Endocrinology 14th October 2016 Growth Hormones and Factors Recap - Hormones Hormones are chemical messengers released from one tissue, which produce a specific, receptor-mediated change in another tissue. Hormones can be peptide (Insulin) or steroid (Testosterone). Hormones have a range of actions and are an essential component of endocrine axis. They are of control and regulated by the hypothalamus and pituitary control. Growth Hormones and Growth factors Growth is tightly regulated by a selection of hormones, as animals need to coordinate the growth of all their cells: - Growth hormone (GH) - Insulin like growth factors (IGFs) - Insulin - Other factors (less common or important, some cell specific) Size 1 Aston University Division Differentiation Growth Hormone Axis The hypothalamus is a specialised region outside the BBB, which instructs the pituitary gland to secrete hormones. Hypothalamus The anterior pituitary gland secretes growth hormone - instructed by the hypothalamus. Anterior Pituitary The liver responds to the hormone and is instructed to secrete another hormone that will instruct the receiving cells. Liver Growth Hormone: Hypothalamic Involvement I The hypothalamus can be divided into discrete areas based on function. Proliferation/Differentiation/Metabolism Hypothalamus regulates the system from the top by releasing stimulatory and inhibitory releasing factors. It releases the Growth Hormone Releasing Hormone (GHRH) (somatocrinin, stimulatory).
14th October 2016 Endocrinology GHRH is a 44 amino acid peptide hormone, which is produced in the arcuate nucleus of the hypothalamus. It is released in a pulsing action from the neurosecretory terminals of the arcuate neurons. Growth Hormone: Hypothalamic Involvement II Hypothalamus regulates the system from the top by releasing stimulatory and inhibitory releasing factors. It releases the Growth Hormone Inhibiting Hormone (GHIH) (somatostatin, inhibitory). GHIH is a peptide hormone with two active forms: 14 and 28 amino acid. It is produced in the periventricular nucleus of the hypothalamus and released from the parvicellular neurones at the median eminence. The release is regulated by high levels of GH and IGFs; it is self regulated - feedback. GHIH is produced in other areas of the body such as the stomach, intestine, and pancreas, where its release regulates peripheral functions. Growth Hormone: Hypothalamic Involvement III GHRH GHIH hypothalamic-hypophysial portal system GHRH receptor GHIH receptors (1, 2, 3 and 5 expressed in pituitary) rsity Anterior Pituitary The hypothalamus can release either or both. Growth Hormone: Pituitary Involvement Anterior Lobe Pars tuberalis Pars distalis Hypothalamus 50% of pituitary cells are 'somatotrophs' - they release Growth Hormone. GH is released from the Pars distalis in the anterior lobe. Growth Hormone Posterior Lobe
14th October 2016 Endocrinology Growth Hormone GH is a 191 amino acid peptide hormone. Its secretion is increased in the first two hours of sleep, using the circadian rhythm. GH circulates bound to specific plasma proteins, and negatively regulates its own production - negative feedback system. Its physiological effects are: - Increases muscle mass - Increases protein mass - Stimulates organ growth - Increases bone mass - Maintains pancreatic islets - Stimulates immune system - Hepatic effects Growth hormone can have