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38 Cards in this Set

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Mechanism of Cardiac Contraction
Heart contains sarcoplasmic reticulum which holds Calcium.
Heart contains calcium induced calcium channels
Rely on calcium in the environment to realease calcium into cardiac muscle
S.R. is the bulk of Calcium source, but not the only source.
T-Tubules in heart contain ____ Channels
Voltage-Regulated Calcium channels which open at +20mV
Sarcoplasmic Reticulum of Heart contains ____ Channels
Ligand Regulated Calcium Channels.
Ligand=Calcium!!!
Mechanism of Cardiac Relaxation
Calcium is pumped back into S.R.
Calcium is pumped back into extracellular fluid.
Why are nerves in heart?
To control rate of contraction, but not to initiate a contraction
Nervous system that controls contraction?
Autonomic (Sympathetic & Parasympathetic)
No nervous connections to contractile cells at all. Connections only in autorhythmic cells in the S.A. and A.V. nodes
Sympathetic pathway in cardiac conduction
Sympathetics-->Norepinephrine (At SA & AV nodes)-->NorE binds to Beta-Receptors-->cAMP (Bind to gates internally)
Beta Receptors
G-Protein Covered Receptors.
If ligand from GPCR binds, then it activates enzyme that results in phosphoryation to initiate cAMP
cAMP-->
If Channels (Na/K) open wider.
Calcium Channels open wider.
Effects of Norepinephrine on heart
1) Sympathetics: increase in conractile cell due to more calcium release from S.R.
(Heart rate up, contractions stronger)
2) Contraction strength is increased
-more cross bridging occurs, power increase
-Contractile Phase, Shorter
-Relaxation Phase, Longer (more blood fill)
Parasympathetic Pathway in Cardiac Conduction
Parasympathetics--> Acetycholine-->Muscarinic Receptors (GPCR)-->Inositol Triphosphate (IP3)
Effects of IP3 (inositol triphosphate)
Calcium channels depolarize at lower voltage (take longer to open)
Potassium channels open for longer period of time (depolarize longer)
Absolute Autorhythmic Rate
Average Rate
100bpm, 72bpm
Parasympathetics (ACh) always working more at rest.
Norepinephrine causes a shorter contractile phase-->
Allows more time for the SR to suck out more calcium for the next contraction
Starlings Law of the Heart
Fill Time (UP)--> Blood Volume Before Contraction (UP)-->Cardiac Stretch (UP)--> Contractile Strength (UP)
Key for stronger contraction
Sarcoplasmic Reticulum.
When cell is stretched, more Calcium channels are opened in SR causing increase in calcium released out of SR
Right Atria
Superior Vena Cava
Inferior Vena Cava
Pulmonary Trunk
Left Atria
Pulmonary Veins
Aorta
Heart Valves
Atrioventricular Valve
Semilunar Valve
A-V Valves
Open when chambers are filling
Close during contraction
Right A-V Valve (Tricuspid)
Left A-V Valve (Bicuspid, Mitral)
-MVP due to higher pressure on left side of heart
Semilunar Valves
Open during contraction, close during relaxation
Right-Pulmonary Valve
Left-Aortic Valve
Cardiac Cycle (how many/name stages)
2 stage cycle of contraction and relaxation
Systole and Diastole
Systole
Systolic BP
Pressure in heart when contracted.
BP in heart is a maximum at systole
Diastole
Diastolic Pressue
Pressure in heart during relaxation
Average pressure is dependent on age
High residual pressure will tear at linings of arteries and overwork the heart
High Blood Pressure
145/90 (over 4 years)
As age increases, BP will increase, vessels lose elasticity over time.
(145/90 for a 70+ year old is perfect)
Detailed Cardiac Cycle Components
Atrial Systole
Ventricular Systole
-Isovolumetric Contraction
-Ejection Phase (Ventricular Ejection)
-Ventricular Diastole
Atrial Systole
Atria squeeze blood into ventricles
Results in end diastolic volume
Ventricular Systole (isovolumetric contraction)
Rise in pressure closes the A-V valves.
'First Heart Sound' (A-V Valves Close)
Can't pump into arteries until pressure is greater than residual pressure in arteries.
Residual Pressure (Of arteries closest to heart)
Aorta-80mmHg
Pulmonary Trunk-10mmHg
Ejection Phase (Ventricular Ejection)
Aorta-Greater than 80mmHg
Pulmonary Trunk-Greater than 10mmHg
Semilunar Valves Open
Blood contracted into arteries
Ejected blood is about 54% of End Diastolic Volume (Ejection Fraction)
End Systolic Volume=EDV-SV
Ventricular Diastole
Muscular Relaxation
A-V Valves Open
Semilunar Valves close, 'Second Heart Sound'
Cardiac Output (affected by)
Heart Rate
Stroke Volume
HRxSV=CO(mL/min)
72bpm X 70mL = 5liters
Parasympathetics on Cardiac Output
Parasympathetics-->ACh-->CO (down)
Sympathetics on Cardiac Output
Sympathetics-->NorE-->HR(UP) -->SV (UP)-->CO(Way Up)
Max Norepinephrine
90% Ejection Fracture
HR=220-age (MaxHR)
Min Stroke Volume
54% Ejection Fracture (at rest)
Min Heart Rate
Requirements of what body needs minimally to stay conscious
Ejection Fracture depends on?
Age
Physical Fitness