Term
| Microcirculation includes all vessels less than ______. What vessels are included in this? |
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Definition
100 um arterioles, capillaries, and venules |
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Term
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Definition
Branch from arterioles and give rise to capillaries or can also serve as bypass channels to the venules; 10-20 um |
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Term
| Which vessels have no sympathetic innervation? |
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Definition
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Term
| Describe the characteristics of capillaries |
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Definition
| 4-10 um in diameter; the walls of the capillaries contain no connective tissue or smooth muscle; they consist of a thin tube of endothelial cells with the capillary wall beign only one cell thick; they have no sympathetic innervation |
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Term
| Where is capillary density high? |
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Definition
| Metabolically active tissue; for example, the heart |
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Term
| What is the capillary flow velocity? What is vasomotion? |
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Definition
0-5 mm/sec Vasomotion is the variation in capillary flow rate; it is due to contraction and relaxation of precapillary vessels |
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Term
| Describe capillary blood flow |
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Definition
| Red blood cells tend to flow in single file formation and are usually folded; in between the rbcs is a bolus of plasma which exhibits turbulent flow characteristics; this mixing of plasma helps to expose all of the plasma to the endothelial surface exchange area |
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Term
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Definition
| Blood flows through capillaries which provides for exchange of nutrients and metabolites |
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Term
| What is non-nutrient flow? |
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Definition
| The blood flow bypasses the capillaries and passes directly from arterioles to venules; true shunts exist in certain areas of the body such as fingertips |
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Term
| What are the major physiological mechanisms modifying vessel radius? |
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Definition
Metabolic activity Activity of autonomic nerves Circulating vasoactive agents Endothelium-derived vasoconstrictors and dilators |
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Term
| What is the primary function of vascular smooth muscle in venules? |
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Definition
| Altering vascular capacitance; has very little effect on vascular flow |
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Term
| What type of stimulation are arterioles most sensitive to? |
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Definition
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Term
| What type of stimulation are precapillary sphincters most sensitive to? |
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Definition
| Tissue metabolites; such as H+, CO2, lactic acid, and adenosine |
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Term
What is vasomotor tone? How is constriction stimulated? Dilation? |
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Definition
Vasomotor tone is tonic neural activity that is always present in sympathetic efferent fibers from the pressor centers in the medulla Constriction is stimulated by increasing neural activity in sympathetic efferents Dilation occurs passively by reducing sympathetic efferent activity |
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Term
Is active vasodilation in vascular beds possible? How is it mediated? |
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Definition
It is possible in some vascular beds It is mediated by sympathetic cholinergic fibers |
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Term
| By-products of metabolism, such as H+ and lactic acid, are all local ________ |
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Definition
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Term
| Oxygen is a vasodilator or a vasoconstrictor? |
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Definition
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Term
| Exchange vessels include what? |
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Definition
| Capillaries, portions of terminal arterioles, and venules not encircled with smooth muscle |
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Term
| Which end of the capillary is most permeable? |
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Definition
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Term
| What are the four types of exchange vessel endothelium and where are they found? |
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Definition
Continuous endothelium - skin, skeletal muscle, smooth muscle, cardiac muscle, and lungs Fenestrated endothelium - GI mucose, renal glomerulus, peritubular capillaries Discontinuous endothelium - liver and bone marrow sinusoids and spleen Tight junction endothelium - CNS and retina |
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Term
| What are the three ways in which substances are taken across the vascular endothelium? |
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Definition
| Simple diffusion, bulk flow (ultrafiltration), and vesicular transport |
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Term
| What functions as the exchange compartment? |
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Definition
| Interstitial fluid; both capillary and cellular exchange processes are accomplished through the interstitial fluid |
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Term
| What 3 factors are involved in movement of substances at the capillary level? |
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Definition
Transport across capillary wall Transport across tissue cell membrane Diffusion distance |
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Term
| Which law describes the characteristics of diffusion? |
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Definition
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Term
| The rate of diffusion in capillaries for most substances is determined by? |
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Definition
| Interstitial fluid concentration |
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Term
| Diffusion of solutes in capillaries can be limited by what? |
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Definition
| Interaction between solute molecules, pore configuration, and charge |
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Term
| What is meant by flow limited diffusion? |
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Definition
| For small molecules less than 60,000 molecular weight, the primary limitation to diffusion across the capillary wall is the rate of delivery of the substance in the blood flow |
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Term
| The rate of diffusion of a substance depends on what? |
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Definition
| Blood-interstitial fluid concentration gradient, membrance characteristics relative to the substance in question, and molecular characteristics of the substance |
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Term
| What is ultrafiltrate? Why is it important? |
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Definition
Ultrafiltrate is plasma which has been seperate from its large molecular weight proteins (colloids); it constantly shifts back and forth between the vascular space and the interstitial space Only about 2% of plasma flowing through the vascular system is involved in ultrafiltration, however, this amounts to about 144 L per day; it aids the diffusion process by keeping tissue fluids in a constant state of motion; regulates plasma volume |
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Term
| What does the Starling Hypothesis describe? |
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Definition
The relationship between the forces governing blood-tissue exchange by ultrafiltration; it predicts the direction of fluid movement along the capillary It relates the follow four variables: Capillary hyrdostatic pressure Interstitial fluid hydrostatic pressure Plasma protein oncotic pressure Interstitial fluid oncotic pressure |
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Term
| What is hydrostatic pressure? What determines it? |
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Definition
Capillary hydrostatic pressure is the principle force favoring filtration across the capillary wall It is determined by: Arterial pressure Venous pressure Precapillary resistance Postcapillary resistance |
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Term
| Tissue colloid osmotic pressure favors _________. Hydrostatic forces favor __________. |
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Definition
reabsorption back into the capillary filtration into the interstitial spaces |
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