Animation E1, 1.1 Ultrafiltration and reabsorption

[Music] the kidneys are organs of the urinary system they regulate the water content of the body and remove metabolic waste through the formation of urine how does urine form [Music] when blood reaches the glomerulus it is maintained at a relatively high pressure the high blood pressure forces water and small soluble molecules such as glucose and amino acids in the plasma through the thin walls of the glomerulus and the bowman's capsule into the capsular space this process is called ultrafiltration the fluid that is filtered into the bowman's capsule is called glomerular filtrate the filtrate has a

similar composition to plasma however no plasma proteins and blood cells are found in the glomerular filtrate because they are too large to pass through the walls of the glomerulus and the bowman's capsule [Music] after ultrafiltration the glomerular filtrate flows through the kidney tubule in the kidney tubule useful substances in the filtrate are absorbed back into the surrounding capillaries so that they are not lost from the body this process is called reabsorption it occurs mainly in the proximal convoluted tubule in the proximal convoluted tubule all glucose amino acids and most salt are reabsorbed by diffusion and

active transport as many solute molecules are removed from the filtrate the water potential of the filtrate rises therefore water in the filtrate enters the blood by osmosis the reabsorption of water raises the concentration of urea in the filtrate thus urea in the filtrate diffuses into the blood further reabsorption of substances takes place in the remaining part of the kidney tubule after reabsorption the remaining filtrate in the collecting duct is called urine which will be passed out of the body when we urinate