THE ENDOCRINE SYSTEM

THE ENDOCRINE SYSTEM•Lecture 2; Holes, Chapter 131THE PITUITARY GLANDSecretes 9 hormonesDivided into 2 parts: Anterior lobePosterior lobeAnterior: glandular tissue.(adenohypophysis)Posterior: nervous tissue(neurohypophysis)Pituicytes (type of glial cell).Secretes neurohormones from hypothalamus2The Pituitary Gland3PITUITARY GLANDAnterior lobe (adenohypophysis)Posterior lobe (neurohypophysis)Glandular tissue. Pituicytes & Nerve cells.Derived from epithelial tissue of oral muscosa.Actually part of the brain.Makes its own hormones.Receives hormones from hypothalamus.Growth hormoneThyroid-stimulating hormoneOxytocinAdrenocorticotrophic hormone (ACTH)Antidiuretic hormone (ADH)Follicle-stimulating hormone (FSH) Luteinizing hormoneProlactin(all use cAMP 2°messenger system)4POSTERIOR PITUITARY GLAND & THE HYPOTHALAMUSHypothalamus:Supraoptic nucleus (ADH)Paraventricular nuclei (Oxytocin)Hypothalamic-hypophyseal tract(hormones travel down neurons)Posterior Pituitary(hormones released into capillary beds when neurons fire)5ANTERIOR PITUITARY GLAND & THE HYPOTHALAMUSHypothalamus sends chemical instructions to the Anterior Pit. GlandPrimary capillary plexusHypophyseal Portal systemSecondary capillary plexusAnterior PituitaryEpithelial tissue 5 types of secretory cells6HYPOTHALAMUS: CONDUCTOR OF THE HORMONE ORCHESTRAHypothalamusHormone releasing chemicalsPosterior Pit. GlandOxytocinADHAnterior Pit. GlandGrowth HormoneTARGET ORGANProlactin(pro-opiomelanocortin)(melanocyte stimulating hormone)TSHACTH“Trophins”FSHOther hormonesLH7GROWTH HORMONE (GH; SOMATOTROPIN) Made and secreted by somatotropic cells in Anterior Pit. Gland Protein hormonePromotes growth/division of most cell types: Major targets: Bone & Muscle (stimulates epiphyseal plate, muscle mass increase) Promotes Anabolic activity Increases Protein Synthesis (amino acid movement) Increases Fat mobilization (alternative fuel to CHO) Conserves carbohydratesActs either directly or via Insulin-like growth factor (IGF)IGF produced by liver, muscle, bone & other tissues.8GROWTH HORMONE FUNCTIONRelease of IGF (liver, muscle, bone)Increase Increase sulfur Decrease Amino Acid uptakeglucose useUptakeStimulation of bone growthIncrease Increase Increased Fat protein cartilage release and synthesisproductionutilization9CONTROL OF GROWTH HORMONE RELEASEHYPOTHALAMUSGrowth hormone releasing hormone Growth hormone inhibiting hormone(GHRH)(somatostatin)ANTERIOR PIT. GLANDGrowth hormone releasedGH release decreasedOther factors: Age SleepGH blood Nutritional statuslevels riseIGF increase10GROWTH HORMONE RELEASEHypersecretion: Gigantism & Acromegaly11GROWTH HORMONE RELEASEHyposecretion: Pituitary dwarfismSynthetic GH now produced and cases of pituitary dwarfism are reduced12THYROID STIMULATING HORMONE Released by thyrotrophin-releasing hormone (hypothalamus) Stimulates secretions from Thyroid gland Rising blood levels of TSH inhibit further release of TRH at ant.pit.gland. Also inhibited at hypothalamus. Also released during pregnancy, emotional stress, cold temperature13THYROID STIMULATING HORMONEHypersecretion: Grave’s disease: overactive thyroidHyposecretion: Cretinism (children): retardation of mental and physical growth Myxedema (adults): lowered mental awareness, fatigue, weakness.14ADRENOCORTICOTROPHIC HORMONE (ACTH)ACTH: Secreted by anterior Pit. GlandControlled by hypothalamic corticotrophin releasing hormone. (daily rhythm: highest in morning).ACTH acts on adrenal cortexAdrenal cortex stimulated to release corticosteriodsGlucocorticoids feedback and inhibit ACTH release15ADRENOCORTICOTROPHIC HORMONE (ACTH)Hypersecretion: Cushing’s disease.Prolonged exposure to elevated corticosteroids: upper body obesity rounded face increased fat around the neck thinning arms and legsChildren tend to be obese with slowed growth rates.16GONADOTROPHINSFollicle-stimulating hormone & Luteinizing hormone (FSH) Gamete production: eggs, sperm (LH) Controls gonad hormones FSH & LH cause maturation of egg follicle; LH causes egg release LH stimulates testes to produce testosterone (male) FSH & LH - maturation of gonads during puberty Both released by gonadotrophin-releasing hormone (GnRH) from the hypothalamus17PROLACTIN Stimulates milk production by the breasts. (increases