Lecture'1:'homeostasis' • Define'anatomy'and'physiology,'and'name'several'branches'of'these'sciences.'' Anatomy!(ana%!=up;!%tomy=!process!of!cutting)!is!the!science!of!body!structures!and!the!relationships! among!them.!It!was!first!studied!by!dissections!(cutting!apart!of!body!structures!to!study!their! relationships.!! Physiology!(physio%!=!nature;!%logy=!study!of)!is!the!science!of!body!functions%!i.e.!how!the!body!parts! work.!! ! Since!structure!and!function!are!closely!interrelated,!the!structure!of!a!part!of!the!body!often!reflects! its!functions.!! E.g.!bones!of!the!skull!join!tightly!to!form!a!rigid!case!that!protects!the!brain.!! E.g.!walls!of!the!air!sacs!are!very!thin,!permitting!rapid!movement!of!inhaled!oxygen!into!the!blood.!! ! • Describe'the'body’s'6'levels'of'structural'organisation.' 1. Chemical!level:!This!basic!level!includes!atoms!(smallest!unit!of!matter!that!participate!in! chemical!reactions)!and!molecules!(two!or!more!atoms!joined!together).!! • C,!H,!O!N,!P,!Ca,!S!are!the!essential!atoms!for!maintaining!life.!! • DNA!and!glucose!(blood!sugar)!are!the!two!molecules!found!in!the!body.!! 2. Cellular!level:!Molecules!combine!to!form!cells%!the!basic!structural!and!functional!units!of!an!organism! composed!of!chemicals.!! • Nerve!cells,!epithelial!cells!and!muscle!cells.!! 3. Tissue!level:!Groups!of!cells!and!materials!surrounding!them!combine!to!form!tissue!and!they! work!together!to!perform!a!particular!function.!! • 4!basic!types!of!tissues:! - Nervous!tissue:!carries!information!from!one!part!of!the!body!to!another!through! nerve!impulses.! - Epithelial!tissue:!covers!body!surfaces,!lines!hollow!organs!and!cavities!and!forms! glands.! - Muscular!tissue:!contracts!to!make!body!parts!move!and!generates!heat.! - Connective!tissue:!supports,!connects!and!protects!body!organs!while!distributing! blood!vessels!to!other!tissues.!! 4. Organ!level:!Tissues!join!together!to!form!organs.!! 5. System!level:!The!digestive!system!which!breaks!down!and!absorbs!food.!It!is!also!known!as! the!organ'system'level.! 6. Organismal!level:!All!the!parts!of!the!human!body!functioning!together.!! ! • List'the'11'systems'of'the'human'body,'representative'organs'present'in'each,'and'their'general' functions.'' Integumentary!system!(skin,!hair,!nails,!sweat!and!oil!glands),!skeletal!system,!muscular! system,!nervous!system,!endocrine!system,!cardiovascular!system,!lymphatic!system,! respiratory!system,!digestive!system,!urinary!system!and!reproductive!systems.!! • Define'the'important'life'processes'of'the'human'body.' Metabolism:!all!chemical!processes!that!occur!in!the!body.!There!are!2'phases:!catabolism' (breaking'down)'and'anabolism'(making'up).' Responsiveness:!ability!to!detect!and!respond!to!changes%!e.g.!increasing!body! temperature.! Movement:!motion!or!the!whole!body,!individual!organs,!single!cells!and!within!cells.! Growth:!increase!in!body!size!resulting!from!the!growth!of!existing!cells!and!the!number!of! cells.! Differentiation:!development!of!a!cell!from!an!unspecialised!state!to!a!specialised!state.!! Reproduction:!formation!of!new!cells!for!tissue!growth,!repair!or!replacement.!Also!the! production!of!a!new!individual.!! • Define'homeostasis.' Homeostasis!(homeo%!=!sameness;!%stasis=!standing!still)!is!the!condition!of!equilibrium!(dynamic)! in!the!body’s!internal!environment!due!to!the!constant!interaction!of!the!body’s!many!regulatory! processes.!A"stable"internal"environment"is"achieved"by"balancing"inputs"and"outputs.!! - By!responding!to!changing!conditions,!the!body’s!equilibrium!can!shift!among!points! that!are!compatible!with!maintaining!life.!! - All!structures!in!the!human!body!contribute!in!some!way!to!keep!the!internal! environment!of!the!body!within!normal!limits.!! - We!aim!to!achieve!homeostasis!as!a!part!(compartmental)!and!as!a!whole.!! An!important!aspect!of!homeostasis:! - Maintaining!the!volume!and!composition!of!body!fluids! - Maintaining!volume!and!composition!of!dilute,!watery!solutions!containing! dissolved!chemicals!that!are!found!inside!cells!as!well!as!surrounding!them.!! • The!fluid!within!cells!is!intracellular"fluid"(ICF).!! • The!fluid!outside!body!cells!is!extracellular"fluid"(ECF).!ECF!also!differs!depending!on!where!it! occurs!in!the!body.!! - Blood!vessels=!plasma! - Lymphatic!vessels=!lymph! - Brain!and!spinal!cord=!cerebrospinal! fluid!! - Joints=!synovial!fluid! - Eyes=!aqueous!humor!and!vitreous! body! • The!ECF!that!fills!the!narrow!spaces!between!cells! of!tissue!is!interstitial!fluid.!It!is!important!for! proper!functioning!of!the!body!cells!that!precise! regulation!of!the!composition!of!the!interstitial! fluid!is!maintained.!Thus,!interstitial!fluid!is!also! referred!to!as!the!body’s!internal!environment.!! • Homeostasis!in!the!human!body!is!regularly!disturbed.!