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81 Cards in this Set
- Front
- Back
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Most important function of circulation; where it occurs:
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Transport of nutrients to tissues, removal of cell excreta; in microcirculation.
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What controls diameters of arterioles?
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Local conditions in the tissues around the arterioles
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What controls blood flow to tissues?
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Arterioles
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Total surface area and number of capillaries in the body:
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SA = 500 - 700 square meters
Total # = about 10 billion |
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Internal Diameter of:
-Arterioles -Capillaries |
Arterioles = 10 - 15 um
Capillaries = 5 - 9 um |
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Which has muscle?
-Arteriole -Metarteriole -Capillary |
Arteriole = abundant muscle
Metarteriole = intermittent Capillary = No smooth muscle except at origin from metaart. |
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What is the point of junction between a metaarteriole and capillary characterized by?
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A Precapillary sphincter - smooth muscle fiber encircling the capillary.
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What is the structure of a capillary wall like?
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-Single layer epithelial cells
-Membrane is 0.5 um thick -Internal diameter 4-9 um -Surrounded by basement memb. |
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What are Intercellular clefts?
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Pores in the endothelial capillary membrane.
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What are Intercellular clefts for?
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Free percolation of fluid between the capillary and interstitial fluid
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How wide is an intercellular cleft?
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6-7 nm - just a little bigger than Albumin
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What are Plasmalemmal Vesicles?
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Small vesicles that take up plasma or ECF and then diffuse through the endothelial cell
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What are pores in the endothelial cells of the brain like?
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Very small so that only water, O2, and CO2 can pass in/out of brain tissue.
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What connects the endothelial cells in brain capillaries?
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Tight junctions
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What are pores in liver capillaries like?
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Wide - to let nutrients and even plasma proteins through.
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What are pores in GI capillary membranes like?
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A little bit wider but not as much as in the liver.
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What are pores in the capillary membranes of the Glomerulus like?
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Fenestrated - allowing tremendous amounts of very small molecules/ions to filter through.
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How are fenestrae different from Intercellular clefts?
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They are pores passing right through middle of endothelial cells - not between like clefts.
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What is bloodflow like in capillaries?
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Not continuous; intermittent.
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What allows for intermittency of bloodflow in capillaries?
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Vasomotion
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Define vasomotion
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Intermittent contraction of metarterioles and precapillary sphincters
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What is the main regulator of vasomotion?
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O2 concentration in the tissues
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How are substances transferred between plasma and interstitium?
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Via diffusion primarily
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What causes diffusion?
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Thermal motion of water molecules and dissolved substances in the fluid.
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What can diffuse directly through capillary endothelial cells?
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Lipid-soluble substances:
-Oxygen -Carbon dioxide |
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What can't just diffuse through the capillary endothelium?
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Water-soluble, lipid-insoluble substances
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What specifically has to go through intercellular pores?
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-Water
-Na Cl ions -Glucose |
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How much of the capillary surface area (total) consists of intercellular clefts?
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Not more than 1/1000
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What is the rate of water compare to plasma movement?
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Water diffuses through pores 80x faster than plasma actually moves through capillaries.
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What are the 4 most permeable substances at muscle capillary pores?
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-Water (freely)
-NaCl -Urea -Glucose |
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What determines the permeability of a substance?
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Its diameter size - water is 20x less than the intercellular cleft diameter
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What does the rate of diffusion of a substance through a capillary membrane depend on?
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Concentration gradient of that substance on either side of the wall.
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How much of the body consists of interstitium?
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1/6
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2 Types of Solid Structure in interstitium:
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-Collagen fiber bundles
-Proteoglycan filaments |
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Purpose of collagen fiber bundles in interstitium:
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Tensional strength
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Where is interstitial fluid found?
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In spaces between proteoglycan filaments (the brushy reticular network of them).
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What is Interstitial fluid made of?
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Same stuff as plasma minus the plasma proteins
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What do proteoglycan filaments and interstitial fluid together make?
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A TISSUE GEL
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What are Rivulets?
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Small pockets of freely flowing interstitial fluid not constrained by tissue gel.
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When do rivulets and free fluid in the interstitium increase?
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In edema
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What forces determine filtration in capillaries?
