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 pH = - log [H + ]  H + is really a proton  Range is from  If [H + ] is high, the solution is acidic; pH < 7  If [H + ] is low, the solution is basic or alkaline ; pH > 7 2

 Acids are H + donors.  Bases are H + acceptors, or give up OH - in solution.  Acids and bases can be:  Strong – dissociate completely in solution HCl, NaOH  Weak – dissociate only partially in solution Lactic acid, carbonic acid 3

 Homeostasis of pH is tightly controlled  Extracellular fluid pH= 7.4  Arterial Blood pH= 7.35 – 7.45  Venous blood is more acidic than arterial?  Because it contains more CO2 than arterial blood.  8.0 death occurs  Acidosis (acidemia) below 7.35  Alkalosis (alkalemia) above

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 Most enzymes function only with narrow pH ranges  Acid-base balance can also affect electrolytes (Na +, K +, Cl - )  Can also affect hormones 6

Sources of acids:  Acids take in with foods  Acids produced by metabolism of lipids and proteins  Cellular metabolism produces CO 2.  CO 2 + H 2 0 ↔ H 2 CO 3 ↔ H + + HCO 3 - 7

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Take up H+ or release H+ as conditions change Buffer pairs – weak acid and a base Exchange a strong acid or base for a weak one Results in a much smaller pH change 9

 Sodium Bicarbonate (NaHCO 3 ) and carbonic acid (H 2 CO 3 ).  It acts both extracellular and intracellular.  Its concentration in blood equals = 27mEq/L and is called alkali reserve.  Maintain a 20:1 ratio : HCO 3 - : H 2 CO 3 HCl + NaHCO 3 ↔ H 2 CO 3 + NaCl NaOH + H 2 CO 3 ↔ NaHCO 3 + H 2 O. 10

 Major intracellular buffer.  It is an important buffer in renal tubules.  H + + HPO 4 2- ↔ H 2 PO4 -  OH - + H 2 PO 4 - ↔ H 2 O + H 2 PO

 Includes hemoglobin, work in red blood cells.  Carboxyl group gives up H +  Amino Group accepts H +  Plasma proteins.  Intracellular proteins. 12

 Exhalation of carbon dioxide.  Powerful, but only works with volatile acids  Doesn’t affect fixed acids like lactic acid  CO 2 + H 2 0 ↔ H 2 CO 3 ↔ H + + HCO 3 -  Body pH can be adjusted by changing rate and depth of breathing.  Hyperventilation wash out excess CO2.  Hypoventilation retain CO2.  This process is controlled by chemoreceptors. 13

 Can eliminate large amounts of acid  Can also excrete base  Can conserve and produce bicarb ions  Most effective regulator of pH  If kidneys fail, pH balance fails 14

 Reabsorption of filtered carbonate.  Generation of bicarbonate.  Excretion of H+ and urine acidification as low as pH of urine =5.0.  For the kidney to continue excretion of acidic urine, the excreted H+ has to be buffered by two buffer systems in the renal tubules: a. Ammonia which binds the secreted H+ and forms ammonium to finally binds CL to give ammonium-CL which is excreted in urine. b. Phosphate buffer: which binds H+ and gives sodium dihydrogen phosphate. 15

 Buffers function almost instantaneously  Respiratory mechanisms take several minutes to hours  Renal mechanisms may take several hours to days 16

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 pH< 7.35 acidosis  pH > 7.45 alkalosis  The body response to acid-base imbalance is called compensation  May be complete if brought back within normal limits  Partial compensation if range is still outside norms. 19

 If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation +buffer system.  If problem is respiratory, renal mechanisms can bring about metabolic compensation. 20

 Principal effect of acidosis is depression of the CNS through ↓ in synaptic transmission.  Generalized weakness  Deranged CNS function the greatest threat  Severe acidosis causes  Disorientation  coma  death 21

A. Respiratory causes: - CNS depression (anaesthesia). - Resp. muscle paralysis/ diaphragm paralysis, rib fractures, etc.. - Obstructive lung diseases A. Metabolic causes: B. - Diabetic ketoacidosis. C. -severe diarrehea. D. -Hypoaldosteronism E. Acute renal failure 22

 Alkalosis causes over excitability of the central and peripheral nervous systems.  Numbness  Lightheadedness  It can cause :  Nervousness  muscle spasms or tetany  Convulsions  Loss of consciousness  Death 23

A- Respiratory: Hyperventilation: - High altitude. - Hysterical. - B. Metabolic: - -Severe vomiting. - Excess antacids. - Hyperaldosteronism. 24

 Carbonic acid excess caused by blood levels of CO 2 above 45 mm Hg.  Causes of respiratory acidosis:  Depression of respiratory center in brain that controls breathing rate – drugs or head trauma  Paralysis of respiratory or chest muscles  Emphysema.  Pulmonary edema. 25

 Kidneys eliminate hydrogen ion and retain bicarbonate ion.  Kidney also generates new bicarbonate. 26

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 Carbonic acid deficit  pCO 2 less than 35 mm Hg (hypocapnea)  Most common acid-base imbalance  Primary cause is hyperventilation 28

 Conditions that stimulate respiratory center and wash out CO2 (Hyperventilation):  Oxygen deficiency at high altitudes.  Anorexia nervosa.  Early salicylate intoxication 29

 Kidneys conserve hydrogen ion  Excrete bicarbonate ion 30

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 Bicarbonate deficit - blood concentrations of bicarb drop below 22mEq/L  Causes:  Loss of bicarbonate through diarrhea or renal dysfunction  Accumulation of acids (lactic acid or ketones) e.g.  Diabetic ketosis.  Failure of kidneys to excrete H+ 32

 Increased ventilation  Renal excretion of hydrogen ions if possible  K + exchanges with excess H + in ECF  ( H + into cells, K + out of cells) 33

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 Bicarbonate excess - concentration in blood is greater than 26 mEq/L  Causes:  Excess vomiting = loss of stomach acid  Excessive use of alkaline drugs  Certain diuretics  Endocrine disorders: Hyperaldosteronism.  Heavy ingestion of antacids  Severe dehydration 35

 Kidney excretes alkaline urine and retain H+  Respiratory compensation difficult – hypoventilation limited by hypoxia. 36

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1. Note whether the pH is low (acidosis) or high (alkalosis) 2. Decide which value, pCO 2 or HCO 3 -, is outside the normal range and could be the cause of the problem. If the cause is a change in pCO 2, the problem is respiratory. If the cause is HCO 3 - the problem is metabolic. 38

3. Look at the value that doesn’t correspond to the observed pH change. If it is inside the normal range, there is no compensation occurring. If it is outside the normal range, the body is partially compensating for the problem. 39

 A patient is in intensive care because he suffered a severe myocardial infarction 3 days ago. The lab reports the following values from an arterial blood sample:  pH 7.3  HCO3- = 20 mEq / L ( )  pCO2 = 32 mm Hg ( ) 40

 Metabolic acidosis  With compensation 41