Cardiac cycle 4- Early ventricular systole

Cardiac cycle 4- Early ventricular systole


– THE MESSAGE HAS BEEN RECEIVED. WE HAD ESSENTIALLY
THE DEPOLARIZATION PASS ALL THE WAY
THROUGH THE VENTRICLES. AND NOW THE NEXT
INEVITABLE STEP IS THAT WE HAVE
VENTRICULAR CONTRACTION. SO THAT IS VENTRICULAR SYSTOLE. ONE OF THE THINGS THAT IS TRUE. AT THIS POINT YOUR VENTRICLES
BEGIN TO CONTRACT. HOWEVER,
THAT SNAPS THE AV VALVES SHUT. AS THE VENTRICLES START
TO CONTRACT, THEY PUSH THE BLOOD UP. THE BLOOD’S GOING TO WANT
TO GO BACKWARDS. WHY NOT JUST GO
INTO THE GIANT ATRIUM, THAT’D BE WAY EASIER? BUT THE AV VALVES SAY,
“NICE TRY, PAL, YOU GOT TO STAY WHERE YOU ARE.” THE AV VALVE SNAPS SHUT,
THAT’S THE FIRST HEART SOUND, THAT’S THE “LUB”
THAT YOU HEAR WITH THE HEART– THE AV VALVES SNAPPING TOGETHER. AT THIS POINT WE ARE
IN EARLY SYSTOLE, WE’RE CONTRACTING,
WE’VE SNAPPED THOSE CLOSED, BUT WE HAVEN’T PUSHED THROUGH
THE SEMILUNAR VALVES YET. SO AT THIS EXACT MOMENT
WE HAVE A STEADY VOLUME. THE VOLUME DOES NOT CHANGE, EVEN THOUGH THE PRESSURE IS
INCREASING IN THIS SPACE. EVENTUALLY WE’RE GOING
TO HAVE THE AMOUNT OF PRESSURE BEING PLACED ON THE BLOOD INSIDE THE VENTRICLE IS GOING
TO BECOME GREATER THAN THE FORCE THAT’S HOLDING
THE SEMILUNAR VALVES CLOSED. SO YOU CAN IMAGINE THAT THE NEXT
STEP IS GOING TO BE THAT THE PRESSURE OF THE BLOOD IN THE VENTRICLE IS GOING
TO OVERCOME THE PRESSURE THAT’S KEEPING
THE SEMILUNAR VALVES CLOSED AND IT’S GOING TO SNAP
THOSE SEMILUNAR VALVES OPEN, WHICH ALLOWS THE BLOOD
TO LEAVE VENTRICLE. NOW THAT’S IN OUR NEXT SECTION, I THINK I STOLE MY OWN THUNDER. BUT THERE’S SOMETHING
IN THE LAST SECTION THAT I WANTED
TO TELL YOU AND MAKE SURE THAT YOU WERE CLEAR ABOUT: THERE’S THIS MOMENT
WHERE VOLUME IS NOT CHANGING, WHERE WE PUSHED
THE MAXIMUM AMOUNT OF BLOOD INTO THE VENTRICLES
AS WE POSSIBLY COULD, AND WE KIND OF STARTED
TO CONTRACT, BUT THE VOLUME
HASN’T CHANGED YET. THAT MOMENT, THIS MAXIMUM
BLOOD VOLUME IN VENTRICLES, IS CALLED THE END DIASTOLIC VOLUME– OR EDV. SO THE END DIASTOLIC VOLUME IS
THE MAXIMUM AMOUNT OF BLOOD, IT’S THE BIGGEST VOLUME THAT YOU CAN HAVE
IN THE VENTRICLE AT THAT MOMENT. NOW HERE’S
THE THING THAT’S CRAZY: YOUR END DIASTOLIC VOLUME
CAN TOTALLY VARY. IF YOU’RE OUT EXERCISING AND YOUR HEART IS BEATING
REALLY FAST, YOUR BLOOD IS MOVING
THROUGH YOUR BODY REALLY FAST, THAT ACTUALLY IS GOING
TO STRETCH YOUR HEART MUSCLE EVEN MORE, WHICH ULTIMATELY, THE MORE
YOUR HEART MUSCLE STRETCHES, THE MORE FORCEFUL
THE CONTRACTION IS IN RESPONSE. SO EXERCISE ACTUALLY LEADS
TO MORE VOLUME BEING THROWN AROUND THE BODY THAN WOULD
OTHERWISE BE THE CASE. THAT’S BECAUSE THE END DIASTOLIC
VOLUME IS GREATER WHEN YOU EXERCISE. IF YOU’RE JUST CHILLIN’
OR SLEEPING, YOUR END DIASTOLIC
VOLUME CAN BE SMALLER. SO THIS ISN’T A NUMBER THAT’S
THE SAME EVERY SINGLE TIME. BUT IT IS A NUMBER THAT HELPS US
EVALUATE VARIOUS SCENARIOS. IF WE HAVE
AN END DIASTOLIC VOLUME, DOES THAT MAKE YOU THINK
THAT WE MIGHT HAVE ANOTHER KIND OF VOLUME
THAT WE MIGHT WANT TO LOOK AT? IN THE NEXT SECTION, LET’S LOOK
AT WHAT HAPPENS WHEN WE DO BUST THROUGH THE SEMILUNAR VALVES