Lecture 11 3/4/14 Flashcards
SA Node
at the junction between the Superior Vena Cava and Right Atrium;
It is still cardiac muscle tissue but with a lot less of the actin and myosin in it. So the SA Node is more conductive in nature than contractile. Still a functional synctium.
We don’t need to send nerve fibers to every single muscle fiber, we have the gap junctions. So basically it is comprised of specialized nerve cells.
It initiates each cardiac cycle. SA Node is controlled by the Vagus Nerve. Vagus Nerve slows the heart rate down. It’s parasympathetic.
Speed can be altered by what nervous system? And what can slow it down?
by the autonomic nervous system. Norepinephrine and Epinephrine, and Thyroid, but thyroid deficiency can slow it down.
How does blood get to the AV Node?
Via the Internodal Pathways
AV Node
(Atrioventricular Node) is located at the junction of the Atria and Ventricles. More to the right side than the left.
Heart Contraction Process
When the heart contracts, the Atria contracts from the top and pushes blood down into the ventricles. And when the ventricles contract, they contract from the bottom and push upward, so that means the electrical wave goes from the top down, and then the ventricles contract from the bottom upward to push the blood up and out.
How does blood go from the AV Node to the Interventricular Septum?
Through the structure called the AV Bundle or Bundle of His
Bundle of His
branches off as bundle branches, left and right bundle branches.
Travels down to between the two ventricles, within the septum. From the left and right branches, we go to the terminal branches called the Purkinje Fibers - terminal walls in the walls of the ventricles.
Purkinje Fibers
End fibers
Terminal Walls in the walls of the ventricles
Order of Heart Muscle Contractions
1) Atria fires (contracts) first from the top down.
2) Then functionally, the Apex, contracts from the bottom towards the top.
3) Then walls of the ventricles contract upwards and out from the apex.
EKG or Electrocardiogram
It measures electrical wave moving through the heart muscle tissue, it doesn’t directly measure heart muscle contraction.
Records the electrical changes that accompany the cardiac conduction cycle.
Electrodes are placed on various places on the chest wall and extremities to monitor the electrical depolarization.
PQRST Sequence
P Wave -> QRS Complex -> T Wave
P Wave
Represents Atrial Depolarization
Relatively small
QRS Complex
Represents Ventricular depolarization.
Relatively larger.
Happens a half second later after the P Wave
T Wave
Represents ventricular re-polarization.
Larger muscle mass.
Happens a fraction of a second later after the QRS Complex.
Always larger than the P Wave. Should not be equal in size to the P Wave.
Atrial Repolarization is hidden by what complex?
QRS Complex
Define Cardiac Cycle
period from the start of one beat to the beginning of the next
Define Systole
Refers to heart muscle contraction (higher number). Pressure in the vessels when the heart is contracting.
Define Diastole
Represents heart muscle relaxation (lower number). Pressure in the vessels when the heart is not contracting.
Normal Cardiac Cycle Refers to What?
refers to the systole and the diastole of both atria and ventricles.
Normal Cardiac Cycle has two parts, what are they?
A) Atria contract while the ventricles relax.
B) Ventricles contract while the atria relax.
Describe Heart Muscle Contraction
happens around a period of .2-.3 seconds, the rest of the time there is no atrial or ventricle contraction.
Atrial Diastole
the atria are relaxing. The AV valves are opened and the semilunar are closed.
There is a period of time that the atria are passively filling up with blood, and that blood is traveling down through those AV Valves and then they are passively filling up in the ventricles.
70% of ventricular volume filling occurs at this time. At 120 ml maximum ventricles are full.
Atrial Systole
period of time where the atria are contracting. The pressure in the atria is going to increase, Topping off ventricular volume.
Increasing volume, bringing it up to 100% which is 120 ml. The SA Node fires, which is causing the contraction to occur.
The AV Valves are opened and the semi-lunar valves are still closed.
Ventricular Systole
Happens after Atrial Systole
Then we get ventricular contraction, ejecting percentage of blood from the ventricles, that percentage of blood is around 60%.
The AV valves are closed and the semi-lunar valves are opened. Occurs when the QRS wave is visible. AV Node fires.
Ventricular Diastole
We’ve ejected the blood out. Now the blood is sent out to the body, some of the blood comes back against the valve cusps causing it to close.
The semi-lunar valves are closed and initially the AV Valves are closed. The first vessels to come off of the Aorta is the Coronary Arteries.
The back flow of blood pushes the valve cusps closed, the blood has nowhere to go but into the coronary arteries.
Heart Sounds
Typical Heart sounds due to the turbulence created
What are the typical heart sounds?
Lubb
Dupp
Describe Lubb Sound
the first heart sound, is a softer sound that represents the AV Valve closing.
Describe Dupp Sound
the second heart sound, that represents the semi-lunar valve cusps closing. And they snap shut making a sharper sound.
There are 4 sounds that you can hear, but only two can be heard. Explain
There are 4 sounds that you can hear, but only two can be heard from the stethoscope and the other two can only be heard when amplified with a amplified stethoscope.
S1 Sound is what Sound? Why?
Lubb, because it’s the first sound heard
S2 Sound is what Sound? Why?
Dupp, because it’s the second sound heard
Pressure changes within the heart chambers and develops due to what?
- Chamber Size
2. Volume Blood
