Exam 2 - Cardio Flashcards
Define cardiac output (CO)
rate at which blood is pumped from the ventricles = Venous Return ( VR) rate at which blood is returned to the heart
Stroke volume x heart rate
Describe pacemaker cells
automaticity
slow response cells - gNa is greater, gCa is greater, gK is lower than in fast response cells
unstable RMP
What phase of the action potential sets the heart rate?
phase 4 of the pacemaker cell
slow depolarization
What effect does acetylcholine have on the SA node?
hyperpolarizes max diastolic potential (makes more negative) by increasing gK
decreases gCa
parasympathetic
slows heart rate
What effect does norepinephrine have on the SA node?
accelerates phase 3 repolarization -> shortens AP duration, increases frequency
increases slope of phase 4 (slow depolarization) -> increases gNa and gCa (T-type)
increases heart rate
sympathetic
Define chronotropic effects
effects on ANS on heart rate
Define dromotropic effects
effects on ANS on conduction velocity
Define inotropic effects
effects of ANS on contractility
Where does the vagus nerve innervate the heart?
SA node, AV node
NO innervation of ventricles unlike sympathetic system
What are the differences between cardiac muscle and skeletal muscle?
- Ca is released into cytoplasm from SR AND extracellular fluid in cardiac
- cardiac cells can contract WITHOUT nerve stimulation as APs start in pacemaker cells
- cardiac cells have gap junctions
Describe preload
the resting length from which the muscle contracts
As volume increases, ventricular pressure increases
Increased preload increases sarcomere length toward the optimum actin-myosin overlap
Describe afterload
the force against which cardiac muscle shortens = the load on the muscle during contraction
ex: for left ventricle the afterload is the aortic pressure
Describe a positive inotropic effect and what drugs cause this
an increase in contractility -> increases in SV and CO for a given EDV
Dopamine, dobutamine, digoxin, amiodarone
Describe a negative inotropic effect and what drugs cause this
a decrease in contractility -> decreases in SV and CO for a given EDV
Beta blockers, calcium, channel blockers
What two factors determine overall force of ventricular contraction?
preload and contractility
Describe the Frank-Starling relationship
the volume of blood ejected by the ventricle depends on the volume present in the ventricle at the end of diastole –> ensures that the volume the heart ejects in systole equals the volume it receives in venous return
Where is the largest pressure drop in the CV system?
arterioles
has the greatest resistance
What blood vessels have the biggest cross sectional area?
capillaries
What blood vessels contain the greatest amount of blood?
veins
In what blood vessels is velocity the fastest? the slowest?
fastest - aorta
slowest- capillaries
What factors increase turbulence?
decreased fluid viscosity, large-diameter tubes, increasing fluid velocity, vessel branching
What two systems control blood pressure?
baroreceptor reflux - neurally mediated
renin-angiotensin-aldosterone system - hormonally mediated
