CHAPTER KEY WORDS
- Adrenal system
You are called to the wrestling room where practice has been in progress for 25 minutes. Upon arriving, you are told that one of the wrestlers has been acting “different” and “not himself.” He is conscious, but anxious and agitated. His speech is mildly slurred, and he feels fatigued. You know the athlete, who has been cutting weight recently, has diabetes mellitus.
You question the athlete regarding his dietary habits for the day and learn that because he is trying to cut weight, he has not had anything substantial to eat today. You immediately measure his blood glucose level and get a reading of 64 mg/dL. You administer a sugar packet to him and check his vital signs. All vitals are within normal limits, and he states he feels better after just a few minutes. After 15 minutes, you recheck his blood glucose level and get a reading of 78 mg/dL. He then eats a carbohydrate snack bar, and after 15 more minutes, his blood glucose level is 112 mg/dL. The athlete is cleared to return to practice, with repeat glucose checks every 15 to 20 minutes.
Every day our body responds nearly instantaneously via the central and peripheral nervous system (CNS and PNS); some of these are conscious and some are subconsciously controlled. This communication is evident in every action we make, but it is also occurring without our realization. The CNS and PNS comprise a collection of specialized cells called neurons that connect our brain to our organs and tissues. The CNS communicates with the hypothalamus in the brain to stimulate certain hormones to be produced. Hormones are regulatory substances generated in specific organs in the body and transported via blood. Every function we perform requires a homeostatic balance to ensure proper body temperature, blood sugar, heart rate, and metabolism. Thanks to the endocrine system, this happens without any conscious effort.
Specifically, the hypothalamus (which interacts with the CNS) and pituitary are responsible for the initial hormones for growth, metabolism, and reproduction, which then stimulate endocrine organs that include the thyroid and adrenal glands (or suprarenal glands, which are found above the kidneys).1 The thyroid gland and adrenal glands then respond to the input from the pituitary as to how much thyroid hormone or cortisol, respectively, to produce.1 The pancreas is both an endocrine and exocrine organ that is responsible for maintaining proper blood sugar levels and preventing life-threatening conditions such as diabetic ketoacidosis. With improved care and early recognition, these conditions can either be prevented before they occur or before they become life-threatening.
The hypothalamic–pituitary–adrenal axis involves a complex group of direct influences and feedback mechanisms among 3 organs: the hypothalamus, the pituitary gland (below the thalamus), and the adrenal (or suprarenal) glands. The hypothalamus connects the neurological system to the endocrine system with neuroendocrine cells that generate hormones (eg, the corticotropin-releasing hormone) to communicate with the pituitary gland to secrete more or less hormones. In response, the pituitary gland generates and secretes stimulating hormones, such as adrenocorticotropic hormone, that travel through the blood to the adrenal cortex to signal rapid production of corticosteroids, including cortisol. The production of cortisol in the adrenal gland will then provide negative feedback to the hypothalamus and pituitary to inhibit production of corticotropin-releasing hormone and adrenocorticotropic hormone, respectively, to prevent overproduction of hormones (Figure 5-1).1
This is an overview of how the entire hypothalamic–pituitary–adrenal axis works to provide our bodies with the appropriate levels of hormones in a given situation. The hypothalamic–pituitary axis specifically generates hormones responsible for metabolism, reproduction, and growth. The adrenal gland is responsible for stress hormones and sex hormones, as well as for assisting with blood pressure regulation. These hormones do not perform these tasks alone; they simply aid the homeostasis to maintain proper function of their respective organs (Figure 5-2).1,2
The thyroid gland is a bilobed gland that sits anterior to the trachea in the neck. The thyroid gland is part of its own neuroendocrine hypothalamic–pituitary axis system referred to as the hypothalamic–pituitary–thyroid axis. The hypothalamus produces thyrotropin-releasing hormone when circulating thyroid levels are low, which stimulates the anterior pituitary to generate the thyroid-stimulating hormone (TSH), which then stimulates the thyroid gland to produce more thyroid hormone.1 Similar to the adrenal gland, the appropriate levels of thyroid in the blood act as negative feedback to the hypothalamus to prevent it from generating too much thyrotropin-releasing hormone. Thyroid hormone specifically helps regulate metabolism and growth. It does so with the help of the mineral iodine, which is obtained from our diet; that is why salt is generally iodized. Without proper amounts of iodine in our diet, we run the risk of hypothyroidism (Figure 5-3).1
Hyperthyroidism is a form of thyrotoxicosis, which is excessive thyroid hormone of any kind. Hyperthyroidism results from an increased production of T3 and/or T4 thyroid hormones produced by the thyroid gland.1 There is a wide range of severity of hyperthyroidism, and the most severe case, thyroid storm, results in confusion, an irregular heartbeat, vomiting, diarrhea, and elevated core body temperature. Thyroid storm is a true medical emergency that can result in death in up to 50% of patients, even if it is identified and treated rapidly.
Causes of hyperthyroidism include Graves’ disease (50% to 80%), thyroid adenoma, multinodular goiter, inflammation of the thyroid gland, endogenous iodine consumption, and excessive synthetic iodine ingestion (for treatment of hypothyroidism). Signs and symptoms include nervousness, tremors, tachycardia, palpitations, irritability, heat intolerance, muscle weakness, diarrhea, enlarged thyroid, weight loss, sleeping difficulty, and possibly an enlarging neck mass called a goiter.1,2 These are often vague, and this diagnosis should be considered frequently, as it may be asymptomatic at the time of diagnosis. Diagnosis of hyperthyroidism is identified with blood tests that include a low TSH and elevated T3 and/or T4 hormones. The appropriate provider should perform further testing to identify the cause of the hyperthyroidism. Treatment depends on the severity, symptoms, and blood levels of T3 and/or T4, but it can include beta blockers, corticosteroids, radioactive ablation, and surgery to remove the thyroid gland.1,2
On the other hand, hypothyroidism results from an underproduction of thyroid hormone by the thyroid gland. Symptoms may include fatigue, weight gain, cold intolerance, constipation, and depression. Just like hyperthyroidism, this too may result in a goiter. This condition is particularly concerning during pregnancy, as it can result in cretinism, with developmental and growth delays in the fetus. The most extreme form of hypothyroidism is myxedema coma, a life-threatening condition that causes low body temperature without compensatory shivering, lethargy, confusion, bradycardia, and bradypnea.3