Endocrine Gland Stimuli (Nursing)

00:00 What causes hormones to be released from their endocrine glands? Most of the time, blood levels of hormones are controlled by a negative feedback system. This happens when an increased hormone is going to affect the target organ and the effect on the target organ will then inhibit further hormone release. The levels that are going to vary between release and inhibition are very narrow and a very small range. Hormone release could be triggered by endocrine gland stimuli as well as nervous system modulation. Endocrine glands can be stimulated to synthesize and release hormones in response to 3 different types of stimuli. The first is the humoral stimuli, second neural stimuli, and third hormonal stimuli. Let's take a closer look. With the humoral stimulus, changing blood levels of certain ions and nutrients are going to directly stimulate the secretion of hormones. A good example of this is the calcium in our blood. Declining blood calcium levels stimulates the parathyroid gland to secrete the hormone parathyroid hormone. In turn, parathyroid hormone causes the calcium concentration to rise by activating osteoclasts which break down the bone minerals and release calcium into the blood. Once there is a sufficient amount of calcium in the blood, the stimulus is removed and the parathyroid hormone is also removed. A second type of stimulus is a neural stimulus.

02:06 With the neural stimulus, nerve fibers are going to stimulate hormone release. For example, sympathetic nervous system fibers stimulate the adrenal medulla to secrete catecholamines.

02:22 Remember that the sympathetic nervous system is our fight or flight system. And also, catecholamines are going to be hormones such as dopamine, norepinephrine, and epinephrine which you may know as adrenaline. Lastly, we have the hormonal stimulus. With the hormonal stimulus, hormones are going to stimulate other endocrine glands to release their hormones.

02:53 A good example of this is the hormones of the hypothalamus. Hypothalamic hormones stimulate the release of most of our anterior pituitary hormones. Anterior pituitary hormones stimulate targets to secrete more hormones. Activity of the hypothalamic pituitary target endocrine organ feedback loop are going to cause hormones from the final target organs to inhibit release of the anterior pituitary organs. The anterior pituitary releases hormones that are going to trigger the release of things like testosterone. Consequently, high testosterone levels inhibit the release of those hormones. The nervous system can make adjustments to hormone levels when needed. This is referred to as nervous system modulation. It can modify stimulation or inhibition of certain endocrine glands. The nervous system can also override normal endocrine controls. An example of this is when you're under severe stress the hypothalamus and your sympathetic nervous system can override the insulin from the pancreas to allow blood glucose levels to increase and prepare your body for the fight or flight response.