PA 502: Medical Physiology- Acid Base Physiology – Flashcards
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Acids
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-H+ donors -strong acids dissociate completely in solution -weak acids do not dissociate completely
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Bases
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-H+ acceptors -can be classified as strong or weak
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pH
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-measure of H+ concentration
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How can the pH of the ECF be measured?
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Henderson-Hasselbach equation pH=pKa + log[HCO3-]/[CO2]
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What are the cells of the body constantly producing?
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H+
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How much H+ do healthy individuals make a day?
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50-100 mEq/L
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What are the 3 ways to control pH?
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1. Buffer System 2. Respiratory Regulation 3. Renal Regulation
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What is the Buffer System?
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-takes a strong base or acid and converts it to weak base or acid -reaction occurs within seconds -prevent changes in pH by binding H+ (acting like bases) whenever the pH of the ECF drops below normal and releasing H+ (acting like acids) whenever the pH of the ECF climbs above normal
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What are the 3 main buffer systems?
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1. Bicarbonate Buffer System 2. Phosphate Buffer System 3. Protein/Amino Acid Buffer System
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Bicarbonate Buffer System
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-If ECF is acidotic, weak acid created: HCL +HCO3- = HCL and carbonic acid -If ECF is alkalotic, weak base created: NaOH + carbonic acid = H2O and sodium bicarbonate
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Phosphate Buffer System
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-If ECF is acidotic, weak acid created: HCL + disodium hydrogen Phosphate (Na2HPO4) = Salt (NaCl) + Sodium dihydrogen phosphate (Na2H2PO4) -If ECF is alkalotic, weak base created: Sodium Hydroxide (NaOH) + Sodium dihydrogen (NaH2PO4) + H2O and Disodium Hydrogen Phosphate (Na2HPO4)
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Protein/Amino Acid Buffer System
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-If ECF is acidotic: the amine group acts as a BASE and picks up an H+ from the fluid -If ECF is alkalotic: carboxyl group acts as an ACID by donating H+ to the fluid
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Respiratory Regulation of pH *memorize this equation!*
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-increases or decreases the amount of CO2 expelled from lungs depending on what is needed by the body -reaction occurs in minutes -Using the equation: CO2 + H2O H2CO3 H+ + HCO3- Hypoventilation: increased CO2, pushing the equation to the right and increased H+ concentration Hyperventilation: decreased CO2, reversing the equation to the left and decreased H+ concentration
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Renal Regulation of pH
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-only process that physically removes H+ or adds HCO3- in the body -reactions occurs in hours to days -If someone is in metabolic acidosis and it won't regulate fast enough, they will die before it gets controlled -Renal Tubules Functionals in 3 ways
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What are the 3 ways Renal Tubules function?
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1. Regulating H+ levels 2. Regulating HCO2- levels 3. Synthesizing HCO3-
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Acidotic conditions:
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-kidneys secret H+ and reabsorb HCO3- -causes urine to become more acidic and blood more basic -Synthesizing HCO3-: renal cells lining the proximal convoluted tubule can also synthesize HCO3- to a certain extent which is then released into the blood stream
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Alkalotic conditions:
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-kidneys reabsorb H+ and secrete HCO3- -causes blood to become more acidic
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Acidemia
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decrease in arterial pH below 7.35
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Acidosis
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condition resulting from acidemia
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Alkalemia
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increase in arterial pH above 7.45
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Alkalosis
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condition resulting from alkalemia
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Arterial Blood Gases: What is this test used to assess the adequacy of?
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-Oxygenation, pO2 -Ventilation, pH and CO2 -Acid-Base Balance, pH, CO2, HCO3-
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What is the normal range of pH?
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7.35-7.45
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What is less that 7.35 pH considered?
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Acidosis
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What is more than 7.45 pH considered?
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Alkalosis
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What is a pH of less than 7.0 or more than 7.8 considered?
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incompatible with life
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What is pCO2?
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-partial pressure of CO2 in arterial blood -the level controlled by the respiratory system -tells how the patient is ventilating normal is: 45-45mmHg
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What is hypocarbia?
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less than 35 pCO2
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What is hypercarbia?
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more than 45 pCO2
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What is Respiratory Alkalosis?
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Increased Respirations, Decreased CO2 -causes hyperventilation (fear, pain, anxiety, crying in babies, exercise, etc.) -stimulation of respiratory center (brain injury, overdose, encephalitis, etc.) -mechanical over-ventilation
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What is Respiratory Acidosis
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Decreased Respirations, Increased CO2 -hypoventilation -COPD, Pneumonia, Atelectasis- collapsed alveoli, Respiratory muscle wall weakness Mechanical under-ventilation, Barbiturate or Sedative OD, Near drowning, Suffocation (choking), Chest wall abnormality (kyphosis, obesity)
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Metabolic Alkalosis
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patient is alkalotic and it is not respiratory alkalosis -accumulation of too much base -loss of too much acid -CO2 should be normal or high, >45 -HCO3- should be high >28 *If the pH is off, but the oxygen level is okay, you need to check! *excessive gastric suctioning *severe vomiting of stomach contents only *Potassium deficit *Medications: Antacids, Diuretics
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Metabolic Acidosis
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-patient is acidotic and it is not respiratory acidosis -accumulation of too much acid and loss of too much base -CO2 normal or low <35 -HCO3- should be low <22 *If the pH is off, but the oxygen level is okay, you need to check! *Diabetic Ketoacidosis- body is starving, even though they do have enough glucose, body moves to ketones, Lactic Acidosis- not enough oxygen, Renal tubular acidosis, Renal failure, Severe diarrhea- body losing stool so fast, body has to replace enzymes in there, Starvation, Poisoning (e.g. methanol, ethylene glycol)
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What is HCO3-?
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-measure of bicarbonate ion in arterial blood -a Base -regulated by kidneys -Normal range: 22-28 mmol/L
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Alkalosis
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-leads to tissue hypoxia -causes vasoconstriction -causes O2 to bind tighter to Hgb, not released to tissues -Remember Oxygen-Hemoglobin Disassociation curve
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pO2, PaO2
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-partial pressure of oxygen in arterial blood -Range 80-100mmHg, age and altitude dependent -values increase with supplemental O2 -tells how well patient is oxygenated
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O2 Saturation, SaO2
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-percentage of hemoglobin actually binding, saturated with oxygen 90-100% age dependent
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FiO2
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fraction inspired air that is oxygen -FiO2 of room air is 21% 2 liters = 28% 3 liters = 32% 4 liters = 36%
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What is the FiO2 of a simple face mask?
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40-60%
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What is the FiO2 of a Nonrebreather mask?
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60-100% (for seizures, no oxygen into their blood...)
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What is the FiO2 of a Bag-Mask Ventilation?
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100%
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Respiratory Failure
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pCO2 greater than 50 pO2 less than 50
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Chronic Respiratory Failure
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pCO2 greater than 50, pH 7.35-7.45 pO2 less than 50, pH 7.35-7.45
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Acute Respiratory Failure
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-pCO2 greater than 50, pH less than 7.35 or greater than 7.45 -pO2 less than 50, pH less than 7.35 or greater than 7.45
