March 26 - Acid Base Flashcards
What is pH?
-log[H+]
What is considered basic?
pH>7.6
What is considered acidic?
pH<7.2
What is the normal blood pH?
7.4 (slightly basic)
What are volatile acids?
Acids that are likely to change. Example: the production of bicarbonate and H ions, which can form carbon dioxide and water
What is a major source of volatile acids?
Major source is oxidative metabolism of carbohydrates and triglycerides. Metabolism produces carbon dioxide, which converts to carbonic acid and back to carbon dioxide for excretion by the lungs
What are non volatile acids?
They are acids that don’t change (you can’t blow these of as carbon dioxide). So they need to excreted by the kidneys. Diets high in protein result in higher non volatile concentrations. They form non carbonic acids (i.e. not broken down into CO2 and excreted by the lungs). Forms sulfuric and hydrochloric acids. Phosphates normally in diet
How can losses in bodily fluid affect the pH of the body?
Vomiting results in the loss of H ions
Diarrhea results in the loss of bicarbonate
Urine results in the loss of bicarbonate
Describe the relationship between pH, carbon dioxide and bicarbonate
pH is directly proportionate to the concentration of bicarbonate the inversely proportionate to dissolved CO2. So a decrease in CO2 and/or an increase in bicarbonate will increase the pH and a decrease in bicarbonate and/or an increase in CO2 will decrease pH
Describe the body’s buffering system
There are buffers in the blood and tissue that are important for acute control of pH and to prevent large shifts in pH
What are the blood buffers?
There are plasma buffers (3/4 of plasma buffers are bicarbonate buffers, but there is also plasma proteins and phosphate buffers) and erythrocyte buffers (mostly bicarbonate but also hemoglobin)
What are the tissue buffers?
There are skeletal muscle buffers (the skeletal muscle stores a large percentage of the total body’s bicarbonate, to be used during strenuous activity) and bone buffers (large stores of carbonate; main source for neutralizing non carbonic acid. Long-term non carbonic acidosis associated with bone breakdown)
Describe respiratory regulation of pH
The respiratory system eliminates carbon dioxide from the blood and shifts the equilibrium away from carbonic acid (and vice versa). If the respiration rate increases, the amount of carbon dioxide decreases, thus pH increases. If respiration rate decreases, the amount of carbon dioxide increases, thus pH decreases
Describe the renal regulation of pH
The kidney serves to fine tune the overall acid base balance in the body. The body’s buffering system and respiratory regulation of pH are typically involved in acute changes, whereas renal regulation is more long term
What are the three renal mechanisms for responding to pH changes
- Bicarbonate reabsorption (reclaimation)
- Formation of new bicarbonate/ammonium:ammonia
- Excretion of hydrogen ions (ammonia/phosphate)
Describe how bicarbonate reabsorption is used to respond to pH changes
This occurs primarily in the proximal tubule (85%)
Some reabsorption in the collecting ducts (10%)
In the process, hydrogen ion is secreted, reabsorbed and secreted (no net hydrogen ion excretion). Also, bicarbonate in the filtrate is broken down and reformed in the cell for reabsorption.
This is important when bicarbonate is required (acidosis)
Describe how the formation of new bicarbonate is used to respond to pH changes
This occurs in the proximal tubule. Glutamine is converted into ammonium (NH4+) and bicarbonate.
Bicarbonate is reabsorbed. Ammonium is secreted into the tubule lumen, reabsorbed by the loop of Henle by a Na/K/Cl transporter. In the interstitium, ammonium is converted into ammonia (NH3) and H ion. Ammonia is “stored” for when it is required by the collecting tubule
Describe net acid excretion (NAE)
There are three parts to net acid excretion: urine ammonium excretion volume, urine titratable acid excretion volume and urine bicarbonate excretion volume. Urine ammonium excretion volume is the most important because ammonia allows the excretion of large amounts of H ions as ammonium. Urine titratable acid excretion allows the excretion of H ions as H2PO4- (useful but limited). NAE = (UNH4V + UTAV) - UHCO3V
Describe how hydrogen ion secretion is used to respond to pH changes
H ions are present in the distal nephron due to the filtration and secretion (but low). The concentration gradient from the plasma to the tubule lumen limits the amount that can be excreted (very little free H ions are excreted). By buffering the H ions in the tubule lumen, net hydrogen excretion is increased (favors H gradient into the tubule). Once the last of the bicarbonate has been used to buffer the H ions, the titratable buffers become important (phosphate and ammonia). Phosphate is limited in the amount but is an effective buffer at higher pHs. Ammonia (present in the interstitium due to Gln metabolism) is the major titratable acid (acts as a buffer). Aldosterone stimulates the H ion secretion
How does the kidney respond to acidosis?
- Increase H ion secretion and increase bicarbonate reabsorption to 100%
- Increase ammonia production and loss of ammonium
- Generate new bicarbonate from glutamine
How does the kidney respond to alkalosis?
- Decrease H ion secretion (less secreted)
2. Decrease bicarbonate reabsorption
How can you tell if a patient is acidotic or alkalotic?
Look at the pH
Low pH = acidotic
High pH = alkalotic
How can you tell if the patient’s acidosis is respiratory or metabolic?
In respiratory acidosis, bicarbonate and carbon dioxide will both be high (respiratory acidosis with compensatory increase in bicarbonate)
In metabolic acidosis, bicarbonate and carbon dioxide will both be low (metabolic acidosis with compensatory decrease in carbon dioxide)
How can you tell if the patient’s alkalosis is respiratory or metabolic?
In respiratory alkalosis, bicarbonate and carbon dioxide will both be low (respiratory alkalosis with compensatory decrease in bicarbonate)
In metabolic acidosis, bicarbonate and carbon dioxide will both be high (metabolic alkalosis with compensatory increase in bicarbonate dioxide)
