Exam 2 Flashcards
What is a PVC?
When the heart contracts prematurely / extrasystole
How are parasympathetic impulses transmitted from the brain to the heart?
Cardioinhibitory center sends impulses through the vagus nerve to decrease HR
How are sympathetic impulses transmitted from the brain to the heart?
The cardioacceleratory center sends impulses through the sympathetic trunk - stimulates the SA node, AV node, myocardium, and the coronary arteries to increase HR and contractility
How do these autonomic systems change the heart rate?
Through the cardiac centers in the medulla oblongata
What does the PNS do to HR?
Can decelerate it
What is the role of artificial pacemakers?
Medical devices that decouple the atria and ventricles - can be programmed to change with changing energy demands and interrogates to with symptoms appear
What is partial heart block?
Only some impulses get through
What is total heart block?
No impulses get through, the ventricles beat at their own intrinsic rate - too slow for adequate tissue perfusion
Why can a PVC feel like a thud in the chest?
Afterwards, the heart has a slightly longer time to fill and the next normal contraction feels like a thud with more fluid
What is an ICD?
Implantable cardioverter defibrillator, devices that continually monitor heart rhythms, they will slow tachycardia and emit an electrical shock in the event of fibrillation
What is defibrillation?
electrically shocking the heart to depolarize the entire myocardium - ideally, the SA node begins to function normally and sinus rhythm is restored
What is fibrillation?
Rapid or irregular contractions of the heart
control of heart by SA node is disrupted
Fibrillation ventricles are not useful pumps
What is an arrhythmia?
Irregular heart rhythm resulting from a defect in the intrinsic conduction system
What is the intrinsic rate set by the AV bundle/Purkinje fibers?
30 beats per min
What is the intrinsic rate set by the AV node?
50 beats per min
What is the intrinsic rate set by the SA node?
75 beats per min
What is the only electrical connection between the atria and ventricles?
AV bundle
Why is there a delay at the AV node?
It allows the atria to complete their contraction
How long does it take an impulse to pass through the entire heart?
0.22s or 220ms
What is the sequence of excitation of the heart?
Sinoatrial node (SA Node)
Atrioventricular node (AV node)
AV bundle / Bundle of His
Right and left bundle branches
Punkinje fibers (subendocardial conducting network)
What is repolarization?
K+ channels open, K+ effluxes, cell’s interior becomes more negative
What is depolarization?
Ca2+ channels open (around -40mV), Ca2+ influxes leading to an AP
What is the intrinsic conduction system?
Noncontractile cells specialized to initiate and distribute impulses throughout the heart
What is the difference between cardiac myocytes and cardiac muscle regarding aerobic respiration?
cardiac myocytes are dense in mitochondria reflecting a great dependence on oxygen
Cardiac muscle is more adaptable to using different nutrient sources as fuel
What is tetany?
In cardiac muscle, the refractory period is longer than contraction to prevent tetany
What is summation?
Occurs in skeletal muscle because the refractory period is short than contraction
What is the absolute refractory period?
The period during an AP when an additional AP cannot be generated
What does depolarization do in cardiac muscle?
Depolarization opens special, slow flow Ca2+ channels in the cell membrane - the combination of extracellular Ca2+ and Ca2+ from the Sarcoplasmic Reticulum allows contraction
What is automaticity/audtorhythmicity?
The ability to spontaneously depolarize
self generated depolarizations travel throughout the heart via gap junctions
No neural input is needed for cardiac myocytes
What are pacemaker cells?
Self excitable, non-contractile cells, SA node
What is the coronary sinus?
cardiac veins merge to form coronary sinus
What is the bicuspid mitral valve?
1 of the 2 AV valves, between LA and LV, 2 flexible cusps
What branches off the descending aorta?
All other systemic arteries
What is the physiology of cardiac tamponade?
Compression of the heart by large amounts of inflammatory fluid in pericardial cavity
hearts ability to pump blood is reduced
Management: removal of excess fluid by syringe
How is calcium delivered?
Fewer, wider, T tubules, 1 per sarcomere, regulate calcium concentration
What are sarcomeres made of?
Myosin, actin, Z discs, A bands, and I bands
What are myosin and actin?
Thick and thin myofilaments part of the sarcomere
What is a functional syncytium?
When the myocardium acts as a single coordinated unit
What are gap junctions?
Part of the intercalated discs, allow ions to pass from cell to cell - transmitting current across the entire heart
What are desmosomes?
Part of intercalated discs, orevtns separation during contraction
What are intercalated discs?
Junctions that the plasma membranes of adjacent cardiac myocytes interlock at