Mouse renal glomerulus. Transmission electron micrograph of a murine renal glomerulus with podocytes, endothelial cells, basal lamina, and mesangial cells shown. The glomerulus is a dense network of capillaries surrounded by the Bowman's capsule in the kidney. High pressure in the capillaries forces water and other small molecules (e.g., water, glucose, amino acids, salts, urea) out of the blood into the proximal convoluted tubule in the nephron. This process is called ultrafiltration and is the first step in urine formation. Magnification: x 6000; image is 14.5 micrometers in length.