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40 Cards in this Set
- Front
- Back
Number of peripheral capillaries and total surface area:
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10 billion capillaries with 500- 700 square meters surface area.
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Usual distance of a functioning cell from a capillary:
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20- 30 micrometers
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Thickness and diameter of capillary:
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0.5 micrometer thick wall and 4-9 micrometer diameter
(RBC 7 micrometers, can squeeze through) |
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Pores of capillaries of certain organs:
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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) |
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Vasomotion:
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Intermittent contraction of metarterioles and precapillary sphincters----> intermittend blood flow (on and of)
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Decreased O2 in tissues:
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Relaxation of precapillary sphincters---> increased blood flow
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Diffusion results from
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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.
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Lipid soluble molecules (O2, CO2):
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Can diffuse directly through the membranes. High rate of diffusion
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Lipid insoluble (Na+, Glc):
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Can only diffuse through the pores/ interendothelial clefts (slow rate)
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Permeability of water through pores of skeletal muscle is 1.0, what is the permeability of NaCl and glucose?
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NaCl: 0.96
Glucose: 0.60 |
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Effect of concentration on rate of diffusion:
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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.
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Composition of interstitial fluid:
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Same as plasma without large proteins.
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Main function of lymph:
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To return back the proteins that leak out of the circulation, back to the circulation
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Starling forces:
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1. Capillary pressure (hydrostatic)
2. Interstitial fluid pressure (hydrostatic) 3. Capillary colloid osmotic pressure (oncotic) 4. Interstitial colloid osmotic pressure |
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Formula for rate of filtration:
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Filtration= Kf (filtration coefficient) x NFP
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CSF pressure:
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+ 10 mmHg
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Brain interstitial fluid pressure:
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+4- +6
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Pressure in epidural space:
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- 4 to - 6 mmHg
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Average interstitial pressure:
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- 3 mmHg
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What creates a negative interstitial pressure:
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Contracting of lymphatic vessels when pumping lymph into the circulation
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Colloid osmotic pressure of plasma:
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28 mmHg. 19 of this caused by proteins, 9 by the Domnan effect; extra osmotic pressure caused by cations such as sodium and potassium
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Osmotic pressure is determined by:
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Number of molecules dissolved in fluid rather than by the mass of these molecules.
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Albumin, concentration and fraction of colloid osmotic pressure:
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4.5 g/dl and 21.8
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Globulins, concentration and fraction of colloid osmotic pressure:
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2.5g/dl and 6.0
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Fibrinogen, concentration and fraction of colloid osmotic pressure:
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7.3 g/dl and 0.2
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Forces tending to move fluid outward at arterial end of capillaries:
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Capillary pressure: 30
Negative interstitial free fluid pressure: 3 Interstitial colloid osmotic pressure: 8 TOTAL= 41 |
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Forces moving fluid inward at arterial end of capillaries:
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Plasma colloid osmotic pressure: 28
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Summation of forces out and in of capillaries at arterial ends:
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Outward: 41
Inward: 28 Net filtration force= 13 |
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Forces moving fluid inward in venous end of capillaries:
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Plasma colloid osmotic pressure: 28
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Forces moving fluid outward at venous ends of capillaries:
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Capillary pressure: 10
Negative interstitial free fluid pressure: 3 Interstitial colloid osmotic pressure: 8 TOTAL OUTWARD= 21 |
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Summation of forced moving fluid at the venous end of capillaries:
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Inward: 28
Outward:21 Net reabsorption force: 7 |
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Why can 9/10th of the filtrated fluid be reabsorbed with a much lower reabsorption pressure (7) then filtration pressure (13):
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Because venous capillaries are more numerous and more permeable the arterial capillaries--> less reabsorption pressure is needed.
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Exceptions where there is no lymph drainage:
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Superficial portions of the skin
CNS Endomysium of muscles and bones |
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Total amount of lymph drainage from interstitial fluid per day:
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1 tenth of the filtrated fluid from capillaries, i.e. 2 to 3 liters each day.
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Why can lymph "reabsorb" high molecular weight compounds such as many proteins, but not the veins:
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Because lymph endothelial cells are attached by anchoring filaments and form one way valves allowing fluid to enter lymphatics but not exit .
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Protein concentration of lymph:
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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.
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Factors increasing interstitial fluid pressure increase lymph flow, e.g.:
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1. Elevated capillary hydrostatic pressure
2. Decreased plasma colloid osmotic pressure 3. Increased interstitial fluid colloid osmotic pressure 4. Increased permeability of the capillaries. |
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Pressure affecting lymph flow:
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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.
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Factors that "pump" lymph:
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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 |
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How do lymph flow control interstitial fluid protein concentration and volume:
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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.
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