Lecture 11: Arterial & Venous Systems And Lymphatics Flashcards Preview

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Flashcards in Lecture 11: Arterial & Venous Systems And Lymphatics Deck (21):
1

What is the definition and formula for vascular distensibility?

Vascular distensibility = Increase in volume/(Increase in pressure X Original volume)

2

How does distensibility compare between veins and arteries

- Veins are about 8 times more distensible than arteries.
- Pulmonary vein distensibilities are about the same as for systemic veins.
- Pulmonary artery distensibilities are about 6 times that of systemic arteries.

3

What is the definition of vascular compliance

- Vascular compliance (capacitance) = Increase in volume/Increase in pressure
- Tells us the total quantity of blood (ml) that can be stored in a given portion of the circulation for each mm Hg rise in pressure.
- Capacitance describes the distensibility of blood vessels.
- Capacitance (mL/mmHg) is inversely proportional to elastance.
- Capacitance is equal to distensibility * volume
- VD * Vorig = (Vinc)/(Pinc) = Compliance

4

How does compliance compare to elastance?

- Capacitance is directly proportional to volume and inversely proportional to pressure.
- Capacitance describes how volume changes in response to a change in pressure.
- Capacitance is much greater for veins than arteries.
- Capacitance of arteries decreases with age.
- The greater the amount of elastic tissue in a blood vessel:
- The higher the elastance
- The lower the compliance
- Compliance is a measure of the ease with which a hollow viscus may be distended; i.e., the volume change resulting from the application of a unit pressure differential between the inside and outside of the viscus; the reciprocal of elastance.
- Vascular compliance = total quantity of blood that can be stored in a given portion of the circulatory system.
- Elastance is a measure of the tendency of a hollow viscus to recoil toward its original dimensions upon removal of a distending or collapsing force.
- A systemic vein is about eight times as distensible as its corresponding artery and has a volume about three times as great. How would its compliance compare to that of a corresponding artery?

5

Be able to explain the following observations

- When the arterial system contains 700 ml of blood, the mean arterial pressure is 100 mm Hg. But when the arterial system contains 400 ml of blood, the mean arterial pressure is 0 mmHg.
- The venous system contains a volume of blood ranging from 2000 to 3500 ml. Removing several hundred ml from the normal venous volume only changes venous pressure 3 to 5 mm Hg.

6

Give the definition for pulse pressure

Pulse pressure ≈ Stroke volume/Arterial compliance

7

What are the two factors that can affect pulse pressure

* Stroke volume output of the heart:
- Most important determinant of pulse pressure
- Diastolic pressure remains unchanged during ventricular systole; pulse pressure increases to the same extent as the systolic pressure.
* Compliance of the arterial tree:
- Decreases in compliance (capacitance), i.e. aging, result in an increase in pulse pressure.

8

What are some conditions that can cause abnormal contours of the pressure pulse wave?

* Aortic valve stenosis
- Diameter of the aortic valve opening is reduced significantly, and the aortic pressure pulse is decreased significantly.
- Blood flow through the aortic valve is diminished.
* Atherosclerosis
* Patent ductus arteriosus:
- Half or more of the cardiac output flows back into the pulmonary artery and lung blood vessels.
- Diastolic pressure falls very low before next heartbeat.
* Aortic regurgitation:
- The aortic valve is absent or will not close completely.
- Aortic pressure may fall all the way to 0 between heartbeats.
- REVIEW SLIDES 13-21

9

Define mean arterial pressure

- Mean arterial pressure is the average arterial pressure with respect to time.
- Because a greater fraction of the cardiac cycle is spent in diastole than in systole, mean arterial pressure is NOT the simple average of diastolic and systolic pressures.
- Calculation:
-- Mean arterial pressure = diastolic pressure + 1/3 pulse pressure.

10

Compare resistance to cardiac output

- Pressure in the right atrium = central venous pressure. Factors that regulate right atrial pressure:
- Ability of the heart to pump blood out of the right atrium/ventricle
- Tendency of blood to flow into the right atrium
- Estimating left atrial pressure: Use pulmonary wedge pressure: Catheter inserted into pulmonary artery will make almost direct contact with the pulmonary capillaries. This pressure is almost equal to the left atrial pressure.

