Flashcards in 5. Fluid Dynamics + Peripheral Circulation Deck (28)

1

## Define velocity

### The rate of movement of fluid particles along a tube

2

## What is the relationship between velocity and radius for a constant flow?

###
Velocity is inversely proportional to the radius squared

(The greater the cross sectional area the slower the velocity)

3

## What is laminar flow?

### Where the velocity is greatest in the middle of the vessel and there is a velocity gradient to the edge

4

## What can cause turbulent flow and what does it result in?

###
Velocity increasing to a point where the flow becomes turbulent

Laminar flow breaks down and resistance is increased greatly

5

## How can you detect turbulent flow?

### Creates a noise called bruit

6

## For a constant pressure what is the relationship between velocity and viscosity?

###
Velocity is inversely proportional to viscosity

The thicker the blood is, the slower it travels

7

## For a constant pressure, what is the relationship between velocity and radius of tube?

###
As flow is determine by the velocity

Velocity is proportional to radius squared

The wider the tube the faster the blood will travel

8

## Why does increasing radius increase velocity at constant pressure?

### The wider the tube the faster the middle layers will move as the velocity gradient is constant

9

## According to poiselles law, what is the relationship between difference in pressure at both ends of a tube and radius at a constant flow and viscosity?

### Difference in pressure is inversely proportional to radius to the power of 4

10

## What is the relationship between resistance and viscosity?

### Resistance increases as viscosity increases

11

## What is the relationship between resistance and radius?

### Resistance decreases with radius to the power of 4

12

## Define flow

### Volume of fluid that passes a given point per unit of time

13

## What variables are pressure equal to?

###
Pressure= flow x resistance

(Similar to ohms law with electrical current)

14

## What is the relationship between flow and radius for a given pressure?

### Flow is proportional to radius to the power of 4

15

## What is the relative pressure size drop over the arteries?

### Small

16

## What is the relative pressure drop size over arterioles?

### Large

17

## What happens to flow in distensible vessels as pressure is increased and why?

###
As pressure increases flow increases because:

Increase in pressure causes vessel to stretch

This increases the cross sectional area of the vessel hence flow increases (to the 4th power of the change in radius)

18

## How do veins have capacitance?

### A transient increase in pressure will cause more blood to flow into the vessel than out (and vice versa) allowing blood to be "stored" in veins

19

## Why does arterial pressure need to be high?

### To drive the cardiac output through the total peripheral resistance

20

## Why do arteries have distensible walls?

###
So in systole they stretch (more blood flows in than out) hence pressure does not rise too much

As arteries recoil flow continues into arterioles

21

## What factors affect systolic pressure?

###
How hard the heart pumps

Total peripheral resistance

Stretchiness of arteries

22

## What factors affect diastolic pressure?

###
Systolic pressure

Total peripheral resistance

23

## What is pulse pressure? (Give a typical value)

###
Difference between systolic and diastolic pressures

Typically about 40mmHg

24

## How is average pressure calculated?

### Diastolic pressure + 1/3 pulse pressure

25

## What properties make arterioles high resistance vessels?

###
Lumen is narrow

High smooth muscle cell content

26

## What are increases and decreases in vasomotor tone called?

###
Vasoconstriction

Vasodilatation

27

## Name 3 vasodilator metabolites

###
H+

K+

Adenosine

28