Hemodynamics II

Question 1

Compared to veins, arteries have a larger tunica ___ comprised mainly of ____.

Answer 1

media comprised mainly of smooth muscle

Question 2

___ have valves to ensue unidirectional flow.

___ consist o fonly a thin endothelial layer of cells.

Answer 2

Veins have valves

Capillaries consist of only a thin endothelial layer of cells

Question 3

Aorta/Large arteries serve to assist blood flow through their compliance.

Arterioles’ function?

Answer 3

Valves - they regulate blood flow to vascular beds & regulate total peripheral resistance via vasoconstriction & vasodilation controlled through neural and humoral input

Question 4

Metarterioles

Answer 4

Specialized type of arteriole that connects to venules.

When open, they allow blood flow to bypass the capillary bed and flow directly from arteiroles to venules.

Most common in finger tips & ears.

Question 5

Blood pressure drops most dramaticlaly across what type of vessel?

Answer 5

Arterioles because they function as the valves.

Their vasoconstriction reduces bp downstream of it.

Question 6

Capillaries

Answer 6

• Smallest - single layer of endothelial cells with pericytes on the outer layer
  
  • 3 types - continuous, fenestrated, sinusoidal
  • Some include fenestrations (pores) to facilitate exchange
  • Pinocytosis, diffusion, filtration
• Nutrient & waste products are exchanged w/surrounding tissue
• Numerous in metabolically active organs

Question 7

The bulk of transcapillary exchange is ___, which follows Fick’s law

Answer 7

Diffusion

Question 8

According to Fick’s law, what factors drive diffusion?

Answer 8

J = -(Permeability_molecule)(Surface area_capillary)(Conc_tissue-Conc_capillary)

• Permeability of the molecule
• SA of the capillary
• Difference in teh conc between capillary and surrounding tissue

Question 9

Two types of diffusion-mediated capillary exchange (from capillary into surrounding tissue)

Answer 9

• Flow limited: diffusion of small molecules with high permeability coefficients (e.g. water, NaCl, urea, glucose)
  
  • Diffuse rapidly from the capillary to the surrounding cells so that there’s few by the time it reaches the venous end of the capillary bed.
• Diffusion limited: large molecules with poor permeability OR small molecules with low capillary density or in the presence of edema
  
  • Remain in the capillary

Question 10

Under conditions that increase distance between the capillary and cells (e.g. edema or low capillary density) what happens?

Answer 10

normally flow-limited molecule sbecome diffusion-limited as the distance between the cells and capillary become too great

Question 11

Filtration/absorption through capillaries

Answer 11

Small water soluble molecules move through pores/fenestrations, intercellular clefts, and channels in the endothelium.

Occurs the most in the liver capillaries.

Question 12

Filtration/Absorption is regulated by

Answer 12

a balance hydrostatic and osmotic pressure nin the capillaries & interstitial fluid

Question 13

Hydrostatic pressure promotes exchange.

Capillary hydrostatic pressure (P_c) =

Tissue hydrostatic pressures (P_i) =

As blood flows from the arterial side to the venous side, what happens to Pc?

Answer 13

Capillary hydrostatic pressure (P_c) = blood pressure determined by arterial & venous pressure; driving force of filtration

Tissue hydrostatic pressures (P_i) = ~0

P_c drops from ~P_arterial to ~P_venous

Question 14

Oncotic pressure (pi) is the osmotic pressure exerted by plasma proteins (esp albumin) that don’t easily pass the capillary wall.

Compare oncotic pressure from capillaries to tissue

Answer 14

Albumin is high in capillary plasma (arterial or venous), so

capillary oncotic force >> interstitial fluid oncotic force.

Since capillary oncotic force inhibits loss of water, it promotes absorption.

Question 15

The Starling equation demonstrates how nutrients are delivered on the arterial side and waste uptake occurs on the venous side. How?

Answer 15

If capillary hydrostatic pressure > capillary oncotic pressure, then +Qf and filtration.

As Pc drops across the capillary bed…

capillary hydrostatic pressure < capillary oncotic pressure, then - Qf and absorption.

Question 16

What effect will vasoconstriction vs vasodilation have on absorption/filatraiton?

Answer 16

Vasoconstriction will decrease pressure on the arteriolar side –> enhanced absorption at the capillary bed

Vasodilation will increase pressure of the arteriolar side –> enhanced filtration/edema

Question 17

What impact does heart failure or venous clots have on filtration/absorption?

Answer 17

Increases pressure in the venous side –> enhanced filtration & edema

Question 18

What impact would hemorrhage have on absorption/filtration

Answer 18

Decreased pressure in the venous side –> enhanced reabsorption

Question 19

Pinocytosis is more common in capillaries within ___ tissue and is more common on the ___ side of the capillary bed

Answer 19

Muscle tissue

Venous side

Question 20

LaPlace’s law: Wall tension = (Transmural pressure)(radius)

How does this explain how capillary walls can withstand pressure from the arterial side?

Answer 20

Capillaries can withstand high pressures without a mscular wall due to their reduced radius.

Having an small radius (R) reduces the effects of elevated transmural pressure on wall tension

Question 21

When wall tension becomes elevated, arteries sometimes compensate by

Answer 21

Expand into a spherical structure (aneurysm) because

T =P(R/2) for a sphere

However, as this continues the risk of rupture increases later as the sphere starts resembling a cylinder again

Question 22

Venous system function

Answer 22

Reservoir for the blood (~70% of blood)

When increased cardiac output is desired, the venous system constricts to increase preload while also partitioning blood o the heart & other organs.

Question 23

How is the venous system able to serve its reservoir function?

Answer 23

Extremely high compliance of the veins

Question 24

Valves in veins

• prevent increased ____ pressure caused by standing.
• facilitate return flow to the heart due to ___ and __.

Answer 24

Valves

• prevent increased hydrostatic capillary pressure caused by standing.
• facilitate return flow to the heart due to muscle contraction and respiration.

Question 25

Lymphatic system collects ___ and ___ from the interstitial space and returns it to the bloodstream via a series of unidirectional vessels and nodes

Answer 25

additional fluid and leaked plasma proteins