{"id":4422314,"date":"2025-01-11T13:22:47","date_gmt":"2025-01-11T19:22:47","guid":{"rendered":"https:\/\/myendoconsult.com\/learn\/topics\/pituitary-physiology\/"},"modified":"2025-01-13T06:47:23","modified_gmt":"2025-01-13T12:47:23","slug":"pituitary-physiology","status":"publish","type":"oen_topic","link":"https:\/\/myendoconsult.com\/learn\/topics\/pituitary-physiology\/","title":{"rendered":"Pituitary Physiology"},"content":{"rendered":"\n

ANTERIOR PITUITARY HORMONES AND FEEDBACK CONTROL<\/h2>\n\n\n\n

Triple-Level Control<\/h3>\n\n\n\n
    \n
  1. Hypothalamic Regulation<\/strong>\n
      \n
    • Releasing and inhibiting hormones (via the hypophysial portal circulation) act on G-protein\u2013linked receptors in the pituitary, altering gene transcription and hormone secretion.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
    • Target Gland Feedback<\/strong>\n
        \n
      • Circulating hormones from target glands (e.g., cortisol, thyroid hormone) exert negative feedback on their respective pituitary trophic hormones.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
      • Intrapituitary Regulation<\/strong>\n
          \n
        • Autocrine and paracrine cytokines\/growth factors locally modulate pituitary cell development and function.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n

          Hypothalamic Releasing\/Inhibiting Hormones<\/h3>\n\n\n\n
            \n
          • Releasing Hormones<\/strong>: GHRH, CRH, TRH, GnRH.<\/li>\n\n\n\n
          • Inhibitory Hormones<\/strong>: Somatostatin (inhibits GH) and Dopamine (inhibits prolactin).<\/li>\n<\/ul>\n\n\n\n

            Anterior Pituitary Hormones<\/h3>\n\n\n\n
              \n
            1. Corticotropin (ACTH)<\/strong><\/li>\n\n\n\n
            2. Growth Hormone (GH)<\/strong><\/li>\n\n\n\n
            3. Thyrotropin (TSH)<\/strong><\/li>\n\n\n\n
            4. Follicle-Stimulating Hormone (FSH)<\/strong><\/li>\n\n\n\n
            5. Luteinizing Hormone (LH)<\/strong><\/li>\n\n\n\n
            6. Prolactin<\/strong><\/li>\n<\/ol>\n\n\n\n
                \n
              • All are secreted pulsatilely<\/strong> into the systemic circulation.<\/li>\n<\/ul>\n\n\n\n

                Hypothalamic\u2013Pituitary\u2013Target Gland Feedback Loops<\/h3>\n\n\n\n
                  \n
                • Negative Feedback<\/strong>: Target gland hormones inhibit further pituitary\/hypothalamic secretion (most common).<\/li>\n\n\n\n
                • Positive Feedback<\/strong>: The target gland hormone or a surrogate may enhance pituitary\/hypothalamic release (less common).<\/li>\n\n\n\n
                • Closed Loop vs. Open Loop<\/strong>:\n
                    \n
                  • Closed Loop<\/strong>: Involves only the trophic hormone and its target gland hormone.<\/li>\n\n\n\n
                  • Open Loop<\/strong>: Includes influence from the nervous system (emotional or external stimuli) that can adjust or override the standard feedback.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n

                    Other Factors in Feedback<\/h3>\n\n\n\n
                      \n
                    • Inhibin<\/strong>: A glycoprotein from Sertoli (testes) or granulosa (ovary) cells provides negative feedback on FSH secretion.<\/li>\n\n\n\n
                    • Endogenous Secretory Rhythms<\/strong>:\n
                        \n
                      • Circadian \/ Diurnal Rhythms<\/strong>: ~24-hour cycle.\n
                          \n
                        • E.g., GH and prolactin peak after sleep onset; cortisol peaks ~2\u20136 AM, lowest ~11 PM; testosterone highest in the morning.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
                        • Ultradian Rhythms<\/strong>: Occur more frequently than once a day.<\/li>\n\n\n\n
                        • Infradian Rhythms<\/strong>: Periods longer than a day (e.g., menstrual cycle).<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n

