Answer
In a model capillary, the relative amounts of fluid given off (filtration) and reabsorbed are not equal. More fluid tends to be filtered out of the capillary at the arterial end than is reabsorbed at the venous end. This filtration-reabsorption imbalance is necessary for delivering nutrients, oxygen, and other essential substances to tissues, as well as for maintaining proper fluid balance in the body.
The exact amounts of fluid filtered and reabsorbed can vary based on factors such as capillary permeability, blood pressure, osmotic pressure, and the specific needs of different tissues. However, as a general overview:
1. **Filtration (Fluid Given Off):** At the arterial end of the capillary, there is a relatively higher capillary hydrostatic pressure (Pc) due to the pumping of the heart. This pressure pushes fluid out of the capillary, along with small solutes like nutrients and gases. A portion of this fluid, along with these solutes, is essential for delivering oxygen and nutrients to the tissues.
2. **Reabsorption (Fluid Reabsorbed):** At the venous end of the capillary, the capillary hydrostatic pressure (Pc) has decreased as a result of fluid loss through filtration. However, the plasma colloid osmotic pressure (πp) remains relatively constant due to the presence of proteins in the blood. This osmotic pressure draws fluid back into the capillary, along with waste products and other substances that need to be transported away from the tissues.
The difference between the amount of fluid filtered out and the amount reabsorbed is referred to as "ultrafiltration." This term signifies the net movement of fluid from the capillary into the interstitial space. Ultrafiltration is necessary to maintain a constant blood volume, deliver nutrients to tissues, and remove waste products.
The difference between filtration and reabsorption is compensated by the lymphatic system. Not all the fluid that filters out of the capillaries is immediately reabsorbed into the capillaries at the venous end. Some of this excess interstitial fluid, along with proteins and waste products, is collected by the lymphatic vessels. These vessels form a network that drains excess fluid from the interstitial spaces and returns it to the bloodstream, ultimately emptying into larger veins near the heart.
The lymphatic system plays a critical role in maintaining fluid balance, preventing tissue edema, and ensuring that the excess fluid filtered out of capillaries is eventually returned to the bloodstream. This compensatory mechanism helps maintain the equilibrium between filtration and reabsorption, allowing capillaries to effectively transport nutrients and waste products while preventing excessive fluid buildup in tissues.
Work Step by Step
In a model capillary, the relative amounts of fluid given off (filtration) and reabsorbed are not equal. More fluid tends to be filtered out of the capillary at the arterial end than is reabsorbed at the venous end. This filtration-reabsorption imbalance is necessary for delivering nutrients, oxygen, and other essential substances to tissues, as well as for maintaining proper fluid balance in the body.
The exact amounts of fluid filtered and reabsorbed can vary based on factors such as capillary permeability, blood pressure, osmotic pressure, and the specific needs of different tissues. However, as a general overview:
1. **Filtration (Fluid Given Off):** At the arterial end of the capillary, there is a relatively higher capillary hydrostatic pressure (Pc) due to the pumping of the heart. This pressure pushes fluid out of the capillary, along with small solutes like nutrients and gases. A portion of this fluid, along with these solutes, is essential for delivering oxygen and nutrients to the tissues.
2. **Reabsorption (Fluid Reabsorbed):** At the venous end of the capillary, the capillary hydrostatic pressure (Pc) has decreased as a result of fluid loss through filtration. However, the plasma colloid osmotic pressure (πp) remains relatively constant due to the presence of proteins in the blood. This osmotic pressure draws fluid back into the capillary, along with waste products and other substances that need to be transported away from the tissues.
The difference between the amount of fluid filtered out and the amount reabsorbed is referred to as "ultrafiltration." This term signifies the net movement of fluid from the capillary into the interstitial space. Ultrafiltration is necessary to maintain a constant blood volume, deliver nutrients to tissues, and remove waste products.
The difference between filtration and reabsorption is compensated by the lymphatic system. Not all the fluid that filters out of the capillaries is immediately reabsorbed into the capillaries at the venous end. Some of this excess interstitial fluid, along with proteins and waste products, is collected by the lymphatic vessels. These vessels form a network that drains excess fluid from the interstitial spaces and returns it to the bloodstream, ultimately emptying into larger veins near the heart.
The lymphatic system plays a critical role in maintaining fluid balance, preventing tissue edema, and ensuring that the excess fluid filtered out of capillaries is eventually returned to the bloodstream. This compensatory mechanism helps maintain the equilibrium between filtration and reabsorption, allowing capillaries to effectively transport nutrients and waste products while preventing excessive fluid buildup in tissues.
