Review blood flow through the heart and the mechanical events that take place. (p.2)
Preload
End-diastolic volume
Blood in each ventricle at end of diastole
Normal = 110-120 mL
Venous return to heart = major factor regulating end-diastolic volume
Preload = degree of tension or distending force on ventricular muscle when it begins to contract
End-systolic volume
Volume of blood in ventricle after contraction
Usually 40-50 mL
Afterload
Pressure or resistance against which ventricle has to pump
Anything that increases pressure (aortic stenosis or peripheral vascular disease) increases afterload
Stroke Volume
Amount of blood ejected from ventricles during contraction
Usually 40-50 mL
Cardiac Output
(Stroke volume) x (Heart rate)
How is Frank-Starling mechanism related to cardiac output?
Greater stretch of muscle fibers = stronger contraction
How does the sympathetic nervous system influence heart rate and force of contraction? (p.6)
Sympathetic nervous system – supplies both atria and ventricles
Sympathetic stimulation –
o Can increase cardiac output 2-3 fold
o Increase rate and force of contractions
o Norepinephrine – released from sympathetic nerve endings
o Epinephrine – released from adrenal glands
o Norepinephrine and epinephrine – enhance depolarization rate of SA node by increasing net flow of calcium ions into cells (slope of phase 4 depolarization)
How does the parasympathetic nervous system influence heart rate and force of contraction? (p.6)
Parasympathetic nerves – primarily supply atria
o Acetylcholine – released from vagus nerve endings of parasympathetic system
o Slow HR and decrease force of contraction, especially atria
o Acetylcholine – slows HR by increasing membrane permeability to K+ and increasing polarization
- (hyperpolarized state)
Where would you find majority of alpha-adrenergic receptors? (p.6-7)
Located mainly in systemic blood vessels (arterioles) of skin, abdominal viscera, and skeletal muscle
Where would you find majority of beta-adrenergic receptors? (p.6-7)
o Lungs (beta-2)
o Heart (beta-1); (also beta-2 and alpha-1 in heart)
o Skeletal muscles (beta-2)
o Blood vessels (arterioles) of these organs (alpha-1, beta 2)
Know general effect of epinephrine on alpha-receptors and beta-receptors.
o Excite alpha and beta receptors equally
o Beta receptors tend to have lower threshold (increased sensitivity) for epinephrine than alpha receptors
- especially on blood vessels in skeletal muscle
Know general effect of norepinephrine on alpha-receptors and beta-receptors.
o Excites alpha receptorsmore than beta receptors
o Alpha receptors less sensitive to epinephrine
o Little effect on beta-2 receptors, but stimulate beta-1 receptors
If you gave a pharmacologic dose of norepinephrine, what would be the anticipated response of blood vessels?