the heart - academic computer centeracademic.pgcc.edu/~aimholtz/aandp/lecturenotes/in...the heart...
TRANSCRIPT
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The Heart
Generates high PRESSURE
Blood flows
Tissue perfusion
O2 & nutrients deliveredCO2 & wastes removed
Cells stay alive!
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• Mediastinum • Apex• Base• Diaphragm
• Medial• Anterior • Posterior
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Fibrous Pericardium
• Collagenous sac
• Encloses ♥
• Anchors ♥ to surrounding structures
• Prevents distention of the ♥
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Serous Pericardium• Fibrous pericardium
• Pericardial cavity
• Parietal serous pericardium
• Visceral serous pericardium
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3 Layers of the Heart Wall• Epicardium (Visceral serous pericardium)
• Myocardium
• Endocardium
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Heart Chambers
• 4 chambers.
• 2 superior atria.
• 2 inferior ventricles.
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Right Ventricle
Pulmonary Circuit
Left Ventricle
Systemic Circuit
Left atrium
Right Atrium
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Right Atrium
• Receives deO2 blood from systemic circuit
• Receives 3 main vessels– SVC– IVC– CS
• Sends blood thru the tricuspid orifice (past the tricuspid valve) to the RV
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Left Atrium• Receives O2 blood from
pulmonary circuit
• Receives 4 vessels– Pulmonary veins
• Sends blood thru the mitral orifice (past the mitral valve) to the LV
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Interatrial Septum separates deO2 blood from O2 blood
• Adult contains• Fossa ovalis
• Fetus contains• Foramen ovale
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How/Why do the fetal atria connect?• Foramen ovale allows blood
flow from RA to LA
• RA BP > LA BP
• Bypasses pulmonary circuit
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Ventricles• Inferior chambers.
• Muscular pumps.
• Separated by IV septum
• Trabeculae carneae
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• Receives deO2 blood from RA.
• Pumps to pulmonary circuit via the pulmonary trunk.
• Pulmonary semilunar valve
• Tricuspid valve
Right Ventricle
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Left Ventricle• Receives O2 blood from LA.
• Pumps to systemic circuit via the aorta.
• Aortic semilunar valve
• Mitral valve
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• Volume
• Pressure
• Muscle
Left Ventricle vs. Right Ventricle
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In a normal heart the amount of blood entering the pulmonary trunk every 5 minutes is _______________ the amount of blood entering the aorta every 5 minutes.
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Coronary Circuit - special branch of the systemic circuit
• Provides blood to the heart wall.
• All 3 layers need O2/nutrient delivery and CO2/waste removal.– Myocardium most of all.
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Left Ventricle
Aorta
Coronary Arteries
Coronary Veins
Coronary Sinus
Right Atrium
Coronary Circuit
Coronary Capillaries
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Heart Valves• Prevent backflow.
• 2 atrioventricular (AV)– Tricuspid– Mitral
• 2 semilunar– Pulmonary– Aortic.
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• Tricuspid valve is open when RAP > RVP.
• Mitral valve is open when LAP > LVP.
Atrioventricularvalve open
Bloodflow
Atrium
Cusp
Chordaetendineae
Papillarymuscle
Ventricle
P
P
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• Tricuspid valve is closed when RAP < RVP.
• Mitral valve is closed when LAP < LVP.
Atrioventricularvalve closed
Blood inventricle
Atrium
Cusp
Chordaetendineae
Papillarymuscle
Ventricle P
P
Prevent prolapse
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Semilunar Valves• “Pocket valves”
• No chordae tendineae
• No papillary muscles.
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Pulmonary valve is open when RVP > Pulmonary Trunk P.
Aortic valve is open when LVP > Aortic P.
Ventricle
Cusps ofsemilunar
valve
Arterialtrunk
(aorta orpulmonary
trunk)
Semilunar valve open
Blood flow
P
P
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Pulmonary valve is closed when RVP < Pulmonary Trunk P.
Aortic valve is closed when LVP < Aortic P.
Semilunar valve closed
Blood flow
Ventricle
Cusps ofsemilunar
valve
Arterialtrunk
(aorta orpulmonary
trunk) P
P
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Stanley has an incompetent atrioventricular valve. This means that the valve is open when it should be closed. As a result, there is a buildup of blood and fluid in his pulmonary circuit.
Which heart valve is the incompetent one?
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Theo has a stenotic atrioventricular valve. This means that the valve is too narrow when it is open. As a result, there is a buildup of blood and fluid in his pulmonary circuit.
Which heart valve is the stenotic one?
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• In btwn epicardium and endocardium
• Mostly cardiac muscle tissue
• Also contains fibrous skeleton of the heart
Myocardium
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• Origin/insertion for cardiac muscle cells.
Fibrous Skeleton of the Heart = Dense CT surrounding the cardiac valves.
• Electrically isolates atria from ventricles.
• Physically separates atria from ventricles.
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Cardiac Contractile Cells• Contract and generate
the pumping force of the heart.
Striation
Branching
Intercalated Disc
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• Gap junctions
Intercalated Discs Contain 2 Structures:• Desmosomes
Electrically join CM cells Mechanically join CM cells
Allows for coordinated synchronized contraction.
Prevents CM cells from separating.
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Autorhythmic Cells
1. Sinoatrial node
2. Atrioventricular node
3. Atrioventricular bundle
4. Right/left bundle branches
5. Purkinje fibers.
1
2
5
3
4
• Spontaneously and rhythmically depolarize.
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• From fastest to slowest:– SA node– AV node– AV bundle– Bundle branches– Purkinje fibers
• Who sets the pace?
