CS - Heart part 2
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20% of the heart returning to the heart return via the thebesian veins, but how does the remaining 80% come back through the heart?
- Return by way of the:
- great cardiac vein
- posterior interventricular (middle cardiac) vein
- left marginal vein
- coronary sinus - collects from other veins and dumps into the right atrium
- anterior cardiac veins - also directly into the cardiac vein
What is a normal HR?
around 75 beats per minute in an adult
What does it mean that the heart is myogenic?
It means that the signal originates with the heart itself. So if its cut up it will still beat.
Even through the heart is myogenic, it is still supplied by nerves from the sympathetic and parasympathetic nervous system. What are the sympathetic and parasympathetic nerves in the heart?
The sympathetic are the cardiac nerves and they go to the ventricle. These increase the force of contraction and help to dilate the coronary vessels during excersize. Can increase HR up to 230 beats/min.
The parasympathetic are the vagus nerves. They help to give the heart it vagus tone, which helps keep the heart at its normal HR. So it slows the heart down. If the vagus is cut the heart rate will increase to about 100 beats/minute.
What is the pathway does the cardiac conduction happen?
- 1. Startes at the SA node in the right atrium where it spreads through the atria
- 2. It then goes the the AV node that is near the right AV valve - this is the electrical gateway to the ventricles
- 3. From the AV node the signal goes to the AV bundle - there are 2 branches the right and left that go towards the apex of the heart
- 4. From the bundle the signal travels to the purkinje fibers which are at the end of the AV bundle branches and go tot the myeocytes of the ventricles
- 5. From the fibers the signal finally ends in the individual myocytes (the heart cells) where the signal is passed from one cell to another.
- - short and thick
- - have large T tubules that allow Ca ++ enter which is key to the HR
- - large mitochondria
- - joined together by intercalaated discs
Cardiac muscles are different than skeletal muscles what are 3 differences?
1. Interdigitating folds that help to increase the contact area
2. Mechanical junctions that enable myocytes to pull on each other without pulling apart
3. Electrical junctions that have gap junctions that allow the flow of ions from one cell to another. This allows the myocardium to contract as one, helps for maintaining heart pump.
Aerorbic respiration is used exculsively only in what type of muscule?
What is systole and diastole?
Systole is contraction
Diastole is relaxation
What is the normal sinus rhytum?
between 70 to 80 bpm but can range from 60 to 100 bpm
What is premature ventricular contraction (or PVC)?
Its when the system fires before the SA node.
What is ectopic focus?
is any region that is firing other than the SA node
Most common is the AV node
What is nodal rhythm?
Its when the HR is slower at around 40 to 50 bpm anything lower than that requires a pacemaker
What is arrhythmia?
Is any abnormal cardiac rhythm like:
- Atrial flutter - 200 to 400 bpm in the atria
- Ventricular fibrillation - a strong electrical shock that is deadly if not corrected and is treated with
What can cause an arrythmia?
A heart block which happens when any part of the conduction system does diliver its signal
What are the 2 types of heart blocks?
A bundle branch block and a total heart clock which happens when damage to the AV node occurs.
What is it called when the SA node becomes a depolarization?
What is pacemake potential?
ITs that gradual depolarization of the SA node.
What happens during pacemaker potential?
Na+ goes slowly in until it reaches the threshold of -40mV. Ca++ goes in threw Ca+ channels from ECF. It then reaches action potential and K+ starts to flow out cause repolarization until the K+ gate close and the cycle starts over again.
***Ca++ allows for longer contration verses skeletal muscle so a longer platau***
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