These!are!caused!by!disruptions!from!the! external!environmental!in!physical!forms%!e.g.!heat!or!a!lack!of!oxygen.! Disturbances!in!the!internal!environment!can!also!cause!disruptions%!e.g.!low!blood!glucose!level.! Psychological!disturbances!can!also!cause!an!imbalance!in!the!homeostasis!of!the!human!body.!! In!most!cases,!these!disturbances!are!only!temporary!and!responses!from!the!body!cells!quickly! restore!balance!in!the!internal!environment.!Prolonged"disturbances"of"homeostasis!may!be! intense:!poisoning,!overexposure!to!temperature!extremes,!severe!infection!and!major!surgery.!! • Blood!has!many!regulating!systems!that!can!bring!the!internal!environment!back!to!a!balance%! often!the!nervous!and!endocrine!system!work!together!or!independently!to!bring!back!the! dynamic!equilibrium!within!the!body.!! - Nervous!system!regulates!homeostasis!by!sending!nerve!impulses!(action! potentials)!to!organs!that!counteract!the!imbalance!in!the!body.! - Endocrine!system!includes!many!glands!that!secrete!messenger!molecules! (hormones)!into!the!blood.! ! • Describe'the'components'of'feedback'system.' • Feedback!system!is!a!cycle!of!events!in!which!the!status!of!a!body!condition!is!monitored,! evaluated,!changed,!remonitored,!reevaluated!etc.!! • Each!monitored!variable!(body"temperature,"blood"pressure"or"blood"glucose"level)!is!known!as! the!controlled"condition.!Any!disturbances!that!changes!a!controlled!condition!is!known!as!the! stimulus.!! • The!feedback!system!includes!3'basic'components:'a'receptor,'a'control'centre'and'an'effector.'' - Receptor:!body!structure!that!monitors! changes!in!a!controlled!condition!and!sends!input! to!a!control!centre!through!the!afferent"pathway.! This!information!is!carried!to!the!control!center! and!this!is!detected!by!the!input%!in!the!form!of! nerve!impulses!or!chemical!signals.!Monitors!the! physiological!variable!and!detects!changes!in!the! variable.!! - Control'center:!the!brain!sets!range!of! values!within!which!a!controlled!condition!should! be!maintained!and!evaluates!the!input!it!receives! from!the!nerve/chemical!signals,!and!then! generates!output!commands!if!needed.!Output! from!the!control!center!typically!occurs!as!nerve! impulses,!or!hormones!or!other!chemical!signals! through!the!efferent"pathway.!Our!brain!acts!as! the!control!center,!receiving!nerve!impulses!from! skin!receptors!and!generating!nerve!impulses!as! output.!! - Effector:!a!body!structure!that!receives! output!from!the!control!center!and!produces!a! response!that!changes"the"controlled"condition.! Organs!and!tissue!in!the!body!can!behave!as!an! effector.!When!body!temperature!decreases,! brain!(control!centre)!sends!nerve!impulses! (output)!to!skeletal!muscles!(effectors)!and!this! causes!shivering%!this!generates!heat!and!increases!body!temperature.!! ! ! • Contrast'the'operation'of'negative'and'positive'feedback'systems.' • Negative'feedback'system:!reverses!a!change!in!a!controlled!condition.!NOT'FAVOURING' STIMULUS'THUS'NEGATING/DECREASING'THE'EFFECT'OF'THE'ORIGINAL'STIMULUS.' E.g.!when!the!heart!beats!faster!or!harder,!BP!increases.!If!some!internal!or!external! stimulus!causes!blood!pressure!(controlled!condition)!to!rise,!the!following!sequence!of! events!occurs.!Baroreceptors!(the!receptors),!pressure%sensitive!nerve!cells!located!in!the! walls!of!certain!blood!vessels,!detect!the!higher!pressure.!The!baroreceptors!send!nerve! impulses!(input)!to!the!brain!(control!center),!which!interprets!the!impulses!and!responds! by!sending!nerve!impulses!(output)!to!the!heart!and!blood!vessels!(the!effectors).!Heart! rate!decreases!and!blood!vessels!dilate!(widen),!which!cause!BP!to!decrease!(response).! This!sequence!of!events!quickly!returns!the!controlled!condition—blood!pressure—to! normal,!and!homeostasis!is!restored.!Notice!that!the!activity!of!the!effector!(heart!and! blood!vessels)!causes!BP!to!drop,!a!result!that!negates!the!original!stimulus!(an!increase!in! BP).! ! There’s!more!negative!feedback!occurring!than!positive!feed!back!in!the!human!body.!! ! • Positive'feedback'system:!tends!to!strengthen!or!reinforce!a!change!in!one!of!the!body’s! controlled!conditions.!It!provides!short!term!control!over!the!internal!environment.!FAVOURING' STIMULUS'THUS'ENHANCE/AMPLIFYING'EFFECT'OF'ORIGINAL'STIMULUS.!' ! The!control!center!still!provides!commands!to!an!effector!but!unlike!the!negative! feedback!system,!the!effector"produces"a"physiological"response"that"reinforces"the" initial"change"in"the"controlled"condition.!' ! Positive!feedback!also!provides!shortFterm!control!over!the!body’s!internal!environment.!It! also!plays!a!minor!role!in!the!maintenance!of!homeostasis.!! ! Since!positive!feedback!continually!intensifies/reinforce!the!initial!stimulus,!a!mechanism! is!needed!to!terminate!the!physiological!response.!!