curs 7 - mgsii.files.wordpress.com · contractia organ versus contractia unitatilor motorii ... -...
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CURS 7 FIZIOLOGIA SISTEMULUI
CARDIOVASCULAR
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INIMA
organ musculo-cavitar- cu formă conică
Peretele inimii are 3 straturi: 1. endocard- ţesut endotelial 2. miocard- muşchiul striat cardiac cuprinde: - celule specializate in contractie - celule celule specializate in geneza si
conducerea impulsurilor -grosimea peretelui VS > 3-4ori VD 3. pericard-membrana externa - foita viscerală şi parietala- cavitatea pericardică, -cu un strat
fin de lichid
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Martini F, Ober WC, Nath JN, Bartholomew EF, Petti K. Visual anatomy and physiology, 2011
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FIBRE MUSCULARE CARDIACE- structura
MUSCHI CARDIAC- striat si se contracta prin alunecarea filamentelor
- Fibre musculare scurte, ramificate si interconectate
- Fiecare fibra contine 1 (max 2) nucleu central
- Sp intercelular- Tesut conjunctiv lax- endomisium- ce contine o serie de capilare
- Tes conjunctiv lax- conectat cu scheletul fibros cardiac care actioneaza ca si tendon
• MIOCARD- SINCITIU FUNCTIONAL- celulele musculare cardiace sunt conectate mecanic, chimic si electric
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FIBRE MUSCULARE CARDIACE- structura
• Membrana plasmatica a celulelor cardiace adiacente- se leaga prin discuri intercalare- contin desmozomi si gap junctions
• desmozomi previn separarea celulelor adiacente in timpul contractiei
• gap junctions- perimit ionii sa treaca de la o celula la alta- transmitere de curent
SINCITIU FUNCTIONAL
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FIBRE MUSCULARE CARDIACE- structura
• mitocondrii- 25–35% din vol cel cardiace- ofera rezistenta la oboseala !!!!!!
• miofibrile- compuse din sarcomere
- Sarcomere disc Z, banda A si I- miofilamente
- miofibrilele m cardiac- variaza in diametru- intre ele mitocondrii
- Benzi mai putin vizibile vs m scheletic
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Marieb EN, Hoehn K. Anatomy and Physiology 2013
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Tortora G, Derrikson B. Principles of anatomy and physiology 12th edition, 2009
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Fox SR. Human Physiology 2011
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Fox SR. Human Physiology 2011
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Fox SR. Human Physiology 2011
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FIBRE MUSCULARE CARDIACE- structura
• Sistemul eliberator de calciu- mai putin elaborat
- tubii T- invaginatii ale sarcolemei - mai largi si mai putini- vs m scheletic - intra in celule- odata pe sarcomer- in
zona discurilor Z - Reticulul sarcoplasmic- este mai simplu si nu
prezinta cisternele largi din m scheletic
- Fibrele M cardiac NU prezinta triada
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Tortora G, Derrikson B. Principles of anatomy and physiology 12th edition, 2009
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Fox SR. Human Physiology 2011
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PARTICULARITATI- m cardiac
• 1. STIMULARE – unele celule cardiace- autoexcitabile
Initiaza propria depolarizare- dar si a cordului SPONTAN SI RITMIC- automatism/autoritmicitate
• 2. Contractia organ versus contractia unitatilor motorii
• TOT SAU NIMIC- contractia are loc unitar- unitate contractila datorata gap junctions- undele de depolarizare trec de la o celula la alta prin pasajul ionic la nivelul gap junctions.
