2402 Endocrine Guided Notes 2.pdf

The Endocrine System Background information: Includes all cells and endocrine tissues that produce hormones or paracrine factors Functions: ● Maintenance of an optimal biochemical environment within the body ● Influences metabolic activities ● Integration and regulation of growth and developmen...

The Endocrine System Background information: Includes all cells and endocrine tissues that produce hormones or paracrine factors Functions: ● Maintenance of an optimal biochemical environment within the body ● Influences metabolic activities ● Integration and regulation of growth and development ● Control, maintenance, and instigation of sexual reproduction Definitions: Paracrine communication -- chemical messengers between cells within one tissue Hormones -- chemicals secreted by cells into the bloodstream for transport to distant target tissues Up-regulation -- target cells form more receptors in response to the hormone Down-regulation -- target cells lose receptors in response to the hormone Tropic -- a hormone that stimulates release of another hormone Trophic -- a hormone that stimulates growth and nourishment of a gland Stress -- any condition that threatens homeostasis Neurohormones-- hormones released and secreted by neurons into the bloodstream, targeting distant cells Pancreatic islets -- clusters of endocrine cells within the pancreas (Islets of Langerhans) Etymology Fun: Hypophysis -- Greek for “lying under”; the pituitary gland’s position underneath the brain Adenohypophysis -- Greek for aden + hypo “underneath” phyein, to grow; the anterior lobe of the pituitary gland which also secretes growth hormone (among others) Somatotropin (GH) -- somato “to grow” ; tropin Key Players: Endocrine glands: ● Hypothalamus ● Pituitary (adenohypophysis) ● Pineal ● Thyroid ● Parathyroid ● Thymus ● Adrenal ● Pancreas ● Gonads The hypothalamus has both neural and endocrine functions The pancreas and gonads produce both hormones and exocrine products Other tissues and organs that produce hormones – adipose cells, cells of the small intestine, stomach, kidneys, and heart How It Works: 1) Hormones bind to their corresponding receptors, inducing events within the target cell that ultimately change its behavior Alter plasma membrane permeability Stimulate gene activation & protein synthesis Activate or deactivate enzyme systems Induce secretory activity Stimulate mitosis & cytokinesis 2) Hormone Concentrations in the Blood Reflect Rate of release Speed of inactivation and removal from the body Removed by degrading and liver enzymes and kidney filtration 3) Nervous System Modulation The nervous system can modify the stimulation of endocrine glands and their negative feedback mechanisms The nervous system can override normal endocrine controls Example: Neural control of BGL under stress 4) The Importance of the Hypothalamus regulates BOTH nervous and endocrine systems; endocrine reflexes are the counterparts of neural reflexes secretes regulatory hormones that control the anterior pituitary gland releases hormones at the posterior pituitary gland exerts direct neural control over the endocrine cells of the adrenal medullae 5) The Importance of the Pituitary Gland releases nine important peptide hormones which bind to membrane receptors and use cyclic AMP as a second messenger attached to the hypothalamus by the infundibulum divided into two parts: Anterior pituitary (Adenohypophysis) and Posterior pituitary (Neurohypophysis) Difference Between: Nervous System Endocrine System Short term crisis management Controls and coordinates activities that require rapid responses Long-term ongoing metabolic activity management Communication is carried out by endocrine cells (glands) that release hormones into the bloodstream in order to alter metabolic activities Classification of Hormones Based on Chemical Composition Classification of Hormones Based on Receptors Amino Acid Membrane Tyrosine Based-Catecholamines (Epi, NE, Dopa) & Thyroid hormones Tryptophan Based – Serotonin & Melatonin Protein Second messenger systems (G protein-linked)* Tyrosine kinase-linked