyroid hormones synthesized?

Answer. Thyroid hormones are synthesized from tyrosyl residues on thyroglobulin in the colloidal space of the thyroid follicular cells. Although tyrosine can be obtained from the diet, it can also be synthesized from the essential amino acid phenylalanine by the action of phenylalanine hydroxylase.

100. A 26-year-old male presents complaining of heat intolerance, heavy sweating, tremulousness, and feeling “jittery inside.” Physical examination reveals reddened conjunctiva and warm and moist palms, but the thyroid gland was not visibly enlarged. Which of the following tests would be most helpful to obtain an accurate diagnosis?

Answer. This patient appears to have a hyperthyroid condition even though the thyroid does not appear to be enlarged. Thyroid function tests would be most helpful to determine if this is the case. The free thyroxine level is a direct measure of the amount of free T₄, the biologically active T₄, in the serum. Elevation of the free T₄ indicates a hyperthyroid condition.