Heart intro and Electrical conduction (B 2 : W 1) Flashcards
What percentage of blood is composed of water?
70-80%
What are the characteristics of the left heart?
- Pumps blood into the systemic circulation
- High pressue - needs to go out to body
What are the characteristics of the right heart?
- Pumps blood to the lungs
- Low pressue - pressure in lungs is very low
Where is the majority of the blood in the body?
Veins. There is very little blood in arteries; most is in the veins. They reserve blood
Describe the P wave in an electrocardiogram and its effect on atria and ventricles
Depolarization across the atria (positive on EKG)
- Atria start to contract - triggered by electrical activity
- Small elevation in intra-atrial pressue
- Associated with increase in intraventricular volume - loads ventricle more
- Active pressure buildup
- The rest is passive
Describe the QRS complex in an EKG and it’s effect on atria and ventricles
Ventricular depolarization
- Triggers ventricular pressure buildup
- Intraventricular pressure exceeds atrail pressue
- Causes AV valve to close - due to larger pressue
- Papillary muscles prevent outflow, but do not open or close the valve
- Only pressure does
- No change in volume
- Slight increse in ventricular pressure, greater than aoritc, causes ejection
- Aortic valve opens –> ejection
- Decrease in ventricular volume
- Ejection fraction is not equal to zero: the amount ejected divided by the total amount
Describe the T wave in an EKG and its effect on atria and ventricles
Ventricular repolarization
- Variable between people
- Triggers muscle relaxation
- Manifested by a decline in intraventricular pressure
- Kinetic energy of blood flowing through allows aortic valve to stay open until now
- When the pressure of the ventricle is lower than the atria, AV valve opens
- S3 can sometimes be heard here: filling
Which are the pacemaker cells of the hear?
- **Sino-Atrial nodal cells **- fastest, set the pace for the rest
- Atrio-Ventricular nodal cells
- Purkinje fiber cells
Which cells are specialized for conduction of cardiac impulse?
- AV node
- Internodal and interatrial (Bachmann’s bundle) tracts
- Bundle of Hiss
- Purkinje fibers
Which muscle cells can/cannot summate into tetanus?
Skeletal muscle can
- Recruits more and more fibers
- Sums into a more powerful sustained contraction called tetanus
Cardiac muscle cannot add onto a contraction by trying to stimulate it faster
- Keeps heart from freezing
- Needs to be able to relax, fill, pump
- Intrinsic mechanism prevents heart from contracting if there was a previous excitation
- Cannot re-excite the heart
- Can do a premature contraction during the down phase
Describe the characteristics of the SA node
- Responsible for pacemaker activity of the heart
- Fastest pacemaker
- Cells are smaller than atrial, ventricular, and AV node cells
- Spontaneous excitation by electrical impulse
- Excites atria as well as 3 internodal pathways for rapid exciation of the AV node
Describe the characteristics of the AV node
- Pauses/slows down excitation
- Allows for proper filling of the ventricle
- Small cells, but larger than in SA
- More actin and myosin, complex structure
- Rapid conduction through AV bundle, becomes bundle of His
- Faster cells transmit impulse to L and R bundle branches
Describe Purkinje fibers
- Fastest conduction fibers in the heart
- Tons of voltage-gated Na channels
- Specialized for high conduction velocity
- Penetrate 1/3 of the way on the endocardial side of the ventricle
- Contraction starts in the apex and moves to base
What is the purpose for the delay in conduction at the AV node?
So that the ventricles can be activated in sequence after the atria
What is the function of the atrioventricular fibrous tissue that the AV bundle passes through?
Acts as an electrical insulator between upper and lower chambers of the heart.
If atrial tissue touches ventricular tissue, we could have premature excitation, then there would be no delay in excitation of ventricular tissue.
