Term
| T/F. Metarteriols have a continuous smooth muscle layer. |
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Definition
| False. Metarterioles lack a continuous smooth muscle coat, however smooth muscle fibers do encircle metarterioles at intermittent points. |
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Term
| What is the main function of capillaries? |
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Definition
| To permit rapid exchange of gases, water, and solutes with interstitial fluid. |
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Term
| What is the major function of arterioles? |
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Definition
| Arterioles are resistance vessels that regulate regional blood flow to the capillary beds. |
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Term
| What is the main function of venules and veins? |
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Definition
| Serve primarily as collecting channels and storage vessels. |
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Term
| What substances pass through capillaries via diffusion? |
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Definition
-gases
-lipid soluble substance (steroid hormones, anesthetics)
-fluid and electrolytes, in part |
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Term
| What variables influence the rate of diffusion of substances? |
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Definition
-the ease w/ which a substance can pass through a capillary wall
-sufrace area available for diffusion
-concentration difference across the barrier
-diffusion distance |
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Term
| What substances are transported from the capillaries via bulk flow? How does this occur? |
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Definition
| Water electrolyes and small moelecules (lipid insoluble substances). Bulk flow occurs through intercellular clefts between endothelial cells. |
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Term
| What are the three different types of capillaries? What are their differences? |
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Definition
-Continuous capillaries-have very tight endothelium and continuous basement membrane
-Fenestrated capillaries-have perforations in the endotheilium resulting in relatively high permeability and bulk flow (exocrine glands, renal glomeruli, and intestinal mucosa)
-Discontinuous capillaries-have large intercellular gaps as well has gaps in the basement membrane, resulting in the highest permeability (liver, spleen, bone marrow) |
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Term
| What molecules are transported across the capillaries via vesicular transport? How big of a role does vesicular transport play in transcapillary exchange? |
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Definition
| Macromolecules such as proteins are transported across the capillaries via vesicular transport. Plays a relatively minor role in transcapillary exchange. |
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Term
| What molecules are transported via active transport? Where is this mechanism of exchange used (in regards to the circulatory system)? |
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Definition
| Some ions, glucose, amino acids, and other molecules are transported via active trnasport. This mechanism is typically used for exchange between an individual cell and its surrounding fluid. |
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Term
| What is carbon dioxide removal dependent on? |
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Definition
| Depends primarily on blood flow--it is not diffusion limited. |
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Term
| Where is most fluid returned to the blood at? |
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Definition
| Most of the filtered fluid returns to the blood at the venular end of capillaries or at the postcapillary venules. |
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Term
| What percentage of capillary filtration is transported out of the tissues by the lymphatics? |
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Definition
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Term
| What are the three physical mechanisms that determine fluid movement across a capillary? |
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Definition
-oncotic pressure
-hydrostatic pressure
-permeability of the capillary wall |
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Term
| What are Starling forces? |
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Definition
Starling forces are four primary hydrostatic and oncotic pressure that determine fluid movement through the capillary membrane.
-capillary pressure (Pc) which tends to force fluid outward through the capillary membrane
-interstitial fluid pressure (Pif or Pi), which tends to force fluid inward through the capillary membrane
-capiilary plasma colloid osmotic (or oncotic) pressure (pi p or pi c) which tends to cause osmosis of fluid inward through the capillary membrane
-interstitial fluid colloid osmotic (or oncotic) pressure (pi if or pi i) which tends to cause osmosis of fluid outward through the capillary membrane |
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Term
| What is colloid or osmotic pressure? |
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Definition
| A form of osmotic pressure that is exerted by proteins in blood plasma or interstitial fluid |
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Term
| What happens if the sum of Starling forces are positive? Negative? |
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Definition
| If the net driving force is positive then there is net fluid filtration across the capillaries (more fluid flowing into interstitial space from capillaries). If the sum of the forces is negative then there is net absorption from the interstitial spaces into the capillaries. |
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Term
| Where is capillary hydrostatic pressure hightest? |
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Definition
| At the arteriolar end of the capillary and lowest at the venular end. Therefore filtration is favored at the arteriolar end. |
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Term
| What does the lymphatic system collect? |
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Definition
| Fluid and proteins that have escaped from blood and transports them back into the veins for recirculation in blood |
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Term
| T/F. Substances of high molecular weight, such as proteins, cannot enter the lymphatics. |
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Definition
| Falso. Substances of high molecular weight can enter the lymphatic capillaries almost unimpeded. |
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