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PARTICULARITATI- m cardiac
• 3. Perioada refractara absoluta
• Perioada inexcitabila- canale de Na sunt deschise sau inactivate
• M cardiac-200 ms aprox egal cu contractia
• !!! Previne contractiile tetanice
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Similitudini m cardiac/scheletic
• Contractia m cardiac- trigger- PA
- 1% din fibrele cardiace sunt autoritmice- “self ritmic”- depolarizare spontana
- Majoritatea- fibre miocardice contractile
- Secventa evenimentelor care duc la contractie- similara cu cea din m scheletic
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Martini F, Ober WC, Nath JN, Bartholomew EF, Petti K. Visual anatomy and physiology, 2011
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Martini F, Ober WC, Nath JN, Bartholomew EF, Petti K. Visual anatomy and physiology, 2011
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PROPRIETATILE MIOCARDULUI
• 1. AUTOMATISM
• 2. CONDUCTIBILITATE – functia dromotropa
• 3. RITMICITATE- functia cronotropa
• 3. CONTRACTILITATE- functia inotropa
• 5. EXCITABILITATE- functia batmotropa
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1. AUTOMATISM CARDIAC
• AUTOMATISM CARDIAC- definitie • ABILITATEA M CARDIAC DE A SE DEPOLARIZA SI DE A SE
CONTRACTA- intrinseca - nu depinde de SN - TRANSPLANT CORD!!!! -DAR!!!! are inervatie autonoma- poate modifica ritmul
cardiac de baza • FIBRE MUSCULARE CARDIACE SPECIALIZATE- AUTORITMICE - implicate in geneza si conducerea impulsurilor nervoase - Genereaza PA – trigger pentru contractiile cardiace - 1% din fibrele m cardiac
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1. AUTOMATISM CARDIAC
• FIBRE MUSCULARE CARDIACE SPECIALIZATE-
• actioneaza ca un pacemaker- dau ritmul excitatiei electrice si determina contractia cardiaca
• 2. formeaza un sistem de conducere- fibre musculare cardiace specializate- excitatia- progreseaza si cuprinde intreg cordul
- sistemul de conducere asigura- stimularea A si a V in vederea contractiei= INIMA POMPA EFICIENTA
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1. AUTOMATISM CARDIAC
• FIBRE MUSCULARE CARDIACE SPECIALIZATE-
• Nodul SA- perete posterior al AD • nodul AV (Aschoff-Tawara)- port inf a sept interatrial • Fascicului Hiss
• reteaua Purkinje – retea subendocardica
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Marieb EN, Hoehn K. Anatomy and Physiology 2013
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PA IN CELULELE PACEMAKER
CELULE CARDIACE PACEMAKER – CELULE AUTORITMICE-
- Diferite fata de cel contractile-
- Celule autoritmice- mici, contin putine fibre contractile
- Nu au sarcomere organizate- nu contribuie la forta contractila a cordului
- potential de repaos instabil care se depolarizeaza continuu- deplasare spre atingerea pragului
• Potential de membrana instabil= POTENTIAL PACEMAKER SAU PREPOTENTIAL- determina contractia ritmica
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PA IN CELULELE PACEMAKER
• 1 Pacemaker potential
• 2 Depolarizare
• 3 Repolarizare
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1 Pacemaker potential.
Datorat proprietatilor speciale ale canalelor ionice din sarcolema • Se datoreaza: • canalelor de K • Canalelor de Na • Canalelor de Ca
• hiperpolarizarea la sf PA-reducerea permeabilitatii pentru K- inchiderea
canalele de K datorata revenirii membranei la potentiale negative
• deschiderea canalelelor lente de Na – la valori negative ale potentialului de membrana- Influxul de Na altereaza balanta intre pierderea de K si intrarea Na- interiorul membranei devine tot mai putin negativ
• Canalele de Ca- se deschid scurt- influx Ca (canale de tip T)
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2 Depolarizare
• Atunci cand potentialul pacemaker atinge pragul - declansarea PA
• Depolarizarea se datoreaza- deschiderii canalelor de Ca (de tip L)- permit intrarea exploziva a acestuia din spatiul extracelular
- Rezulta- in celulele pacemaker- influx de Ca care produce faza de crestere a PA si inverseaza potentialul de membrana
• Depolarizare mai lenta in raport cu canalele de Na voltaj- gated- propagarea este mai lenta – explica transmiterea lenta a excitatiei prin nodul AV
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3 Repolarizare
• Canalele de Ca se inchid • Diminuarea PA- si repolarizarea reflecta DESCHIDEREA
