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Phys Exam 2: Ch 16

Capillaries & Lymph

What is a precapillary sphincter? A smooth muscle cell around the beginning of a capillary
Define vasomotion Intermittent contraction of the precapillary sphincters
What is the flow rate generally dependent upon? Local O2 concentration affecting the precapillary sphincter
TRUE or FALSE: "True" capillaries have no smooth muscle TRUE
Describe the structure of a capillary The wall is a single layer of ECs w/a basement membrane on the outside; there are prominent intercellular clefts
TRUE or FALSE: Individual epithelial cells have no intercellular clefts FALSE: ECs are separated by intercellular cleft, thru which fluid & small dissolved molecules can flow
What is the fxn of the plasmalemma in regards to material transport? Plasmalemmal vesicles can "ferry" specific material thru the cell
What are vesicular channels? Rare combinations of vesicles
What sorts of nutrients can diffuse directly thru a cell membrane? Lipid-soluble materials (O2, CO2)
How do water soluble materials diffuse? Diffuse only thru intercellular clefts ("pores"); H2O can fit easily, serum albumin can barely fit
Compare the pores of the brain vs. the pores in the liver Brain: pores are almost sealed by tight jxns; Liver: pores are much larger
Define interstitial fluid Fluid in the spaces b/n the cells
Describe interstitial fluid Bundles of collagen fibers and proteoglycan filaments form a gel w/the plasma water, slowing bulk flow, but not small nutrient diffusion
What happens when there is a lot of intercellular water flow? Edema
What determines the osmotic pressures of a capillary? Primarily by protein concentrations
How do you calculate net filtration pressure? NFP = Capillary pressure - Interstitial fluid pressure - Plasma colloid pressure + interstitial fluid colloid osmotic pressure
Which forces are responsible for the pressure pushing/pulling out of the capillary? Pushing/pulling into the capillary? OUT = Capillary pressure (Pc), Interstitial fluid colloid osmotic pressure (Pi-if); IN = Plasma colloid osmotic pressure (Pi-p), Interstitial fluid pressure (Pif)
What is the value of capillary hydrostatic pressure when indirectly measured? By an isogravimetric method - ~17mmHg
What is the value of capillary hydrostatic pressure when measured by a micropipette? Why does this average out to be about the same as measuring indirectly? ~25mmHg; when the precapillary sphincter is closed, pressure equals that of a venule (~10mmHg), so the pressure averages ~17mmHg
What is the value of interstitial fluid hydrostatic pressure in loose subQ tissue? -2 to -3 mmHg
What is the value of interstitial fluid hydrostatic pressure in synovial spaces of joints? ~ -5mmHg
What is the value of interstitial fluid hydrostatic pressure in the epidural space? ~ -5mmHg
What is the value of interstitial fluid hydrostatic pressure in the intrapleural space? ~ -8mmHg
What causes the negative interstitial fluid hydrostatic pressure values? Removal of fluid from the interstitial space by the lymph system.
Describe Plasma Colloid Osmotic Pressure Plasma osmotic pressure (Pip) depends upon the protein concentration (colloid): most solutes pass thru the capillary wall, but plasma proteins normally do not.
What is normal value of plasma colloid osmotic pressure, and what causes this value? Normal = 28mmHg; 19mmHg due to dissolved protein, 9mmHg due to Na & K "held" by that protein (called the Donnan effect)
What is interstitial fluid osmotic pressure? What is the normal value Some protein does leak from the plasma; Net interstitial fluid (Pi-if) = 8mmHg
What is the net filtration force at the ARTERIAL end of the capillary? Does this value indicate net fluid into or out of the capillary? Outward forces = 41mmHg; Inward forces = 28mmHg; NET forces = 13mmHg; NET is OUTWARD
What is the net filtration force at the VENOUS end of the capillary? Does this value indicate net fluid into or out of the capillary? Outward forces = 21mmHg; Inward forces = 28mmHg; NET forces = 7mmHg; NET is INWARD
What force moves plasma out of the capillaries? Hydrostatic force (BP)
What force moves plasma back into the venules? Osmotic pressure
Why does it not patter that filtration pressure (13mmHg) is greater than reabsorption pressure (7mmHg)? Venules are more numerous & more permeable (remember, venous is net INWARD), and the lymph system picks up the extra (~2mL/min)
What are the 5 functions of the lymphatic system? 1. Returns ~3L fluid/day to circulation; 2. Returns serum proteins to the circulation; 3. Clears tissue debris out of interstitial spaced; 4. Absorption of fats from digestive system; 5. Concentration of bacteria in lymph nodes
What drains into the left thoracic lymph duct? Lymphatics from the lower half of the body, left arm, shoulder, and upper chest
Where does the left thoracic duct join? The left thoracic duct joins the left subclavian vein hear the jxn w/the internal jugular vein
What drains into the right lymphatic duct? Lymphatics from the right arm, shoulder,and upper chest
Where does the right thoracic duct join? The right lymphatic duct joins the right subclavian vein near the jxn w/the right internal jugular vein
Discuss the valves of the lymphatic capillaries At each EC overlap, the inside cell is anchored farther from its end, creating 1-way flaps available when interstitial pressure increases.
What happens when the pressure equilibrates and the lymphatic capillary is compressed? The valves remain closed
What is the space b/n the flat ECs? Lymphatic capillary
What are the cellular extensions into the main lymphatic channel called? Valves of the lymphatic capillary
What happens when interstitial pressure is greater than the intra-lymphatic pressure? The valves are pushed open
What happens when the lymphatics are compressed? The intracellular valves close and the secondary valves are opened.
What are the forces driving lymph flow Smooth muscle cells on the walls of each lymphatic capillary contract when stretched. Contraction of adjacent skeletal muscles, pulsation of adjacent arteries, and external compression of body tissue all compress the lymphatic capillaries.
When smooth muscle cells on the walls of lymphatic capillaries contract, about how high can the pressure in the large thoracic duct reach? 50-100mmHg
Created by: hclark86



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