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Ch 9.4A -- Cardiac Output and Its Control -- VTPP 435
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Cardiac Output (CO)
-volume of blood pumped by each ventricle per minute
-HR x SV
Stroke Volume (SV)
volume of blood pumped out of each ventricles with each contraction or beat of heart
Cardiac Reserve
difference between CO at rest & max volume of blood heart can pump per minute
Vagus Nerve
-parasympathetic nerve to heart
-decreases heart rate
-innervates SA and AV nodes but not ventricles
-stimulates by releasing ACh to muscarinic receptors
Cardiac Sympathetic Nerves
-increase heart rate
-supply atria, SA, AV, and ventricles
-NE binds with beta 1 receptors
Parasympathetic on SA Node
-decreases HR
-ACh increases K+ permeability in pacemaker cells
Parasympathetic on AV Node
-decreases AV node excitability to prolong AV nodal delay
-increases K+ permeability
Parasympathetic on Atrial Muscle
decreases contractility to weaken strength of contraction
Sympathetic on SA Node
-speeds up depolarization by increasing Na+ and Ca2+
-increases HR
Sympathetic on AV Node
reduces AV nodal delay by increasing conduction velocity by increasing T-Type channel
Sympathetic on Ventricular Conduction Pathway
-increases excitability
-hastens conduction thru Bundle of His and Purkinje fibers
Sympathetic on Atrial Mucle & Ventricular Muscle
-strengthens contractions
Cardiovascular Control Center
integrating Center in Medulla of Brain Stem that controls mean arterial blood pressure
2 types of Control influence SV
1) Intrinsic Control -- extent of venous return
2) Extrinsic Control -- extent of sympathetic stimulation to heart
Venous Return
volume of blood to each atrium per minute form veins
Frank-Startling Law of the Heart
intrinsic control of heart such that increased venous return results in increased EDV leads to increased strength of contraction & increased SV
Preload
extent of filling of heart from venous return
Ejection Fraction
ratio of SV to EDV (SV/EDV)
Strength of Cardiac Muscle Contraction & SV can be graded by:
1) Varying initial length of muscle fibers
2) Varying extent of Sympathetic Stimulation
Afterload
-arterial blood pressure
-workload imposed on heart after contraction has begun