Endocrine System

The endocrine system functions to maintain homeostasis of the body’s internal environment. It maintains a fine balance between too much or too little-too much glucose or not enough thyroid hormone. The endocrine system secretes chemical substances called hormones directly into the bloodstream. The concentration is maintained at an appropriate level in the bloodstream by a "feedback" control mechanism. If the hormone concentration increases, further production of the hormone is inhibited. When the concentration decreases, production of the hormone is then stimulated. Hormones are the main regulators of metabolism, growth and development, reproduction and stress response. All endocrine disorders are caused by either excess or deficiency of the hormones.

The thyroid is located in the neck and has an "H" shaped appearance. The hormones formed are T3 and T4. Iodine is necessary for the formation of T3 and T4. If iodine is lacking in the diet, the thyroid fails to make the hormone and gets very large, increasing tissue in an effort to compensate-resulting in a goiter.

The hypothalamus secretes TRH-Thyroid Releasing hormone which stimulates the pituitary to secrete TSH-Thyroid Stimulating Hormone which stimulates the thyroid to produce T3 and T4. The blood level of T3 and T4 functions as the feedback control mechanism for pituitary and hypothalamus.

1. Normally when T3 and T4 levels fall, TRH and TSH levels should be increased to stimulate the thyroid.

2. Normally when T3 and T4 levels rise, TRH and TSH levels should be decreased to inhibit the thyroid.

Look at the patients neck from the front. Note the presence of old surgical scars, distended veins, or redness. Watch the movement of the thyroid gland the patient swallows. Examine the head and neck distal to the thyroid; observe the position of the trachea. Then examine the thyroid: one widely recommended method is to palpate the patients neck with the fingertips of both hands while standing behind the seated patient. Locate the cricoid cartilage, a very important step when the thyroid gland is normal or subnormal in size. When your index fingers rest just under the lower rim of the cricoid, the lower portion of those fingers is over the top of the thyroid. Rotate your second and third fingers over the rest of the gland, evaluating its size, contour, consistency, and freedom of movement.

HYPOTHYROIDISM: Results from inadequate production of the thyroid hormone, causing a hypometabolic state. If very severe it is also called Myxedema.

HYPERTHYROIDISM: Is the result of excessive production of thyroid hormone. The most common cause is Graves disease. This is an autoimmune disorder. Abnormal antibodies are made that stimulate the thyroid by binding at the same site as the TSH. With the increased T3 and T4 production, TSH stimulation is stopped by the feedback mechanism, but the hormone production continues. This is due to the antibodies taking over the function of stimulating the thyroid and all control is lost. Hyperthyroidism may also be caused by a tumor in the thyroid or by a tumor in the pituitary that secrete excessive TSH.

NOTE: Exophthalmos is caused by disposition of fat in back of the globe causing forward protrusion.

The pancreas is located behind the stomach horizontally. It’s head is attached to the duodenum and its tail reaches to the spleen. Scattered throughout the spleen are groups of cells referred to as the islets of Langerhans that secrete insulin. Insulin lowers the blood glucose by assisting the movement of glucose into the cells. The blood glucose level rises because glucose cannot enter the cells where it is used for energy. Without insulin the serum glucose level rises because the glucose cannot enter the cells, it then spills over into the urine. How much insulin is released into the body is normally determined by the level of sugar in the blood which works as a feedback system.

Diabetes Mellitus: A disorder of carbohydrates (glucose) metabolism, characterized by hyperglycemia (elevated level of glucose in the blood) and glycosuria (glucose in the urine). This is the result of inadequate production or utilization of insulin. There are two types.

April, 1999

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Operational Medicine 2001

Health Care in Military Settings

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