Cardiovascular Physiology Flashcards
Characteristics of cardiac muscle tissue
Made up of cardiac cells –> individual cells but work as one unit
Has intercalated discs: connects ends of muscle cells to each other
What is found in the intercalated discs?
Desmosomes: type of cell junction that holds fibers together
Gap junctions: allow action potentials to conduct from 1 muscle fibre to its neighbour
Importance of the SA node
Natural pacemaker of the heart –> initiates AP 100/min
Nerve impulses from ANS + hormones can modify the speed
APs from SA node go throughout both atria via gap junctions + excite contractile fibers
Importance of the AV node
Located in the interatrial septum
AP slows down here (has smaller fibers + less gap junctions)
Why is it important that the AP slows down at the AV node?
The delay allows for the atria to empty their blood into the ventricles
What happens if the SA node gets damaged?
AV node picks up pace making tasks (at a slower rate)
Purpose of AV bundle
So AP can conduct from atria –> ventricles
Where are the R + L bundle branches found?
They extend down through the interventricular septum toward the heart apex
Purpose of purkinje fibers
APs rapidly conduct from heart apex –> ventricular myocardium
How to inotropes work?
A substance that alters the movement of calcium through its channels (affects strength of heart contractions)
Positive inotrope = more calcium (epinephrine)
Negative inotrope = less calcium
What does the P wave represent?
Small wave –> atrial depolarization
What does the QRS complex represent?
Depolarization of the ventricles (repolarization of the atria also occur; masked)
What does the T wave represent?
Ventricular repolarization
De/repolarization and heart muscle
Depolarization = contraction of heart muscle
Repolarization = relaxation of heart muscle
S1 heart sound
AV valve closure
S2 heart sound
SL valve closure
S3 heart sound
Ventricular filling
S4 heart sound
Atrial systole
What are isovolumetric contractions?
Ventricles have started to contract but no change in volume
What is isovolumetric contraction?
When all 4 valves are closed
What is stroke volume?
Volume of blood ejected from LV/RV into aorta/PT
SV = EDV - ESV
Which ventricle expels more volume?
They expel the same BUT L side has to travel farther –> more force
What is cardiac output?
Volume of blood ejected from the LV/RV into aorta/PT
CO = HR x SV
What is cardiac reserve?
Cardiac output (max) - CO (at rest)
In healthy youth, max is 4x the rest output
Factors that regulate stroke volume (x3)
- Preload = degree of stretch on heart before contraction
- Contractility = force of contraction on individual muscle fibers
- Afterload = pressure ventricles must overcome before SL valves open
Preload
More blood in ventricles = larger EDV = more stretch = larger output
Muscle stretch is proportionate to EDV
Changes to preload
Heart rate: slow HR = longer ventricle diastole = more filled = more stretch
Venous return = more blood going into heart = more stretch
Contractility
Intrinsic ability of myocardium to contact
Strength of contraction at any given time
What changes heart contractility?
Calcium!
Positive inotropes = epinephrine
Negative inotropes = hypoxia, acidosis
Afterload
Pressure ventricles must overcome before SL valves open
Factors that affect after load (x2)
Blood pressure = increased = increased afterload
Vessel structure = narrow = increased afterload
What does an increased afterload mean?
Decreased in SV and more blood will remain in ventricles
Factors that regulate heart rate (x4)
ANS = sympathetic = increase
Chemical regulation = epinephrine & calcium = increase
Age = young age = increase
Increased body temp = increase
Nervous system control of the heart
CV center on medulla oblongata
Affects rates of spontaneous depolarization in SA and AV nodes
Sympathetic stimulation can increase contractility and stroke volume
