Renal Handling of Sodium (Na+) - PDF

Okay, here is the conversion of the images into a structured markdown format: ### RENAL HANDLING OF $Na^+$: #### 1. $Na^+$ reabsorption in PCT (70%): * About 70% of $Na^+$ load is reabsorbed in PCT. * At the luminal border: * $Na^+$ is transported from lumen to inside cells by facilitate...

Okay, here is the conversion of the images into a structured markdown format: ### RENAL HANDLING OF $Na^+$: #### 1. $Na^+$ reabsorption in PCT (70%): * About 70% of $Na^+$ load is reabsorbed in PCT. * At the luminal border: * $Na^+$ is transported from lumen to inside cells by facilitated diffusion under effect of: 1. Concentration gradient. 2. Electrical gradient (in lumen - 3 mv & inside cell - 70 mv). * This is helped by large surface area of brush border of PCT. * At baso-lateral border: * $Na^+$ crosses to interstitial fluid by primary active transport against its electro-chemical gradient by $Na^+ - K^+$ ATPase activity (for each 3 $Na^+$ pumped out only 2 $K^+$ ions are carried in). * After entering the cell $K^+$ ions diffuse back again to the interstitium helped by concentration gradient and high permeability of cell membrane. * $\implies$ maintain the intracellular negativity in relation to luminal fluid $\implies$ $\uparrow$ $Na^+$ entry to the cell (help the facilitated diffusion). * This reabsorption result in: 1. Reabsorption of 70% of water (obligatory water reabsorption) because of the high osmolality created by $Na^+$ reabsorption. 2. Active co-transport transport of glucose, amino acids, $HCO3^-$ and other organic acids (these substances are carried by same carrier of $Na^+$). 3. Passive diffusion of $Cl^-$ (in 2nd half of PCT due to $Cl^-$ concentration). #### 2. $Na^+$ reabsorption in the loop of Henie (20%): * Thin descending part: * The only part in the nephron in which $Na^+$ is not reabsorbed (also this part is freely permeable to water $\implies$ hypertonic tubular fluid). * Thin ascending part: * The only part in the nephron in which $Na^+$ is reabsorbed passively. * Thick ascending part: * Active reabsorption of 20% of $Na^+$ by co-transport protein carrier (1 $Na^+$, 2 $Cl^-$ and 1 $K^+$) mechanism (also this part is poorly permeable to water $\implies$ fluid leaving this thick part is hypotonic). #### 3. $Na^+$ reabsorption in the DCT & collecting tubules (10%): * 10% of $Na^+$ is actively reabsorbed, in exchange with $H^+$ or $K^+$ by the help of Aldosterone hormone.