canalelor K si efluxul de K din celula
• ATUNCI CAND REPOLARIZAREA ESTE COMPLETA- canalele de K se inchid- efluxul de K scade- si se reinstaleaza depolarizarea lenta spre valoarea prag
• Revenirea la potentiale negative reactiveaza mecanismul de pacemaker si ciclul se repeta
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Vander’s Human Physiology, 13th edition, 2014
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PA IN FIBRELE MIOCARDICE CONTRACTILE
• Celulele miocardice contractile- POTENTIAL MEMBRANAR DE REPAOS DE - 90 mV
• PA initiat de nodulul SA este transmis prin sistemul de conducere si se raspandeste- determina excitatia si contractia fibrelor contractile ale A si ale V
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PA IN FIBRELE MIOCARDICE CONTRACTILE
●1 Depolarizare- DE LA -90 mV la +30 mV
- sub actiunea PA din fibrele vecine- in fibrele contractile se
atinge o valoare prag- se deschid canalele de Na voltaj dependente- feedback pozitiv
- canale de Na “rapide”- se deschid f rapid - Na intra in celule- deoarece!!!!! - intrarea Na determina- DEPOLARIZARE RAPIDA - determina faza ascendenta a PA de la -90 mV la +30 mV
• Perioada f scurta- canalele de Na se inactiveaza rapid si influxul de Na
scade
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PA IN FIBRELE MIOCARDICE CONTRACTILE
●2 FAZA DE PLATOU- perioada de mentinere a depolarizarii - se datoreaza canalelor lente de Ca din sarcolema - fluidul interstitial- conc Ca!!!! - INFLUX de Ca determina tot mai mult eliberarea calciului din reticulul
sarcoplasmic (RS) in citosol prin canale aditionale din membrana RS - trigger pentru contractie - canalele de K voltage-gated -inainte de instalarea fazei de platou
unele canale de K se deschid permitand ionilor de K sa paraseasca fibra contractila
!!!! DEPOLARIZAREA este sustinuta in faza de platou deoarece influxul de Ca balanseaza
efluxul de K - 0.25 s - pot de membrana aprox 0 mV !!!!! Neuron, m scheletic- lipseste faza de platou
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PA IN FIBRELE MIOCARDICE CONTRACTILE
• ●3 FAZA DE REPOLARIZARE- revenirea la potentialul de repaos
• Dupa o intarziere- specific prelungita in m cardiac- se deschid alte canale de K
• Efluxul de K reface potentialul de membrana negativ
• Canalele de Ca din sarcolema si RS se inchid- contribuie la repolarizare
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Vander’s Human Physiology, 13th edition, 2014
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Marieb EN, Hoehn K. Anatomy and Physiology 2013
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Tortora G, Derrikson B. Principles of anatomy and physiology 12th edition, 2009
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Marieb EN, Hoehn K. Anatomy and Physiology 2013
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2. CONDUCTIBILITATE- functia dromotropa
- Definitie-
- Are loc prin:- tesut miocardic si
- tesut specific
Nodul sinoatrial
Nodul artrioventricular
Fascicul His
Reteaua Purkinje
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Vander’s Human Physiology, 13th edition, 2014
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Nodul sinoartrial NSA
• 1 NSA in atriul drept- inferior Venei cave superioare
• PA se raspandeste in miocard-atrii- de la celula la celula via gap junctions.
• Cea mai rapida rata de depolarizare!!!!
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Silverthorn’s Human Physiology, 2013
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Nodul atrioventricular NAV
• 2. de la nodul SA- depolarizarea se imprastie via cailor internodale spre NAV- aflat in portiunea inf a sept interatrial – sinus coronarian
• In NAV- impulsurile intarzie 0.1 s- permit atriilor sa raspunda si sa finalizeze contractia inainte de contractia V
• INTARZIERE- reflecta diametru redus al fibrelor-
- putine gap junctions
NAV conduce impulsuri mai lent- “just as traffic slows when cars are forced to merge from four lanes into two”
Marieb EN, Hoehn K. Anatomy and Physiology 2013
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Fasciculul lui Hiss
• 3. de la NAV- PA se transmite prin fasciculul His aflat in partea superioara a sept interventricular
• Fascicului lui His- ramura dreapta si ramura stanga
• Atriile si Ventriculele NU sunt conectate prin gap junctions.
