Cardiac Physiology - Heart Flashcards
fibrous skeleton of the heart traits
- composed of dense connective tissue
- lies in the plane between atria and ventricles
- corresponds to atrioventricular groove/orifices of heart
- is present in the form of circular fibrous ring
- surrounds the 4 valves
myocardium
thickest region of heart, contains myocytes
endocardium
- thin layer of connective tissue
- covers valves
- contiuous with endothelium layer of vessels
cardiac muscle cell traits
- arranged in layers
- all slow fiber types
- innervated like smooth muscle
- absolute refractory period
- highly aerobic
- require a continuous O2 supply
cardiac muscle cell traits pt2
- calcium regulation: like smooth muscle
- fibers contract simultaneously but in a graded fashion
- gap junctions/intercalated disks
- intrinsic HR
- Purkinjee fibers: conduct current that initiates cardiate muscle contraction
cardiac cycle
- blood moves from high to low pressure
- pressure gradients lead to expulsion of blood from chamber
- volume changes in left chambers equal to right chambers
- cardiac valves control blood flow in context of pressure gradients
ventricular systole
- ejection continues until ventricular pressure < vessel pressure
- outflow doesn’t stop immediately after end of contraction
- ventricular pressure continues to fall after valve closes and myocardium relaxes
Ventricular diastole
- ventricles relax, pressure low
- ventricles fill with blood, increasing volume
- Atrial systole forces blood into ventricles (<30% of total ventricular filling)
Atrial diastole
- pressure < vena cava pressure
2. blood moving into atria, venous return
Atrial systole
- p wave initiates atrial contraction
- forces blood into ventricles
- “tops off the tank”
How do you track the electrical signal of the cardiac cycle?
EKG
What are the phases identified by heart sounds?
S1-4
T/F: pressure changes in R ventricle and pulm arteries are the same as those in the LV
False
the are very much smaller.
LV: 120/80
PA: 25/10
SA node
- responsible for initiating heart beat
- node cells slowly depolarize by themselves (pacemaker potential)
- vagus nerve stim decreases discharge rate of SA node
- autonomic nerve stim increases discharge rate of SA node
Positive chronotropic effect
increases HR (sympathetic)
Negative chronotropic effect
Decreases HR (parasympathetic)
sympathetic innervation
- increases HR x3
- increases contraction strength x2
- net effect: increase in CO
- inhibition of sympathetic nerves = dec HR and contractility
Parasympathetic innervations
“vagal stim”
- slows hr
- dec strength of contraction
- dec CO
- vagal fibers distributed mainly to SA and AV nodes
vagal stim regulates HR more than contractility
SA node/Pacemaker potential
- pacemaker cells don’t need any outside innervation from ANS for AP
- Autonomic innervation can regulate depolarization w/pacemaker cells
if CO is 5L and bpm is 72, then L/beat is
.07 L/beat
what 3 variables influence SV
preload
afterload
contractility
What happens with increased EDV?
stretches myocardium which increases the stretch of the heart muscle and increases the sensitivity of cardiac myocytes to Ca2
Describe how frank starling mechanism allows for rapid adjustment to rise in peripheral resistance or afterload
- increased peripheral resistance temporarily decreases SV causing backup into ventricles
- more blood remains in ventricles, increasing EDV
- increased EDV causes ventricles to be stretched more, so they contract more strongly during next ventricular contraction
increased afterload tends to _ SV
reduce
increased afterload tends to _ SV
reduce
contractility
- measure of cardiac pump function
- degree to which muscle fibers can shorten and generate force
- intrinsic ability of heart to contract
- reflects force or strength of cardiac contraction
How do we assess contractility clinically?
ejection fraction
ejection fraction
- under resting conditions: 50-75%
- Increased contractility increases EF
- decreased contractility decreases EF
- EF reflects basic muscle mechanics (rate and amount of cross bridge cycling)
what increases and decreases contractility?
increase: sympathetic stim
decrease: parasympathetic stim
