When blood flows through the glomerulus, the direct driving force for the production of primary urine is glomerular capillary pressure. Normally, glomerular capillary pressure originates from the abdominal aorta of the human body, and the renal artery forms interlobar arteries and arcuate arteries to the kidney, and at the same time is divided into small interlobar arteries as well as small bulbous arteries, and the small bulbous arteries enter each renal unit to form a glomerular capillary network, and when the blood passes through the glomerular capillary network, the majority of water is filtered out to form the primary urine. Primary urine is the precursor of urine, which contains water, urea, glucose, trace small molecule protein and inorganic salts, and can be classified as colorless, white and yellow, etc., while urine is produced after primary urine is reabsorbed by the kidneys. So when the blood flows through the glomerulus, the direct driving force to promote the production of primary urine is the glomerular capillary pressure, which is the lateral pressure of blood on the vessel wall.