MAPIISG1 - Heart Flashcards
What are the muscle types of Cardiac Muscle? (3)
- Atrial Muscle
- Ventricular Muscle
- Specialized excitatory and conductive muscle fibers
What is the purpose of Intercalated discs?
cell membranes that separate individual cardiac muscle cells
these, desmosomes, and adherns junctions help hold muscle cells together
What is the purpose of gap junctions?
communication pathway between cells
at intercalated discs where cell membranes fuse with each other in a way that they form permeable “communication”junctions - allow almost free diffusion of ions
What are the two similarities between skeletal and cardiac muscle?
- Striated (myosin/actin mechanism)
2. T-tubule mechanism (acting on sarcoplasmic reticulum)
What are the three differences between cardiac and skeletal muscle?
- T-tubule mechanism (direct diffusion of Ca2+, tubules store more)
- Action Potential (cardiac muscle plateau results in longer contraction)
- Strength of contraction (dependent on extracellular Ca2+)
What is the ventricular muscle fiber plateau due to?
presence of slow Na+ / Ca2+ channels
Is the ability of cardiac muscle to depolarize and contract extrinsic or intrinsic?
intrinsic
What are the 5 components of the intrinsic conduction system?
- Sinus Node = sinoatrial / S-A node
- Internodal pathway
- A-V Node
- A-V bundle of HIS
- Left and Right bundle branches of Purkinje fibers
Are the S-A node muscle fibers small or large in diameter?
small
Are the S-A node muscle fibers mostly contractile or non-contractile?
almost no contractile muscle fibers
How do the S-A node muscle fibers connect with the atrial muscle fibers?
directly
Does the S-A node have a less or more negative resting membrane potential than other cardiac muscle cells?
less negative resting membrane potential
Why does the S-A node have a less negative resting membrane potential?
cell membranes are naturally leaky to Na+ and Ca++ ions
What allows the sino-atrial node to self-excite?
Rate of discharge of SA is faster than AV or Purkinje fibers; it reaches threshold before others and can override self-excitation of others under normal circumstances
In the Cardiac Cycle, what is happening during diastole?
period of relaxation, heart filling with blood
What is End Diastolic Volume (EDV)?
amount of blood in ventricle at end of diastole or filling
In the Cardiac Cycle, what is happening during Systole?
period of ventricular contraction, ejects blood
What is End Systolic Volume (ESV)?
amount of blood left in ventricle after contraction
What is Ejection Fraction (EF)? (EDV - ESV) / EDV
fraction of EDV ejected
What is normal Ejection Fraction?
~60%
What is happening during the P wave?
spread of depolarization through atrial tissue followed by contraction (increase in atrial pressure)
What is happening during the QRS Complex?
spread of depolarization through ventricular tissue followed by contraction (increase in ventricular pressure)
What is happening during the T wave?
repolarization of the ventricles which represents ventricular relaxation
Majority of venous blood flows directly from the ___ to the ventricle.
atrium
Explain how the atria acts as a “primer pump”
atrial contraction usually causes additional 20% of ventricle filling
When is atrial function necessary?
“unnecessary” except during exercise
Atrial Pressure Changes:
a wave -
c wave -
v wave -
Atrial Pressure Changes:
a wave - during atrial contraction
c wave - onset of ventricular contraction
v wave - end of ventricular contraction
What is the status of the A-V valves during ventricular filling?
after systole, a-v vales open due to a build up of pressure in atria
What is the status of the A-V valves and semilunar valves during Isovolumic Contraction?
early systole, AV and semilunar valves closed (no volume change in ventricle)
What is the status of the A-V valves and semilunar valves during Isovolumic Relaxation?
early diastole, AV and semilunar valves closed (no volume change in ventricle)
Define preload
end-diastolic pressure when the ventricle is filled; amount of tension on the muscle when it begins to contract
Define afterload
pressure in the artery leading from the ventricle; load against which the muscle exerts its contractile force
How do the chemical energy requirements differ between cardiac and skeletal muscle?
Cardiac has a greater dependency/almost exclusive relative on O2 for energy metabolize (oxidative) compared to skeletal muscle which can utilize anaerobic metabolic sources as well.
How does cardiac muscle primarily derive its energy?
from oxidative metabolism of fatty acids (70-90% of energy sources)
What are the other 10-30% energy sources cardiac muscle gets its energy?
some lactate and glucose
What can cardiac muscle use from skeletal muscle?
lactic acid generated by skeletal muscle activity
How many liters of blood does the heart beat per minute?
4-6?
With heavy exercise, how many more times blood does the heart pump?
4-7x
What 2 things are the blood volume pump regulated by?
- intrinsic cardiac regulation of pumping in response to changes in volume of blood flowing into the heart
- extrinsic control of heart rate and strength of heart pumping by the Autonomic Nervous System
Describe the frank starling method
Heart automatically pumps incoming blood; amount of blood pumped determined primarily by rate of blood flow into heart
As cardiac muscle is stretched with returning blood volume, approach optimal length of actin and myosin fibers for contraction
What effect does the SNS have on Cardiac Output and How?
(fright, exercise) via norepinephrine increases Cardaic Output
both via HR (pacemaker fires more rapidly) and contractility
What effects does the PSNS have on Cardiac Output and How?
via vagus nerve decreased Cardiac Output
primarily via HR
acH hyperpolarizes membranes of cell - opens K+ channels
During resting conditions, is the S-A node receiving impulses from the SNS or PNS?
both autonomic divisions continuously
Is the dominant influence said the be inhibitory or excitatory during resting conditions?
inhibitory
What is “vagal tone”?
if you disconnect the vagal nerves, HR increases ~25bmp almost immediately
In what part of the cardiac cycle EKG would you expect to hear the first heart sound? Second?
First: QRS Complex Ventricular Contraction (depolarization)
Second: P Wave Ventricular Relaxation (repolarization)
Define Isovolumic contraction
after AV valves close, before SL valves open; pressure rises and ~0.2 seconds requires for ventricle to build up sufficient pressure to push semilunar vales open - tension is building but little or no contraction is occurring
Define Isovolumic relaxation
ventricles relax (blood remaining - ESV) and valves shut quickly by blood pushing back from from newely filled vessles ~.03 second ventricular muscles continue to relax even through no change in ventricular volume - interventricular pressure rapidly drop to their low diastolic levels
