Arteries and Veins (B 2: W 2) Flashcards
What does it mean to say that arteries are a hyraulic filter?
- Initially, the arteries have pulsatile flow
- Due to resistance and compliance, the arterioles and capillaries face constant flow
Why is it important that arteries store ejected blood during systole?
- Arteries accommodate blood that is coming from the heart
- They recoil during diastole because the pressure is decreased
- Pushes blood to capillaries
- Capillaries receive constant flow - important for their function
What are the functions of veins?
- Conduits
- Major reservoir of blood
- Regulate cardiac output
What is the tunica intima composed of?
Endothelium
What is the tunica media composed of?
Smooth muscle
Collagen
Elastin
What is the tunica adventitia composed of?
Collagen
Fibroblasts
Vasa vasorum
Nerves
Which has a larger tunica media: elastic artery or muscular arter?
Elastic artery
- Elastic: many elastic fibers throughout (high pressure)
- Muscular: less elastic fibers (lower pressure)
What happens to the wall thickness of an artery as its radius decreases?
Wall thickness increases (in proportion to radius)
How are smooth muscle cells arranged in an artery?
In a spiral
How are smooth muscle cells arranged in in a vein?
In a helix
Better contraction (vasodilation/vasoconstriction)
What is resistance?
The force that impedes blood through the system
Large veins have little resistance
How do veins return blood to the heart?
- Compression by the surrounding tissues generates resistance to flow
- Veins rely on peripheral pressure to return blood to the heart
- Generated by surrounding tissues
- Pressure in large veins is 4-7 mmHg greater than the pressure in the right atrium
- Usually 0 mmHg or less
How is compliance (capacitance) calculated?
C = dV/dP
Increase in volume/increase in pressure
Which blood vessel is most distesible?
Veins
- Even slight increases in pressure causes the veins to store 0.5 to 1 liter of extra blood
- Veins are compliant because they are distensible
What is the relationship between compliance and distensibility?
Compliance and distensibility are not the same
Compliance = Distensibility x Volume
C = D x V
How much more distensilbe than a vein compared to its corresponding artery?
- Vein - 8 times as distensible as corresponding artery
- Vein - 3 times greater volume than artery
- Vein - compliance is 24 times greater than artery
C = D x V
What is the pressure-volume relationship in arteries?
Very little change in volume will cause very large change in pressure
Not that compliant
What is the pressure-volume relationship in veins?
Large change in volume doesn’t create a drastic change in pressure
Very compliant
Can accommodate a large amount of blood
What causes delayed compliance?
Vasoconstriction and dilation
- Large volume increase - increased pressure
- Blood vessel streches so pressure decreases
- Large volume decrease - decrease in pressure
- Blood vessel shrinks back down so pressure increases
What happens to blood flow through the capillaries when arteries are rigid?
- When arteries are rigid, blood flows through the capillaries during systole, but ceases during diastole
- When the arteries are normally compliant, blood flows through capillaries throughout the cardiac cycle
How do we label the sympathetic nerves?
Use tyrosine hyrdoxylase - synthesizes catecholamines
Labels nerves that release catecholamines. We see these in the adventitia
What happens to blood vessels when they are sympathetically stimulated?
- Increase in vascular smooth muscle tone
- Constriction
- Increase in pressure at each volume
What happens to blood vessels when there is sympathetic inhibition?
- Smooth muscle relaxes
- Dilation
- Decrease in pressure at each volume
What determines a change in the central venous pressure?
dCVP = dV/C
Change in volume of blood within thoracic veins divided by the compliance of these veins
- Increased by increase in venous blood volume
- Or a decrease in venous compliance
How does central venous pressure influence venous return?
As CVP increases, venous return decreases
If the pressures are equal, there is no venous return
What happens when CVP increases?
- R ventricular stroke volume increases (Starling’s law)
- This causes increased cardiac output of right heart
- Right heart output temporarily exceeds that of the left heart
- As long as this imbalance exists, blood accumulates in the pulmonary vasculature and raises pulmonary venous and left atrial pressure
- Increased L atrial pressure increases L ventricular stroke volume (Starling’s law)
- Very quickly a new steady state will be reached when L atrial pressure has risen sufficiently to make L ventricular stroke volume exactly equal to the increased R ventricular stroke volume
What factors would increase right ventricular preload?
- Increase in atrial contractility
- Increase in ventricular compliance
- Increase in venous pressure
- Increase in venous volume
- Decrease in venous compliance
- Increase outflow resistance and afterload (e.g. pulmonic valve stenosis)
What factors would decrease right ventricular preload?
- An increase of heart rate
- A increase in inflow resistance (e.g. tricuspid valve stenosis)
What is the pressure difference between arteries and veins while lying, standing, and walking?
- Consistent pressure change between the two while lying down and standing up
- Both increase when we stand
- When we walk, skeletal muscle affects venous return
- Pressure in the veins is low
- There is a greater difference in pressure between arteries and veins
- Due to the skeletal muscle pump
