acid-base Flashcards
what is pH?
-a measurement of its H+ concentration
-pH of 7 is neutral, if a solution is below 7.0 the H concentration is greater than 1x10e-7 M and considered acidic
-if a solution is above 7.0 it has a H below 1x10e-7 M and is considered alkaline (basic)
-a change of 1 pH unit represents a 10-fold change in H concentration
what is normal pH in the body?
-the H concentration of normal arterial plasma is 0.00004 mEq/L (very small compared to other ions, Na 140mmol/L) and is usually expressed on a logarithmic pH scale of 0-14
-normal pH of the body is 7.40, slightly alkaline (7.38-7.42)
how do pH changes denature proteins?
-pH is closely regulated, intracellular proteins such as enzymes and membrane channels are sensitive to changes in pH
-function of these proteins depend on their normal three-dimensional structure
-changes in H concentration results in disruptions in hydrogen bonds altering, altering the structure
what is acidosis and alkalosis?
-acidosis: very low pH (excess H)=CNS depression, confusion, coma
-alkalosis: high pH (low H)= hyperexcitability in sensory neurons and muscles, sustained respiratory muscle contraction
what is the daily challenges of the body regarding pH?
-in day to day functioning, the body is challenged by intake and production of acids more than bases
what is acid input a result of?
-diet as well as acids produced during metabolism
-the largest source of acid on a daily basis is from CO2 from aerobic metabolism
pH homeostasis depends on three mechanisms:
- Buffers (first line of defense)
- ventilation (handles 75% of disturbances)
- renal regulation of H and HCO3- (slowest)
what are buffers?
-include proteins, phosphate ions and HCO3-
-a buffer is a molecule that moderates, but does not prevent changes in pH by combining with or releasing H
-in the absence of a buffer, adding acid to a solution causes a sharp change in pH
-in the presence of buffers, the H added is bound and pH change is slightly moderated or may even be unoticeable
where are buffers found?
within cells and in the plasma
-intracellular buffers include cellular proteins (hemoglobin), phosphate ions (HPO4, H2PO4)
what do buffers systems in the blood result in?
-in a large amount of HCO3-, the most important extracellular buffer system (can now buffer H from non-respiratory sources)
what is the HCO3- plasma concentration?
-plasma HCO3- concentration is approximately 600,000 times concentrated as plasma H (H bound to Hb)
-the relationship between CO2, HCO3- and H in the plasma is expressed by
how does the law of mass action relate to HCO3-?
-according to law of mass action, any change in amount of CO2, HCO3- or H in solution causes reaction to shift until new equilibrium is reached
what shifts the HCO3- equation to the right and left?
what do peripheral and central chemoreceptors do for pH?
-sense changes in plasma PCO2 and/or H and signal to the respiratory control center to adjust ventilation accordingly
how does ventilation help pH?
-compensates for pH disturbances
-alterations in ventilation can correct disturbances in acid-base balance as well as cause them
what handles the remaining 25% of pH disturbances?
-the kidneys handle it slowly
-use ammonia and phosphate buffers
what are the two mechanisms that the kidneys use to handle pH disturbances
- directly, by altering the rates of excretion or reabsorption of H
- indirectly, by changing the rate at which HCO3- buffer is reabsorbed or excreted
what do the kidneys do during acidosis?
-in general, during acidosis, excess H is buffered by ammonia within tubule cells or enters lumen and is buffered by phosphate ions
-H is not filtered, enters tubules via secretion only
how does the proximal tubule secrete H and reabsorb HCO3-?
-high amount of HCO3- filtered
-no apical HCO3 transporter so it occurs via indirect methods
what controls acid excretion?
the distal nephron
-initial portion of the collecting duct plays a significant role in the fine regulation of acid-base balance
what does the collecting duct do when in acidosis and alkalosis?
acidosis (Type A): intercalated cells function to increase H secretion and HCO3- reabsorption
-usually accompanied by increase K reabsorption (hyperkalemia)
alkalosis (Type B): intercalated cells function to increase H reabsorption and HCO3- secretion
-usually accompanied by increase K secretion (hypokalemia
how can acid-base disturbances be classified?
-three compensatory mechanisms (buffers, ventilation and renal excretion) take care of most variations in plasma pH
-can be classified by both the direction of the pH change (acidosis or alkalosis) and by the underlying cause (metabolic or respiratory)
-by the time an acid-base disturbance causes a change in plasma pH, the body’s buffers are ineffective leaving respiratory and renal compensation to alleviate the change in pH
what are the categories of acid/base disturbances?
-respiratory acidosis
-respiratory alkalosis
-metabolic acidosis
-metabolic alkalosis
respiratory induced changes in pH must be resolved via _____________
renal mechanisms
what is respiratory acidosis?
-occurs when alveolar hypoventilation results in CO2 retention and elevated plasma CO2
-because of respiratory origin, compensation must occur via renal mechanisms (excrete H, reabsorb HCO3-)
what is respiratory alkalosis?
-much less common, occurs as a result of hyperventilation in the absence of increased metabolic CO2 production
-compensation occurs via renal HCO3- excretion and H reabsorption
what is metabolic acidosis?
-occurs when dietary and/or metabolic input of H exceeds H excretion
-lactic acidosis as a result of anaerobic metabolism
-ketoacidosis from excessive breakdown of fats and amino acids
-can also occur from excessive HCO3 loss (diarrhea)
what is metabolic alkalosis?
-two common causes: excessive vomiting of acidic stomach contents or excessive ingestion of bicarbonate-containing antacids
-usually rapidly resolved by decrease in ventilation, but effectiveness is limited because it can cause hypoxia
-renal response: HCO3- excreted, H reabsorbed
