Urinary 5

• pH is a symbol (power of hydrogen) to represent the negative log of the number of hydrogen ions in 1 litre of solution. the pH scale goes from 0-14
• As the concentration of hydrogen ions increase, the pH goes down (acidic solution) and as the concentration of hydrogen ions goes down the pH goes up (basic solution)
• A neutral pH is a 7. If the pH is less than 7,35 it is considered acidosis mais pH is greater than 7,45 it is considered alkalosis. Venous blood has a pH of 7.36 and arterial blood has a pH of 7.40
• Acids and bases are always entering the blood from food and metabolism of nutrients. The body needs a way to neutralize these compounds or eliminate them to keep blood pH constant.
• Two major control system for maintaining pH in the body are chemical buffers and physiological buffers (respiratory and urinary). The chemical buffers respond immediately but if they are not enough, the physiological buffers take over
• A buffer is a substance that prevents marked changes in the pH of a solution when an acid or a base is added to it. Buffers do not prevent pH changes but they help minimize them
• Buffers consist of two kinds of substances and are therefore often referred to as buffer pairs. These pairs present in body fluids as bicarbonate pairs, hemoglobin pairs and phosphate buffer pairs.
• Buffering alone cannot maintain homeostasis of pH because they will run out. Respiratory and urinary mechanisms must therefore function with buffers to remove the extra hydrogen ions
• As we keep adding a little bit of hydrogen ions to the blood they are still there even with buffering and eventually need to be removed to avoid acid blood
• CO2 enters our blood as a waste product. An enzyme contained in red blood cells coverts water and CO2 to carbonic acid and then to acid bicarbonate.
• Respiratory adjustment to counter pH changes

  The more you breathe, the less CO2 you have, the less carbonic acid you have, the less hydrogen ions you have which means the pH will go up
• Decrease in pH (acidosis) stimulates increase in respiration (hyperventilation) which will increase pH back towards the normal.
• Increase in blood pH (alkalosis) triggers hypoventilation (slow breathing) which brings pH down since more CO2 in the blood means more carbonic acid.
• Prolonged hyperventilation may lead to alkalosis (too basic) and prolonged hypoventilation may lead to acidosis (too acidic)
• Kidneys can excrete various amounts of acid and base which makes the urinary mechanism much more effective at adjusting hydrogen ion concentration than the respiratory system
• Distal tubules and collecting ducts can secrete hydrogen ions into the urine. A decrease in pH accelerates renal tubule ion exchange thereby acidifying urine and increasing blood pH to normal.
• Kidneys can also excrete the other part of the buffer pair to lower pH
• Na/H pump is only active when an acid problem is present. Considering there is a limited amount of sodium, this affects the sodium potassium pump and means less potassium will be secreted (risk of hyperkalemia)
• Acid base imbalances

  Metabolic disturbances: metabolic acidosis and alkalosis

  Respiratory distrubances: respiraory acidosis (hypoventilation) and respiratory alkalosis (hyperventilation)