Figure 36.11: The Mammalian Kidney The Bowman’s capsules and convoluted tubules of the nephrons are in the kidney’s outer region, the cortex. Other tubules are in the internal region, the medulla. The loops of Henle run parallel to one another in the medulla, where they create a steep gradient of osmotic pressure in the medullary tissue fluid. After tubular fluid leaves each nephron, it flows through a collecting duct to exit the kidney. As the tubular fluid within the collecting duct moves deeper and deeper into the medulla during this process, it passes by tissue fluids that are more and more concentrated.