The Circulatory System 3 Flashcards
general properties of cardiac cells
automaticity
- ability to initiate/fire APs spontaneously
- called automatic/pacemaker activity
- normal cardiac/automatic/pacemaker cells: SA node, AV node, His-Purkinje system
- primary vs latent/subsidiary pacemakers
- intrinsic + extrinsic control
what is the basis of automaticity?
I^f current + spontaneous phase 4 depolarisation
natural pattern of excitation of the heart
- heart beats spontaneously + rhythmically
- triggered by spread of AP across muscle cell memb
- AP CYCLICALLY initiated + conducted in ORDERLY SEQ
SAN -> atria -> AVN -> bundle of his -> purkinje fibres -> ventricles
how are electrical currents generated?
by cardiac muscle during depolarisation + repolarisation
conducted through bodily fluids + into tissues around heart
detected on body surface + recorded as ECG/EKG (electrocardiogram)
what is an ECG?
summation of overall spread of electrical activity throughout heart during depolarisation and repolarisation
what are the standard 12-lead ECG recordings?
six limb heads (I-III, aVR, aVL + aVF)
six chest leads (V1-V6)
what are the 3 distinct waveforms a normal ECG has?
- P wave
- QRS complex
- T wave
P wave represents…
atrial depolarisation
the QRS complex represents…
ventricular depolarisation
the T wave represents…
ventricular repolarisation
individual cardiac muscles … to form branching fibres
interconnect
what are intercalated discs?
adjacent cells joined end to end at specialised structures
what are the 2 types of membrane junctions present within intercalated disc?
- desmosomes
- gap junctions
desmosomes
cell to cell anchoring junctions
gap junctions
cell to cell communication junctions
muscle mass forms a ….
functional syncytium (becomes excited + contracts as single unit)
systole
- ventricular contraction + emptying
- 2 sub phases / periods = isovolumetric contraction + ejection periods
diastole
- ventricular relaxation + filling
- 2 sub phases / periods = isovolumetric relaxation + filling periods
cardiac cycle?
- LATE DIASTOLE - both sets chambers relaxed + ventricles fill
- ATRIAL SYSTOLE - atrial contraction forces small mount blood into ventricles
- ISOVOLUMETRIC VENTRICULAR CONTRACTION - 1st phase of v. contraction pushes AV closed but doesn’t create enough pressure to open SL valves
- VENTRICULAR EJECTION - ventricular pressure rises + exceeds pressure in arteries.
SL valves open + blood = ejected - ISOVOLUMETRIC VENTRICULAR RELAXATION - ventricles relax, pressure in ventricles falls.
blood flows back into cups of SL valves and snaps them closed
1st heart sound (Lub)?
closure of AV valves at start of ventricular contraction
2nd heart sound (Dub)?
due to closure of aortic + pulmonary valves at end of v.systole
3rd heart sound?
heard in early diastole
due to inrush of blood during rapid ventricular filling
4th heart sound (Dub)?
heard immediately before 1st sound (in late diastole)
due to ventricular filling
excitation contraction coupling process
- action potential enters from adjacent cell
- voltage-gated Ca2+ channels open. Ca2+ enters cells
- Ca2+ induces release through ryanodine receptor channels
- local release -> Ca2+ spark
- summed Ca2+ sparks -> Ca2+ signal
- Ca2+ ions bind to troponin to initiate contraction
- relaxation happens when Ca2+ unbinds from troponin
- Ca2+ pumped back into SR for storage
- Ca2+ exchanged with Na+
- Na+ gradient maintained by Na+-K+-ATPase