• Nodul AV si Fascicului His- singura conexiune electrica intre A si V
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Reteaua Purkinje
• 4. Reteaua Purkinje- Retea subendocardica- putine miofibrile
• Reteaua Purkinje- continua calea de conducere interventriculara- penetreaza in apex- si apoi se indeapta superior spre peretii ventriculelor-
• Depolarizarea ventriculara depinde de fibrele retelei Purkinje si de transmiterea impulsului de la celula la celula via gap junctions intre celulele musculare ventriculare
• Reteaua subendocardica a ventriculului stang este mai bine
reprezentata fata de cea a V drept • !!!! FINAL- contractie eficienta care impinge sangele spre valve
“like squeezing a tube of toothpaste from the bottom up”
Marieb EN, Hoehn K. Anatomy and Physiology 2013
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Tortora G, Derrikson B. Principles of anatomy and physiology 12th edition, 2009
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Vander’s Human Physiology, 13th edition, 2014
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2. CONDUCTIBILITATE- functia dromotropa REZUMAT
• 1. Depolarizarea NSA
• 2. Transmiterea activitatii electrice spre NAV prin cai internodale
• 3. Depolarizarea se raspandeste incet in atrii- Conductibilitatea este incetinita la nivelul NAV
• 4. Depolarizarea se deplaseaza rapid prin sistemul de conducere ventricular spre apex
• 5. Unda de depolarizare se raspandeste de la apex spre baza inimii
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2. CONDUCTIBILITATE- functia dromotropa
• Influentata de:
- Factori fizici- caldura- creste conductibilitatea
- frig- scade conductibilitatea
- Substante medicamentoase- digitala reduce C
- Impulsuri simpatice- cresc viteza de conducere
- Impulsuri vagale- intarzie conducerea
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3. RITMICITATE-functia cronotropa
Definitie- proprietatea inimii de a emite ritmic impulsuri datorate tesutului nodal cardiac
Ritm cardiac- impus de nodulul sinoatrial- 70-80/min NAV- 40-60/min F Hiss/Reteaua Purkinje- 20-40/min - atletii- 50/min sau mai redus - stari agitatie, emotii- >125/min - copii vs adulti - modelat de factori neurvosi si hormonali
SILVERTHORN
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3. RITMICITATE-functia cronotropa
• Reglare
- factori nervosi- SNS si SNPS
Silverthorn’s Human Physiology, 2013
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3. RITMICITATE-functia cronotropa
Silverthorn’s Human Physiology, 2013
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3. RITMICITATE-functia cronotropa
• CONTROL PARASIMPATIC - ACETILCOLINA
- Ach- activeaza rec muscarinici colinergici ce influenteaza canalele de K+ si Ca2+ in celulele pacemaker - - permeabiliatea pentru K- creste- hiperpolarizarea celulelor
- potentialul pacemaker incepe la o valoare mai negativa
- permeabilitatea pentru Ca2+ a pacemaker scade - scaderea permeabilitatii reduce rata la care potentialul pacemaker se depolarizeaza
- timp prelungit pt a atinge valoare prag- intarzie instalarea PA
REDUCE FRECVENTA CARDIACA
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Silverthorn’s Human Physiology, 2013
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Silverthorn’s Human Physiology, 2013
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3. RITMICITATE-functia cronotropa
• CONTROL SIMPATIC- CATECOLAMINE
• Catecolamine- cresc fluxul de ioni prin canalele Na si Ca - Cresc rata de depolarizare a pacemaker - celulele ating pragul PA rapid - Cresc rata PA
• EFECTE- se leaga si activeaza rec b1-adrenergici de la nivelul
celulelor auto-ritmice • b1-receptorii folosesc cAMP ca mesager de ordin 2- modificarea
transportului ionic de la nivelul canalelor
• Cresterea permeabilitatii – pentru Na+ si Ca2+ in timpul fazei de pacemaker potential- grabeste depolarizarea si Frecventa Cardiaca
CRESTE FRECVENTA CARDIACA
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Silverthorn’s Human Physiology, 2013
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3. RITMICITATE-functia cronotropa
• CONTROL TONIC-
• in conditii de rapaus- activitatea cardiaca este dominata de SNPS- cu efecte inhibitorii
• Cordul- tonus vagal
• Blocarea tonusului vagal- determina cresterea frecventei cardiace cu 25 batai/min
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3. RITMICITATE-functia cronotropa
• Factori chimici - Calciu ↑- acc ritm cardiac- opreste inima in
sistola - calciu ↓ determina insuficienta mecanica- oprire
instantaneu - crestere a K- rareste ritm cardiac- oprire in
diastola- determina hiperpolarizare - digitala- rareste ritm cardiac Factori fizici-