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Starling's forces
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NFP is what
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Sum of starling forces
-Hydrostatic F inside/outside -Osmotic F inside/outside |
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What is the eqn for NFP?
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Pc-Pif-Pip+Piif
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What is the normal NFP?
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Slightly positive - net filtration into tissues
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What determines the RATE of capillary filtration?
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-# of capillaries thru which blood is flowing
-# and size of pores in capillaries |
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What term encompasses the factors determining filtration rate?
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Kf - Capillary filtration coefficient
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Define Kf
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A measure of the capacity of capillary membranes to filter water for a given NFP
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Units of Kf
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ml/min/mmHg
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How is filtration rate of a capillary calculated?
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Frate = Kf x NFP
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2 Methods for estimating Capillary hydrostatic pressure:
What pressure did each give? |
1. Direct micropipette cannulation - 25 mm Hg
2. Indirect functioal measurement - 17 mm Hg |
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How is micropipette cannulation done?
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By shoving a pipette right into the capillary and measuring pressure.
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What does the gravimetric method for measuring Pc tell you?
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The functional hydrostatic pressure in a capillary
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What is the functional Pc in a normal capillary?
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17 mm Hg.
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What's more accurate; cannulation or gravimetric?
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Gravimetric
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3 Most Common methods for msring Interstitial Fluid Hydrostatic Pressure:
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1. Micropipette cannulation
2. Implanted perforated capsules 3. Cotten wick insert in tissue |
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What pressure does the micropipette cannulation of interstitium give?
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That of a free fluid pocket - b/c the tip can't be small enough to fit between proteoglycans.
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What is the interstitial fluid pressure in loose subcutaneous tissue?
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Negative: -3 mm Hg
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What causes the tissue pressure to be negative?
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Pumping by the lymphatic system.
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What is another name for Colloid Osmotic Pressure?
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Oncotic pressure
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Normal Colloid Osmotic pressure of human plasma:
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28 mm Hg
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What are the actual components of Plasma oncotic pressure?
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-19 mm Hg is protein
-9 mm Hg is cation held onto by the negatively charged protein |
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What is the term for proteins holding onto cations in plasma?
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Donnan effect
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What are the plasma proteins?
What does each contribute to oncotic pressure? |
Albumin - 21.8 mm Hg
Globulins - 6.0 mm Hg Fibrinogen - 0.2 mm Hg |
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Average interstitial fluid oncotic pressure:
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8 mm Hg
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What is the avg NFP at the arterial end of a capillary?
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13 - moves fluid out
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What is the avg NFP at the venous end of a capillary?
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-7
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Why is the NFP negative at the venous end of a capillary?
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Because the hydrostatic pressure inside the capillary is reduced from 30 to 10
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How much fluid that is filtered at the arterial end of a capillary is reabsorbed at the venous end?
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9/10
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What happens to the other 1/10 of the filtered fluid?
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It is absorbed into the lymph system.
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What is the normal Starling's equilibrium value for NFP?
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0.3 outward
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What happens to the 0.3 mm Hg caused fluid that is filtered?
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Returned to circulation via the lymphatic system.
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What is the normal rate of net filtration in the entire body?
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2 mL/min
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What is the value of the whole body capillary filtration coefficient?
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6.67 ml/min/mm Hg
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What is important to remember about the filtration coefficient?
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It varies a TON between different body tissues
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Where is the filtration coeff:
-Large -Medium -Small |
Extreme = kidney/liver
Large = intestine Medium = subcutaneous tissue Small = brain/muscle |
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What happens to filtration if the mean capillary pressure rises from 17 to 37 mm Hg?
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There will be 68x more net filtration, the lymphatics wouldn't be able to handle it, EDEMA would ensue.
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What happens if the mean capillary pressure fell very low?
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Net reabsorption; tissue fluid would decrease and plasma volume would increase.
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Main function of the lymphatic system:
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to remove protein and large particulate matter from the ISF and return it to circulation.
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Total amt of lymph typically recycled in a day:
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2-3 L
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What attaches lymphatic capillary endothelial cells to surrounding connective tissue?
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Anchoring filaments
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What allows lymphatic capillaries to absorb proteins and large molecules?
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The design of adjacent cells; they overlay ea other creating a flap/valve. Fluid can enter but can't leave.
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