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Growth Hormone Releasing Hormone
Stimulates the release of Growth Hormone from the anterior pituitary
Growth Hormone Inhibiting Hormone
Inhibits the release of Growth Hormone from the anterior pituitary
Corticotropin Releasing Hormone
Stimulates the release of Adrenocorticotropic Hormone from the anterior pituitary
Gonadotropin Releasing Hormone
Stimulates the relase of Luteinizing Hormone and Follicle Stimulating Hormone from the anterior pituitary
Thyrotropin Releasing Hormone
Stimulates the release of Thyroid Stimulating Hormone from the anterior pituitary
Hypothalamohypophysial Portal System
Blood vessels that extend from the hypothalamus to the ANTERIOR pituitary
How does the hypothalamus control the anterior pituitary?
1. Stimuli within the nervous system increase or decrease the secretion of releasing hormones and inhibiting hormones from neurons of the hypothalamus
2. Releasing hormones and inhibiting hormones pass through the hypothalamohypophysial portal system to the anterior pituitary
3. Releasing hormones and inhibiting hormones bind to membrane-bound receptors and stimulate or inhibit the release of hormones from anterior pituitary cells
4. Anterior pituitary hormones are carried in the blood to their target tissues, which in some cases are other glands
How does the hypothalamus control the posterior pituitary?
1. Stimuli within the nervous system stimulate hypothalamic neurons to either increase or decrease their action potential frequency
2. Action potentials are carried by axons of the hypothalamic neurons through the hypothalamohypophyseal tract to the posterior pituitary. The axons of the neurons store hormones in the posterior pituitary
3. In the posterior pituitary gland, action potentials cause the release of hormones from axon terminals into the circulatory system
4. The hormones pass through the circulatory system and influence the activity of their target tissues
Function of GHRH and GHIH
1. Stress and decreased blood glucose levels increase the release of Growth Hormone Releasing Hormone (GHRH) and decrease the release of Growth Hormone Inhibiting Hormone (GHIH)
2. GHRH and GHIH travel through the hypothalamohypophyseal portal system to the anterior pituitary
3. Increased GHRH and reduced GHIH act on the anterior pituitary and result in increased Growth Hormone secretion
4. Growth Hormone acts on target tissue
5. Increasing growth hormone has a negative feedback effect on the hypothalamus, resulting in decreased GHRH and increased GHIH
Function of TRH
1. Thyrotropin Releasing Hormone (TRH) is released from the hypothalamus. It passes through the hypothalamohypophyseal portal system to the anterior pituitary
2. TRH causes cells of the anterior pituitary to release Thyroid Stimulating Hormone (TSH), which passes through the general circulation to the thyroid gland
3. TSH causes increase release of T₄ and T₃ into the general circulation
4. T₄ and T₃ act on target tissues
5. T₄ and T₃ also have an inhibitory effect on the secretion of TRH from the hypothalamus and TSH from the anterior pituitary
1. Corticotropin Releasing Hormone (CRH) is released from the hypothalamus in response to stress or low blood glucose. It passes through the hypothalamohypophyseal portal system to the anterior pituitary
2. CRH stimulates the secretion of Adrenocorticotropic Hormone (ACTH) from the anterior pituitary
3. ACTH stimulates the secretion of cortisol from the adrenal cortex
4. Cortisol acts on target tissues, resulting in increased fat and protein breakdown, increasing glucose levels and anti-inflammatory effects
5. Cortisol has a negative feedback effect because it inhibits CRH release from the hypothalamus and ACTH release from the anterior pituitary
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