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The Endocrine Glands Their hormones, their target organs and major functions The Endocrine system I Hormones are generally secreted into the blood and then circulate trough the body to exert an effect only on their target cells. They act by binding in a lock-and-key manner with specific receptores found only in the target tissues. The Endocrine system II Hormones can be classified as either steroid or non-steroid. Steroid hormones are lipid soluble, and most are formed from cholesterol. Non-steroid hormones are formed from proteins, peptides or aminoacids The Endocrine system III Steroid hormones pass trough cell membranes and bind to receptors inside the cell. They use a mechanism called direct gene activation to cause protein synthesis. Nonsteroid hormones cannot enter the cells easily, so they bind to receptors on the cell membrane. This activates a second messenger within the cell, which in turn can trigger numerous cellular processes. Endocrine System: Steroid Hormone Action The Endocrine system III Steroid hormones pass trough cell membranes and bind to receptors inside the cell. They use a mechanism called direct gene activation to cause protein synthesis. Non-steroid hormones cannot enter the cells easily, so they bind to receptors on the cell membrane. This activates a second messenger within the cell, which in turn can trigger numerous cellular processes. Endocrine System: Non Steroid Hormone Action The Endocrine system IV A negative feed-back system regulates secretion of most hormones. The number of receptors for a specific hormone can be altered to meet the body’s demands. Up-regulation refers to an increase in receptors and down-regulation in a decrease. These two processes change cell sensivity to hormones. The negative feedback system A negative feedback system regulates secretion of most hormones. The major exemples are give by the hormones which secretion is controlled by pituitary tropins such as TSH, LH, FSH and ACTH. The pituitary tropin secretion is inibited by raising blood concentration of the hormone released by the tropin target gland Pituitary Gland tropin Target gland Circulating Hormone NEGATIVE FEEDBACK The negative feedback system Pituitary Gland + tropin Target gland Circulating Hormone NEGATIVE FEEDBACK The Pituitary gland I Anterior lobe GH Growth hormone Prolactin ACTH Adrenocorticotropin TSH Thyroid-stimulating hormone FSH Follicle-stimulating hormone LH Luteinizing hormone The Pituitary gland II POSTERIOR LOBE (from Hypotahalamus) ADH Antidiuretic hormone or Vasopressin Oxytocin The Pituitary gland III Anterior lobe Growth hormone (GH) TARGET ORGAN All cells in the body MAJOR FUNCTIONS Promotes developement and enlargement of all body tissues up through maturation; increases rate of protein syntesis; increases mobilization of fats and use of fat as an energy source; decreases rate of carbohydrate use Secrezione e meccanismo di azione del GH Secrezione di GHRH e SS Inibisce GHRH Stimola SS Feedback Ipofisi Inibisce sintesi e rilascio di GH Fegato GH IGF-1 Cappa 1999 Bersaglio Cellulare Secrezione e meccanismo di azione del GH Secrezione di GHRH e SS Inibisce GHRH Stimola SS Feedback Inibisce sintesi e rilascio di GH Ipofisi GH Fegato ed altri organi Azione diretta Azione indiretta Somatomedine Tessuto Adiposo Azioni scheletriche Azioni non scheletriche Formazione collagene Aumento sintesi proteica e crescita cellulare Induce crescita scheletrica Rilascio Trigliceridi Riduce l’assorbimento di Glucosio McArdle 1996 Regolazione della secrezione del GH da parte dei nutrienti e dei substrati metabolici Glucosio FFA Glucosio IPOTALAMO SS GHRH Aminoacidi Intestino FFA IPOFISI GH Muscolo Fegato I GF-1 Gliconeogenesi TessutoAdiposo Lipolisi Sintesi Proteica Utilizzazione del Glucosio Cappa.M: Endocrin.Eser.Fis. Utet 1999 The Pituitary gland IV Anterior lobe HORMONE TARGET ORGAN MAJOR FUNCTIONS Thyroid gland Controls the amount of T3 and T4 produced and released by the thyroid gland ACTH Adrenal cortex Controls the secretion of hormones from the adrenal cortex