Week$of$2/20/17$Thyroid$gland$• Straddles$the$trachea$below$the$adam’s$apple$and$above$the$clavicle$• Secretes$2$hormones$o Thyroid$hormone$§ Permissive$hormone:$it$allows$other$hormones$to$do$their$jobs$properly$§ Affects$growth-if$not$enough,$child$will$be$short$§ Major$metabolic$hormone$o Calcitonin$§ Plays$role$in$regulation$of$blood$calcium$§ Lowers$blood$calcium$§ Weak$concentrations$of$calcitonin$in$human$blood$• Goiter=swelling$of$thyroid$gland$Thyroid$hormone$(TH)$• Only$acid$based$hormone$that$binds$to$intracellular$receptors$• So$it$is$lipid-soluble$• Consists$of$two$related$iodine-containing$compounds$o T4$–$thyroxine;$has$two$tyrosine$molecules$plus$four$bound$iodine$atoms$§ Called$T4$because$it$has$4$iodines$attached$to$the$amino$acids$(tyrosine)$o T3$–$triiodothyronine;$has$two$tyrosines$with$three$bound$iodine$atoms$§ Called$T3$because$it$has$3$iodines$attached$to$the$amino$acids$(tyrosine)$• Potassium$iodide$is$added$to$salt$to$make$sure$people$get$enough$iodine$• TH$is$concerned$with:$o Glucose$oxidation$§ Stimulates$glucose$oxidation…this$means$it$also$contributes$to$increasing$metabolic$rate$and$heat$production$o Increasing$metabolic$rate$$o Heat$production$• TH$plays$a$role$in:$o Maintaining$blood$pressure$o Regulating$tissue$growth$o Developing$skeletal$and$nervous$systems$o Maturation$and$reproductive$capabilities$o Permissive$hormone$• It$basically$makes$everything$function$better$• Under$hypothalamic$control$o Hypothalamus$secretes$Thyrotropin$releasing$hormone$(TRH)$o To$the$anterior$pituitary$gland$which$releases$thyroid$stimulating$hormone$(TSH)$o This$enters$general$circulation$where$it$will$reach$the$thyroid$gland$$o Thyroid$gland$will$release$T3$and$T4$o Process$is$under$negative$feedback$control$(T3$and$T4$levels$get$too$high,$and$limits$hypothalamus$from$releasing$TRH)$• Hypo-thyroid$disorder$o Childhood-cretinism$§ low$metabolic$rate$§ growth$retardation$§ developmental$delay$§ other$abnormal$features$§ Can$be$due$to$deficiency$of$iodine$in$the$mother's$diet$during$pregnancy$$§ Scaly$skin$§ Layer$of$adipose$under$the$skin$§ Can’t$be$reversed$by$adding$iodine$to$the$diet$o Adulthood-Myxedema$§ Low$metabolic$rate$§ skin$and$tissue$disorder$usually$due$to$severe$prolonged$hypothyroidism$$§ scaly$skin$§ lethargic$o Goiter$§ Swollen$thyroid$gland$§ Goiter$itself$is$not$harmful,$but$it$indicates$something$is$wrong$with$the$thyroid$gland$• Hyper-thyroid$disorder$o Grave’s$disease$§ Autoimmune$disorder$§ Over-activity$of$the$thyroid$gland$$§ inflammation$of$the$tissues$around$the$eyes$causing$swelling$$§ ↑$metabolic$rate,$sweating,$rapid$&$irregular$heart$beat,$nervousness,$weight$loss,$protruding$eyeballs$(exophthalmos)$§ caused$by$chronic$elevation$of$thyroid$hormone$o goiter$§ can$occur$for$hyper$or$hypo$thyroid$disorders$Calcitonin$• amino$acid$based$hormone$• secreted$when$blood$calcium$levels$rise$above$normal$(homeostasis)$• Ca2+$is$2x$more$charged$than$K+$or$Na+$o Too$much$Ca2+=hyper$polarized$o