 Dear students in this topic, we shall discuss pressure and flow in capillaries Dear students the wall of the arteries and arterioles has smooth muscles These smooth muscles become discontinuous when they Subdivide to form the meta arterioles. So meta arteriolar wall is not smooth muscle but discontinuous. And till the capillary starts, that is the capillary end here smooth muscle ends but before ending it forms a ring. This ring is called peri-capillary a pre-capillary sphincter. This pre-capillary sphincter along with the innervated smooth muscles of the arterioles play an important role in the control of circulation in capillary beds. The pre-capillary sphincter or smooth muscle of the arterioles they can alter the blood distribution within the tissue. Dear students the tissues have networks of capillaries but all capillaries are not open or closed at a time. In most tissues about 30 to 50 percent of the capillaries are open to flow at a time. While in some tissues like the skin most of the capillaries tend to remain closed at a time. Dear students all capillaries in a network are only a short distance away from the arterioles. Pressure or flow, the trans-mural pressures within a capillary bed are around 10 millimeter mercury. The capillary pressures result in the filtration are coming out of fluid from blood into the interstitial spaces. In most tissues the net movement is minimal. Because of this volume of the tissue remains constant. Increase in capillary pressure increases the outflow of fluid from the blood into the tissue. This causes rise in the volume of the tissue which is called tissue edema just make a tissues can the fluid key quantity in kidneys we see that the capillary pressure is always high this pressure is known as filtration pressure. With the help of this pressure kidneys make ultrafiltrate which is converted into urine. Kidneys are encapsulated to prevent the swelling of the tissue or edema.