Flashcards in Patho Exam 5 Deck (77):
What are the three junctions of the intercalated disks and their functions
1. Desmosomes - AKA Macula Adherens, They prevent separation during contractions
2. Fascia Adherens - the anchoring sites for actin and they mechanically attach one myocyte to another
3. Gap Junctions - Allow the AP to spread by permitting ions to pass from one myocyte to another
What is the function of a T tubule?
- Allows faster access of ions to myofibrils
- Transmission of AP's from the sarcolemma to the myofibrils
- AP stimulation releases Ca from the SR
What is an A band
Also called the anisotropic band. Is the dark band on myocardial cells. It is composed of the thick filaments of myosin.
What is the I band
The light bands comprised of thin filaments of actin which extend from the Z line
What is located in the H zone?
A single Tropomyosin relaxing protein and 7 actin filaments
What are the three phases of ventricular activation in order?
3. Basal and posterior
Facts about the LAFB
- passes the left anterior papillary muscle
- crosses the aortic outflow tract
- Damage to the LV or Aortic valve an impact it
Facts about the LPFB
- Well protected from damage because blood flow is not turbulent here
Why does the SA node have automaticity?
Slow leaky Ca channels cause it to not have a stable resting membrane potential. -60 mv
What are the phases of cardiac depolarization in order?
What occurs in Phase 0?
Depolarization. Threshold is reached in the SA. Na VG channels open and rushes into the cell
What occurs in Phase 1?
Early repolarization.VG Na channels rapidly shut. VG Ca channels open.
What occurs in phase 2?
Plateau phase. Rapid reversal in membrane polarity to -15 mv. Slow influx of Ca balances out Efflux of K
What occurs in phase 3?
Rapid repolarization. VG K channels open and K exits the cell. Return to resting membrane potential
What occurs in Phase 4?
Resting membrane potential. -80 to -90 mv. The time between AP's
What are the A bands composed of?
Thick filaments of myosin.
What are the I bands composed of?
Thin filament of actin
What is the function of Troponin I?
Inhibits the ATPase of actomyosin. It prevents the breakdown of ATP into ADP and Pi. Thus it inhibits myosin cross bridging
What is the function of Troponin T?
It binds tropomyosin to Aictin
What is the function of Troponin C?
It has the Ca receptor
What are considered the relaxation proteins?
because they cover the actin binding site.
Where is Ca stored in the cardiac cells
In the Sarcoplasmic Reticulum
What are the two types of Ca channels?
- L Type are the predominant type which are long lasting and affected by Ca Channel Blockers
- T Type are transient and are much less common. They are not affected by any Ca Channel Blockers
What changes occur when Ca binds to troponin
Ca binding inhibits Troponinc C which when resting enhances Troponin I to cover actin. This leads to the uncovering of the actin sites.
Resting membrane potentials for SA Node, AV Node and Myocardial cells
- SA -50 to -60 mv
- AV -60 to -70 mv
- Myocardial Cell -80 to -90 mv
Why can tetany not occur in cardiac tissue
Because the RRR is nearly as long as the AP.
Can cardiac tissue be summated?
What are the 5 phases of the cardiac cycle?
Phase 1 atrial systole
Phase 2 Isovolumetric ventricular contraction
Phase 3 Ventricular Ejection
Phase 4 Isovolumetric ventricular relaxation
Phase 5 Passive ventricular filling
What makes the first heart sound?
It is the closing of the AV valves. Produced immediately after the QRS is observed.
What causes the second heart sound?
The closing of the semilunar valves. Produced just after the T wave is observed.
What causes the third heard sound?
It is tension being applied to the chordae tendineae during rapid ventricular filling. Normaly heard in children and some athletes
What causes the fourth heart sound?
It is a pathologic sign caused by blood being forced into a stiff/ hypertrophic ventricle
What are the waves on an atrial pressure graph?
- A wave is atrial contraction
- X descent wave is Atrial diastole
- V wave is atrial filling
- Y descent wave is blood from the veins and atrium into the RV
- C wave is the bulging of the mitral valve into the LA
Which parts of the heart are innervated by the SNS?
All parts of the A and V
What parts of the heart are innervated by the PNS?
