EXSC%224:%Week%of%2/13%Lecture%2/14%Notes%What%is%the%endocrine%system?%• the%body’s%second%largest%regulatory%system%• an%integrated%system%of%small%organs%(glands)%that%involve%the%release%of%extracellular%signaling%molecules%known%as%hormones.%%• Compare%with%exocrine%o Exocrine%glands%secrete%outside%the%body%(Ex:%sweat%glands)%o So%endocrine%glands%secrete%inside%the%body%• How%it%differs%from%nervous%system%o Neurons%directly%innervate%a%tissue%o Stimulation%is%direct%and%immediate%• Regulates%through%the%secretion%of%hormones%(chemical%messengers)%o Hormones%can%have%short%(minutes)%or%long-term%(days)%regulatory%functions%o Hormones%act%at%sites%independent%of%secretion%o Hormone%secretes%throughout%the%body,%so%normally%long%lasting%and%not%localized;%whereas,%nervous%system%is%precise%and%brief%Major%endocrine%organs%• Hypothalamus%o has%neural%and%endocrine%functions%and%releases%hormones%(neuroendocrine)%o “master%regulator%of%endocrine%system”%o controls%everything%that%the%pituitary%gland%releases%• pituitary%gland%o storage%site%and%also%regulates%secretion%of%other%hormones%o 2%anatomical%regions%§ Anterior%§ Posterior%• Thyroid%gland:%Sits%on%either%side%of%trachea,%at%about%the%collar%bone%• Parathyroid%gland:%Embedded%in%the%thyroid%• Pancreas%o Can’t%live%without%it%o It%is%an%endocrine%and%an%exocrine%gland%• Adrenal%gland:%Sit%on%top%of%kidneys%• Gonads%• Other%tissues%and%organs%that%produce%hormones%o Adipose%cells%o Pockets%of%cells%in%the%walls%of%the%small%intestine%o Stomach%o Kidneys%o Heart%Hormones%• chemical%messenger%secreted%by%cells%into%the%extracellular%fluids%that%affect%other%parts%of%the%body%• secreted,%travels%throughout%the%body,%has%an%action%somewhere%else%other%than%where%it%was%secreted%• long%distance%messenger%• characteristics%o Have%lag%times%ranging%from%seconds%to%hours%§ Once%the%hormone%is%secreted,%it%tends%to%stay%away%for%awhile%o Tend%to%have%prolonged%effects%§ It%takes%a%long%time%for%the%hormone%to%be%eliminated%from%the%blood%§ Hormones%are%removed%from%the%blood%at%the%liver%and%kidney%• Classifications%o 2%major%classifications%of%hormones%§ Amino%acid-based%–%1%or%more%amino%acids%§ Steroids%–%derived%from%cholesterol%o Eicosanoids%–%biologically%active%lipids%with%local%hormone–like%activity%§ NOT%an%actual%hormone%§ Signaling%molecule%Other%types%of%signaling%molecules%(not%hormones)%• Autocrine:%chemicals%that%exert%effects%on%the%same%cells%that%secrete%them%o Acts%locally%• Paracrine:%locally%acting%chemicals%that%affect%cells%other%than%those%that%secrete%them%o Acts%in%the%vicinity%of%where%it%was%secreted%• They%aren’t%hormones%because%they%act%locally%• Eicosanoids:%%Amino%acid%based%hormones%• Amines%o Derived%from%tyrosine%o Ex:%norepinephrine%• Peptide%o Made%of%about%2-25%amino%acids%o Ex:%thyroid%• protein%hormones%o larger%sequences%of%amino%acids%and%has%a%folded%pattern%or%shape%o more%complex%o ex:%insulin%steroid%hormones-remember%all%of%them%are%derivatives%of%cholesterol%• gonadal%o estrogen%• adrenocortical%o cortisol%o testosterone%o aldosterone%eicosanoids%• leukotrienes%and%prostaglandins%• arachidonic%acid%(essential%fatty%acid)%converted%to%prostaglandin%(local%inflammatory%molecule)%How%do%hormones%exert%a%biological%effect%on%a%tissue?%• Receptors!%o Must%have%the%appropriate%receptor%to%receive%the%hormones%• Types%of%receptors%o Membrane%bound:%embedded%in%the%membrane%o Intracellular:%in%the%cytosol%• The%same%hormone%can%affect%some%tissues%and%organs%differently%based%on%the%receptor%that%is%located%there%• Target%cell%specificity:%hormone%only%has%an%effect%on%the%cell%if%it%has%a%receptor%for%it%o Not%all%cells%receive%all%hormones%o Hormone%has%no%effect%if%the%cell%does%not%have%a%receptor%for%it%Amino%acid%based%hormone%action:%cAMP%second%messenger%• Hormone%never%enters%the%cell%• Excitation%of%cAMP%production%o Hormone%(1st%messenger)%binds%to%receptor%o Receptor%activates%G%protein%o G%protein%activates%adenylate%cyclase%o Adenylate%cyclase%converts%ATP%to%cAMP%(2nd%messenger)%o cAMP%activates%protein%kinases%• OR%it%can%inhibit%the%production%of%cAMP%o G%protein%binds%%o GTP%binds%to%adenylate%cyclase%which%inhibits%production%of%cAMP%o This%doesn’t%affect%the%cAMP%that%already%exists%§ To%get%rid%of%it,%there%is%an%enzyme%called%phosphodiesterase%§ It%is%always%present%and%always%working%in%the%cytosol%§ It%breaks%down%cAMP%• Hormone%A%might%be%excitatory%and%encourage%cAMP%production,%but%hormone%B%might%be%inhibitory%and%preventing%cAMP%production,%all%while%phosphodiesterase%is%breaking%down%cAMP%• There%are%other%second%messenger%systems%that%exist%other%than%the%cAMP%example%above%(another%example%is%the%PIP%mechanism%[don’t%need%to%know%it]).%Steroid%based%Intracellular%hormone%signaling%• Takes%place%inside%the%cell%• Hormone%is%lipid%soluble%because%it%has%to%diffuse%across%the%membrane%(a%lipid)%• Under%normal%conditions,%a%receptor%(in%the%cytosol)%is%associated%with%a%chaperone%o The%chaperone%prevents%the%receptor%from%moving%to%the%nucleus%• When%a%hormone%binds%to%the%receptor,%the%chaperone%falls%off%• Receptor%and%hormone%move%from%the%cytosol%into%the%nucleus%• In%the%nucleus,%this%receptor-hormone%complex%binds%to%segments%on%the%DNA%o Segments%known%as%response%elements%o Ex:%estrogen%binds%to%the%estrogen%response%elements%• The%hormone%regulates%genes%o Ex:%regulation%of%the%development%of%secondary%sex%characteristics%• All%steroid%hormones%bind%to%intracellular%receptors%• One%amino%acid%hormone%(thyroid)%binds%to%an%intracellular%receptor%How%do%we%regulate%hormone%activity?%• Hormone%Concentration%o Rate%of%Release%o Rate%of%Inactivation/Removal%§ Broken%down%by%liver%and%removed%by%the%kidney%§ ½%Life:%the%time%required%for%a%hormone’s%blood%level%to%decrease%by%half%• Receptor%Concentration%o Cells%can%increase%or%decrease%the%number%of%receptors%expressed%o Changes%the%amount%of%receptors%that%are%available%o Cells%will%decrease%the%number%of%receptors%available%if%a%hormone%is%in%the%blood%for%a%really%long%time%in%large%amounts%(overstimulated)%o Cells%will%increase%the%number%of%receptors%available%if%they%are%not%getting%enough%of%a%hormone%(understimulated)%o
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