QuestionSBA
QuestionChoice
Viscosity has more effect on the flow in vessels than density as most flow is laminar (except some turbulent at branch points). The role of viscosity in laminar flow resistance is described by Poiseuille's law: resistance is proportional to the length of the tube multiplied by the viscosity of the fluid divided by the 4th power of the radius of the tube. Density has more effect on resistance during turbulent blood flow.
10001182
b
In the majority of the lumens of blood vessels, the density of the blood has more effect than the viscosity
QuestionChoice
In small vessels such as capillaries, erythrocytes tend to flow centrally and the plasma peripherally. This causes a cell-free plasma layer which effectively decreases the viscosity of the blood, decreasing resistance to flow. This is known as the Fahraeus-Lindqvist effect in which the effective viscosity of a fluid changes depending on the diameter of the tube it is flowing through.
10001184
d
In small vessels, erythrocytes tend towards the peripheries
QuestionChoice
The majority of the total peripheral resistance of vessels is due to the arterioles, otherwise known as the resistance vessels. Indeed, the decrease in mean pressure from the large arteries to the capillaries is the largest change in any part of the vascular system. This is one of the reasons why altering tunica media contraction in arterioles is one of the main methods used to regulate the blood flow to a tissue.

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10001185
e
The majority of total peripheral resistance comes from the capillaries
QuestionChoice
This is true as the resistance of a liquid in a tube is inversely proportional to the 4th power of the radius of the tube. This is described by Poiseuille's law: resistance is proportional to the length of the tube multiplied by the viscosity of the fluid divided by the 4th power of the radius of the tube.
10001181
a
Dilating a vessel to double the diameter will reduce its resistance to 12.5% of the previous value
QuestionChoice
Longer tubes have higher resistances to fluid flow than shorter tubes. This is described by Poiseuille's law: resistance is proportional to the length of the tube multiplied by the viscosity of the fluid divided by the 4th power of the radius of the tube.
10001183
c
The longer the vessel, the lower the internal resistance
Concept
Chapter
2693
3809
Structure and physiology of blood vessels
Topic
159
Cardiovascular physiology
12783
Which of the following statements about vascular resistance is true?
a