This movement, often referred to as bulk flow, involves two pressure-driven mechanisms: Volumes of fluid move from an area of higher pressure in a capillary bed to an area of lower pressure in the tissues via filtration. In contrast, the movement of fluid from an area of higher pressure in the tissues into an area of lower pressure in the capillaries is reabsorption. Two types of pressure interact to drive each of these movements: hydrostatic pressure and osmotic pressure.
The primary force driving fluid transport between the capillaries and tissues is hydrostatic pressure, which can be defined as the pressure of any fluid enclosed in a space. Blood hydrostatic pressure is the force exerted by the blood confined within blood vessels or heart chambers. Even more specifically, the pressure exerted by blood against the wall of a capillary is called capillary hydrostatic pressure CHP , and is the same as capillary blood pressure.
CHP is the force that drives fluid out of capillaries and into the tissues. As fluid exits a capillary and moves into tissues, the hydrostatic pressure in the interstitial fluid correspondingly rises. This opposing hydrostatic pressure is called the interstitial fluid hydrostatic pressure IFHP. Generally, the CHP originating from the arterial pathways is considerably higher than the IFHP, because lymphatic vessels are continually absorbing excess fluid from the tissues.
Thus, fluid generally moves out of the capillary and into the interstitial fluid. This process is called filtration. The net pressure that drives reabsorption—the movement of fluid from the interstitial fluid back into the capillaries—is called osmotic pressure sometimes referred to as oncotic pressure. Whereas hydrostatic pressure forces fluid out of the capillary, osmotic pressure draws fluid back in. Osmotic pressure is determined by osmotic concentration gradients, that is, the difference in the solute-to-water concentrations in the blood and tissue fluid.
A region higher in solute concentration and lower in water concentration draws water across a semipermeable membrane from a region higher in water concentration and lower in solute concentration.
As we discuss osmotic pressure in blood and tissue fluid, it is important to recognize that the formed elements of blood do not contribute to osmotic concentration gradients. Rather, it is the plasma proteins that play the key role. Solutes also move across the capillary wall according to their concentration gradient, but overall, the concentrations should be similar and not have a significant impact on osmosis. Because of their large size and chemical structure, plasma proteins are not truly solutes, that is, they do not dissolve but are dispersed or suspended in their fluid medium, forming a colloid rather than a solution.
The pressure created by the concentration of colloidal proteins in the blood is called the blood colloidal osmotic pressure BCOP. Its effect on capillary exchange accounts for the reabsorption of water. The plasma proteins suspended in blood cannot move across the semipermeable capillary cell membrane, and so they remain in the plasma. As a result, blood has a higher colloidal concentration and lower water concentration than tissue fluid.
It therefore attracts water. We can also say that the BCOP is higher than the interstitial fluid colloidal osmotic pressure IFCOP , which is always very low because interstitial fluid contains few proteins.
Thus, water is drawn from the tissue fluid back into the capillary, carrying dissolved molecules with it. The thin walls of the capillaries facilitate this diffusion. Hydrostatic pressure. Blood and Oxygen. Carbon dioxide enters the bloodstream at the systemic capillaries. It leaves the bloodstream at the alveolar capillaries. Fluid and particles absorbed into lymph capillaries. Oxygen enter the capillaries by diffusion due to difference in oxygen concentrations.
Blood flows in capillaries, but there is blood leaks out from the capillaries, known as tissue fluid or interstitial fluid. An increase in capillary pressure will shift fluid into or out of the capillaries. The only place gas can enter or leave the blood stream is in the capillaries. Interstitial fluid is left over fluid from the blood capillaries. The blood capillaries will get lots of pressure causing them to get full, fluid is then leaked out into surrounding tissue.
This fluid is called interstitial fluid. The lymphatic capillaries then suck this fluid up. It is now lymph. The lymphatic system then transports it back to the bloodstream. Fluid enters the lymphatic system this system returns fluid and proteins to blood by diffusing into lymph capillaries. This fluid is now called lymph and is kind of like interstitial fluid in composition. This movement of fluid is determined by net balance.
It only diffuses into the capillaries if there isn't enough fluid there to begin with. Generally the blood pressure at arterial end of the capillaries is about 30 mm of mercury. The blood pressure at the venous end of the capillaries is about 15 mm of mercury. The fluid exit the capillaries at arterial end. Fluid enters the capillaries at venous end. The capillaries are the site of diffusion of wastes, oxygen, and nutrients. This allows these materials to enter and leave body tissues.
False, would increase the amount of fluid leaving the capillaries. Plants also exchange gases through diffusion during photosynthesis and respiration. When photosynthesis occurs, carbon dioxide diffuses into the leaf through the stomata pores, or tiny holes, in the leaf while oxygen moves out of the leaf in the same way. NOTE : stomata is plural, stoma is singular.
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