The capillary bed is an interlaced network of capillaries that services an organ. The network size of the capillary bed depends on how active the particular organ is. Usually, the more active organs require more nutrients and produce more waste products. Capillary beds may control their blood flow via autoregulation. This allows an organ to maintain constant flow despite achange in central blood pressure. This is achieved by myogenic response and in the kidney by tubuloglomerular feedback. When blood pressure increases the arterioles that lead to the capillaries bed are stretched and subsequently constrict (a phenomenon known as the Bayliss Effect) to counteract the increased tendency for high pressure to increase blood flow. In the lungs special mechanisms have been adapted to meet the needs of increased necessity of blood flow during exercise. When the heart rate increases and more blood must flow through the lungs, capillaries are recruited and are also distended to make room for increased blood flow. This allows blood flow to increase while resistance decreases. A capillary bed can consist of two types of vessels: true capillaries which branch mainly from metarterioles and provide exchange between cells and the circulation. Secondly, capillary beds also consist of a vascular shunt which is a short vessel that directly connects the arteriole and venule at opposite ends of the bed.