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4 Cards in this Set
- Front
- Back
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Describe how the skeletal muscle pump works to increase venous return. |
Skeletal muscle is contained on either side of a vein. Skeletal muscle contracts and the vein is squeezed. The valve closest to the heart opens and blood is pushed forward to the heart. The farthest valve from the heart closes to prevent back-flow of blood. |
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Describe how the respiratory pump works to increase venous return. |
Breathing in: diaphragm contracts, pressure on outside of veins of abdominal cavity increases (because abdominal cavity gets smaller). This pushes blood through veins. Also, the pressure in the thorax decreases (because the thorax gets bigger) so the pressure in the thoracic veins decreases. This pulls blood through veins. The blood flows to the heart due to the created pressure gradient. Breathing out: diaphragm relaxes, and the situation reverses. Thoracic venous pressure increases (thorax gets smaller) and blood gets pushed out through veins. Abdominal venous pressure decreases (abdominal cavity gets bigger) and blood gets pulled through veins. |
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Define the relationship that must exist between cardiac output and venous return under normal physiological conditions. |
Cardiac output = venous return |
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Describe the anatomy of the lymphatic system and its physiological role. |
The lymphatic system has its own capillaries that are separate from the blood capillaries. The lymphatic system is parallel to the systemic venous system. Lymphatic capillaries are found in almost all tissue and organs, and are permeable to anything found in the interstitial fluid, even proteins. Lymphatic capillaries become bigger and bigger until they end in two lymphatic ducts, which empty into the subclavian veins in the lower neck. There are valves here to keep blood from getting into the lymphatic system. Lymphatic capillaries carry extra proteins back to the heart and therefore back into the bloodstream that have leaked out from systemic capillaries into the interstitial space. The lymphatic system prevents extra fluid buildup in the interstitial space by reabsorbing it into the lymphatic system (and dumping it back into bloodstream via subclavian veins). About 4 L/day of excess fluid is taken up by the lymphatic system. |