11

Discuss factors that increase venous return

* Factors that increase venous return (and increase right atrial pressure):
- Increased blood volume
- Increased peripheral venous pressures due to increased large vessel tone
- Dilation of arterioles
* Large veins offer some resistance:
- In a person lying down the pressure in peripheral veins is +4 to +6 mm Hg greater than the right atrial pressure.
- When intra-abdominal pressure increases, the venous pressure in the legs must increase above the abdominal pressure before blood can flow from the legs to the heart through the abdominal veins.
- Review 15-9, 15-10, 15-12, and 15-13

12

Review 15-2, and 15-11

Do it

13

Describe Arterioles

- Small arterioles control blood flow to each tissue.
- Local conditions in tissues control diameters of arterioles.
- Arterioles are highly muscular.
- Continuous muscular coat is lost in metarterioles.

14

Define and describe capillaries

* Smooth muscle fiber encircles capillary at point where it originates from a metarteriole:
- Referred to as a precapillary sphincter (Refer to Figure 16-1) • Capillary wall:
- Unicellular layer of endothelial cells
- Thin basement membrane
- Total wall thickness = 0.5 μm.
- Internal capillary diameter = 4-9 μm.
Slit pores:
- (intercellular clefts); spacing of 6-7 nm.
- Allow for rapid diffusion of water/water-soluble ions/small solutes
* Plasmalemmal vesicles (Refer to Figure 16-2):
- Formed from caveolins
- Play a role in endocytosis and transcytosis
* Some capillaries in certain organs have pores:
- I.e., liver, GI tract, kidneys

15

What is the most important factor in regulating vasomotion

The concentration of oxygen in the tissues

16

Describe diffusion and capillary exchange

- Diffusion is the most important means for the exchange of substances between the blood and the interstitial fluid (Refer to Figure 16-3).
- Lipid-soluble substances can diffuse readily through the capillary cell membranes:
- Oxygen
- Carbon dioxide
- Non-lipid-soluble substances diffuse through the intercellular pores/clefts.
- Rate of water diffusion through the capillary membrane is 80x faster than flow of plasma within the capillary.
- Remember that rate of diffusion is directly proportional to concentration differences of the diffusing substance.
- Passage of substances through the interstitium is mostly via diffusion rather than flow. (Refer to Figure 16-4).
- This is because of the large numbers of proteoglycan filaments found in the interstitium.
- Rivulets that allow fluid flow through the interstitium do sometimes form.

17

Describe starling forces

Starling forces determine direction of diffusion into or out of a capillary (Refer to Figure 16-5):
- Capillary pressure (outward force) • Interstitial fluid pressure (inward force)
- Capillary plasma colloid osmotic pressure (inward force)
- Interstitial fluid colloid osmotic pressure (outward force)
- Sum of the above forces = Net Filtration Pressure
* Capillary filtration coefficient:
- Kf
- Takes into consideration the number and size of pores.
- Filtration = Kf x NFP
* When fluid enters the lymphatics, the lymph vessel walls contract momentarily and pump fluid into the blood circulation.
- Creates a slight negative pressure in the interstitial spaces.

18

What is the definition for net filtration pressure?

NFP = Pc –Pif –Πp+ Πif
- Pc = cappilarry pressure (outward)
- Pif = interstitial fluid pressure (inward)
- Πp = plasma colloid osmotic (oncotic) pressure (inward)
- Πif = interstitial colloid osmotic (oncotic) pressure (outward)

19

Describe filtration at the arterial end of the capillary

* Forces moving fluid outward:
- Capillary pressure (30 mm Hg)
- Negative interstitial free fluid pressure (3 mm Hg)
- Interstitial fluid colloid osmotic pressure (8 mm Hg)
* Total Outward Force = 41 mm Hg
- Forces moving fluid inward:
-- Plasma colloid osmotic pressure (28 mm Hg)
* Total Inward Force = 28 mm Hg
* Net Outward Force = 13 mm Hg

20

Describe filtration at the venous end of a capillary

- Forces moving fluid inward:
- Plasma colloid osmotic pressure (28 mm Hg)
* Total Inward Force = 28 mm Hg
- Forces moving fluid outward:
- Capillary pressure (10 mm Hg)
- Negative interstitial free fluid pressure (3 mm Hg)
- Interstitial fluid colloid osmotic pressure (8 mm Hg)
* Total Outward Force = 21 mm Hg
* Net Inward Force = 7 mm Hg
- = net reabsorption force
- See Slides 52 and 53

21

What is lymphatic return?

- Lymph vessels possess 1-way valves.
- Lymph flow reaches maximum when interstitial pressure rises slightly above atmospheric pressure.
- Factors that increase lymph flow (and also interstitial fluid pressure):
-- Elevated capillary hydrostatic pressure
-- Decreased plasma colloid osmotic pressure
-- Increased interstitial fluid colloid osmotic pressure
-- Increased permeability of capillaries
- Rate of lymph flow = interstitial fluid pressure X activity of lymphatic pump
- Review slide 56 & 57