Ultrafiltration in the kidney takes place in Bowman's capsule.
Bowman's capsule is a cup-shaped structure located in the outer part of the kidney, called the cortex. It surrounds a cluster of blood vessels called the glomerulus. The glomerulus and Bowman's capsule together form a structure called the renal corpuscle.
During ultrafiltration, blood from the glomerulus flows into Bowman's capsule. The glomerulus is made up of a network of capillaries with very small pores. These pores allow small molecules such as water, salts, and waste products to be filtered out of the blood and into the Bowman's capsule. The larger molecules such as proteins and blood cells cannot pass through the pores and remain in the bloodstream.
The filtered fluid in Bowman's capsule is called the glomerular filtrate. It contains water, salts, glucose, and other small molecules. This filtrate then passes through the rest of the nephron, where it is further processed and modified before being excreted as urine.
So, in summary, ultrafiltration in the kidney takes place in Bowman's capsule, where small molecules are filtered out of the blood and into the nephron to form the glomerular filtrate.