Lecture 9 Flashcards
What are heart valves for?
-to ensure unidirectional flow of blood, open and close passively because of pressure differences
What are the three layers in the heart?
- myocardium (mainly that= muscle)
- endocardium(middle layer of cardiac muscle between an endothelial layer and the-
- epicardium (thin outer sheath)
What does the myocardium consist of?
- interlacing bundles of cardiac muscle fibres arranged spirally around the heart circumference
- when ventricular muscle contracts= chamber reduces in size
What’s an intercalated disk?
-specialised cells joining adjacent muscle cells end to end
What are the two types of membrane junctions within an intercalated disk?
- desmosomes=type of adhering junction that mechanically holds cells together under high mechanical stress
- gap junctions=channels allowing AP to spread from one cardiac cell to the next
What initiates heart contraction?
- pacemaker activity
- group of cells that can self excite
- myogenic= self excitable
Do pacemaker cells have a constant resting potential?
- no
- the membrane potential slowly depolarises or drifts between APs until threshold is reached= AP
What are the three important changes in ion movement in terms of pacemaker potential?
- an increased inwards Na+ leakage
- decreased outwards K+ leakage
- an increased inwards Ca2+ leakage
What is the pacemaker? Where is it?
sinoatrial node (SA) -the normal atriventricular node (AV) - base of the right atrium just above the junction of the atria and ventricles
How is AP generated in the heart?
-pacemaker
-open Na+
-close Na+/open Ca2+
-close Ca2+/open K+
Ca2+ from ECF and ICF
How does AP spread in the heart?
SAN- atria- AV=stops it for 0.1s to allow for the atria to be depolarised-ventricles (travels theer along Purkinje fibres)
Describe the action potential of cardiac muscle cells?
- open Na+
- close Na+/open Ca2+
- close Ca2+/open K+
- Ca2+ from ECF and INF
What is EEG?
-electrocardiogram
- electrical currents generated by the cardiac muscle spread into surrounding tissue where it can be detected
- it therefore records only a portion of the electrical activity, just what gets to skin
What does the P wave represent?
-atrial depolarisation
What does the QRS complex represent?
-ventricular depolarisation
What does the T wave represent?
-ventricular repolarisation
What is the PR segment?
AV node delay