3.2 Cardiac Function Flashcards
General parts of CV system
Blood, heart and vasculature
Which side of the heart is pulmonary?
Right
Which side of the heart is systemic?
Left
Which side of the heart has significant musculature?
Left
3 layers of cardiac histology
inner to outer
Endocardium
Myocardium (cardiac muscle)
Epicardium
Endothelial cells always…
Touch blood (In the endocardium)
Heart muscle cells (name)
Cardiomyocytes
What are the general features of cardiomyocytes similar to? (Z-discs, I/A bands, thin / thick filaments of myosin?
Skeletal muscle sarcomere
Why are cardiomyocytes similar to neurons?
They maintain a resting membrane potential
Two types of cardiomyocytes
Pacemaker (1%) and contractile cells (99%)
How do cardiomyocyes maintain negative membrane potentials?
Na / K+ Pumps
Pumping out Ca2+
How do cardiomyocytes pump out Ca2+?
Secondary active transport with Na+
Do pacemaker cells have a true RMP?
No but they bottom out at -60 mV
Do contractile cells have a true RMP?
Yes, -90mV
Mitochondria are what percent of cardiomyocytes?
25%
What are cardiomyocyes reliant upon?
Aerobic cellular respiration
What is coronary ischemia?
Essentially a heart attack, blockage of blood flow, cells die because they are so reliant on oxygen
What does hypoxia do? (depolarize / hyper polarize)
Depolarize, bring them more positive, away from RMP
Cardiac pacemaker and conductile tissue is..
Autorythmic
Does reaching threshold to cause an action potential in cardiomyocytes require neuronal action potentials or acetylcholine?
NO
What is normally the cardiac pacemaker?
SA node
Depolarization rate: location
SA node > AV node > Purkinje
If unmodified by ANS, what does the SA node set the heart rate as?
100 BPM
What happens if there is SA node damage?
AV node assumes (slower) pacemaker role which leads to Brachycardia
Ectopic foci
AKA ectopic pacemaker, other irritated of hypoxic tissue can cause premature contractions
Any region can become the pacemaker if…
It is the fastest to depolarize
What causes the gradual rise in RMP of pacemaker cells?
Na + leakage (until threshold) through slow voltage gated channels
Determines heart rate!
What rapid influx causes depolarization in pacemaker cells?
Influx of Ca+ through fast voltage gated Ca2+ channels
What outflow causes repolarization in pacemaker cells?
Outflow of K+ through voltage gated K+ channels
In order to increase heart rate, what would your body do?
Leak more sodium faster (sympathetic influence)
Do neurons leak sodium like pacemaker cells?
NO
Cardiomyocte cells are _____ coupled
Electrically
Cardiac mycoses share a “continuous” cytoplasm via…
Intercalated discs, leaky interconnections containing gap junctions (large pores) and desmosomes ( strong cell-cell ties or anchors)
Why are cardiomyocytes electrically coupled?
Creates a synctium where electrical depolarization spreads between cells
What connects every cell in heart? (notes)
Gap junctions
What keeps cells physically connected to each other? (notes)
Intercalated disks
What are found within intercalated disks? (notes)
Gap junctions and desmosomes
What must the depolarizing current travel through to reach the ventricles?
AV node (delays impulse)
What occurs during the depolarization phase of contractile cardiomyocytes?
Na+ influx through fast Na+ voltage gated channels
What occurs during the plateau phase of contractile cardiomyocytes?
- Voltage gated K+ channels open and K+ flows out
- Slow voltage gated Ca2+ channels open (prolonging depolarization)
What occurs during the repolarization phase of contractile cardiomyoctes?
Voltage gated Ca2+ channels close, voltage gated K+ channels remain open, potassium flows out of the cell
What is the function of the plateau?
Prevents tetany and is a potent signal for contraction of sarcomere
What cells does an EKG measure?
Contractile cardiomyocytes
Why can’t you see atrial repolarization?
“Buried” by depolarization occurring in ventricles
What is an EKG?
Myocardial electrical currents detected on skin
What occurs during the p-wave?
Atrial depolarization
What occurs during the QRS complex?
Ventricular depolarization
What occurs during the T-wave?
Ventricular repolarization
Ventricular systole
Ventricles are contracting and emptying blood to arteries
Ventricular Diastole
Ventricles are relaxed and then filled by the atria
What interval is systole?
Q-T interval
When on the EKG does diastole occur?
End of T to beginning of next Q
What would an enlarged P or R wave be indicative of?
Atrial or ventricular hypertrophy
What would a larger Q wave or flattened T wave mean?
Myocardial infarction
What would elongation of the P-Q interval indicate?
Scarring from coronary artery disease
What would an S-T interval raised above baseline indicate?
Scarring from coronary artery disease
What would an elongated Q-T interval indicate?
Oxygen deprived ventricles
What is cardiac output?
Volume of blood pumped per minute
Equation of cardiac output
CO = Heart Rate x Stroke Volume
HR =
Beats / minure
Stroke volume =
Volume of blood ejected / beat OR (EDV - ESV)
End diastolic volume
The amount of blood into the relaxed volume
End systolic volume
Amount of blood left in heart after contraction
Chronotropic agents
Affect heart rate
(sympathetic nervous system)
Alter SA and AV node
Inotropic agents
Affect stroke volume
Alter Ca2+ levels in sarcoplasm
Brainstem Cardiovascular Center and the Autonomic Nervous system
Based on peripheral inputs to the brainstem CV center
Sympathetic influence on the heart
Cardiac accelerator nerves release norepinephrine to increase HR and ventricular contractility
Parasympathetic influence on the heart
Vagus nerves release acetylcholine to decrease HR and ventricular contractility
How does epinephrine and norepinephrine create a stronger contraction (and increase stroke volume)?
Increases Ca influx into cardiomyocytes
What do thyroid hormones do?
Increase heart rate and contractility
