acids are transported by secondary active mechanism(correlated with Na),where H20,CI-,and HCO3-are transported passively.The distal convoluted tubule and collecting duct reabsorb NaCl,K+,HCO3-,in a hormone-dependent fashion.The secretion of K+,H+,and NH3 by the tubule cells promote reabsorption of plasma HCO3-,which plays a predominant role in homeostatic regulation 2.1Type ofreabsorption (1)Passive transport:Water and solutes are transported across the tubular epithelial cells into the extracellular fluid that is mediated by electronic and chemical forces (2)Active transport:Active transport can move a solute against an electrochemical gradient and requires energy derived from metabolism. 2.2 Reabsorption ofsome substances (1)Na+:i)Proximal tubule:active transport in pump-leak model DThere is a concentration gradient favoring sodium diffusioninto the cell. 2The cell has sodium pump to transport sodium out of the cell into the interstitial. 3Water moves to the interstitial by osmosis,and it leads to a high level of hydrostatic pressure in interstitial. 4 Sodium and water are reabsorbed from the interstitial fluid into the peritubular capillaries by hydrostatic pressure ,meanwhile,there also exits leakage from interstitial fluid to tubule. ii)Henle's loop ascending limb:passive transport. (2)CI:When sodium is reabsorbed through the tubular epithelial cell,negative ionsacids are transported by secondary active mechanism(correlated with Na +),where H2O,Cl-,and HCO3-are transported passively.The distal convoluted tubule and collecting duct reabsorb NaCl,K+,HCO3-,in a hormone-dependent fashion.The secretion of K+,H+,and NH3 by the tubule cells promote reabsorption of plasma HCO3-,which plays a predominant role in homeostatic regulation 2.1Type of reabsorption (1) Passive transport: Water and solutes are transported across the tubular epithelial cells into the extracellular fluid that is mediated by electronic and chemical forces. (2) Active transport: Active transport can move a solute against an electrochemical gradient and requires energy derived from metabolism. 2.2 Reabsorption of some substances (1)Na+: i) Proximal tubule: active transport in pump-leak model ①There is a concentration gradient favoring sodium diffusion into the cell. ②The cell has sodium pump to transport sodium out of the cell into the interstitial. ③Water moves to the interstitial by osmosis, and it leads to a high level of hydrostatic pressure in interstitial. ④ Sodium and water are reabsorbed from the interstitial fluid into the peritubular capillaries by hydrostatic pressure ,meanwhile, there also exits leakage from interstitial fluid to tubule. ii) Henle‘s loop ascending limb: passive transport. (2)Cl- : When sodium is reabsorbed through the tubular epithelial cell, negative ions