Cardiac cycle 2- Atrial ventricular diastole

Cardiac cycle 2- Atrial ventricular diastole


– DON’T FORGET: WE COULD START ANYWHERE. WE COULD START ANYWHERE
IN THIS PROCESS. WHERE I’M CHOOSING
TO HAVE US START IS THIS MOMENT WHEN EVERYTHING IS RELAXED. AND IT JUST GIVES US
KIND OF A NICE MARKER. THERE’S NO ACTION POTENTIALS
RUNNING THROUGH. EVERYTHING, ALL THE MUSCLES, ARE JUST COMING BACK
AND REPOLARIZING; AND THE MYOFIBERS ARE
JUST STRETCHING APART, THE SARCOMERES ARE LENGTHENING, THE WHOLE THING IS JUST RELAXED. IT’S VENTRICULAR
AND ATRIAL DIASTOLE. AND YOU CAN SEE THAT HERE,
IN THIS VISUAL. THIS IS FROM YOUR TEXT. YOU CAN SEE THAT THERE AREN’T
ANY COLORS AND THERE ISN’T ANYTHING INDICATING THAT WE’VE
GOT A CONTRACTION TAKING PLACE. DURING THIS TIME,
NOW KEEP IN MIND, IT’S A CYCLE; SO SOMETHING HAD
TO HAPPEN DOWN HERE IN ORDER TO CREATE
THE SITUATION HERE. BUT UNTIL WE GET DOWN HERE, WE MIGHT JUST
HAVE TO ACCEPT THAT, OKAY, THESE ARE THE THINGS THAT ARE
HAPPENING AT STAGE I. FIRST OF ALL,
THE ATRIA ARE FILLING. THEY’RE FILLING FROM THE VEINS –THE LEFT ATRIUM IS FILLING
FROM THE PULMONARY VEINS; THE RIGHT ATRIUM IS FILLING FROM
SUPERIOR AND INFERIOR VENA CAVA. THE AV VALVES ARE OPEN. AV VALVES ARE OPEN. AND REMEMBER, AV VALVES ARE BETWEEN THE ATRIA
AND THE VENTRICLES. THE AV VALVES ARE OPEN; AND SO AS THE ATRIA FILL,
SO DO THE VENTRICLES. THE MYOCARDIUM IS RELAXED. AND WHAT THAT MEANS IS
THAT WE’RE FILLING PASSIVELY. SO ESSENTIALLY THE VOLUME IN THE ATRIA AND
THE VENTRICLES IS INCREASING, BUT MY PRESSURE ISN’T CHANGING. I DON’T KNOW HOW TO SAY
THERE IS NO CHANGE. HERE, THAT MEANS CHANGE. NO-CHANGE. THE PRESSURE ISN’T CHANGING.
YET. MOSTLY BECAUSE WE AREN’T
HAVING ANY KIND OF CONTRACTION. DURING THIS FIRST STAGE,
THIS DIASTOLE STAGE, NOW THINK
ABOUT THIS FOR A SECOND: WE’RE ACTUALLY GOING
TO FIRE THE SA NODE. DOES THAT FREAK YOU OUT? IF WE FIRE THE SA NODE,
WHAT SHOULD HAPPEN? WHAT SHOULD FOLLOW? REMEMBER, HERE’S MY SA NODE, AND WE’RE GOING TO BEGIN
DEPOLARIZING THE ATRIA, WHEN WE FIRE THE SA NODE. AND IF WE DEPOLARIZE THE ATRIA, WHAT’S GOING TO HAPPEN NEXT? WE’RE GOING TO EXPECT
THE ATRIA TO CONTRACT. DO THEY CONTRACT
DURING THIS STAGE? NO! IT TAKES TIME! IT TAKES TIME FOR THE SA NODE TO SEND A MESSAGE
TO EVERYBODY ELSE, IT TAKES TIME FOR THE MESSAGE
FROM THE AUTO RHYTHMIC CELLS TO REACH THE CONTRACTILE CELLS. SO THE SA NODE FIRES, BUT WE DON’T ACTUALLY END UP
WITH A CONTRACTION YET. LET’S SEE IF ANYTHING
ELSE IS IMPORTANT. NO. CAN YOU ANTICIPATE WHAT THE NEXT
STAGE IS GOING TO BE? WE JUST FIRED THE SA NODE
IN THIS STAGE.