The adrenal medulla is the central portion of the adrenal gland. In this lesson, you will learn about the two hormones secreted by the adrenal medulla - epinephrine and norepinephrine - and how they help you deal with short-term stressors.
The adrenal glands are found just above the kidneys.
The adrenal glands sit on top of your kidneys. If you were to slice an adrenal gland in half, you would notice that it is more like two separate endocrine glands in one. The outer adrenal cortex secretes steroid hormones, and the central adrenal medulla is stimulated by the sympathetic nervous system to secrete catecholamines, which are hormones that help you deal with short-term stress. In this lesson, we will learn about the two catecholamines from the adrenal medulla - epinephrine and norepinephrine - and how they help you cope with everyday stressful situations.
It is not often that we see an endocrine gland stimulated by the nervous system. However, this is the case with the adrenal medulla. When you feel scared or physically threatened, your sympathetic nervous system springs into action to prepare you for fight or flight. For instance, if you are out for a peaceful hike in the woods and all of a sudden a bear appears, your sympathetic nervous system sends split-second impulses that help you make the decision to stay and fight or take flight. I recommend taking flight!
The sympathetic nervous system stimulates the adrenal medulla to secrete its hormones.
One of the glands that the sympathetic nervous system stimulates is the adrenal medulla. Upon stimulation, the gland secretes its hormones into your bloodstream.
One of these hormones is epinephrine, which can be defined as a hormone secreted by the adrenal medulla in response to short-term stress. Epinephrine is also called adrenaline, and you may have heard of this term before. Typically, when we think of adrenaline, we think of the adrenaline rush we get when we act like a daredevil or do something risky or exciting.
This is a good way to recall the actions of epinephrine: When this hormone is secreted, it increases heart rate, blood pressure, cardiac output and blood glucose levels. These actions result in more blood to the muscles and more glucose available for quick energy. And, this makes us better prepared to deal with the stressful event that we are facing, whether it's a bear jumping out at us or riding a rollercoaster.
In addition to epinephrine, we see norepinephrine, which is a second hormone secreted by the adrenal medulla that increases heart rate, blood pressure, cardiac output and blood glucose levels. So, we see that norepinephrine is very similar to epinephrine. One difference we see is that norepinephrine is not only a hormone secreted by the adrenal medulla, it is also a neurotransmitter found at nerve endings within the sympathetic nervous system. We previously learned that a neurotransmitter is a substance that transmits impulses from a nerve to another structure.
So, here again we see the close relationship of the adrenal medulla hormones and the sympathetic nervous system. In fact, it's interesting to note that if the adrenal medulla were destroyed and unable to secrete its hormones, there would be few noticeable effects as long as the sympathetic nervous system remained undamaged. Regardless of where norepinephrine is secreted from, its actions are always working synergistically with epinephrine to help your body cope with short-term stressful situations.
Let's review. At the center of the adrenal gland, we see the adrenal medulla. This portion of the gland is stimulated by the sympathetic nervous system to secrete catecholamines, which are hormones that help you deal with short-term stress. There are two catecholamines. One is called epinephrine or adrenaline. The second hormone is called norepinephrine. If you have ever experienced an adrenaline rush, then you have experienced the effects of epinephrine and norepinephrine because they are hormones that increase heart rate, blood pressure, cardiac output and blood glucose levels. Together, these hormones makes us better prepared to deal with short-term stressful situations.
Following this video, you should be able to:
- Explain how catecholamines are released from the adrenal medulla
- Differentiate between epinephrine and norepinephrine and describe their effects on short-term stress