Introduction To Endocrine PhysiologyArnold A Berthold (1803-1861)Ablation and replacementSlide 4Endocrine system maintains homeostasisCharles Edouard Brown-Séquard (1817-1894)Ernest Henry Starling (1866-1927)Sensing and signalingEndocrine vs. Nervous SystemNervous systemHormones travel via the bloodstream to target cellsA cell is a target because is has a specific receptor for the hormonePrincipal functions of the endocrine systemTypes of cell-to-cell signalingResponse vs. distance traveledMajor hormones and systemsTypes of hormonesPeptide/protein hormonesSlide 19Slide 20Peptide/protein hormone synthesisAmine hormonesThyroid HormoneThyroid hormonesCatecholamine hormonesSynthesis of catecholaminesAmine HormonesSteroid hormonesTypes of steroid hormonesSlide 30Slide 31Steroid hormone synthesisSlide 331,25-Dihydroxy Vitamin D3Fatty Acid Derivatives - EicosanoidsSlide 36Regulation of hormone secretionControl of Endocrine ActivitySlide 39Slide 40Slide 41Slide 42Feedback Control of Hormone ProductionInputs to endocrine cellsNeural controlFeedback controlNegative feedback effects of cortisolSubstrate-hormone controlFeedback control of insulin by glucose concentrationsIntroduction To Endocrine PhysiologyArnold A Berthold (1803-1861) •In one of the first endocrine experiments ever recorded, Professor Arnold A. Berthold of Gottingen did a series of tests on roosters in 1849 while he was curator of the local zoo.Ablation and replacement•Bethold found that a rooster's comb is an androgen-dependent structure. Following castration, the comb atrophies, aggressive male behavior disappears, and interest in the hens is lost.•Importantly, Berthold also found that these castration-induced changes could be reversed by administration of a crude testicular extract (or prevented by transplantation of the testes).Claude Bernard(1813-1878)Claude Bernard stated that the endocrine system regulates the internal milieu of an animal. The “internal secretions” were liberated by one part of the body, traveled via the bloodstream to distant targets cells. Circa 1854Bernard's charge was to demonstrate that medicine, in order to progress, must be founded on experimental physiology.Endocrine system maintains homeostasisThe concept that hormones acting on distant target cells to maintain the stability of the internal milieu was a major advance in physiological understanding. The secretion of the hormone was evoked by a change in the milieu and the resulting action on the target cell restored the milieu to normal.The desired return to the status quo results in the maintenance of homeostasisCharles Edouard Brown-Séquard (1817-1894) •Brown-Sequard further piqued mainstream scientific interest in the chemical contents of the testes with his famous auto-experimentation. On June 1, 1889, before the Sociète de Biologic in Paris, Brown-Sequard reported that he had increased his physical strength, mental abilities and appetite by self-injection with an extract derived from the testicles of dogs and guinea pigs•Although never substantiated, this claim prompted researchers around the world to pursue the new field of organotherapyErnest Henry Starling (1866-1927)•Besides "his" law of the heart, Starling discovered the functional significance of serum proteins. •In 1902 along with Bayliss he demonstrated that secretin stimulates pancreatic secretion. •In 1924 along with E. B. Vernay he demonstrated the reabsorption of water by the tubules of the kidney.•He was the first to use the term hormoneSensing and signalingEndocrine “glands” synthesize and store hormones. These glands have a sensing and signaling system which regulate the duration and magnitude of hormone release via feedback from the target cell.Endocrine vs. Nervous System•Major communication systems in the body•Integrate stimuli and responses to changes in external and internal environment•Both are crucial to coordinated functions of highly differentiated cells, tissues and organs•Unlike the nervous system, the endocrine system is anatomically discontinuous.Nervous system•The nervous system exerts point-to-point control through nerves, similar to sending messages by conventional telephone. Nervous control is electrical in nature and fast.Hormones travel via the bloodstream to target cells•The endocrine system broadcasts its hormonal messages to essentially all cells by secretion into blood and extracellular fluid. Like a radio broadcast, it requires a receiver to get the message - in the case of endocrine messages, cells must bear a receptor for the hormone being broadcast in order to respond.A cell is a target because is has a specific receptor for the hormoneMost hormones circulate in blood, coming into contact with essentially all cells. However, a given hormone usually affects only a limited number of cells, which are called target cells. A target cell responds to a hormone because it bears receptors for the hormone.Principal functions of the endocrine system•Maintenance of the internal environment in the body (maintaining the optimum biochemical environment).•Integration and regulation of growth and development.•Control, maintenance and instigation of sexual reproduction, including gametogenesis, coitus, fertilization, fetal growth and development and nourishment of the newborn.Types of cell-to-cell signalingClassic endocrine hormones travel via bloodstream to target cells; neurohormones are released via synapses and travel via the bloostream; paracrine hormones act on adjacent cells and autocrine hormones are released and act on the cell that secreted them. Also, intracrine hormones act within the cell that produces them.Response vs. distance traveledEndocrine action: the hormone is distributed in blood and binds to distant target cells.Paracrine action: the hormone acts locally by diffusing from its source to target cells in the neighborhood.Autocrine action: the hormone acts on the same cell that produced it.Major hormones and systems•Top down organization of endocrine system.•Hypothalamus produces releasing factors that stimulate production of anterior pituitary hormone which act on peripheral endocrine gland to stimulate release of third hormone–Specific examples to follow•Posterior pituitary hormones are synthesized in neuronal cell bodies in the hypothalamus and are released via synapses in posterior pituitary. –Oxytocin and antidiuretic hormone (ADH)Types of