Too$little$=$depolarized$• Drink$milk$• Too$much$calcium$in$blood$• Thyroid$gland$secretes$calcitonin$• Calcitonin$stimulates$calcium$to$be$deposited$in$the$bone$• End$result:$mineralizes$the$bone$• Stimulates$osteoblast$to$deposit$calcium$into$new$bone$• Inhibits$parathyroid$hormone$• Humoral$(some$factor$in$the$blood)$in$this$case,$refers$to$calcium$ion$concentration$in$the$blood$• It$is$not$a$primary$hormone$so$it$doesn’t$matter$if$there$is$too$much$or$too$little$Parathyroid$gland$• Embedded$in$the$thyroid$gland$• 4$clusters$of$cells$• secretes$parathyroid$hormone$(PTH)$o chief$(principal)$cells$secrete$PTH$o antagonistic$to$calcitonin-raises$blood$calcium$levels$o secreted$when$blood$calcium$levels$are$low$o stimulates$osteoclast$activity$(breakdown$bone)$• cells$are$sensitive$to$calcium$levels$in$the$blood$and$detect$when$it$is$too$low$• hyper-parathyroidism$o rare$o leach$bone$minerals$o likely$to$develop$kidney$stones$• hypo-parathyroidism$o deficiency$o causes$hypocalcemia$o increases$spontaneous$membrane$depolarization$o treated$relatively$easily$by$taking$PTH$made$in$the$lab$Adrenal$(suprarenal)$glands$• 2$glands$in$1$o Adrenal$medulla$–$neural$tissue$that$acts$as$part$of$the$SNS$o Adrenal$cortex$–$Secretes$steroid$hormones$§ Synthesizes$and$releases$steroid$hormones$called$corticosteroids$§ Different$corticosteroids$are$produced$in$each$of$the$three$layers$§ Zona$glomerulosa$–$mineralocorticoids$$(chiefly$aldosterone)$§ Zona$fasciculata$–$glucocorticoids$$(chiefly$cortisol)$§ Zona$reticularis$–$gonadocorticoids$$(chiefly$androgens)$Aldosterone$(primary$mineralocorticoid)$• Steroid$hormone$• Binds$to$intracellular$receptors$• Regulates$body$water$• 4$ways$to$regulate$it$o K+$increase$in$the$blood$(primary$regulator)$§ Stimulates$the$release$of$aldosterone$§ Directly$affects$cells$in$the$adrenal$cortex$§ Here$it$stimulates$the$reabsorption$of$Na+$• Energy$requiring$process$• Sodium$potassium$pump$• Gets$the$K+$out$of$the$blood$and$Na+$into$the$blood$• Pumping$sodium$creates$an$osmotic$gradient,$so$water$follows$o Blood$volume$increases$o Blood$pressure$increases$o Drop$in$blood$volume$and/or$blood$pressure$(primary$regulator)$§ Kidneys$detect$this$drop$§ Release$renin$§ Angiotensin$II$is$made$§ Stimulates$aldosterone$secretion$§ Aldosterone$goes$to$kidney$§ Sodium$reabsorbed$§ Water$follows$§ Increases$blood$volume$and$blood$pressure$o Increase$in$stress$§ Causes$ACTH$to$be$released$from$anterior$pituitary$§ Stimulates$aldosterone$secretion$§ Aldosterone$goes$to$kidney$§ Sodium$reabsorbed$§ Water$follows$§ Increases$blood$volume$and$blood$pressure$o Increase$in$blood$pressure$and$or$blood$volume$§ Heart$does$not$like$this$added$stress$§ Volume$overload$causes$the$chambers$of$the$heart$to$stretch$§ This$causes$the$release$of$atrial$natriuretic$peptide$(ANP)$§ ANP$inhibits$aldosterone$secretion$§ So$sodium$isn’t$reabsorbed,$so$water$isn’t$reabsorbed$§ Decrease$in$blood$volume$and$blood$pressure$• Hypo-aldosteronism$o Addison’s$disease$§ Hyposecretion$of$adrenal$cortex$§ Includes$• Mineral$corticoids$• Glucocorticoids$§ Symptoms$• Severe$dehydration$• Hypotension$• Low$Blood$glucose$• Low$Na+$• High$K+$•
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