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Transcript
Endocrine System Dr Khamis Al Hashmi Department of physiology Room # 006 Ext. 3435 Email: [email protected] 1 Nervous Vs Endocrine system Nervous and endocrine systems acts together to coordinate functions of body system. Nervous system releases; Neurotransmitors Endocrine system releases; Hormones 2 Nervous Vs Endocrine system (cont.) Characteristic Nervous system Endocrine system Mediators molecules Neurotransmitters Hormones Site of mediator action Close to site of release Far from site of release Types of target cells Muscle cells, Cells throughout the body Time to onset of action Seconds to hours Duration of action gland cells, other neurons Within milliseconds Briefer (milliseconds) Longer (seconds 3 to days) Endocrine Vs Exocrine glands Exocrine gland: secrete their products into ducts that carry the secretion into body cavities, into lumen of organs, or to the outer surface of the body. E.g. Sweat, sebaceous, mucus, digestive glands. Endocrine glands: secrete their products into the interstitial fluid surrounding the secretory cells diffused into blood capillaries carried to target cells. 4 Definitions Hormone: is a mediator molecule that is released in one part of the body but regulates activity of cells in other parts of the body. Target cell: A cells whose activity is affected by a particular hormone. Receptor: A specific molecule or cluster of molecules that recognizes and binds a particular ligand (hormone) 5 Circulating hormones Vs Local hormones A) Circulating hormones 6 B) Local hormones: 1) Paracrines E.g. Nitric oxide. IL2 7 2) Autocrines E.g. IL2 Local hormones usually are inactivated quickly 8 Chemical classes of hormones a) Water-soluble hormones: - Amine hormones (Retain an amino group (NH3+) - - Peptide and protein hormones Eicosanoid hormones (derived from arachidonic acid. Eg. Prostaglandins, leukotrienes) b) Lipid-soluble hormones: - Steroid hormones Thyroid hormones Nitric oxide 9 a) Water soluble hormone 10 b) Lipid soluble hormone 11 Hormone transport in the blood Water soluble hormones circulate in a free form (Unbound). Lipid soluble hormones bound to transport proteins. (>90%). Importance: - Increase the solubility in blood. - Slow the rate of excretion by kidney or degradation by liver. - Provide a ready reserve of hormone. 12 Responsiveness of a target cell to a hormone depend on: 1) Concentration of the hormone 2) Number of receptors 3) Influence by other hormone (hormones interaction) 1) Concentration of the hormone – The hormone’s rate of secretion (all hormones) – Rate of metabolic inactivation and excretion (all hormones) – Rate of metabolic activation (few hormones) – Extent of binding to plasma protein (lipophilic hormones) 13 Control of hormone secretion Important to prevent overproduction or underproduction Three types of signals: 1. Signals from the nervous system Eg. Nerve impulse to adrenal medulla 2. Chemical changes in the blood. Eg. Blood Ca2+ level 3. Epinephrine parathyroid hormone Other hormone Eg. Ant. Pituitary hormones glands hormones of other 14 Negative-feedback control Short loop feedback long loop feedback 15 Positive-feedback control 16 Diurnal (circadian) rhythm The secretion rate of many hormones rhythmically fluctuate up and down as function of time. – Diurnal (or circadian), i.e. “day-night”. characterised by repetitive oscillations in hormone levels that are very regular and have a frequency of one cycle every 24 hours. Eg. Cortisol secretion. – Other rhythm. Monthly menstrual period. Negative feedback control mechanisms operate to maintain whatever set point is established for that time. 17 Clearance of hormones from the blood – Metabolic destruction by the tissues – Binding with the tissues. – Excretion by the liver into the bile. – Excretion by the kidneys into urine. 18 2) Number of receptors Down regulation: A hormone present in excess – – – – – Receptors Destruction of the receptor by lysosomes Decrease production of receptors Inactivation of some of the receptor molecules Inactivation of some of the intracellular signaling molecules Temporary sequestration of the receptor to the inside of the cell. Up regulation: A hormone is deficient Receptors 19 3) Hormones interaction: Permissiveness (permissive effect): powerful action of a hormone on target cells require a simultaneous or recent exposure to a second hormone. Eg. Epinephrine and thyroid hormones in lipolysis. Synergism (synergistic effect): the effect of two hormones acting together is greater or more extensive than the effect of each hormone acting alone. Eg. FSH and estrogen for normal development of oocytes in ovaries. Antagonism (antagonistic effect): one hormone opposes the action of another hormone. Eg. Insulin and glucagon. 