Blood Pressure And Cardiac Cycle Flashcards
Annulus fibrosis- CVS
▪️rings of fibrous fatty tissue that surround the atrio-ventricular junction
▪️electrically insulate atria from ventricles
Heart rhythm
▪️normal-sinus rhythm
▪️without regular rhythm- arrhythmia
Characteristics of cardiac conduction cells
▪️automaticity-ability to initiate an electrical impulse- SAN, AVN, bundle of his (spontaneous depolarises)
▪️excitability-ability to respond to an electrical impulse (contract when a neighbour cell has contracted)
▪️conductivity-ability to transmit an electric pulse from one cell to another
Cardiac cycle
▪️atria systole
▪️isovolumetric ventricular contraction
-increase in pressure, no change in volume (need to overcome pressure in PA/A)
▪️rapid ventricular ejection
-pressure in ventricles had overcome pressure in PA/A so blood can be pushed out
▪️isovolumetric ventricular relaxation
-decrease in pressure, no change in volume
▪️rapid ventricular filling
-when heart chambers are relaxed blood flows passively through atria, through open AV valves and into ventricles
▪️cycle continues
Resting potential of a myocyte
▪️Na/K co-transporter pumps 3Na+ out and 2K+ in
▪️Na/Ca co-transporter pumps 3Na+ in and 1Ca2+ out
▪️K+ channel and plasma membrane allows ot to flow in
▪️more negative inside the cell than outside (-90mV)
-Na+ ⬇️ conc inside
- K+ ⬆️ conc inside
- Ca2+ ⬇️ conc inside
SAN action potential
▪️resting potention -60mV
- gradual rise in membrane potential due to leakage of Na+ ions into the cell making it more positive
- threshold is reached (-40mV) causing a large influx of Ca2+ ions into cell (depolarisation)
- maximum depolarisation is reached closing Ca2+ channels (+30mV)
- K+ channels open and K+ moves out of the cell, they then close when it reaches -60mV (repolarisation)
- cycle continues
Non-pacemaker action potentials
▪️resting potential -90mV
- senses neighbour is depolarised
- Na+ channels open very rapidly and Na+ moves in down conc gradient (depolarisation +30mV)
- K+ channels open and K+ ions leak out (early repolarisation 0mV)
- Ca2+ channels sense change and open and Ca2+ gradually flows. As K+ is still flowing out, the balance of these two actions leads to a plateau (0mV)
- Ca2+ channels then closes leaving only K+ flowing out, therefore voltage drops down to -90mV (repolarisation)
- cycle repeats
Refractory period in non-pacemaker cells
▪️longer than in skeletal muscle
▪️prevents spasms in the muscle from occurring
▪️ensures each contraction is followed by enough time to allow heat to refill with blood before next contraction
-absolute refractory period- time where second AP absolutely cannot be initiated no matter how large the stimulus
-effective refractory period-time after ARP where 2nd AP is inhibited but not impossible
-after ERP- where a propagated AP can be generated
Nervous system regulation of heart rate
▪️medulla (CV centre) receives signals from:
▪️higher brain centres
-eg fight or flight, emotions
▪️sensory receptors
-chemoreceptors (blood chemistry), baroreceptors (BP)
▪️signals then sent by PNS or SNS to heart to:
-increase or decrease heart rate through SAN
-increase or decrease contractility of AandV
SNS control of heart
▪️releases noradrenaline
▪️binds to B1 receptors in SAN,AVN and purkinje fibres
▪️increases heart rate and contractility
PNS control of heart
▪️releases ACh
▪️binds to muscarinic receptors in SAN and AVN
▪️decreases heart rate and prolongs delay at AVN
Balance of PNS and SNS
▪️⬆️ SNS means that threshold is reached faster than normal therefore quicker and shorter AP
-leads to tachycardia
▪️⬆️PNS means that threshold is reached slower than normal therefore longer AP
-leads to bradycardia
Electrocardiogram
▪️vector measurement
- magnitude and direction of depolarisation
- P - atria depolarise
- R - ventricles depolarise
- T - ventricles repolarise
Cardiac output
▪️volume of blood pumped each minute (L/min)
-normal volume 5L/min
▪️CO=SVxHR
-stroke volume- volume of blood pumped in each heartbeat
-heart rate per minute
▪️to increase CO need to increase SV or HR or both
Stroke volume determinants
▪️determined by:
- preload- volume of blood that the ventricle has available to pump
- contractility- force that the muscle can create
- afterload -arterial pressure against which muscle will contract
