Hypothyroidism
Hypothyroidism occurs when the gland produces insufficient T3 and T4.
- Primary Hypothyroidism: Caused by issues within the thyroid itself, such as iodine deficiency, gland atrophy, or drugs like lithium and amiodarone. In congenital cases, this can lead to cretinism, characterized by mental retardation and stunted growth.
- Secondary Hypothyroidism: Results from dysfunction in the hypothalamus or anterior pituitary.
- Clinical Manifestations: Patients often experience "slowness"—mental and physical lethargy, weight gain (mostly fluid), cold intolerance, constipation, and dry skin.
- Severe Cases: Myxedema presents with a puffy face and periorbital edema. The most critical state is myxedema coma, a life-threatening slowing of all body activities, including hypoventilation and hypothermia.
- Treatment: Typically involves hormone replacement therapy with levothyroxine.
Hyperthyroidism
Hyperthyroidism is the overproduction of thyroid hormones, leading to an increased metabolic rate.
- Graves Disease: The most common cause, often presenting with a goiter (enlarged thyroid) and exophthalmos (bulging eyes).
- Clinical Manifestations: Symptoms include weight loss despite increased appetite, tachycardia (rapid heart rate), heat intolerance, tremors, and nervousness.
- Treatment: Options include radioiodine therapy to destroy thyroid cells, surgical removal, or antithyroid medications such as methimazole.
Parathyroid Glands and Calcium Regulation
The four small parathyroid glands are embedded in or attached to the thyroid gland. They are the primary regulators of calcium and phosphate metabolism via parathyroid hormone (PTH).
Hyperparathyroidism
Excessive PTH causes increased bone resorption (releasing calcium from bones into the blood).
- Manifestations: Hypercalcemia leads to bone demineralization, renal calculi (kidney stones), muscle weakness, and constipation.
- Labs: High calcium, low phosphorus, and elevated PTH.
Hypoparathyroidism
Often a complication of thyroid surgery where the glands are accidentally damaged, this leads to low PTH and hypocalcemia.
- Manifestations: Muscle spasms, laryngospasms, and paresthesia. Clinicians look for Chvostek’s sign (facial twitching) or Trousseau’s sign (carpal spasm).
- Labs: Low calcium, high phosphorus, and low PTH.
Clinical Calculation: Corrected Calcium
Because much of the calcium in the blood is bound to albumin, a low albumin level can make total calcium appear low even if the active calcium is normal. To get an accurate picture, use the corrected calcium formula:
Corrected calcium=serum calcium+0.8×(4−serum albumin)
The Adrenal Glands
The adrenal glands are composed of two distinct functional layers: the adrenal medulla and the adrenal cortex.
Adrenal Medulla
The medulla is responsible for the "fight or flight" response, secreting catecholamines: epinephrine, norepinephrine, and dopamine. A tumor in this region, known as a pheochromocytoma, can cause unpredictable attacks of extreme hypertension, headache, and diaphoresis (sweating).
Adrenal Cortex
The cortex produces three main types of steroid hormones:
- Mineralocorticoids (e.g., Aldosterone): Regulate salt and water balance ("Salt").
- Glucocorticoids (e.g., Cortisol): Regulate glucose metabolism and stress response ("Sugar").
- Androgens: Regulate sexual characteristics ("Sex").
Adrenal Dysfunctions
- Addison’s Disease (Primary Insufficiency): A deficiency in both mineralocorticoids and glucocorticoids. This leads to sodium loss, potassium retention, hypoglycemia, and characteristic "bronzing" of the skin. An Addisonian Crisis is a medical emergency involving severe hypotension and volume depletion.
- Cushing’s Syndrome (Overactivity): Caused by excess cortisol, often from exogenous steroid use or tumors. Symptoms include hyperglycemia, sodium retention, and physical changes like a "moon face" or buffalo hump.
- Hyperaldosteronism (Conn’s Syndrome): Excessive aldosterone leads to sodium and water retention (causing hypertension) and potassium depletion (causing weakness and dysrhythmias).
Pituitary-Related Fluid Imbalances
Disorders of the posterior pituitary often involve Antidiuretic hormone (ADH), which regulates water reabsorption in the kidneys.
- Diabetes Insipidus (DI): Caused by a deficiency of ADH (either central or nephrogenic). This results in the excretion of massive amounts of dilute urine (>250 mL/hour), leading to extreme thirst (polydipsia) and dehydration. Treatment often involves desmopressin (DDAVP).
- SIADH (Syndrome of Inappropriate Antidiuretic Hormone): The opposite of DI, where there is an excess of ADH. This causes the body to retain too much water, leading to "dilutional hyponatremia" (low sodium levels). Treatment focuses on fluid restriction and treating the underlying cause.
