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Made up of numerous glands, the endocrine system works with the nervous system to regulate the body. One gland involved in body regulation is the pituitary gland, which secretes different hormones, including growth hormone. Growth hormone release from the pituitary gland is controlled by a growth-hormone-releasing hormone, and is inhibited by a growth-hormone-inhibiting hormone, also called somatostatin. This inhibition occurs when somatostatin binds to a somatostatin receptor located near the front of the pituitary called the anterior pituitary. A protein located on the neuron's cell membrane, a somatostatin receptor recognizes and binds to the hormone somatostatin.
Being an endocrine gland, the pituitary gland is involved in homeostasis, a process that regulates organs in the body according to internal and external changes. One of the major interactions between the brain and the endocrine system is between the hypothalamus and the pituitary gland. The pituitary gland secretes hormones within the body, and the hypothalamus regulates those secretions via the hypothalamohypophysial portal system.
The hypothalamohypophysial portal system runs between the hypothalamus the anterior pituitary, to which it is connected. This system is made up of a primary capillary network located in the hypothalamus and a secondary capillary network located in the anterior pituitary. Growth hormone is produced by neurons in the hypothalamus that move through the primary capillary network into the secondary capillary network, causing either releasing hormones or inhibiting hormones in the anterior pituitary.
Growth hormone secreted by the pituitary gland works to stimulate cell division and bone growth in the body, thereby determining how tall an individual will be. It also plays a role in the regulation of metabolism by controlling nutrient levels in blood during fasting and after meals. The hypothalamus secretes two hormones — growth-hormone-releasing hormone (GHRH) and growth-hormone-inhibiting hormone (GHIH), also called somatostatin — which regulate the secretion of growth hormone.
Just as the names indicate, GHRH acts to release growth hormone from the anterior pituitary, while GHIH, or somatostatin, acts to inhibit or stop growth hormone release. Somatostatin can inhibit growth hormone from releasing when it binds to a metabotropic receptor called a somatostatin receptor. A metabotropic receptor is one that does not have ion channels where ions can move through. A flow of ions through ion channels either activates or inhibits the neuron on which the receptor is located, so in order for a metabotropic receptor to be activated or inhibited, several metabolic processes must occur. When the hormone somatostatin binds to a somatostatin receptor, it results in the activation of a second messenger system, which inhibits the release of growth hormone.