All parts of the A and V along with the SA and AV nodes.
Where are cardiac B1 receptors found?
- SA node
- AV node
- Purkinje fibers
- Atrial and Ventricular myocardium
Where are cardiac B2 receptors found?
Mostly in the coronary arteries.
Effects of cardiac adrenergic receptor activation
A1 - NE Coronary artery constriction
A2 - NE Inhibition of NE release leading to vasodilation
B1 - NE Increase HR and contractility
B2 - Epi Coronary artery dilation
Which dominates SNS or Vagal stimulation?
What is the optimal sarcomere length when referring to the Frank - Starling Law?
2.2 - 2.4 mm
What happens if the sarcomere is stretched beyond 2.2 - 2.4 mm?
The force of contraction declines because actin and myosin are partially disengaged
What happens if the sarcomere is stretched beyond 3.65 mm?
Actin and myosin become completely disengaged and contractile force drops to zero.
Why does the strength of contraction vary directly with EDV?
Frank- Starling Law
The workload on the heart prior to contraction. AKA EDV.
What can occur from increased LVEDV?
Increased pulmonary pressure, forcing plasma through the vessel walls which created pulmonary edema.
The load which the ventricle must move in order to eject blood. Think Aortic pressure
What does Laplace's Law state?
The amount of tension needed to produce a pressure is dependent on the size of the vessel
What 3 variables regulate SV?
- Contractility (which is related to Ca)
What two mechanisms of the Medulla can decrease HR?
1. Inhibition of Sympathetic stimulation of the SA node
2. Activation of parasympathetic stimulation of the SA node
Which condition of aging is associated with a dysfunctional baroreceptor reflex?
What is the Bainbridge reflex?
In increase in HR after an IV infusion.
What is the normal EF?
Examples of Positive Inotropic Agents
- Excess Thyroid Hormone
- Calcium Salt infusion
Examples of Negative Inotropic Agents
What is the equation for blood flow?
Q= Pressure difference/R
Blood Flow = P1 - P2/ TPR
Where are Baroreceptors located?
- Carotid Sinus
Where are chemo receptors located and what do they do?
Located throughout the body and they stimulate respiration after a drop in SpO2
Define vascular compliance
Increase in the volume of a vessel to accommodate for a given pressure.
The average arterial pressure during the cardiac cycle
What is the equation for MAP?
Diastolic pressure + 1/3 pulse pressure
What is the equation form pulse pressure?
Systolic - Diastolic
When is ADH released? and what does it do?
ADH is released when osmoreceptors detect an increase in plasma osmolality. It produces thirst sensation and stimulates H2O reabsorbtion
Where are the osmoreceptors located
In the hypothalamus
What factor stimulate the release of Renin?
- Drop in renal artery BP
- Decrease in Na and Cl delivered to the kidney
- Stimulation of B1 and B2
- Angiotensin II
- Low K
What does the AT1 angiotensin receptor do?
Proinflammatory effects such as myocyte hypertrophy and vasocinstriction
What does the AT2 angiotensin receptor do?
Counterregulatory mechanism such as Mediates vasodilation by the natriuretic cascade
What stimulates the release of ANP and BNP? What do they do?
Stretching of the atria release them. They increase Na and H2O excretion. They are antagonists of Aldosterone and Angiotensin II
Where is urodilatin produced and what is it's function?
Produced in the kidney and it increased Na and H2O excretion.
What is Adrenomedulin and what is its function?
ADM it is secreted from the vascular endothelium and smooth muscle cells. It is a vasodilator
What paracrine regulators/vasodilators are secreted by the vascular endothelium?
How is NO produced?
Arterioles contain eNOS which produce NO
MOA of NO
It diffuses into the smooth muscle of the vessel. Here it activates guanylate cyclase thus cGMP and lowers cytoplasmic Ca
What is the systolic compressive effect?
- Aortic valve cusps obstruct the coronary bloodflow during systole
- Coronary vessles constrict during systole
Define coronary perfusion pressure?
The difference between the pressure in the Aorta and the pressure in the coronary vessel of the RA
Most coronary blood flow occurs duing which cycle?
An increase of adenosine K or Co2 will do what to blood vessles?