testosterone in males) Release controlled by hypothalamus - Prolactin-releasing hormone (serotonin) & Prolactin-inhibiting hormone (dopamine) PIH and PRH affected by estrogen; increased estrogen causes increase in prolactin. Prolactin levels rise toward end of pregnancy. Sustained rise results in milk production by breast tissue18POSTERIOR PITUITARY (HYPOTHALAMIC) HORMONES Oxytocin and Antidiuretic Hormone.Posterior Pituitary stores the hormonesReleased by neural stimulation from hypothalamus19OXYTOCIN (GR. SWIFT BIRTH)Causes smooth muscle contractionsuterus wall - childbirthmyoepithelial cells in breast tissueNumber of receptors increase near end of pregnancyContractions cause increased release via stimulation of the hypothalamus. (Positive feedback).Suckling child stimulates ‘letdown’ reflex - release of oxytocin and stimulation of breast to release milk.Synthetic Oxytocin used to induce laborMales: plays a role in sexual arousal and nurturing behavior (‘cuddle hormone’)20ANTIDIURETIC HORMONE (ADH)(Diuresis - production of urine)Dehydration: high salt concentration in bloodOsmoreceptors in hypothalamus start firingRelease of ADH in to bloodstreamTarget organ: KidneyOsmoreceptors in stop firingKidney tubules reabsorb more waterBlood Salt concentration Blood volume rises, urine decreasesproduction slows21ANTIDIURETIC HORMONE (ADH) Alcohol: dehydration Drug: antagonist to ADH to induce diuresis In high concentrations, ADH is powerful vasoconstrictor (vasopressin)Hyposecretion: e.g. Diabetes insipidus - damage to pit.gland or hypothalamus means less ADH, means more urine produced.Hypersecretion:e.g. meningitis, hypothalamic injury - blood retention, head ache, hypotonic blood.22THE THYROID GLANDButterfly shaped glandLargest gland in bodyVery high blood supplyHollow folliclesSquamous/cuboidal epithelium (follicular cells)Inside lumen:Thyroglobulin + iodine = colloid = precursor to Thyroid hormoneParafollicular cells: producing calcitonin23THYROID HORMONE (TH)Two forms of the hormone (both amines, both with iodine):Triiodothyronine (T3) - Thyroxine (T4) - secreted by follicle converted from T4 at target cellscellsTarget cells: everywhere BUT brain, spleen, testes, uterus and thyroid itself.TH stimulates glucose oxidation (increases metabolism)Essential for normal bone and nerve development and reproductive development.24TRANSPORT OF THYROID HORMONE (TH) T4 & T3 are bound to transport proteins Both forms can bind to receptors; T3 much more readilyHypothalamusThyrotropin-releasing Peripheral tissues have enzymes to convert T4 to T3hormone T4 & T3 both act like steroids and act in the nucleusRegulation:Anterior Pit.Gland If T4 blood levels fall, thyroid-stimulating hormone (TSH) is Thyroid Stimulating released.Hormone T4 is released from gland to increase blood levelsThyroid gland TSH levels fall, T4 release is slowedThyroid hormone(Can be over-ridden is times of need: cold temperature, pregnancy)TARGET CELLS25DISORDERS OF THYROID HORMONE (TH)Hyposecretion:Hypersecretion: Endemic - lack of dietary iodine Grave’s disease Autoimmune disease - constant stimulation of thyroid to release TH. Cretinism, myxedema - low metabolic rate, chills, mental retardation (children) or High metabolic rate, nervousness, weight sluggishness (adults)loss, protusion of eyeballs (Exophthalmos)26CALCITONIN Produced by parafollicular cells (or C cells) Released when blood Ca++ is high Lowers blood Calcium. Inhibits ________ activity, stimulates ________ activity Increases Ca++ excretion by the kidney Humoral stimulus (raised Ca++ levels) Fast, but short acting response.27PARATHYROID GLANDFour small glands Posterior surface of the thyroid glandVary in number and positionGland made up of: Chief cells - PTH Oxyphil cells - ?28PARATHYROID HORMONEPTH release stimulated by falling blood Ca++Raises falling Ca++ levels.Stimulates, bone, kidney and intestine.Activates Vitamin D - precursor of calcitrol29DISORDERS OF PARATHYROID HORMONEHypersecretionHyposecretionHyperparathyroidism Surgery or trauma(rare, cancer)Bones are broken downLower Ca++ : Increased excitability of Raised Ca++ :neurons Depression of Nervous Tetany - loss of Systemsensation, muscle twitches, Muscle weaknessconvulsions Kidney stones Paralysis Metastatic calcification30