                          Clinical Considerations<\/h3>\n\n\n\n
                            \n
                          • Pulsatile Secretion<\/strong>: A single GH measurement may not reflect overall GH status; IGF-1<\/strong> is a more stable index.<\/li>\n\n\n\n
                          • Time-of-Day Reference Ranges<\/strong>: E.g., cortisol reference range differs between morning and afternoon blood draws.<\/li>\n\n\n\n
                          • Loss of Normal Rhythms<\/strong>: E.g., high midnight cortisol supports the diagnosis of Cushing syndrome (disrupted circadian rhythm).<\/li>\n<\/ul>\n\n\n\n
                            \n\n\n\n

                            POSTERIOR PITUITARY GLAND<\/h2>\n\n\n\n

                            Anatomy and Embryology<\/h3>\n\n\n\n
                              \n
                            • Neural Tissue<\/strong>: Formed by the distal axons<\/strong> of neurons in the supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus.<\/li>\n\n\n\n
                            • Hormones Stored<\/strong>: Vasopressin (ADH) and Oxytocin.<\/li>\n\n\n\n
                            • Vasopressin & Oxytocin<\/strong>: Nonapeptides (6\u2013amino acid ring with disulfide bridge + 3\u2013amino acid tail).<\/li>\n\n\n\n
                            • Blood Supply<\/strong>: Inferior hypophysial arteries, draining into the cavernous sinus \u2192 internal jugular vein.<\/li>\n<\/ul>\n\n\n\n

                              Storage and Release<\/h3>\n\n\n\n
                                \n
                              • Storage Capacity<\/strong>: Enough vasopressin to sustain basal release ~30 days and maximal release ~5 days.<\/li>\n\n\n\n
                              • Axonal Transport<\/strong>: ~90% of SON neurons produce vasopressin; the PVN also makes other peptides (somatostatin, CRH, TRH, opioids).<\/li>\n\n\n\n
                              • Secretion<\/strong>: An action potential from SON\/PVN travels down the axon, causing Ca\u00b2\u207a influx and exocytosis of neurosecretory granules into fenestrated capillaries in the posterior pituitary.<\/li>\n<\/ul>\n\n\n\n

                                Posterior Pituitary Bright Spot<\/h3>\n\n\n\n
                                  \n
                                • MRI Feature<\/strong>: T1-weighted hyperintensity reflecting vasopressin stored in neurosecretory granules.<\/li>\n\n\n\n
                                • Absent<\/strong> in central diabetes insipidus.<\/li>\n\n\n\n
                                • Ectopic Location<\/strong>: In some congenital cases, the bright spot is found along the stalk or at the hypothalamic base; can be associated with a hypoplastic anterior pituitary and variable anterior pituitary dysfunction.<\/li>\n<\/ul>\n\n\n\n
                                  \"Anatomical
                                  MRI of the pituitary gland (coronal section) showing its relevant anatomical relationships<\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"

                                  ANTERIOR PITUITARY HORMONES AND FEEDBACK CONTROL Triple-Level Control Hypothalamic Releasing\/Inhibiting Hormones Anterior Pituitary Hormones Hypothalamic\u2013Pituitary\u2013Target Gland Feedback Loops Other Factors in Feedback Clinical Considerations POSTERIOR PITUITARY GLAND Anatomy and Embryology Storage and Release Posterior Pituitary Bright Spot<\/p>\n","protected":false},"featured_media":0,"template":"","oen_topic_chapter":[682],"class_list":["post-4422314","oen_topic","type-oen_topic","status-publish","hentry","oen_topic_chapter-pituitary-gland","post-wrapper","thrv_wrapper"],"_links":{"self":[{"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/oen_topic\/4422314","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/oen_topic"}],"about":[{"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/types\/oen_topic"}],"version-history":[{"count":3,"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/oen_topic\/4422314\/revisions"}],"predecessor-version":[{"id":4422778,"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/oen_topic\/4422314\/revisions\/4422778"}],"wp:attachment":[{"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/media?parent=4422314"}],"wp:term":[{"taxonomy":"oen_topic_chapter","embeddable":true,"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/oen_topic_chapter?post=4422314"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}