EndocrinologyHypothalamic Control of the Hypophysis



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Source: The McGraw-Hill Companies, Inc.





The hypophysis, or pituitary gland, is divided into two lobes, the anterior or adenohypophysis and the posterior or neurohypophysis, and is attached to the hypothalamus by the infundibulum. These two parts are not only structurally divided, but also functionally divided. The anterior pituitary produces and secretes its own hormones into the blood stream, while the posterior pituitary stores hormones produced in the hypothalamus and the release of these hormones is controlled by neural regulation.

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Source: Addison Wesley Longman, Inc


The actions of the anterior pituitary gland are controlled by hormones produced in the hypothalamus. Hormones that control the adenohypophysis are produced by neurons in the hypothalamus, but because there are no neurons connecting the hypothalamus to the adenohypophysis, these hormones are transported to an area called the median eminence where axons release the hormones. The median eminence contains blood capillary beds that are drained into a second capillary bed in the anterior pituitary gland. This portal system is known as the hypothalamo-hypophyseal portal system. The hormones received by the anterior pituitary regulate the secretion of its hormones. For example, the hypothalamus will release the hormone TRH, thyrotropin-releasing hormone, which causes the adenohypophysis to release TSH, thyroid stimulating hormone.

The hypothalamus controls the neurohypophysis with neuroendocrine reflexes. As the hypothalamus produces hormones they are sent to the posterior pituitary via axons through the hypothalamo-hypophyseal tract. The secretion of these hormones from the neurohypophysis are triggered by reflexes via sensory nerve impluses. For example, when a baby suckles at his mother's breast, nerve impulses will trigger the release of oxytocin.

Understanding the hypothalamus may help you to understand how it controls and sends hormones to the hypophysis. This video from www.youtube.com explains this in an easy to understand format. http://www.youtube.com/watch?v=PMrPlCDGUwo


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Areas that the hormones of the pituitary gland affect. Source: www.cartage.org.lb/.../NervousEndocrine.htm


The hormones secreted by the anterior pituitary gland are known as trophic hormones. Trophic hormones in high concentrations can cause their targets to hypertrophy or have high blood levels. If in low concentrations, it would be called atrophy or have low blood levels. Basically, the hormones in the anterior pituitary influence another gland to secrete a hormone. An example of this would be the thyroid-stimulating hormone. The anterior pituitary gland produces and secretes TSH which, in turn, causes the thyroid gland to produce and secrete thyroxine (T4) and triiodothyronine (T3). In hormones of the anterior pituitary gland, trophic has been shortened to tropic, meaning attracted to. For example, growth hormone is also known as somatotropin.


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Pituitary Hormones Source: www.medical-look.com/.../Pituitary_hormones.html


As a practical nursing student, it is important that I am aware of not only what the glands and their hormones regulate, but also what excessive or deficient secretion will do to the patient. In hypothyroidism, the patient may have dry skin and hair, goiter, intolerance to cold, bradycardia, and many other symptoms. It is necessary to monitor patients for these signs and symptoms to not only make sure that they are receiving the proper nursing cares, but to also chart them so the doctor can determine if the treatments are effective. I am also careful to watch for the signs in myself as my mom, her sisters, and her mom all have this condition, thereby increasing my risk for developing the same problem. I am very aware of my dry skin and hair, my level of thirst, and my weight. It has been several years since I have been tested, but know that I must keep my doctor informed of any changes to determine if further testing is necessary.



Sources:
Fox, Stuart Ira. Human Physiology, 10th Edition. Chapter 11 Endocrine Glands: Secretion and Action of Hormones
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Video: www.youtube.com/How It Works