receptors Hormone-gated ion channels Intracellular and Intranuclear Glycoproteins – carbohydrate + protein Short Polypeptides – chains of less than 200 amino acids Lipid Steroids – gonadal and adrenocortical hormones *Most amino-acid based hormones use G protein-linked receptors for signal transduction Eicosanoids – lipid based hormones that act locally on the same cell **Most steroid hormones can diffuse through the membrane and bind to that released it or nearby cells (autocrine and paracrine mediators) receptors in cytosol and nucleus to activate or repress genes Target Cell Characteristics: Specificity Activation dependent on Sensitivity Hormones circulate to all tissues but only Blood levels of the hormone Up-regulation – target cells form more Relative number of receptors on the target cell activate target cells receptors in response to the hormone Target cells must have specific receptors to The affinity of those receptors for the hormone Down-regulation – target cells lose receptors in which the hormone binds response to the hormone Control of Hormone Release: Humoral (of body fluids, ie: blood)Neural Hormonal Hormones are Released in Response to: changing blood levels of ions, nutrients, and gases neural stimulation originating fromhormones produced by other endocrine organs the CNS (brain, spinal cord) Example [Ca2+] in the blood Action potential travels along Hypothalamic “releasinghormones” stimulate the anterior sympathetic nerve fibers that synapse at the adrenal medulla pituitary to release hormones !"#$%2+] in blood stimulates Anterior pituitary’s tropic parathyroid glands to secrete PTH Chromaffin cells in adrenal hormones stimulate target glands (parathyroid hormone) medulla respond by releasing to secrete still more hormones catecholamine hormones (EPI and Tropic &"'()"*%+,-,"#$%2+] in bloodNE) into the blood -stimulates the release of another 2+ to rise (Ca is reabsorbed in hormone Trophic kidneys and leached from bones) -stimulates the growth and and the stimulus is removed nourishment of a gland Three Methods of Hypothalamic Control over the Endocrine System: Adenohypophysis Pituitary Regulates secretion of hormones Releasing Factors Inhibiting hormones Adrenal Medullae Control of sympathetic output Sends releasing/inhibiting hormones to the adenohypophysis via the hypophyseal portal system Sends neural stimuli to the neurohypophysis via the hypothalamic hypophyseal tract Adenohypophysis: synthesizes and releases six hormones that regulate activity of other endocrine glands Pars distalis - largest division of the adenohypophysis Tropic hormones: TSH, ACTH, FSH, and LH Name of Hormone Released from Hypothalamus Name of Hormone Function Released from Anterior Pituitary Extra information Cell type released by in anterior pituitary 1.TRH Thyrotropin TSH releasing hormone Thyroid stimulating Tropic hormone that Rising blood levels of Thyrotropic hormone stimulates the normal thyroid hormones act development and on the pituitary and secretory activity of hypothalamus to block the thyroid gland; the release of TSH triggers the release of thyroid hormones (T3 & T4) from thyroid gland 2.CRH Corticotropin ACTH releasing hormone Adrenocorticotropic stimulates the release Internal and external Hormone of glucocorticoids by factors such as fever, the adrenal gland hypoglycemia, and stressors can trigger stimulates the adrenal the release of CRH cortex to release corticosteroids 3.GnRH Gonadotropin FSH releasing hormone Follicle Stimulating stimulates gamete Hormone (egg or sperm) production Corticotropic *also releases melanocyte-stimulating hormone (MSH) to produce melanin FSH stimulates gameteGonadotropic (egg or sperm) production follicle development and estrogen secretion in females and sperm production in males 4.GnRH Gonadotropin LH releasing hormone Luteinizing Hormone causes ovulation and progestin production in females and androgen production in males LH in Female Gonadotropic --stimulates maturation of ovarian follicle --triggers ovulation --stimulates release of estrogens and progesterone LH in Male --stimulates testes to produce testosterone 