PROLACTIN Breasts TSH Stimulates breasts developement and milk secretion The Pituitary gland V Anterior lobe HORMONE TARGET ORGAN FSH LH Ovaries, Testes Ovaries, Testes MAJOR FUNCTIONS Initiates growth of follicles inthe ovaries and promotes secretion of estrogen from the ovaries. Promotes developement of sperm in testes. Promotes secretion of estrogen and progesterone and causes the follicle to rupture, releasing the ovum. Causes testes to secrete testosterone The Pituitary gland VI Anterior lobe Hypothalamic Controlling Factors The anterior pituitary gland, also called adenohypophysis, secretes six hormones in response to releasing and inibiting factors (peptides) secreted by hypothalamus. ACTH : stimulated by CRH (corticotropic-realising hormone) GH : stimulated by GHRH (growth hormone realising hormone) Inibited by SOMATOSTATIN TSH : stimulated by TRH (thyrotropin-realising hormone) The Pituitary gland VI Anterior lobe Hypothalamic Controlling Factors FSH : stimulated by GnRH (gonadotropin-realising hormone) LH : stimulated by GnRH PROLACTIN : stimulated by PRH (prolactin-realising hormone) Inibited by PIH (prolactin-inibiting hormone) The Pituitary gland VI Posterior lobe HORMONE TARGET ORGAN ADH Kidneys Uterus, OXYTOCIN Breasts MAJOR FUNCTIONS Assist in controlling water excretion by the kidneys. Elevates blood pressure by constricting blood vessels Stimulates contraction of uterine muscles ; milk secretion The Thyroid gland HORMONES TARGET ORGAN T3 , T4 All cells in Calcitonin MAJOR FUNCTIONS the body Increases the rate of cellular metabolism, increases rate and contractility of the heart Bones Controls calcium-ion concentraction in the blood The Parathyroid glands HORMONE TARGET ORGAN Bones PTH (parathormone) Intestines Kidneys MAJOR FUNCTIONS Controls calcium-ion concentraction in extracellular fluid trough its influence on bones, intestines and kidneys The Adrenal gland Medulla HORMONE TARGET ORGAN Epinephrine Most cells in the body Norepinephrine MAJOR FUNCTIONS Mobilizes glycogen; increases skeletal muscle blood flow; increases heart rate and contractility; oxygen consumption Constricts arterioles and venules, thereby elevating blood pressure The Adrenal gland Cortex HORMONE TARGET ORGAN Mineralcorticoids (Aldosterone) Kidneys Glucocorticoids (Cortisol) Androgens Most cells in the body Ovaries, Testes MAJOR FUNCTIONS Increases sodium retention and potassium axcretion trough the kidneys Controls metabolism of carbohydrates, fats and proteins; anti-infiammatory action Assist in the developement of female and male sex characteristics The Endocrine Pancreas HORMONE TARGET ORGAN MAJOR FUNCTIONS INSULIN Most cells in the body Controls blood glucose levels by lowering glucose levels GLUCAGON Most cells in the body Increases blood glucose; stimulates the breakdown of protein and fat Islets of Langherans SOMATOSTATIN and gastroDepresses the secretion of both intestinal tract insulin and glucagon GONADS I Testes HORMONE TESTOSTERONE TARGET ORGAN Sex organs MAJOR FUNCTIONS Promotes developement of male sex characteristics including growth of testes, Skeletal muscle scrotum and penis, facial hair and change in voice; promotes muscle growth GONADS II Ovaries HORMONE TARGET ORGAN Sex organs ESTROGENS Adipose tissue Bones MAJOR FUNCTIONS Promotes developement of female sex organs and characteristics; provides increased storage of fat; assist in regulating the mestrual cycle. Promotes turn-over of bone tissue stimulating osteoblastyc activity Kidney’s endocrin activity HORMONE ERYTROPOIETIN (EPO) TARGET ORGAN Bone marrow MAJOR FUNCTIONS Stimulates erytrocyte production and realisig Hormonal effects on metabolism and energy I Plasma glucose is increased by the combined actions of glucagon, epinephrine and cortisol. These hormones promote glycogenolysis and gluconeogenesis, thus increasing the amount of glucose available for use as a fuel source. Insulin helps the released glucose enter the cells, where it can be used for energy production.But insulin levels decline during prolonged exercise, indicating that exercise facilitates the action of