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What is the normal pH for blood?
- > 7.45 alkalosis
- < 7.35 acidosis
How does the concentration of H+ in the body compare to Na+ ?
Na+ is present at a concentration aprox 3.5 million times more than H+
What is the pH of a substance?
The negative logarithm of the H+ concentration in milliequivalents per liter (mEq/L). Ex: pH of 7 is an H+ concentration of 10^-7 or 0.0000001 mEq/L
What are the two types of acids in the body?
- volatile acid which is H2CO3
- all other acids are non-volatile or fixed acids and are not eliminated by the lungs
What enzyme catalyzed the reaction between CO2 and water and how much does it increase it?
carbonic anhydrase, increases the reaction by 5000 times
How do you estimate the amount of H2CO3 in the blood?
- multiply the PCO2 by 0.03
- Ex: 40mm PCO2 * 0.03 = 1.20 mEq/L H2CO3
What are the three major buffer systems that protect the pH of body fluids?
- chemical buffer system of body fluids
- the lungs - eliminate CO2
- the Kidneys - eliminate H+
What are the 3 chemical buffer systems in body fluids?
- bicarbonate buffer system
- protein buffer system
- Na+ / K+ exchange system
How does the bicarbonate (HCO3 -) buffer system work?
- To increase pH HCl + NaHCO3 - <--> NaCl + H2CO3
- To decrease pH NaOH + HCO3 <--> NaHCO3 + H2O
How does the protein buffer system work?
proteins are amphoteric and can bind or release H+ ions, albumin and plasma globulins are the major buffer in the vascular compartment
What is the largest buffer system in the body?
the protein buffer system
How does the H+ / K+ exchange system work?
H+ and K+ move between ECF and ICF in exchange for each other. If excess K+ is in the ECF it will move into the ICF in exchange for H+ lowering the pH of the ECF
How effective is the respiratory control mechanism in controlling pH?
- only 50-75% effective
- Ex: pH change from 7.4 to 7.0
- respiratory can only bring it back up to 7.2 or 7.3
What two major roles do the kidneys play in regulating acid base balance?
- reabsorbtion of HCO3- filtered in glomerulus
- excretion of H+ from fixed acids generated by metabolism
Where do most of the acid base regulation activities of the kidney take place?
in the PCT
What is the minimum pH of urine? (any lower would damage urinary tract)
4.4 to 4.5, once pH reaches this level H+ secretion ceases in the kidneys
What are two important intratubular buffer systems?
phosphate and ammonia buffer systems
What laboratory test can be used in assessing acid base balance?
- arterial blood gasses and pH
- CO2 and HCO3- levels
- base excess or deficit
- blood and urine anion gaps
Does blood pH provide much information about the CAUSE of an acid base disorder?
What does base excess indicated? base deficit?
- base excess - metabolic alkalosis
- base deficit - metabolic acidosis
What does an increased anion gap indicate? a low anion gap?
- increased - lactic acidosis, ketoacidosis
- low - fall in albumin or rise in unmeasured cations - i.e. hyperkalmeia/calcemia/magnesemia, lithium intoxication or multiple myeloma
What is the difference between respiratory and metabolic acidosis/alkalosis?
- metabolic acidosis - desceased HCO3-
- metabolic alkalosis - increased HCO3 -
- respiratory acidosis - increased PCO2 decreased pH
- respiratory alkalosis - decreased PCO2 increased pH
What are four mechanisms of metabolic acidosis?
- increased production or ingestion of fixed acids
- inability of the kidneys to excreted fixed acids
- excessive loss of HCO3- thru kidney or GI
- increased plasma Cl-
How is the anion gap used in the differential diagnosis of metabolic acidosis?
- decreased gap <8 = hypo albumin, multiple mylenoma, or hyper(Ca,K,Mg,Li)
- increased gap >12 = ketoacidosis, lactic acidosis, starvation, renal insufficiency, drug or chemical anion poisoning
- normal gap 8-12 = loss of bicarb - diarrehea, ileostomy, chloride retention, parenteral nutrition
What are the signs and symptoms of metabolic acidosis?
Anorexia, nausea and vomiting, abdominal pain, weakness, lethargy, depression of vital signs, decreased heart rate, increased rate and depth of respiration, acid urine, skin warm and flushed
What are the signs and symptoms of metabolic alkalosis?
decreased depth and rate of respiration, hyperactive reflexes, tetany, convulsions, hypotension, arrhythmias, increased urine pH
What are the causes of metabolic alkalosis?
- excessive gain of bicarbonate or alkali
- excessive loss of hydrogen ion
- increased bicarbonate retention
- volume contraction - diuretic, hypovolumic
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