Microcirculation

Question 1

At high or low flow rates does blood behave anomalously?

Answer 1

Low flow rates - formation of rouleauxs

-inc viscosity

Question 2

What is polycythemia ?

Answer 2

abnormal increase in RBCs

-viscosity and resistance double

Question 3

How does hematocrit affect viscosity?

Answer 3

• low hemat - inc bc of stickiness

- high hemat -inc bc of cell deformation

Question 4

How does vessel radius affect viscosity?

Answer 4

• relatively insensitive for large vessels
• decreases steeply with dec in radius for small vessels

-this occurs because of axial streaming

Question 5

What is a rouleaux?

Answer 5

chain like aggregates of RBCs which form at low flow rates

Question 6

Where are continuous capillaries present?

Answer 6

Skeletal muscle

Question 7

Where are fenestrated capillaries present?

Answer 7

Exocrine glands or epithelial membranes

Question 8

Where are discontinuous capillaries present?

Answer 8

Liver sinusoids

Question 9

What two methods alter the rate at which substance is carried to an organ?

Answer 9

1. change in flow rate

2. change in arterial concentration

Question 10

What four factors determine the diffusion rate of a substance btwn blood and interstitial fluid?

Answer 10

1. concentration difference
2. Surface area
3. Permeability
   - -these are all directly correlated with diffusion rate
4. Diffusion distance
   - -indirectly correlated

Question 11

What are net shifts in fluid btwn capillary and interstital compartments important for?

Answer 11

• maintenance of blood volume
• fluid absorption
• edema
• saliva and sweat production
• urine production

Question 12

What are the four pressures that control transcapillary fluid movement and what are their aproximate values?

Answer 12

1. Capillary hydrostatic ~25
   - directed out of vessel
2. interstial hydrostatic pressure ~0
3. capillary osmotic pressure
   - directed into vessel
4. Interstital osmotic pressure ~3
   - directed out of vessel

Question 13

In which way is the transcapillary fluid movement a positive value ?(Jv)

Answer 13

-from capillaries to interstitium

Question 14

What happens to capillary hydrostatic pressure down it’s length?

Answer 14

It drops - venule end has lower hydrostatic pressure than arteriole end

Question 15

What occurs as a result of arteriolar dilation or venular constriction?

Answer 15

-Filtration - movement out of capillaries

Question 16

What occurs as a result of ateriolar constriction or venular dilation ?

Answer 16

Fluid reabsorption - movement into capillaries

Question 17

What is the Pif in loose tissues? in rigid closed compartments?

Answer 17

Loose - negative
-drives filtration
Closed - positive
-drives absorption

Question 18

Ignoring the rate in the kidneys, does a higher rate of filtration or absorption occur throughout the capillaries? What is an aprox value for the net rate?

Answer 18

• Filtration

- Net filtration of 2-4 L/day

Question 19

Describe the process by which lymph enters lymphatics

Answer 19

Expansion phase

1. Hydrostatic P in interstitium > initial lymphatic
2. Microvalves open and fluid enters

Compression phase

3. Hydrostatic P inside the initial lymphatic rises closing the microvalves
4. Opens secondary lymph valves – flow downstream

Question 20

Where do the large lymphatics drain into?

Answer 20

R and L subclavian veins

Question 21

Does filtration or absorption occur at arteriolar ends? venular ends?

Answer 21

arteriolar - filtration

venular - absorption