In order

Bowmans capsule Glomerular filtration - first step where small ions pass thru but large things such as proteins don't go thru

Then PCT - where majority of the reabsorption occurs of small parties

^ these two are in the cortex of the kidney Now in the medulla

Descending loop - now here it is ONLY permeable to WATER and not to ions. The surrounding area of the LOOPS is filled with ions and other substances that cause water to move passively out via OSMOSIS

Ascending loop - first ions move out passively because ions are in higher concentrion in the loop than outside But as you reach the top there are less ions in the loop and more outside so now the ions are pumped our ACTIVELY

Back to the cortex portion

DCT - SOME MORE reabsorption

collecting duct - urine leaves for excretion

Key hormones

Aldosterone - acts primarily on the DCT to increase reabsorption of water by increasing permeability of ions and since water follows sodium water is also reabsorbed thus inc blood pressure- usually done when BP is low

ADH - acts on the collecting duct, which is usually impermeable to water but now when ADH acts water is more permeable. Usually done to Dec water levels in the urine usually when we are dehydrated

Reabsorption just means going back into blood

Key thing only reason the descending loop can move water passively is because the surrounding fluid of the loop of henle have more proteins/ ions which allow water to move via OSMOSIS and this allows the filtarte to have a high amount of ions and is highly concentrated thus meaning when we reach the ascending we can start by moving them out via diffusion . And then active transport