Regulation of Hormone Secretion 14-May-19 Regulation of Hormone Secretion

Negative Feedback Mechanism Hormones produce biological effects On attaining sufficient magnitude Inhibit further secretion 14-May-19 Regulation of Hormone Secretion

Components of the System (1) A detector of the Actual or threatened homeostatic imbalance (2) means of signaling secretion (3) the secretory cells 14-May-19 Regulation of Hormone Secretion

Components of the System (4) an end organ or Organ capable of an appropriate response to the hormone (5) A means of promptly shutting of secretion When response becomes adequate to restore homeostasis 14-May-19 Regulation of Hormone Secretion

Components of the System In simpler cases Parathyroid, -cells of the pancreas Components 1, 2, 3, & 5 reside in the same secretory cells In complex situation Thyroid secretion Complex interactions between CNS, anterior pituitary gland & thyroid gland 14-May-19 Regulation of Hormone Secretion

Regulation of Hormone Secretion Types of Imputes Most hormones are released in short burst With no or little release in between the bursts 14-May-19 Regulation of Hormone Secretion

Regulation of Hormone Secretion Types of Imputes Plasma concentration of hormones may fluctuate rapidly over brief times Hormones also manifest 24 hrs cyclical variation in their secretory pattern Circadian pattern differ in different hormones Some are linked to sleep GH - during early period of sleep 14-May-19 Regulation of Hormone Secretion

Control of Hormone Secretion Some of factors that influence the secretion of hormones include Neurotransmitters Another hormone Changes in plasma conc of nutrients Changes in plasma conc of mineral ions Neurotransmitters Another hormone Plasma conc of organic nutrient Endocrine cell Changes in plasma conc of mineral ions Hormone secretion 14-May-19 Regulation of Hormone Secretion

Control of Hormone Secretion Endocrine cells like neurons May be subject to multiple simultaneous inputs Sometimes opposing The resulting output Rate of secretion of hormone Reflect the integration of all these inputs 14-May-19 Regulation of Hormone Secretion

Control by conc of Nutrient  Plasma glucose conc Hormone secretion is controlled by Plasma conc of nutrient or organic ions The function of the hormone To regulate in negative manner Plasma conc of nutrient or ions Controlling its secretion Insulin secreting cells  INSULIN in plasma  Action of insulin by target cells  Plasma glucose conc 14-May-19 Regulation of Hormone Secretion

Regulation of Hormone Secretion Control by Neurons Hypothalamus Has neural control over hormone secretion by the posterior pituitary 14-May-19 Regulation of Hormone Secretion

Hypothalamic –Hypophysial Axes Secretory activity of anterior pituitary Controlled by hypothalamic hormone Secreted into hypothalamic hypophysial portal system Supra optic nucleus Hypothalamic neurosecretions Hypo-physiotropic hormones secreted Superior hypophysial artery Posterior pituitary hormones Anterior pituitary hormones vein 14-May-19 Regulation of Hormone Secretion

Hypophysial Portal System Median eminence Specialized area of hypothalamus Located beneath the 3rd ventricle It is a release center for hypophysiotropic hormones Supra optic nucleus Hypothalamic neurosecretions Hypo-physiotropic hormones secreted Superior hypophysial artery Posterior pituitary hormones Anterior pituitary hormones vein 14-May-19 Regulation of Hormone Secretion

Hypothalamic –Hypophysial Axes Limbic system The hypothalamus Secrete releasing or inhibiting hormone Hypophysiotropic hormone These act on the anterior pituitary Anterior pituitary then secrete Trophic hormone Hypothalamus Hypophysiotropic hormones Adeno-hypophysis Pit. Tropic hormones Target gland hormone Target gland 14-May-19 Regulation of Hormone Secretion

Hypothalamic –Hypophysial Axes Limbic system The trophic hormone then Act on target gland Secrete the hormone Hypothalamus Hypophysiotropic hormones Adeno-hypophysis Pit. Tropic hormones Target gland hormone Target gland 14-May-19 Regulation of Hormone Secretion

Feedback Control Systems Limbic system The unbound circulating hormone Produced by target gland Inhibit hypothalamic pituitary system Cause  secretion of pituitary tropic hormone Control the secretion of target gland Hypothalamus Hypophysiotropic hormones Adeno-hypophysis Pit. Tropic hormones Target gland hormone Target gland 14-May-19 Regulation of Hormone Secretion

Feedback Control Systems Limbic system Negative feedback control occur on 3 levels Long loop feedback Peripheral gland hormones or Substrate arising from metabolism Hypothalamus Hypophysiotropic hormones Adeno-hypophysis Pit. Tropic hormones Target gland hormone Target gland 14-May-19 Regulation of Hormone Secretion

Feedback Control Systems Limbic system Can exert long-loop feedback control on Hypothalamus Anterior pituitary Long-loop feedback system Usually are negative feedback But can be positive feedback as well Hypothalamus Hypophysiotropic hormones Adeno-hypophysis Pit. Tropic hormones Target gland hormone Target gland 14-May-19 Regulation of Hormone Secretion

Feedback Control Systems Limbic system Short-loop feedback system Negative feedback can be exerted by Anterior pituitary hormone on the Synthesis and release of hypothalamic releasing or inhibiting hormones Hypothalamus Hypophysiotropic hormones Adeno-hypophysis Pit. Tropic hormones Target gland hormone Target gland 14-May-19 Regulation of Hormone Secretion

Feedback Control Systems Limbic system Ultra-short loop feedback Hypophysiotropic hormones Can inhibit their own synthesis and secretion Hypothalamus Hypophysiotropic hormones Adeno-hypophysis Pit. Tropic hormones Target gland hormone Target gland 14-May-19 Regulation of Hormone Secretion