Back To CoursePathophysiology Textbook
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Jen has taught biology and related fields to students from Kindergarten to University. She has a Master's Degree in Physiology.
Steroids may have a less than perfect reputation in the media, but some steroids naturally occur in the body and function as a vital part of our endocrine system. For example, estrogens and testosterone serve important roles in human reproduction, while cortisol and aldosterone are integral in helping the body maintain equilibrium, especially in times of stress.
Addison's disease is defined as the condition in which the steroid hormones produced by the adrenal cortex are either low or absent. It's known by other names, too: chronic adrenal insufficiency, hypocortisolism, and hypoadrenalism, to name just a few. But what do these terms mean, and how do they describe what's really going on in the bodies of those who have this disease?
Addison's is characterized by a consistent insufficient production of steroid hormones called 'glucocorticoids' and 'mineralocorticoids.' For this lesson, we'll focus on the most important hormone in each group: cortisol for the glucocorticoids and aldosterone for the mineralocorticoids. Cortisol has many functions, including maintaining a consistent blood glucose level, reducing inflammation, and regulating water balance. Aldosterone primarily maintains sodium and water balance, which are necessary for keeping a consistent blood volume and pressure.
Both cortisol and aldosterone are produced by the adrenal glands, small endocrine glands that rest on top of both kidneys. The adrenal glands have two layers: the medulla, or inner, layer, and the cortex, the outer layer. In most cases of Addison's disease, the cells that make up the adrenal cortex are destroyed. The destruction of these cells results in primary adrenal insufficiency, because cortisol and aldosterone are simply not produced. This is different from secondary insufficiency, in which either one or both hormones are made, but the body is unable to use them properly. Although Addison's disease can be caused by secondary adrenal insufficiency, this lesson will focus on primary insufficiency.
So, how does this fit into those other names for Addison's disease? Since hypo means 'low' and the primary glucocorticoid is cortisol, a low amount of cortisol is 'hypocortisolism.' As you might guess, Addison's is also characterized by hypoaldosteronism, low amounts of aldosterone. You'll want to remember the roots hypo and its opposite hyper, which means 'high,' as they'll be used throughout the rest of this lesson. Just remember: 'hyper' and 'high' both start with the same sound.
Let's take a look at what happens to destroy the cells of the adrenal cortex. In about 80% of patients that have Addison's, primary adrenal insufficiency is caused by an autoimmune response in which the body's immune system mistakes its own cells or biochemicals for pathogens. Specifically, the body sees some part of a pathway used by the body for synthesis or use of cortisol and aldosterone as a threat and targets it for destruction.
Other things that cause primary adrenal insufficiency are:
Symptoms of Addison's can also occur after a patient stops steroid use, especially if the medication taken has been taken for a long period of time or in high doses. Sustained use of medications like hydrocortisone and prednisone can desensitize the adrenal gland to the chemical that normally stimulates cortisol production, cause its cells to shrink, and impair its ability to make natural steroid hormones. This is called a iatrogenic response, an instance where treatment causes a disorder.
The symptoms of Addison's disease are caused by the absence of aldosterone and cortisol. If you think about the functions of these two hormones, then it's less difficult to determine the symptoms that arise when they're not present. Here's where 'hyper' and 'hypo' start to come into play.
Cortisol keeps blood sugar levels in balance by stimulating the creation of glucose in the liver. Its absence means a drop in blood glucose, which, in turn, leads to fatigue and lethargy. Cortisol and aldosterone work together to maintain salt and water balance, so their loss leads to orthostatic hypotension, a sudden low blood pressure that occurs on standing. Aldosterone absence also causes a drastic upset in electrolyte balance, leading to nausea, diarrhea, and vomiting. Together, these pose a real danger of causing dehydration, and, eventually, hypovolemia or low blood volume. Because electrolytes like sodium and potassium ions are crucial for nerve and muscle function, symptoms like heart arrhythmia and nervous system changes (especially in the form of mood disorders) are common, as is a craving for salt in an effort to replace the sodium being over-excreted in the urine.
One symptom that stands out for Addison's is hyperpigmentation, or darkening of the skin, in places not necessarily exposed to the sun, like creases of the palms, or inside of the cheeks. Normally, the pituitary gland sends a chemical signal called ACTH to the adrenal gland, signaling it to release glucocorticoids. Once there is an increase of glucocorticoids in the blood, the pituitary stops releasing ACTH. In Addison's, however, there are no cells to respond to ACTH, so the pituitary sends out more and more ACTH in an effort to get the adrenals to make glucocorticoids. Some of the ACTH that accumulates is turned into a hormone that stimulates production of skin pigment.
Addison's patients present many blood abnormalities, all of which logically follow a lack of aldosterone and cortisol. A blood test will show the following:
In order to make sure a patient has primary adrenal insufficiency (again, as opposed to a problem using cortisol), a synthetic form of ACTH is given. Low or absent cortisol after this injection signifies a lack of production of cortisol.
Treatment for Addison's is lifelong and consists primarily of cortisol and aldosterone replacement therapy, usually through medications like hydrocortisone and fludrocortisone, respectively. Because of cortisol's role in mediating stress, people with Addison's must be especially vigilant about monitoring their health during times of stress and illness. Addisonian crisis is defined as the life-threatening symptoms that occur due to a lack of cortisol. Signs of such a crisis include, in addition to the symptoms we discussed earlier:
Treatment must be immediate and usually involves cortisol injection and fluids to stabilize the patient's fluid and electrolyte balance. People who have Addison's usually carry hydrocortisone to self-administer in case of severe and sudden stress.
Addison's is not more prevalent in either sex or any ethnicity. The primary risk factor is the presence of other autoimmune diseases such as type 1 diabetes, hypothyroidism, or myasthenia gravis. Unmonitored steroid use is also considered to be a risk factor.
Let's briefly review what we've learned. Addison's disease is the condition in which the steroid hormones produced by the adrenal cortex are either low or absent. The steroid hormones in question are called cortisol and aldosterone and are produced by the adrenal glands, small endocrine glands that rest on top of both kidneys. In most cases of Addison's disease, the cells that make up the adrenals' outer layer, or cortex, are destroyed. The destruction of these cells results in primary adrenal insufficiency because cortisol and aldosterone are not produced.
In most cases of Addison's, primary adrenal insufficiency is caused by the autoimmune destruction of the adrenal cells. Other causes include tuberculosis, HIV, or invasion by cancerous cells. Sustained use of steroids can also impair adrenal function and cause the symptoms of Addison's. This is an example of an iatrogenic response, an instance where treatment causes a disorder.
Symptoms of Addison's are caused by lack of cortisol and aldosterone, and include:
Treatment of Addison's is lifelong and consists primarily of replacement of cortisol and aldosterone. Patients with Addison's must be especially aware of their condition in times of stress to prevent Addisonian crisis, the life-threatening symptoms that occur due to a lack of cortisol.
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Back To CoursePathophysiology Textbook
20 chapters | 274 lessons