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.
Our nervous system functions a bit like a like a well-engineered electrical system. Its neurons hum with activity, sending impulses speeding to and from the brain, relaying information from our senses and returning with the instructions our muscles and organs need to respond. If the nervous system is 'short circuited,' there's going to be a problem. Tumors of the adrenal gland called pheochromocytomas do just that and are the focus of this lesson.
Before we tackle what these tumors are and why they're so dangerous, let's review a little about the nervous system. The nervous system can be divided into parts based on function. One of them, the sympathetic nervous system, is largely responsible for what we call the fight or flight response - that is, sympathetic nerves transmit signals that help us respond to stress. Need a tip for remembering this? Just think that we've all been stressed out for one reason or another - that is, we have sympathy for our fellow human beings under stress.
Let's examine the sympathetic nervous system a little further by looking at an example. Say we're walking alone at night down a dark street. The sympathetic nervous system does things like dilate our pupils to let in the maximum amount of light, get our heart pounding to prepare us to flee if necessary, and dilate the bronchioles in the lungs to make sure we've got plenty of oxygen on hand.
The sympathetic nervous system relies on chemical neurotransmitters called catecholamines to transmit signals from one nerve to another. There are several in play, but let's take a look at one in particular, one that's not only a neurotransmitter but is also a hormone: norepinephrine. As a hormone, norepinephrine (which is sometimes called noradrenaline) has many functions, among them working with the sympathetic nervous system during times of stress and helping to maintain consistent blood pressure.
In addition to being released from nerve cells, norepinephrine is also made and released by the adrenal glands, two small glands that rest on top of our kidneys. Norepinephrine is made by the cells of the medulla, the inner layer. Specifically, norepinephrine is made by adrenal medulla cells called chromaffin cells. Other catecholamines are made in the adrenal medulla, too, such as epinephrine, and, to a lesser extent, dopamine.
Pheochromocytomas, sometimes abbreviated 'PCCs,' are tumors that form in the adrenal glands, specifically in the chromaffin cells of the adrenal medulla. You'll notice that both words contain the root 'chrom,' which means color. 'Pheo' is derived from the Greek word for dark, while 'cyto' means cell. Rounding out this word is, of course, the root '-oma,' which indicates a tumor. Put them together, and you have a literal definition of what pheochromocytoma is: a darkly staining tumor made of chromaffin cells. More chromaffin cells means more adrenal hormones, especially norepinephrine. More norepinephrine means more sympathetic nervous system activity. And that means that the actions our body normally reserves for stressful situations can come up at any time.
What are the symptoms of pheochromocytoma, and why is this type of tumor so dangerous? Specific symptoms depend on the size of the tumor, as well as whether it affects one or both adrenal glands, but, in general, major symptoms include 'spells' of:
These spells generally occur in a fairly regular pattern and can last anywhere from about 15 minutes to an hour. Sometimes, spells are triggered when the body needs to change its blood pressure, such as upon standing or during exercise or other types of exertion.
But what causes these symptoms?
As we discussed earlier, norepinephrine plays lots of roles in the body. One of them is to bind to receptors on blood vessels, causing the smooth muscle inside of them to tighten and narrowing their diameter. The smaller diameter of the vessels means the heart has to work harder to push blood through, and blood pressure rises. Norepinephrine also acts on the heart muscle itself to drive up heart rate and stimulates the sweat glands in preparation to keep the body cool. In an Olympic sprinter ready to run a heat, none of this is a problem. But in the case of PCC, the excess norepinephrine secreted by the chromaffin cells can cause blood pressure to skyrocket and then crash at inappropriate times. Consistent high amounts of norepinephrine are also toxic to heart cells and can cause them to stop functioning, and even die. This puts patients at risk for heart attack, stroke, arrhythmias, and organ failure.
Patients who have undiagnosed PCC face other serious problems, too. High amounts of norepinephrine upset the renin-angiotensin-aldosterone system's equilibrium. This system consists of the series of hormones that regulates the body's blood volume and water balance and involves the kidneys, lungs, and adrenal glands. The normal activation of these three hormones causes the kidneys to retain water, increasing blood pressure. The bodies of people with pheochromocytomas suppress the action of these hormones in an effort to offset the hypertension caused by the extra norepinephrine in circulation. This results in large amounts of fluid loss in an attempt to keep blood pressure low and can be critical during treatment.
Pheochromocytomas are primarily diagnosed by blood and urine tests that look for high levels of norepinephrine or their metabolites, which are called metanephrines. PET or MRI imaging is usually used for confirmation.
Whenever possible, pheochromocytomas are treated with laparoscopic surgery, which has about a 90% cure rate. Surgery isn't without its risks, though. As we discussed earlier, patients with PCC have extremely high levels of norepinephrine circulating in their bloodstreams. Recall that the body will suppress the renin-angiotensin-aldosterone system in order to offset the hypertension caused by the extra norepinephrine. Sudden removal of the source of all of this extra norepinephrine without allowing the body to recover would cause catastrophically low blood pressure. In preparation for surgery, patients with PCC are treated with high levels of sodium in order to increase blood volume and to prevent this sudden crash of blood pressure.
If the patient's health doesn't permit surgery, or if the PCC is fairly small, then medication is used. Specifically, alpha-adrenergic blockers, drugs that block receptors for norepinephrine, are used. These medications prevent norepinephrine from constricting smooth muscle, and therefore function by lowering blood pressure. Beta-adrenergic blockers are also sometimes used to slow heart rate.
The incidence of PCC is between 2 and 8 million of people yearly in the U.S. There are no known lifestyle factors that put someone at risk for a PCC, but there are some genetic diseases that correlate with the condition, such as neurofibromatosis and some forms of multiple endocrine neoplasia.
Let's look at some of the important things we've covered about pheochromocytomas, tumors that form in the medulla of the adrenal glands. Formed specifically by chromaffin cells, cells of the adrenal medulla that secrete norepinephrine and epinephrine, pheochromocytomas are very dangerous because they cause the body to be exposed to high levels of these chemicals that function both as neurotransmitters and hormones. Norepinephrine, especially, plays an important role in the sympathetic nervous system, which is responsible for our fight or flight response. Because there is a high amount of circulating norepinephrine in the body, our body's stress system is always working. This leads to symptoms, such as:
Pheochromocytomas are treated using laparoscopic surgery and, in some cases, alpha adrenergic blockers, medications that lower blood pressure.
Following this video lesson, you should be able to:
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Back To CoursePathophysiology Textbook
20 chapters | 274 lessons