Chapter 1: Overview of the Cardiovascular System Flashcards
Slowing of action potential conduction through the AV node will slow the heart rate. True or false?
False. Slowing conduction through the AV node will have no effect on the heart rate but will increase the interval between atrial and ventricular excitation. The heart rate is normally slowed by decreases in the rate of action potential initiation by pacemaker cells in the SA node.
Why is total circulating blood volume more than intravascular water/plasma volume?
e.g., blood volume dog 90 mL/kg but 5% (50 mL/kg) plasma water volume
Because 45-55% of blood volume contains blood cells (Hct)
Name the percentage of blood flowing through each of these organs (at rest):
* lungs
* myocardium
* brain
* skeletal muscles
* bones
* GI system
* liver
* kidneys
* skin
* other
- lungs - 100%
- myocardium - 3%
- brain - 14%
- skeletal muscles - 15%
- bones - 5%
- GI system - 21%
- liver - 6%
- kidneys - 22%
- skin - 6%
- other - 8%
Explain how blood-conditioning organs/tissue withstands a greater reduction in blood flow than other organs?
typically receive far greater blood flow than needed for their own tissue needs, e.g., kidney receives 22% of CO but only needs a fraction of this to sustain their basal metabolic needs
organs where blood soley flows to supply that tissue (e.g., myocardium, brain), a reduction in blood supply is not well tolerated
What percentage of the oxygen supplied to it, does the myocardium consume?
75%
Name the basic flow equation (including units!)
Flow (Q) = change in Pressure / resistance
Flow = volume/time
change in pressure = mm Hg
resistance = mm Hg x time/volume
What are the 2 ways blood flow through an organ can be changed?
changes in pressure gradient
changes in resistance
Name Poiseuille’s equation
Blood flow (Q) = change in pressure x [(pi x r^4) / (8 L n)]
L = length
n = viscosity
Explain the Fick principle and how it is used to calculate the transcapillary efflux rate
By measuring the rate of blood flowing through a tissue and the concentration difference between the arterial and venous blood, one can calculate how much of the substance of removed/used by the tissue (transcapillary efflux rate)
Transcapillary efflux = blood flow (Q) x (arterial concentration - venous concentration)
Explain the effects of sympathetic innervation of the heart
sympathetic nerve fibers release norepinephrine –> acts on beta1-adrenergic receptors of the myocardium
- increased action potential conduction velocity
- increased heart rate
- increased contractility
Explain the effects of cholinergic parasympathetic innervation of the heart
parasympathetic nerve fibers travel to the heart via the vagus nerve
–> innervate the SA node, AV node, and atrial muscles
when activated –> release acetylcholine –> acts on muscarinic receptors of the cardiac muscle cells
effects:
- SA node –> decreased HR
- AV node –> decreased action potential conduction velocity
- decreased atrial myocyte contraction force
Describe and compar the anatomic and functional characteristics of arteries, arterioles, capillaries and venous vessels
Arteries
* thick walled
* some smooth muscle
* large component: elastin and collagen fibers –> can extend under increased pressure and then recoil passively
* “conduit vessels”, i.e., relatively low resistance to flow, which does not change much
Arterioles
* much ticker walls than arteries
* more smooth muscles and less elastic material
* can actively change their diameter
* “resistance vessels” - high resistance that can actively change
Capillaries
* single layer endothelial cells
* no smooth muscles
* cannot actively change their diameter
Venous vessels
* thin walls compared to their diameter -> quite distensible
* smooth muscles -> can actively change their diamter
* larger ones have one-way valves to prevent reverse flow
* “capacitance vessels” - contain a large proportion of blood volume