insulin so that less hormone is required during exercise than at rest. Hormonal effects on metabolism and energy II When carbohydrate reserves are low, the body turns more to fat oxidation for energy, and this process is facilitated by cortisol, epinephrine and GH Cortsol accelerates lipolisys, realising free fatty acid into the blood so they can be taken up by the cells and used for energy production. But cortisol levels peak and then return to near normal levels during prolonged exercise. When this happens, the cathecholamines and GH take over cortisol’s role Hormonal effects on metabolism and energy III. ( Fluid balance ) The two primary hormones involved in the regulation of fluid balance are Aldosterone and ADH (antidiureti hormone) When plasma volume or blood pressure decrease, kidneys form and release in the blood a proteolitic enzyme called Renin that converts Angiotensinogen (a liver producted protein) in Angiotensin I (AT I) , a ten aminoacid peptide with no byological effects. AT I is then converted in AT II by the Angiotensin Converting Enzyme (ACE), in all vascular sides. AT II increases peripheral arterial resistence, raising blood pressure. Hormonal effects on metabolism and energy III. ( Fluid balance ) AT II also triggers the release of Aldosterone from the adrenal cortex. Aldosterone promotes sodium reabsorption in the kidneys, which in turn causes water retention, thus increasing the plasma volume. ADH is released in response to increased plasma osmolarity. When hypothalamic osmoreceptores sense this increase, induce the ADH release from the posterior hypophysis. ADH acts on the kidneys promoting water conservation. Trough this mechanism plasma volume is increased and blood osmolarity is decreased by dilution of plasma solutes. The endocrine response to exercise I HORMONE EXERCISE RESPONSE Catecholamines GH ACTH-Cortisol TSH-thyroxine SPECIAL RELATIONSHIPS PROBABLE SIGNIFICANCE Greater increase with Intense exercise, NOR > EP, increase less after Training Increased blood glucose Increases more in unfit person Declines faster in fit person Greater increase with intense Exercise; increase less after Training with submaximal exercise Increased thyroxine turnover with Training but no toxic effects evident ? Increased gluconeo genesis in liver ? The endocrine response to exercise II HORMONE LH Testosterone EXERCISE RESPONSE No change EstradiolProgesterone Insulin Glucagon SPECIAL RELATIONSHIPS None None PROBABLE SIGNIFICANCE None ? Increases durig luteal phase of cycle ? Decreases less after training Decreased stimulus To use blood glucose Increases less after training Increased blood glucose via glycogenolysis and gluconeogenesis The endocrine response to exercise III EXERCISE RESPONSE HORMONE RAS (reninAngiotensin system) ADH Expected PTH-Calcitonin EPO ? ? SPECIAL RELATIONSHIPS Some increase after traning in rats None None None PROBABLE SIGNIFICANCE Sodium retention to maintain plasma volume Water retention to maintain plasma volume Needed to estabilish Proper bone development Would be important to increase red blood cell production Study Questions I What is an endocrine gland and what are the functions of hormones? Explain the difference between steroid and nonsteroid hormones How can hormones have very specific functions when they reach nearly all parts of the body trough the blood? How are plasma levels of specific hormones controlled? Explain the relationship between the hypothalamus and the pituitary gland Briefly outline the major endocrine glands, their hormones and the specific action of these Study Questions II Which of the hormones outlined in previous question are of major significance during exercise? What is hemoconcentration and how does the endocrine system relate to it? Describe the hormonal regulation of metabolism during exercise. What hormones are involved and how do they influence the avaliabilty of carbohydrates and fats for energy during exercise lasting for several hours? Describe the hormonal regulation of fluid balance during exercise Whath is hemodiluitio and how does the endocrine system relate to?