PV2 Week 1
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What structures are visible from the diaphragmatic (inferior) view of the heart?
LV and RV, RA that receives blood from the IVC
What separates the inferior LV and RV on the exterior of the heart?
posterior interventricular groove
What structure makes up the majority of the left side of the heart?
What structure makes up the majority of the right side of the heart?
What separates the RA and RV on the exterior of the heart?
The atrioventricular groove
Where does the RA receive blood from?
SVC, IVC, coronary sinus, and anterior cardiac vein
Describe the flow of blood thru the heart.
Unoxygenated blood enters RA, goes thru tricuspid valve, RV, pulmonic valve, PA to lungs
Oxygenated blood from lungs enters LA, goes thru mitral valve, LV, aortic valve, to aorta, to systemic circulation
What are the aortic sinuses and where are they located?
- Aortic sinuses are dilations of the ascending aorta that give rise to left and right coronary arteries.
- They are located above the AV cusps, are patent throughout the entire cardiac cycle.
How is the heart itself perfused?
By the coronary arteries and by the action of the heart pumping.
Which side of the heart is more prone to disease?
the left side
AV valves- names, location, closure, do they have papillary muscles?
- Mitral (L) and tricuspid (R), located between atria and ventricles.
- Soft closure (close passively due to pressure gradients)
- Yes, they have papillary muscles
What is the purpose of the papillary muscles?
Papillary muscles contract in systole which keeps the vanes of the valves from bulging back into atrium (prolapse) during ventricular contraction.
They are NOT responsible for helping the valves close.
What can happen if the papillary muscles rupture?
The vanes bulge into the atria (prolapse) and the valve can become leaky.
What attaches the papillary muscles to the valves?
The chordae tendinae
Semiluminar valves- names, location, closure, do they have papillary muscles?
- Aortic (L) and pulmonic (R), located between ventricle and aorta or pulmonary artery.
- Snap closure due to high pressures in PA and aorta.
- Heavier than AV valves and require more backflow to close.
- No chordae tendinae or papillary muscles.
Which type of valve is more likely to be damaged and why?
The semiluminar valves are more likely to be damaged. They have smaller valve openings than the AV valves, smaller area leads to greater velocity, and thus the edges are more likely to be damaged.
What are the layers of the heart from outside to inside?
- Pericardium- sac that surrounds the heart (3 layers of its own)
- Epicardium- outer surface of heart
- Myocardium- muscle layer
- Endocardium- innermost layer
What are the 3 layers of the pericardial sac from outside to inside?
- -Fibrous- outer most layer, attaches to diaphragm and sternum
- -Parietal- middle layer
- -Serous (visceral)- contains fluid
What is the purpose of the pericardial fluid and between which 2 layers is it located?
Purpose is to lubricate the movement of the heart around surrounding structures.
Located between parietal and visceral layers.
What can cause excess fluid to accumulate in the pericardial sac?
Infection, TB, metastatic disease (or radiation used to treat it), trauma
Why is excess fluid in the pericardial sac that accumulates gradually less serious than that which develops acutely?
- There is an important pressure / volume relationship.
- If the fluid develops gradually, the pericardium can stretch to accommodate the increased volume without increasing the pressure.
- If it develops suddenly, pressure and volume both increase and tamponade develops.
The best way to manage tamponade is to give general anesthesia with PPV so a window can be placed, T or F?
False! Should not use PPV when a patient has cardiac tamponade. Pericardiocentesis should be performed with local anesthesia, then a window can be placed with GA and PPV.
What areas of the heart does the RCA supply?
- -RA, most of the RV, diaphragmatic surface of the LV, posterior 1/3 AV septum
- -SA and AV nodes in most people (so can have conduction issues) (SA in 60% and AV in 80%)
What branches does the RCA give off?
marginal and interventricular (PDA)
What areas of the heart does the LCA supply?
- -LA, most of LV, part of RV, most of interventricular septum (2/3's)
- -SA node in 40% of pts, AV node in 20% pts
What 2 major branches does the LCA give off?
LAD and left circumflex
Which is larger, LCA or RCA?
T or F, the RCA anastamoses with the LAD?
What are the 2 major coronary veins that drain into the RA?
Coronary sinus and anterior cardiac vein
What 4 smaller veins feed into the coronary sinus?
great, middle, small, and oblique cardiac veins
Where do the coronary sinus and anterior cardiac vein drain into?
Describe the path of blood in the fetal heart.