20 Endocrine dysfunction a) Decrease in hormone activity Decrease in hormone secretion by the endocrine gland (hyposecretion). Increase removal of the hormone from the blood Abnormal tissue responsiveness to the hormone: Lack of target cell receptors. Lack of an enzyme essential to the target cell response 21 b) Increase in hormone activity Increase in hormone secretion by the endocrine gland (hypersecretion) Reduced plasma protein binding of the hormone (too much free, biologically active hormone Decreased removal of the hormone from the blood: Decreased inactivation. Decreased excretion 22 Location of endocrine glands Organ Hormones secreted Hypothalamus Releasing and inhibitory hormones (e.g. thyrotropin releasing hormones, growth hormone inhibitory hormone), ADH, oxytocin. Anterior pituitary gland Tropic hormones: ACTH, LH,FSH), GH, prolactin. Posterior pituitary gland Oxytocin, ADH (vasopressin) Thyroid gland Thyroxine, Tri- iodothyronine. Adrenal gland Mineralocorticoids (e.g. aldosterone), glucocorticoids (e.g. cortisol), catecholamines (e.g. epinephrine, nor-epinephrine). Parathyroid glands Parathyroid hormone. Pancreatic Islets Insulin, glucagon. Gonads Testosterone, estradiol. TSH 23 Hypothalamus and pituitary gland Anterior pituitary HypothalamicHypophyseal portal system 24 Posterior Pituitary Hypothalamohypophyseal tract 25 Hypothalamus Hormones Target cells Major function Releasing hormones: TRH, CTR, GnRH, GHRH, PRH Anterior pituitary Stimulate release of particular anterior pituitary hormone. Inhibiting hormones: GHIH, PIH Anterior pituitary inhibit release of particular anterior pituitary hormone. 26 Anterior pituitary gland Hormones Target cells Major function Thyroid stimulating hormone (TSH) Thyroid follicular cells Stimulates T3 and T4 secretion Adrenocorticotropic hormone (ACTH) Zona fasciculata and reticularis of adrenal cortex Stimulates cortisol secretion Growth hormone (GH) Bone; soft tissue Essential for growth Metabolic effects; protein metabolism, fat mobilization and glucose conservation Liver Stimulates IGF secresion Female: ovarian follicles Promote follicular growth and development; stimulates estrogen secretion Follicle-stimulating hormone (FSH) Males: Seminiferous tubules in testes Luteinizing hormone Prolactin Females: ovarian follicle and corpus luteum Stimulates sperm production Stimulates ovulation, corpus luteum development, estrogen and progesterone secresion Males: inerstitial cells of leydig in testes Stimulates testosterone secretion Females: mammary glands (breast) Promotes breast development; stimulates milk secresion Males Uncertain 27 Posterior pituitary Hormones Target cells Major function Antidiuretic hormone (ADH), Vasopressin Kidney tubules Increase water reabsorption Arterioles Produces vasoconstriction Uterus Increase contractility Oxytocin Mammary glands Causes milk ejection (Breast) 28 Thyroid Gland Hormones Target cells Major function Tetraiodothyronine (T4 or thyroxin); Triiodothyronine (T3) Most cells Increase metabolic rate; essential for normal growth and nerve development Calcitonin Bone Decrease plasma calcium concentration Parathyroid Gland Hormones Target cells Major function Parathyroid hormone (PTH) Bone, kidneys, intestine. Increases plasma calcium concentration; decrease plasma phosphate concentration; stimulates vitamin D activation 29 Adrenal gland Hormones Target cells Major function Cortex: Zona glomerulosa Mineralocorticoid (Aldosterone) Kidney tubules Increases Na+ reabsorptionand K+ excresion Zona Fasiculata and reticularis Glucocorticoid (cortisol) Most cells Increases blood glucose at the expense of protein and fat store; contributes to stress adaptation Androgens Female: bone and brain Pubertal growth spurt and sex drive Sympathetic receptor site throughout the body Contributes to stress adaptation and blood pressure regulation Medulla Epinephrine and norepinephrine 30 Pancreas (Islets of langerhans) Hormones Target cells Major function Beta (β) cells Insuline Most cells Promotes cellular uptake, use and storage of absorbed nutrients Alpha (α) cells Glucagon Most cells Important for maintain nutrient levels in blood during postabsorptive state D cells Somatostatin Digestive system Pancreatic islet cells Inhibits digestion and absorption of nutrients Inhibits secretion of all pancreatic hormones 31 Ovaries Hormones Target cells Major function Estrogen Female sex organs; body as whole. Promotes follicular development, development of secondary characteristics, stimulate uterine and breast growth. Bone Promotes closer of epiphyseal plate Uterus Prepare for pregnancy Progesterone 32 Testes Hormones Target cells Major function Testosterone Male sex organs; body as whole Stimulate sperm production; development of secondary characteristics; Promotes sex drive Testes and ovaries secret inhibin that acts on the anterior pituitary to inhibit secretion of follicle stimulating hormone. 33