5.GHRH Growth hormone GH releasing hormone Release of Growth stimulates cell growth Hormone and replication Stimulates liver, skeletal muscle, bone, and cartilage to release insulin-like growth factors (IGFs) Increases cell metabolism and blood glucose level Promotes use of fats for fuel (lipolysis & gluconeogenesis) and protein synthesis Somatotropic cells GHIH/ Growth hormone- GH Somatost inhibiting hormone atin Inhibits release of Growth Hormone Somatotropic 6.PRH Prolactin releasing PRL hormone Stimulates release stimulates the of Prolactin development of mammary glands and milk production Stimulates milk Mammotropic production in breasts of females Blood levels rise towards the end of pregnancy Suckling stimulates PRH release and encourages continued milk production PIH/ Prolactin Inhibiting PRL Dopamine Hormone Inhibits release of stimulates the Prolactin development of mammary glands and milk production Mammotropic Neurohypophysis Two neurohormones are synthesized in the hypothalamus and released by the neurohypophysis Neurohormones ADH Function Additional Information Antidiuretic hormone Decreases the amount of water lost at theADH reduces urine formation in order to avoid dehydration kidneys Elevates blood pressure Solute concentration of blood is measured by osmoreceptors: With high solutes, ADH is synthesized and released, thus preserving water With low solutes, ADH is not released, thus allowing water loss from the body Alcohol inhibits ADH release and causes copious urine output OXT Oxytocin Stimulates contraction cells in mammary Oxytocin is a strong stimulant of uterine contraction glands Stimulates smooth muscle cells in uterusRegulated by a positive feedback mechanism to oxytocin in the blood This leads to increased intensity of uterine contractions, ending in birth Oxytocin triggers milk ejection (“letdown” reflex) in women producing milk Synthetic and natural oxytocic drugs are used to induce or hasten labor Plays a role in sexual arousal and satisfaction in males and nonlactating females G-Word Review Glucose A six carbon sugar that is a major energy source for the body Glycolysis Breakdown of glucose to 2 pyruvate and 2 ATP Gluconeogenesis Formation of glucose from noncarbohydrate precursors, especially amino acids Glycogen Polysaccharide of glucose that serves as energy storage Glycogenesis Synthesis of glycogen from glucose Glycogenolysis Breakdown of glycogen into glucose Glucagon Hormone produced by the pancreas Helpful tips: gluco-, glyco- = sweetness or glucose neo- = new -genesis = formation of -gen = produced by lysis = breakdown or “loosening of Thyroid Gland Background Info Hormones Function Regulation Four Parathyroid Glands The largest endocrine gland, T3 (Triiodothyronine) Regulate metabolism negative feedback loop Embedded in the posterior composed of circular follicles and T4 (Thyroxine) --Promote glycolysis, (NFbL) surface of the thyroid gland Colloid fills the lumen of the are two closely gluconeogenesis, glucose Stimulus: Low circulating Chief cells produce follicles and is the precursor of related iodineuptake T3,T4 detected by parathyroid hormone thyroid hormones containing --Glucose oxidation hypothalamus and (PTH) in response to lower Parafollicular cells (C cells) compounds --Increase metabolic rate adenohypophysis than normal calcium produce the hormone calcitonin T3 is ten times more --Heat production Hypothalamic Thyrotropin- concentrations Thyroid gland contains numerousactive than T4 Releasing Hormone (TRH)Parathyroid hormones are follicles Bind to thyroid can override the short-loopregulators of calcium levels Release several hormones such binding globulins negative feedback in healthy adults Regulate growth and as thyroxine (T4) and (TBG) or albumin for development triiodothyronine (T3) that regulatetransport in the --Regulate tissue growth metabolism increases protein blood --Increase protein synthesis Mechanisms of synthesis promotes glycolysis, activity are similar to --Developing skeletal and gluconeogenesis, glucose uptakesteroids – they are nervous systems C cells produce calcitonin - helpstransported across --Maturation and regulate calcium concentration incell membrane reproductive capabilities body fluids Homeostatic Regulation of Calcium Concentrations: Thyroid Gland Parathyroid Gland Produces/secretes Calcitonin Parathyroid hormone (PTH) Response Increased excretion of calcium in kidneys Calcium deposition in bone Inhibition of osteoclasts Release of stored calcium from bone Stimulation of osteoclasts Enhanced reabsorption of calcium in kidneys Stimulation of calcitriol production at kidneys; enhanced Ca2+, PO4-3, absorption by digestive tract Effect Calcium levels decline Calcium levels rise Adrenal (Suprarenal) Glands Pyramid-shaped organs atop the kidneys; structurally and functionally are two glands in one Gland Adrenal Medulla Adrenal Cortex Type of tissue Nervous; functions as part of Sympathetic Nervous System Glandular Secretes Catecholamines --Epinephrine (75-80%) --Norepinephrine (25-30%) Corticosteroids --Mineralocorticoids --Glucocorticoids --Gonadocorticoids The Corticoids: (“cortico” refers to steroid hormones produced by adrenal cortex) Name Mineralocorticoids Glucocorticoids Gonadocorticoids (Sex Hormones) Function Maintain electrolyte balance Help the body resist stress by sparing glucose and reducing inflammation Androgens contribute to: Onset of puberty Appearance of secondary sex characteristics Sex drive in females Most important Aldosterone: stimulates reapsorbtion ofCortisol: stimulates Na+ by kidneys, reducing excretion fromgluconeogenesis body Increases blood glucose, fatty acids, and amino acids Most secreted are androgens Testosterone Stimulated by *can be converted into estrogens after menopause Rising blood levels of K+ Low blood Na+ Decreasing blood volume or pressure The Case Study of Insulin and Glucagon: *Normal blood glucose level (BGL): 70-110 mg/dL Insulin Glucagon Function Lowers blood glucose by increasing the rate of glucose uptake Raises blood glucose by increasing the rates of glycogen and utilization breakdown and glucose manufacture by the liver When BGL Rises β cells respond by secreting insulin: Increased rate of glucose transport into target cell Increased rate of glucose utilization and ATP generation Increased conversion of glucose to glycogen (liver, skeletal muscle) Increased amino acid absorption and protein synthesis Increased triglyceride synthesis (adipose tissue) >> Blood glucose concentration declines back to normal range When BGL Drops α cells respond by secreting glucagon: Increased breakdown of glycogen to glucose (liver, skeletal muscle) Increased breakdown of fats to fatty acids (adipose tissue) Increased synthesis and release of glucose (liver) >> Blood glucose concentration rises back to normal range The Case of Exercise: Hormonal Responses Glucagon Promotes liver glycogenolysis Epi and Norepi Increase glycogenolysis Cortisol Protein catabolism for later gluconeogenesis Growth hormone Mobilizes free fatty acids Thyroxine (T4) Promotes glucose catabolism Regulation of Glucose Metabolism Regulation of Fat Metabolism During Exercise During Exercise Hormonal Effects on Fluid and Electrolyte Balance Insulin is usually required for cell uptake of glucose but exercising skeletal muscle does not! May enhance insulin’s binding to receptors Up-regulation of GLUT receptors occurs after four weeks of exercise Reduced plasma volume leads to release of Aldosterone from adrenal cortex, which increases Na+ and H2O reabsorption by the kidneys and renal tubes. When low plasma glucose levels occur, the catecholamines are released to accelerate lypolysis Triglycerides are reduced to free fatty acids (lipolysis) by lipase which is activated by: -Cortisol -Epinephrine -Norepinephrine -Growth Hormone Osmoreceptors in hypothalamus sense dehydration, Antidiuretic Hormone (ADH) is released from the posterior pituitary, and water is then reabsorbed by the kidneys. Three Phases of GAS (General Adaptation Syndrome): Alarm Phase Resistance Phase Exhaustion immediate, fight or flight, directed by the sympathetic nervous system dominated by glucocorticoids breakdown of homeostatic regulation and failure of one or more organ systems