- -Oxygenated blood from placenta goes thru umb vein to IVC to RA thru FO to LA
- -Deoxygenated blood from SVC goes thru tricuspid valve to RV
- -LA blood and small amt blood from lungs to LV to ascending aorta and to brain and heart-Unoxygenated blood in RV to PA trunk to DA to descending aorta to lower limbs and organs, then shunted back to placenta for oxygenation via umb arteries
T or F, the fetal heart shunts oxygenated blood (from placenta) to vital organs (brain and heart), and leaves unoxygenated blood for less important organs
In the fetal circulation, oxygenated and deoxygenated blood both enter the RA, how is mixing prevented?
The valve that overlies the IVC orifice (IVC has oxygenated blood), directs the flow of oxygenated blood from IVC thru FO, to LA
In the fetal circulation, what happens to the unoxygenated blood in the RV?
It goes through the PA to the ductus arteriosis (DA), then to the descending aorta and to the lower limbs and abdominal organs
What is the purpose of the umbilical vein?
Carries oxygenated blood from placenta to fetus
What is the purpose of the umbilical artery?
Carries unoxygenated blood from the fetus to placenta
What occurs in the fetal heart at birth?
- At birth the lungs expand, increased blood flow thru PA, PVR is decreased (no HPV), increased systemic circulation, decreased RA pressure, increased LA pressure, septa 1 and 2 line up and close due to pressure changes in RA and LA
- -With increased PO2 wall of DA contracts and it closes (takes 2-3 months to fully close)
With PFO, which is more severe, an issue with sept. 1 or 2?
- -An issue with sept. 1 is more severe as it is immediately above the aorta and may be associated with a defect of the ventricular septum as well.
- -Sept. 2 is higher and easier to close
What is an example of an atrial septal defect?
Patent foramen ovale
What 4 issues make up tetralogy of fallot?
- 1) pulmonary stenosis
- 2) septal defect
- 3) overriding aorta
- 4) RV hypertrophy
What are the manifestations of TOF?
- -Blood shunts thru the left heart (mixing of oxygenated and deoxygenated blood) causing cyanosis
- -Blood takes the path of least resistance
What causes RV hypertrophy in TOF?
Pressure overload due to pulmonary stenosis
What does the sarcoplasmic reticulum do? Where is it located?
- -Located in cardiac myocyte
- -Stores intercellular calcium
-Releases calcium into sarcoplasm (cytoplasm of muscle cell) as part of excitation-contraction coupling
What is the cell membrane of the cardiac myocyte called?
What is the cardiac myocyte?
The functional unit of pumping mechanism in the heart
What are the 3 types of cardiac muscle in the heart?
- 1) atria
- 2) ventricular
- 3) excitatory and conducting
What are differences between skeletal and cardiac muscle?
- Cardiac muscle has a longer duration of contraction
- Cardiac muscle has automaticity
What is a syncytium?
- -A lattice of many individual cardiac cells connected by intercalated discs forming gap junctions
- -Allows AP to go thru entire lattice of cells
What are the 2 types of syncytiums?
The AV bundle connecting tissue connects the 2, allows atria to contract ahead
What are gap junctions? How are they formed?
- -Gap junctions are formed from intercalated discs fusing together cells
- -Allows ions (and AP) to go from 1 cell to another
- -Are a type of electrical synapse
Name 3 ways in which cardiac muscle action potential differs from skeletal muscle action potential.
- Cardiac AP:
- 1) self propagating
- 2) conduction from 1 cell to another (due to intercalated discs)
- 3) long DOA
Which 3 ions are most important for the cardiac AP? Which are in the ICF and which are in the ECF?
- Na+ (ECF)
- Ca++ (ECF)
- K+ (ICF)
In a generic AP, what maintains polarization of the cell?
Na-K-ATPase pump and K leak channels
In a generic AP, what causes depolarization? (going from negative to positive)
- -Influx of Na+ thru voltage gated Na+ channel
- -Same in cardiac cells
In a generic AP what causes repolarization (going from positive to negative)?
K+ leaving cell via voltage gated K+ channels
In the cardiac cell, what sustains AP and causes the "plateau"?
1) Slow influx of Ca++ thru voltage gated Ca++ channel
2) Also K+ can't exit the cell as quickly as in other tissues
What is the major characteristic of cardiac muscle fibers?
Longer depolarization, plateau can be as long as 0.2 - 0.3 seconds
What is the function of the Ca++ pump?
- -Moves Ca++ to the ECF or into SR, creates a gradient so Ca++ can enter the cell during depolarization
- -Helps to maintain RMP
- -Moves Ca++ against the gradient so needs ATP
Describe the 4 phases of the AP.
