Concept explainers
Introduction:
Due to the presence of small vessels, it is hard to measure the pressure in the capillaries. These factors make it difficult to understand the mechanism of the capillary exchange; theories of capillary exchange remain disputed. The stereomicroscope observation on the fingernail bed and eponychium has been the basis of study. The blood pressure of capillaries at the arterial end is about 32 mm Hg, and 15 mm Hg is found in the venous end. Due to their small narrow vessels, the blood pressure drops rapidly. The three routes in which the chemicals pass through capillary walls are the endothelial cell cytoplasm, intercellular clefts between the endothelial cells, and filtration pores of the fenestrated capillaries. The chemicals move through the capillary wall by diffusion, filtration, transcytosis, and reabsorption.
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- What force is responsible for moving fluids out of capillaries at the arteriole end and moving fluids back into the capillary at the venule end? What happens to fluids that do not re-enter the capillaries?arrow_forwardWhat is the vasa vasorum? What is its function?arrow_forwardWhat four variables determine the net filtration pressure across the capillary wall? Give representative values for each of them at the arteriolar and venous ends of a systemic capillary.arrow_forward
- Hydrostatic pressure inside the capillary = 34 mmHgColloid osmotic pressure of the blood plasma = 27 mmHgHydrostatic pressure in the interstitial fluid = 2 mmHgColloid osmotic pressure in the interstitial fluid = 4 mmHgWhat is the total pressure favoring filtration?What is the total pressure favoring absorption?What is the net effect of these forces on fluid movement across the wall of the capillary?arrow_forwardWith respect to the hydrostatic pressure and osmotic pressure, which one is greater at the capillary end, and which one is greater at the venous end?arrow_forwardWhat is colloid osmotic pressure? In which direction does colloid osmotic pressure drive the movement of water in a capillary?arrow_forward
- Given the following pressures on the venous end of a capillary, calculate the NET pressure and determine if this pressure is in favor of filtration or reabsorption. Blood pressure: 15 mmHg Hydrostatic pressure in the tissues: -3 mmHg Colloid Osmotic Pressure in a capillary: 28 mmHg Colloid Osmotic Pressure in tissue: 8 mmHgarrow_forwardAccording to Poiseuille's Law, vasodilation is associated with increased blood flow. Knowing that capillaries cannot change diameter but arterioles can, how do your observations support this?arrow_forwardWhy does the total cross-sectional area in the capillary system lower the resistance to flow?arrow_forward
- What is the function of the kidney in regulating erythrocyte concentration within the blood?arrow_forwardWhy is the fluid movement out of a capillary greater at its arteriolar end than at its venular end?arrow_forwardWhich vessels have the slowest velocity of flow? Why is this functionally important?arrow_forward
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