<prompt> What are the major functions of P cells present in coical collecting ducts?Sodium water reabsorption from the lumen.Potassium secretion into the lumen.ADH controlled water reabsorption.All of the above  <response>: Sodium water reabsorption from the lumen.Potassium secretion into the lumen.ADH controlled water reabsorption.FUNCTIONS OF P CELLS:1. Sodium water reabsorption:Reabsorbed from lumen.Occurs through Na2 channels ENaC channels. Approximately 3 Na reabsorption occurs.2. Potassium secretion:Secreted into lumen.K both secreted reabsorbed.Note: Na2 reabsorption K secretion depends on,Na2-K-ATPase activity in basolateral membrane.Aldosterone.3. Water reabsorption:ADH Controlled.Stimulates water channel, aquaporin-2. 