Briefly describe the processes of ultrafiltration and selective reabsorption in the nephron

Ultrafiltration, the first stage of urine formation, begins when blood enters the glomerulus via the afferent arteriole. Water, glucose, ions and amino acids leave the blood and enter the bowman’s capsule. The diameter of the afferent arteriole is wider than that of the efferent arteriole, generating a high hydrostatic pressure, and leaky capillaries facilitate the movement of fluid out of the blood. The glomerular filtrate then enters the proximal convoluted tubule which is the primary site of selective reabsorption. Here, all glucose and amino acids are reabsorbed by active transport and most of the water is passively reabsorbed by osmosis.