- Phase 0- Na+ rushes into cell, begins when phase 4 depolarization gets to threshold
- Phase 1- start of repol., Na+ channels close, K+ goes out, see "dip"
- Phase 2- Plateau (Ca++ slow channels)
- Phase 3- return of normal permeability to Na, K leaves cell
- Phase 4- Na/K/ATPase pump activated, baseline resting state
What AP phases make up repolarization?
Describe phase 4 of the pacemaker cells.
small amt of Ca++ and Na+ entering the cell, decreased outward flow to K+, this causes higher RMP and makes depolarize spontaneously
How does the RMP of the pacemaker cells compare to other cardiac cells?
PM RMP is less negative (more positive) and spontaneous depolarization occurs
Describe phase 0 of the PM cells.
Rate of rise is slower and more gradual. Slope is dependent on rate of Na+ and Ca+ going in
Describe phases 1 and 2 of the PM cells.
The PM cells don't have a phase 1 or 2, there is no plateau
When does repolarization of the PM cells occurs?
When Ca++ influx stops and K+ efflux begins
What factors influence the rate of depolarization in the PM cells?
- 1) Slope of phase 4 r/t rate of impulse formation (HR), steeper slope = faster HR
- 2) Threshold
- 3) RMP
What is the refractory period?
- -Period when a stimuli won't cause depolarization of the ventricles.
- -Extends thru phases 1, 2, 3
What is the relative refractory period and when does it occur?
- -Period when a stimuli with greater than normal intensity could cause depolarization
- -Occurs later part of phase 3
What is the general MOA of anti-dysrhythmic drugs?
decrease the rate of spontaneous depolarization by blocking passage of ions across cardiac muscle membrane
Von Williams classifications: class 1
inhibits fast Na+ channels (affects phase 0)
Von Williams classifications: class 1a
- Ex: quinidine
- Increases duration of AP and effective refractory period, moderate Na+ channel inhibition, K+ channel blockade, inhibits repolarization
Von Williams classifications: class 1b
- Ex: lido
- less potent
- slight slowing in Na+ influx
Von Williams classifications: class 1c
- Ex: flecanide
- Potent Na+ channel blocker, marked slowing of Na+ ion influx
Von Williams classifications: class II
- Ex: beta blockers
- Decrease rate of spontaneous phase 4 depolarization
Von Williams classifications: class III
- Ex: amio
- Blocks K+ channels causing prolonged depolarization, increased duration of AP, increased duration of effective refractory period
Von Williams classifications: class IV
- Ex: Ca ch blockers
- Blocks calcium channels by inhibiting slow Ca++ channels
T or F, the tissues in the atria and ventricles have different DOA of AP phases, because they have different densities of ion channels in different areas of conduction system
Describe excitation contraction coupling.
- -AP passes over cardiac muscle membrane. -AP moves to interior of cardiac muscle fiber along T tubule membrane.
- -Calcium ions diffuse from T tubules at time of AP via voltage gated Ca+ channels
- -This Ca+ release induces Ca+ release from SR into sarcoplasm.
- -Ca+ ions diffuse into myofibrils and catalyze reactions causing myosin and actin sliding then muscle contraction.
What is the significance of the T tubules?
- -Carries AP to inner sections of cell
- -Also releases Ca++ directly (unlike in skeletal muscle; cardiac SR can't store as much Ca+ as skeletal SR), this ensures there is enough Ca++ to generate a full contraction.
Why can't tetany occur in cardiac cells?
Cardiac muscle can't have sustained contraction like in skeletal muscle. Cardiac muscle must relax before it can contract again.
What does the dicrotic notch on the a-line tracing represent?
Aortic valve closure
What does the a wave of the atrial pressure wave represent?
- atrial contraction
- RAP= 4-6 mmHg
- LAP= 7-8 mmHg
What does the c wave of the atrial pressure wave represent?
Start of ventricular contraction. Pressure of ventricular contraction pushes blood back against AV valve into atria which causes small rise and fall in atrial pressure
What does the v wave of the atrial pressure wave represent?
End of ventricular contraction. Filling of atria.
What is isovolumetric contraction?
Occurs at start of ventricular contraction after AV valves closes and before semilumimar valve opens.
Increase in pressure with no change in volume.
What is isovolumetric relaxation?
Occurs at the end of systole after semiluminar valves close and before AV valves open.
All valves close and ventricle is relaxed.
Which Ca++ channels are involved in the AP of the PM cells? (slow or fast)
slow, they are also called calcium sodium channels
What is the normal area of the aortic valve ?
2.5 - 3.5 cm2
What is the normal area of the mitral valve?
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