Guyton Kap. 16. Microcirculation & Lymph

Front 1

Number of peripheral capillaries and total surface area:

Back 1

10 billion capillaries with 500- 700 square meters surface area.

Front 2

Usual distance of a functioning cell from a capillary:

Back 2

20- 30 micrometers

Front 3

Thickness and diameter of capillary:

Back 3

0.5 micrometer thick wall and 4-9 micrometer diameter
(RBC 7 micrometers, can squeeze through)

Front 4

Pores of capillaries of certain organs:

Back 4

1. Brain: Tight junctions, only allowing small molecules to pass (H2O, O2, CO2)
2. Liver: Wide open clefts (proteins can pass)
3. GIT: Intermediate between liver and brain
4. Glomerulus of kidneys: Fenestrae (allowing large amounts of small molecules to pass, but not proteins)

Front 5

Vasomotion:

Back 5

Intermittent contraction of metarterioles and precapillary sphincters----> intermittend blood flow (on and of)

Front 6

Decreased O2 in tissues:

Back 6

Relaxation of precapillary sphincters---> increased blood flow

Front 7

Diffusion results from

Back 7

Thermal motion of the water molecules and dissolved substances in the fluid, the different molecules and ions moving first in one direction and then another, bouncing randomly in every direction.

Front 8

Lipid soluble molecules (O2, CO2):

Back 8

Can diffuse directly through the membranes. High rate of diffusion

Front 9

Lipid insoluble (Na+, Glc):

Back 9

Can only diffuse through the pores/ interendothelial clefts (slow rate)

Front 10

Permeability of water through pores of skeletal muscle is 1.0, what is the permeability of NaCl and glucose?

Back 10

NaCl: 0.96
Glucose: 0.60

Front 11

Effect of concentration on rate of diffusion:

Back 11

The net rate of diffusion of a substance through any membrane is proportional to the concentration difference of substance between the two sides of the membrane.

Front 12

Composition of interstitial fluid:

Back 12

Same as plasma without large proteins.

Front 13

Main function of lymph:

Back 13

To return back the proteins that leak out of the circulation, back to the circulation

Front 14

Starling forces:

Back 14

1. Capillary pressure (hydrostatic)
2. Interstitial fluid pressure (hydrostatic)
3. Capillary colloid osmotic pressure (oncotic)
4. Interstitial colloid osmotic pressure

Front 15

Formula for rate of filtration:

Back 15

Filtration= Kf (filtration coefficient) x NFP

Front 16

CSF pressure:

Back 16

+ 10 mmHg

Front 17

Brain interstitial fluid pressure:

Back 17

+4- +6

Front 18

Pressure in epidural space:

Back 18

- 4 to - 6 mmHg

Front 19

Average interstitial pressure:

Back 19

- 3 mmHg

Front 20

What creates a negative interstitial pressure:

Back 20

Contracting of lymphatic vessels when pumping lymph into the circulation

Front 21

Colloid osmotic pressure of plasma:

Back 21

28 mmHg. 19 of this caused by proteins, 9 by the Domnan effect; extra osmotic pressure caused by cations such as sodium and potassium

Front 22

Osmotic pressure is determined by:

Back 22

Number of molecules dissolved in fluid rather than by the mass of these molecules.

Front 23

Albumin, concentration and fraction of colloid osmotic pressure:

Back 23

4.5 g/dl and 21.8

Front 24

Globulins, concentration and fraction of colloid osmotic pressure:

Back 24

2.5g/dl and 6.0

Front 25

Fibrinogen, concentration and fraction of colloid osmotic pressure:

Back 25

7.3 g/dl and 0.2

Front 26

Forces tending to move fluid outward at arterial end of capillaries:

Back 26

Capillary pressure: 30
Negative interstitial free fluid pressure: 3
Interstitial colloid osmotic pressure: 8
TOTAL= 41

Front 27

Forces moving fluid inward at arterial end of capillaries:

Back 27

Plasma colloid osmotic pressure: 28

Front 28

Summation of forces out and in of capillaries at arterial ends:

Back 28

Outward: 41
Inward: 28
Net filtration force= 13

Front 29

Forces moving fluid inward in venous end of capillaries:

Back 29

Plasma colloid osmotic pressure: 28

Front 30

Forces moving fluid outward at venous ends of capillaries:

Back 30

Capillary pressure: 10
Negative interstitial free fluid pressure: 3
Interstitial colloid osmotic pressure: 8
TOTAL OUTWARD= 21

Front 31

Summation of forced moving fluid at the venous end of capillaries:

Back 31

Inward: 28
Outward:21
Net reabsorption force: 7

Front 32

Why can 9/10th of the filtrated fluid be reabsorbed with a much lower reabsorption pressure (7) then filtration pressure (13):

Back 32

Because venous capillaries are more numerous and more permeable the arterial capillaries--> less reabsorption pressure is needed.

Front 33

Exceptions where there is no lymph drainage:

Back 33

Superficial portions of the skin
CNS
Endomysium of muscles and bones

Front 34

Total amount of lymph drainage from interstitial fluid per day:

Back 34

1 tenth of the filtrated fluid from capillaries, i.e. 2 to 3 liters each day.

Front 35

Why can lymph "reabsorb" high molecular weight compounds such as many proteins, but not the veins:

Back 35

Because lymph endothelial cells are attached by anchoring filaments and form one way valves allowing fluid to enter lymphatics but not exit .

Front 36

Protein concentration of lymph:

Back 36

Generally the same as interstitial fluid (2-4 g/dl), but might be higher in thoracic duct due to high protein concentration (6 g/dl) in lymph from liver and intestines.

Front 37

Factors increasing interstitial fluid pressure increase lymph flow, e.g.:

Back 37

1. Elevated capillary hydrostatic pressure
2. Decreased plasma colloid osmotic pressure
3. Increased interstitial fluid colloid osmotic pressure
4. Increased permeability of the capillaries.

Front 38

Pressure affecting lymph flow:

Back 38

With increasing pressure up to a maximum at atmospheric pressure (0 mmHg) flow increases. With further increasing pressure flow falls due to compression of lymph vessels.

Front 39

Factors that "pump" lymph:

Back 39

1. Contraction of smooth mm. of lymph after stretching
2. Muscle pump of skeletal muscles
3. Arterial pulsations
4. Compression of tissues by objects outside of the body

Front 40

How do lymph flow control interstitial fluid protein concentration and volume:

Back 40

Proteins leak out of plasma---> increased oncotic pressure---> increased filtration---> increased interstitial space pressure---> increased lymph flow ==> return of excess interstitial proteins and fluid to the circulation.