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4. CONTRACTILITATEA- functia inotropa
Contractia- similara m scheletic
• Nu atat de rapid ca in m. scheletici
• Raspuns tot sau nimic
• Actina, Miozina, Troponina, tropomiozina
• Troponina- proteina receptoare de Ca
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4. CONTRACTILITATEA- functia inotropa
• Contractia incepe la ms dupa depolarizare
• Tensiunea musculara se dezvolta in timpul platoului si atinge varful dupa sf platoului- Tensiunea max- in timpul repolarizarii
• Relaxarea- la 50 ms dupa restabilirea Potential de Repaos
• Nu se tetanizeaza • M cardiac- AP- dureaza 200 ms iar tensiunea persista-
200 ms sau peste-
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4. CONTRACTILITATEA- functia inotropa
• CATECOLAMINE, DIGITALA- cresc contractilitatea
• Creste- odata cu cantitatea de calciu-
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. 4. CONTRACTILITATEA- functia inotropa
• CATECOLAMINE cresc depozitele de Ca- fosfolamban- • ↑ activitatea Ca2+-ATPazei din RS- concentreaza Ca2+ in RS- ↑ Ca2+
disponibil pentru a fi eliberat
• ↑ Calciu citosolic- mai multe punti active • Forta de contractie e proportionala cu nr puntilor active
• Catecolaminele- cresc forta de contractie - scurteaza durata de contractie Cresterea Ca2+-ATPazei- grabeste indepartarea Ca2+ din citosol - Reduce timpul de fixare a Ca2+ de troponina - Reduce timpul activ al puntilor de miozina
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Silverthorn’s Human Physiology, 2013
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4. CONTRACTILITATEA- functia inotropa
DIGITALICE- glicozide cardiace-Digitalis purpurea digitoxina- ouabain-
• Cresc contractilitatea prin incetinirea indepartarii Ca2+ din citosol
• Depreseaza activitatea Na+-K+-ATPazei in toate celulele
• Na+ se acumuleaza in citosol- gradient de concentratie gradient pt Na+ SCADE
• SCADE ENERGIA PENTRU TRANSPORT ACTIV indirect
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5.Excitabilitatea- functia batmotropa
• Definitie- proprietatea celulelor vii de a raspunde la stimuli
• EXCITATIA= DEPOLARIZAREA SARCOLEMEI
• EXCITATIA- transmisa tuburilor transversali si discurile intercalare
• CUPLARE EXCITATIE CONTRACTIE- prin depolarizarea sistem sarcoplasmic longitudinal- aflat in contact cu sistemul tubular transversal- eliberarea Ca stocat
• Ca provine si din lichidul extracelular
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CUPLARE EXCITATIE CONTRACTIE
• 1. Potential de actiune- in celulele contractile • 2. Deschiderea canalelor de Calciu L din membrana celulara
• 3. calciu intra in celula
• 4. Calciu care a intrat in celula- stimuleaza eliberarea de calciu din RS ELIBERARE DE CALCIU INDUSA DE CALCIU Calciu din RS- 90% din Ca2+ necesar pentru contractia musculara 10% din Ca- din spatiul extracelular
• 5. Legarea Calciului de troponina
• 6. contractia are loc similar m scheletic
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Relaxarea
• 7. Relaxarea- similara m scheletic
Reducerea Ca citoplasmatic- Ca2+ se desprinde din troponina, miozina se decupleaza de actina- filamentele revin la pozitia de repaus
• 8. Ca2+ este transport inapoi in RS prin Ca2+-ATPaza
• 9. Ca2+ indepartat in afara celulei la schimb cu Na+ via Na+-Ca2+ exchanger
1 Ca2+- la schimb cu 3 Na+
• 10. Na care intra in celula este indepartat apoi de catre Na+-K+-ATP aza
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5.Excitabilitatea- functia batmotropa
• !!!! Cresterea conc Ca citosolic in timpul excitatiei- determinant major al fortei de contractie-
• !!!! forta de contractie este crescuta daca o cantitate mai mare de Ca este eliberata din RS
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Vander’s Human Physiology, 13th edition, 2014
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Fox SR. Human Physiology 2011
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Fox SR. Human Physiology 2011
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Fox SR. Human Physiology 2011
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Fox SR. Human Physiology 2011
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Inexcitabilitatea periodica a inimii
• Perioada refractara absoluta- perioada din timpul si dupa un PA cand o membrana excitabila nu poate fi re-excitata
• Inactivarea can de Na
• Per refractara absoluta- durata= contractia absoluta (aprox 250 msec)
• Excitabilitatea reapare- cand repolarizarea atinge valoarea de -55mV
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Vander’s Human Physiology, 13th edition, 2014