after tt2

• foods rich in protein are converted to amino acids
• amino acids can either deaminated or secreted to tissues
• kidney secretes urea
• ammonia enters the urea cycle in the liver
• ammonia is highly toxic
• urea reabsorption is low in high urine flow rates
• normally, around 50% of urea is reabsorbed
• urea moves passively thru urea transporters
• urea transporter is on the luminal side of the collecting duct cell
• vasopressin increases urea transporter activity by phosphorylation by PKA
• most potassium is in the intracellular compartment
• kidney likely evolved in a potassium rich environment
• only 2% of potassium is outside of the cell
• movement of potassium out of the cell through potassium channels maintain a negative cell interior
• insulin promotes cellular potassium uptake by promoting sodium potassium ATPase
• nernst equation: conc potassium outside cell/ conc potassium inside cell,¥
• nernst equation is a major determinant of cell transmembrane potential gradient
• beta 2-catecholamine increases cAMP and PKA acticity to phosphorylate sodium potassium ATPase (increased activity)
• increase in beta 2 catecholamine increases potassium uptake of cell
• during acidosis

  • high concentration of H ions outside of the cell
  • low activity of sodium-H exchanger
  • low entry of sodium in cell
  • low activity of sodium potassium ATPase
  • low entry of potassium in cell
• hyperpolarization: high potassium inside the cell, low outside of cell

  = less likely to fire AP
• hypokalemia def and symptoms

  • high K inside cell
  • muscle weakness
  • cardiac arrhythmias
• hyperkalemia def and characteristics

  • low K inside cell
  • abnormal ECG (stretched out)
  • muscle stiffness and weakness
  • cardiac arrhythmias
• potassium is reabsorbed in the proximal tubule due to solvent drag and paracellular diffusion
• potassium is reabsorbed in the ascending loop of henle by the sodium potassium chloride cotransporter
• ROMK: renal outer medullary potassium channel
• all potassium in urine is secreted by the collecting duct
• potassium is secreted (into the lumen) from the collecting duct by membrane protein channels (ROMK and max K) down its concentration gradient
• potassium moves down a concentration electrical gradient in the collecting duct

  • conc gradient: ENac and sodium potassium ATP-ase maintain a low sodium, high potassium cell interior
  • electrical gradient: sodium leaving makes the lumen more negative, potassium moves readily because it is positively charged
• low potassium inhibits aldosterone secretion
• aldosterone effect on potassium secretion

  • increase sodium reabsorption and sodium channels
  • increase lumen negativity
  • increase potassium channels
• mechanism of K balance by change in ECG volume

  1. high salt intake leads to increased ECF
  2. high ECF inhibits renin (and angiotensin II, aldosterone)
  3. high ECF increase GFR, inhibits reabsorption, increased flow
  4. increased flow and low aldosterone counteract each other
• increased renal flow will increase secretion of K
• low aldosterone will inhibit secretion of K
• metabolism generates about 70mmols of H ions per day
• an acid can donate a hydrogen ion
• a base can bind a hydrogen ion
• hydrogen ions come from our diet (amino acids fatty acids) and metabolism (CO2, ketoacids)
• main buffers

  • bicarbonate
  • ammonia
• pH is regulated by both CO2 and buffers