Bulk flow - Factors that influence bulk flow
Date Uploaded: 10/08/2019
Tags: homeworkclinic.com Homework Clinic HWC interstitial fluid interstitium reabsorption capillary exchange Blood hydrostatic pressure Blood colloid osmotic pressure Interstitial fluid osmotic pressure Interstitial fluid hydrostatic pressure Net filtration pressure and lymph formation lymphatic capillaries edema capillary hydrostatic pressure Blood velocity
• Bulk flow helps regulate the relative volumes of blood and interstitial fluid. • Flow from blood to interstitium is called filtration. ■ Flow from interstitium to blood is called reabsorption. ■ Four factors determine the net direction of capillary exchange. ■ These factors include: • Blood hydrostatic pressure (BHP), which pushes fluid out of the capillary and promotes filtration. • Blood colloid osmotic pressure (BCOP), which acts as if it "pulls" fluid into the capillary and promotes reabsorption. • Interstitial fluid osmotic pressure (IFOP), which is the slight pull of fluids towards the interstitium promoting filtration. • Interstitial fluid hydrostatic pressure (IFHP), which is near zero under normal conditions. Net filtration pressure and lymph formation • The net filtration pressure (NFP) is the force promoting filtration minus the force promoting reabsorption. ■ At the arterial end of an ideal capillary, the filtration pressures are stronger. The result: net filtration. ■ At the venous end of an ideal capillary, the reabsorption pressures are stronger. The result: net reabsorption. ■ About 90% of the fluid that is filtered at the arterial end is reabsorbed at the venous end. ■ The remaining fluid drains into lymphatic capillaries to form lymph. Edema ■ An abnormal buildup of interstitial fluid results in swelling known as edema. • Major causes of edema include: • Increased capillary hydrostatic pressure • Increased capillary permeability • Decreased blood colloidal osmotic pressure • Blockage of lymphatic drainage Blood velocity ■ Blood velocity is inversely related to total cross-sectional area; the greater the area, the slower the velocity. • Capillaries have a higher total cross-sectional area; therefore blood flows more slowly. ■ Slower blood flow allows greater time for exchange of materials. ■ Arteries and veins have lower total cross-sectional areas; blood flows more quickly. • Blood velocity slows as blood travels away from heart, increases as it returns to heart.
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