Formed as the result of a fusion between an upward growing ectodermal extension from the roof of the primitive buccal cavity called Rathke s pouch and a The Pituitary Gland 1 The Anterior Lobe Adenohypophysis Introduction Embryological derivation Regulation of hormone production by other endocrine glands elsewhere in the body downward ectodermal extension from the developing diencephalon during the fifth week of development The part of the gland which developed from the buccal cavity forms the anterior lobe of the pituitary The downward growth forms the posterior lobe General structure The pituitary gland lies within a depression in the sphenoid bone sella turcica Nerve terminals and Herring bodies of the magnocellular neurons are full of secretory granules pars tuberalis Posterior lobe During pregnancy the anterior pituitary increases in size Specialized glial cells called pituicytes Pars intermedia unknown function in humans The anterior pituitary and its link to the hypothalamus primary capillary plexus The main bulk of the anterior lobe of the pituitary is called the pars distalis while the upper part which wraps around the infundibulum is known as the Hypothalamic control over the adenohypophysis was exerted by molecules released from nerve terminals in close proximity to the capillary walls of the Identification of TRH and GnRH by Roger Guillemin and Andrzej Schally won the Nobel Prize in Medicine in 1977 Hypothalamic hormones stimulate specific endocrine cells in the adenohypophysis and are therefore called releasing hormones Hypothalamic neurons and their hormones The axons of many hypothalamic neurons terminate adjacent to the capillaries in the median eminence Neurons function like other neurons when stimulated appropriately Neurosecretion is released into the surrounding interstitial fluid from which the molecules enter the blood flowing through the primary capillary plexus in the The pulsatile nature of hypothalamic hormone release into the median eminence is essential in determining not only the nature but also the amount of anterior median eminence Portal system carries hormone to target cell in the anterior pituitary pituitary hormone to be released TRH mainly exerts stimulatory control of TSH CRH acts in conjunction with vasopressin VP to regulate ACTH release If a pituitary tumor develops and grows to such a size that it pushes up into the hypothalamus above it can disrupt the optic nerve fibers crossing over in the cid 127 Occasionally the loss of vision from the outer temporal visual fields is an early indicator of the presence of a growing pituitary tumor Stimulate the growth and maintenance of their target tissues trophins cid 127 GnRH controls the release of LH and FSH cid 127 GHRH controls the release of growth hormone Inhibited by somatostatin Pituitary tumors and the optic chiasma optic chiasma Known as bitemporal hemianopia The adenohypophysial hormones Prolactin breast Somatotrophin general soma liver cid 127 Gonadotrophins testis male ovary female Thyrotrophin thyroid Corticotrophin adrenal cortex Pulsatile release The adenohypophysial protein hormones Somatotrophin GH Synthesis storage release and transport Synthesized by somatotrophs cid 127 Greatly influenced by the CNS through the hypothalamus and its hormones cid 127 Most of them have other endocrine glands as their principal targets Stored in intracellular granules secreted into the blood by exocytosis Stimulate the growth and maintenance of the general tissues of the body Released in pulses throughout the day The GH receptor and mechanism of action Binds to the extracellular component of two receptors which then dimerize Intracellular messenger system involves JAK2 tyrosine kinase induced autophosphorylation cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 Stimulate specific target gene transduction and new protein synthesis Stimulates its own self regulation by the activation of another set of intracellular proteins called suppressor of cytokine signaling proteins which disrupt the JAK2 pathway Receptors are found in most tissues and organs of the body with a particularly high concentration on liver cells The liver is an important target organ for GH and is an endocrine gland in its own right The structural similarities between the IGF and insulin molecules account for the affinities of these hormones for each other s receptors Produces insulin like growth factors 1 and 2 The insulin like growth factors IGF1 and IGF2 Both IGF1 and IGF2 are important in promoting fetal growth Carried in the blood by IGFBPs IGFR1 and IGFR2 are specific for the IGF molecules The insulin receptor also binds 100 fold lower affinity Physiological actions of GH cid 127 Metabolic and growth promoting actions Protein metabolism increased muscle mass Carbohydrate metabolism raise blood glucose concentration Fat metabolism stimulates lipolysis cid 127 Other GH actions IGFR2 has higher affinity for IGF2 and appears to mainly direct it to an intracellular degradation pathway Acts on tissues directly via its own receptors and indirectly by stimulating the release of IGF1 from the hepatocytes of the liver Immunoregulation stimulates the proliferation of T and B cells Prolactin like effects promotes ductal elongation in the mammary glands during puberty Central effects Reproduction promotes the growth and development of secondary sexual characteristics Clinical presentations of hypo and hyper production of GH Lack of GH results in short stature pituitary dwarfism while an excessive production results in gigantism In hypo secretion of GH there is a tendency for increased adiposity and decreased muscle mass while in the hypersecretion state acromegaly gigantism increased insulin resistance can manifest itself ultimately as secondary diabetes mellitus together with the excessive growth of soft tissues Control of GH secretion Central influence Chiefly from the hypothalamus via GH releasing hormone GHRH Circadian variation with greater pulses during the night cid 127 Metabolic and associated factors increase GH synthesis Exercise is a potent stimulator of GH release Hormonal influences Certain amino acids including excitatory amino acids such as glutamate and aspartate as