How do tissue fluids enter and leave the circulatory system?

Answer 1

What you are talking about is the lymphatic system. The fluid is pushed out between endothelial cells of the blood vessels. it is then collected into the lymph ducts and slowly transported back into the blood stream by way of the thoracic duct.

Answer 2

Fluids enter and leave the capillaries of the circulatory system due to differences in pressure at either end of the capillary bed. To explain better there is a constant osmotic pressure at both ends of the capillay bed of 25mmHg (because of solute concentrations). On the areriole side there is a hydrostatic pressure of 36mmHg in the interstitial fluid, the net pressure difference of 11mmHg favoring the interstitial fluid, causes fluid to move out at the arteriole end. On the venule side the hydrostatic pressure of the interstitial fluid is now 15mmHg, so threre is a net pressure of 10mmHg forcing fluid into the venule end and back into the blood stream.

The fluid that is not reabsorbed due to the pressure gradients is absorbed into the lymphatic system. The lymph vessels all flow toward one another and eventually converge and empty into the blood circulation at the thoracic duct and drain into the major veins leading toward the right atrium.

Answer 3

Through opening of the tight junctions between the endothelial cells that line blood vessels.