Autorhythmic Cell Depolarization Rates
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Depolarization wave slows down @ the AV node. This allows the atria to contract before the ventricles.
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The electrical signal goes down the septum – not the sides or front or back.
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Look where ventricular contraction starts. Analogous to toothpaste squeezing
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• Cardioacceleratory center
• Cardioinhibitory center
Medullary Cardiac Centers
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• Sympathetic cardiac nerves
• Norepinephrine
• Innervates nodes and ventricular myocardium
• Increased heart rate and contractile force.
Cardioacceleratory center
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• Vagus nerve (CN X)
• Acetylcholine
• Innervates nodes
• Decreased heart rate
Cardioinhibitory center
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Resting parasympathetic influence on the heart.
Resting sympathetic influence on the heart.
What about during exercise?
Vagal Tone
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• What would happen to HR in each of the following situations:– Increased CAC activity– Increased CIC activity– Infusion of a drug that blocked ACh– Infusion of a drug that mimics NE– Severe damage to the CIC– Cutting the vagus nerve
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Heart rate is also affected by...
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• All the events associated with one heartbeat.
• Includes systole and diastole of all chambers.
• Pressures and volumes of all 4 chambers change in a predictable way during each cycle.
Cardiac Cycle
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Ventricular Filling
Isovolumetric Relaxation
Isovolumetric Contraction
Ventricular Ejection
Phases of the Cardiac Cycle
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Ventricular Filling• LV volume is increasing.
• Mitral valve is open.
• LVP < LAP
• LV is in diastole.
• Aortic valve is closed.
• LVP < Aortic P
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• First 80% vs. Last 20%
• End Diastolic Volume.
Ventricular Filling
Passive Due to atrial systole
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Time
Time
Ventricular Filling
Aorta
Left atrium
Left ventricle
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• LV contracts and LVP begins to rise.
• LVP quickly exceeds LAP and AV valves shut.
• However Aortic P is still really high so the ASL doesn’t open yet.
Isovolumetric Contraction
LUB
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• Mitral valve is closed.
• Aortic valve is closed.
• LV volume is not changing.
• LVP > LAP
• LVP < Aortic P
Isovolumetric Contraction
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Time Time
Isovolumetric Contraction
Aorta
Left atrium
Left ventricle
EDV
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• LV is still contracting and now LVP exceeds Aortic P
• Aortic valve is now open.
• And LV volume will decrease.
• Mitral valve is still closed because LVP > LAP
Ventricular Ejection
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• The amount that leaves is called the stroke volume.
• The amount that remains is called the end systolic volume.
Ventricular Ejection
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• Vol. ejected by a ventricle per cardiac cycle.
• Stroke Volume = End diastolic volume – End systolic volume
• SV = EDV – ESV
• Ventricular Balance
Stroke Volume
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Time
Ventricular EjectionEDV
ESV
SV
Calculate the stroke volume in this example.
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Ventricular EjectionWhy isn’t the entire EDV ejected?
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Time
Ventricular Ejection
Aorta
Left atrium
Left ventricle
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Isovolumetric Relaxation• LV relaxes and LVP begins to
drop.
• LVP drops below Aortic P and semilunar valves shut.
• However LVP is still much higher than LAP so the mitral valve doesn’t open yet.
DUP
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Isovolumetric Relaxation• Mitral valve is shut.
• Aortic valve is shut.
• LV volume is not changing.
• LVP > LAP
• LVP < Aortic P
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Time
Isovolumetric Relaxation
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Time
Isovolumetric Relaxation
Aorta
Left atrium
Left ventricle
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• Given that:– Aortic Pressure = 82mmHg– Left Atrium Pressure = 11mmHg– Left Ventricle Pressure = 61 mmHg and falling
• Answer the following:– The mitral valve is…– The tricuspid valve is…– The aortic semilunar valve…– The pulmonary semilunar valve is…– LV volume is…– LA volume is…– The current phase of the cardiac cycle is…– The previous phase of the cardiac cycle was…– The next phase of the cardiac cycle will be…– The most recent heart sound was caused by…– The next heart sound will be caused by…
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• Volume of blood pumped by a ventricle per minute.
• Cardiac Output = Heart Rate x Stroke Volume
• Units are mL/min or L/min.
Cardiac Output
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Hector had a cardiac output of 6000 mL/min and a heart rate of 100 beats/minute. How much blood left his heart during each cardiac cycle?
a) 58.6 mLb) 62 mLc) 100 mLd) 120 mLe) 180 mL
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Ventricular Imbalance
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Regulating Stroke Volume
• Primary influence on stroke volume is:– Preload
• Other influences:
– Contractility
– Afterload
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• Degree of ventricular stretch.
• In other words – the EDV
Preload
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Whatever goes in the heart gets pumped out.
Frank-Starling Law
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More blood returns to the heart.
Ventricular stretch increases
Ventricular tension increases
Overlap btwn actin & myosin gets more optimum
Stroke volume increases
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• Strength of ventricular squeezing regardless of how stretched it is.
• ↑ in contractility will cause SV to increase.
• Norepinephrine and epinephrine
Contractility
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• Pressure that the LV must overcome in order to open the semilunar valve and eject blood.
• Aortic blood pressure.
Afterload
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• More energy will be expended on opening the ASV.
• Less energy will be available for ejecting blood.
• SV would then decrease.
Suppose Aortic P is high:
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• How would each of the following affect SV?
– Activation of the CAC
– Infusion of epinephrine
– A decrease in time between heart beats
– Hypocalcemia and a resulting decrease in contractility
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• How does endurance training affect:– Left ventricular contractility– Left ventricle chamber size– Coronary circulation