Lecture 10 Flashcards
What is the purpose of the heart?
To supply the rest of the body with oxygenated blood to satisfy the metabolic demands of all the other tissues and organ systems
What is the pumping action of the heart influenced by?
Preload and after load
What is preload?
Volume of blood returned from venous circulation - the amount of blood that the rest of the body is trying to pump from the heart
What is after load?
Resistant to blood exiting the ventricles to the rest of the body
How do you know if after load has increased?
If it becomes more difficult to pump against the pressure
What are the two main mechanisms that help the heart adapt to changing circumstances?
Stretch-sensitive contraction and sympathetic drive
Who found the stretch sensitive contraction?
Frank starling
Describe the stretch sensitive contraction
the greater the stretch on the myocardium before systole (preload, the stronger the ventricle contraction
What does the length tension relationship indicate - from frank -starlings law?
Indicates an optimal range of sarcomere length (1.6-1.2 microns)
What is a process that initiates the frank-starling technique?
Running up the stairs - not just the ventricle that responds
What happens in the frank starling mechanisms for increased venous return?
Increased venous return usually distends ventricles within the range of the optimal sarcomere length and this facilitates increased force of next contraction
What did brain bridge discover?
Discovered the right atrial response
What did bainbridge show?
That increasing the amount of blood returning to the heart stretched the right atrium
What is the stretch of the heart sensed by?
By lots of mechanical-sensed channels, which induces the elevation of cytosolic ca2+ due to the opening of L type channels - increased the SA node
What is cardiac rhythmicity matched to?
Matched to mechanical preload in beat-to-beat manner
What are the 4 mechanisms in the sympathetic drive?
Chronotropic, ionotropic, lusitropic and dromotropic
What is chronotropic?
Increased heart rate
What is ionotropic?
Increased force of contraction, via a cellular process occurring at the level of myofilaments
What is luistropic?
Increased relaxation
What is dromotropic?
Increased conduction
What des the sympathies drive occur from?
As a result of the beta-agonist signal transduction and the phosphorylation of many potential targets
What happens when you activate the sympathetic nervous system?
You have an activation of adrenergic receptors
What happens when adrenaline adrenergic receptors are activated?
Adenylyl cyclase increases production of protein kinase A which phosphorylates proteins
What happens when you phosphorylate a protein?
Change the conformation of the protein, structure which influences the shape and what the protein binds to.
What can the phosphorylated protein sometimes be?
Inhibitory or stimulators - depends on the nature of the phosphorylation changes the structure of the protein
Where are the substrates of cardiomyocytes located?
Located on contractile proteins on the myofilaments
In cardiomyocytes what does the beta agonist isoprenaline do?
Decreases action potential duration, action potential is shortened
What else does the beta agonist isoprenaline do?
Increase T-type current and increase L-type ca2+ current
How can the ion channel be altered - from isoprenaline?
The PKA can target the T type and L type channels and increase the opening of the channels and increase the flow of ion current through those channels with beta receptors stimulation
What happens in a shorter periods of duration of the ca2+ - due to isoprenaline?
Get more influx over the plasma lemma which activates been more CICR at the junctions of the SR
What happens in a single isolated cardiomyocytes by the beta-agonist isoprenaline
Increase in ca2+ amplitude, contraction, rate of ca2+ returning to the base line and rate of relaxation
Why is the rate of relaxation increased?
Because of phospholamban which contributes to the SERCA pump in the SR to regulate the dynamic
What effect does phospholamban have on the SERCA pump?
Inhibitory effect
What needs to happen because you have a shorter action potential?
The contraction needs to have a shorter period as well
What does an increase of contraction shorter time period need?
Cardiac troponin and myosin binding protein C
what is the stretch of the chamber sensed by?
myofilaments which enhances the contraction of the stroke volume of the heart
