Peripheral Vascular System - Nordgren

Question 1

What factors determine transport of substances within the vascular system?

Answer 1

• Pressure/Pressure changes
• Resistance
• Homeostatic needs

Question 2

What factors determine diffusion of substances across the capillary wall?

(hint: passive transcapillary solute diffusion)

Answer 2

• Concentration difference
• Surface area for exchange
• Diffusion distance
• Permeability of capillary wall to the substance
• Pressure differences
  
  • Hydrostatic pressure (OUT)
  • Oncotic pressure (IN)

Question 3

How does capillary wall permeability to a solute relate to the size and lipid solubility of the solute?

Answer 3

***

Question 4

What factors influence transcapillary fluid movement?

Answer 4

• Hydrostatic Pressure (P):
  
  • pressure forcing blood OUT
  • causes filtration (+ pressure gradient)
• Oncotic Pressure (π):
  
  • attraction of water IN
  • causes reabsorption (– pressure gradient)

Question 5

What is the role of the lymphatic vessel system in preventing fluid accumulation in the interstitial space (i.e. edema.)?

Answer 5

• Keeps interstitial protein concentration LOW
  
  • removes excess capillary filtrate from the tissues
  • collects large particles → move them to lymph nodes → return fluid to peripheral venous blood

Question 6

What is the Starling Hypothesis?

Answer 6

Net filtration rate =

K(P_capillary–P_interstitial) – (π_capillary–π_interstitial)

• P : hydrostatic pressure
• π : oncotic pressure
• K : constant

+Net filtration = filtration

–Net filtration = reabsorption

Question 7

How do you calculate the vascular resistances of networks of vessels arranged in parallel?

Answer 7

• If all vessels have different resistances:
  
  • 1/R_parallel = (1/R₁) + (1/R₂) + (1/R₃)
    
    • total cross-sectional area of ALL capillaries
• If all vessels have same resistance:
  
  • R_p = R_x/n

Question 8

How do you calculate the vascular resistances of networks of vessels arranged in series?

Answer 8

• Total Resistance equals the SUM of all the individual resistances:
  
  • R_series = R₁ + R₂ + R₃

Question 9

What vessel in a series will have the greatest impact on pressure and flow?

Answer 9

the vessel with the HIGHEST resistance

Question 10

What is total peripheral resistance (systemic vascular resistance)?

Answer 10

Overall resistance to flow through the ENTIRE systemic circulation.

Question 11

What is the relationship between TPR (Total Peripheral Resistance) and the vascular resistance of each systemic organ?

Answer 11

• Organs are arranged in parallel
  
  • contribute to TPR following the parallel resistance equation
  • 1/TPR = (1/R_organ1) + (1/R_organ2) + (1/R_organ3)
    
    • adding an organ → decreases TPR
    • decreasing resistance in any organ will decrease TPR

Question 12

What is vascular compliance?

Answer 12

• Elastic nature of blood vessels
• How much pressure will change (ΔP) in response to a change in volume (ΔV)
  
  • C=ΔV/ΔP

Question 13

What is the role of arterial compliance in storing energy for blood circulation?

Answer 13

• Acts as a PRESSURE RESERVOIR
  
  • convert pulsatile flow coming out of the heart into a steady flow of blood through the vascular bed
  • store pressure energy in walls during expansion
    
    • release of this potential energy on recoil drives blood through the periphery

Question 14

What is the relationship between arterial pressure, cardiac output, and total peripheral resistance?

Answer 14

MAP = CO x TPR

• MAP : Mean Average Pressure
  
  • assume central venous pressure is 0

Question 15

How can you estimate the mean arterial pressure when given the arterial systolic and diastolic pressures?

Answer 15

MAP = 2/3(P_D) + 1/3(P_S)

Question 16

What is the relationship between pulse pressure, stroke volume, and arterial compliance?

Answer 16

P_p = SV / C_A

• Arterial pulse pressure (P_p) is equal to systolic minus diastolic pressures
  
  • P_p = P_s – P_D

Question 17

How will pulse pressure be changed with changes in stroke volume or arterial compliance?

Answer 17

• The greater the compliance:
  
  • ​the smaller the pulse pressure
• The larger the volume ejected (SV):
  
  • the larger the pulse pressure

Question 18

How does arterial compliance change with age? How does this affect arterial pulse pressure?

Answer 18

• As we age:
  
  • decreased arterial compliance
    
    • due to increased arterial stiffness
  • increased arterial pulse pressure
    
    • due to increased arterial volume and decreased C_A

Question 19

What is the “central venous pool”?

Answer 19

Blood in the great veins in the thorax and the right atrium

Question 20

What is the “peripheral venous pool”?

Answer 20

blood returning from the capillaries to the venous system