Term
| What is the minimum pH the kidneys will function at? |
|
Definition
| pH 4.5, which is the lowest pH of urine. This is why kidneys do not excrete free H+, must combine with a buffer |
|
|
Term
| What is the difference between volatile and non-volatile acids? |
|
Definition
- Volatile acids - CO2 - 15,000 mEq/day
- Non-volatile acids - ingested and produced by the body - 80 mEq/day |
|
|
Term
| What buffer systems are used to neutralize non-volatile acids? |
|
Definition
- Bicarbonate system - works fastest, depleted very rapidly
- Phosphate - depleted rapidly, replenishes bicarbonate
- Ammonia - Long term, replenishes bicarbonate |
|
|
Term
| What is the formula for the bicarbonate buffer system? |
|
Definition
CO2 + H2O --> H2CO3 (weak acid) --> H+ + HCO3- (weak base)
Acidic hydrogens bind to HCO3 to form acidic form of bicarbonate, increase CO2 levels
CO2 levels remain relatively constant due to respiration |
|
|
Term
| How does the addition of an acid or a base to the bicarbonate buffer system alter the bicarbonate equation? |
|
Definition
Acid - increased hydrogens bind to HCO3- (basic bicarbonate) --> H2CO3 (weak acid), depleting bicarbonate levels and increasing CO2, which is expired by the lungs.
- Base - Hydroxy groups bind to hydrogen ions and bicarbonate, H2CO3 (weak acid) dissociates into it's basic form to replenish hydrogen and bicarbonate. CO2 decreases, as does expiration |
|
|
Term
| How is bicarbonate regulated? |
|
Definition
By the kidneys.
- Too much bicarbonate formed by addition of a base - excreted by the kidneys
- Too little bicarbonate due to neutralizing an acid - kidney makes NEW bicarbonate |
|
|
Term
| How is the buffering power of a buffer determined? |
|
Definition
A strong buffer has a pKa close to the pH of the system it is buffering, and one that is in high concentrations
pH of blood is 7.4, pKa of bicarbonate is 6.1. Bicarbonate is not a good buffer |
|
|
Term
| What is the formula for pH and pKa? |
|
Definition
pH = pKa + log base/acid
The basic form will be protonated and have less hydrogens to be able to neutralize acids
The acidic form of a buffer will have more hydrogens, to be able to neutralize hydroxy groups |
|
|
Term
| How does the phosphate buffer system act in the plasma? |
|
Definition
A poor buffer - pKa 6.8<7.4 and lower concentrations than bicarbonate. Better in the kidneys due to higher concentrations and pKa closer to pH
HPO4 + H --> H2PO4(weak acid) |
|
|
Term
| Which buffer systems buffer the pH of the urine? |
|
Definition
| phosphate and then ammonia |
|
|
Term
| How is pH controlled by the lungs? |
|
Definition
| Volatile acid/CO2 is blown off by the lungs when in excess. When H+ is in excess and neutralized by bicarbonate, this produces CO2. A decrease in CO2 by expiration will slightly increase pH (more basic). The respiratory center in the brain controls the lungs, and is stimulated by CO2 levels and H+ levels |
|
|
Term
| What is the buffering power of the respiratory system? |
|
Definition
| 1 or 2x as great as any other chemical buffer in our system, acts rapidly and keeps H+ concentrations in check until Kidney kicks in. |
|
|
Term
| How do the kidneys control acidic/basic urine? |
|
Definition
- If there is an excess of base/pH is basic, filtered bicarb is excreted. H+ secreted less to bring pH down. So, if more bicarb is filtered than H+ is secreted --> pH goes down/less basic
- If less bicarbonate is filtered/excreted and more H+ is excreted --> less acidic/higher pH |
|
|
Term
| How is bicarbonate reabsorbed in the kidneys? |
|
Definition
Bicarbonate MUST be reabsorbed --> 24mEq in the blood is normal * 180 L/day.
Bicarbonate that is filtered assists in the formation of NEW bicarbonate by binding to an EQUAL amount of H+
In the PT, TAL, and DCT --> Na is reabsorbed in the lumen exchanging for H+, H+ binds to FILTERED bicarbonate. CO2 produced is reabsorbed, and carbonic anhydrase makes NEW bicarbonate, which is reabsorbed with sodium |
|
|
Term
| What is the fundamental rule for understanding bicarbonate reabsorption in the kidney? |
|
Definition
| For every H+ secreted, a bicarbonate is reabsorbed. There is no net gain in bicarbonate |
|
|
Term
| How is bicarbonate reabsorbed in Type A intercalated cells of the distal tubule? |
|
Definition
Chlorine is secreted with H+ ions, H+ binds to FILTERED bicarbonate. CO2 produced is reabsorbed, and carbonic anhydrase makes NEW bicarbonate, which is reabsorbed in exchange for more chlorine.
** chlorine is secreted while bicarbonate is reabsorbed. H+ ions exchange for potassium |
|
|
Term
| What is the function of Type B intercalated cells in the CD? |
|
Definition
| In the case of metabolic alkalosis, secretion of excess bicarbonate and H+ is reabsorbed |
|
|
Term
| How are secreted H+ ions buffered in the kidney? |
|
Definition
- Phosphate - H2PO4 excreted (acid bound to H+), HPO4 reabsorbed (lipid soluble base). When bicarb runs out, phosphate kicks in, binds to H+, and a NEW bicarb is reabsorbed. Titratable acid
- Ammonia - system after phosphate for buffering acids in the kidneys |
|
|
Term
| What are the 2 places the ammonia buffering system kicks in? |
|
Definition
After phosphate, ammonia buffer kicks in
- PT - Glutamine uses 2 H+ to make 2 ammonium (acid) AND 2 bicarb ions. Ammonium is excreted and bicarb is reabsorbed.
- Collecting duct - Ammonia (NH3, basic form) buffers excreted H+, bicarbonate is reabsorbed. |
|
|
Term
| How does the kidney handle the addition of bases? |
|
Definition
- excess base is excreted in the urine
- excess basic bicarbonate is secreted by type B intercalated cells and excreted |
|
|
Term
| How does the kidney handle the addition of acids? |
|
Definition
- CO2 eliminated by respiratory system
- buffer of nonvolatile acids by bicarb
- Filtered bicarbonate produces new bicarbonate
- Secreted H+ combines with phosphate and ammonia, generating more new bicarbonate |
|
|
Term
| What stimuli change the rate of secretion of H+ by tubular epithelium? |
|
Definition
- Levels of CO2
- Levels of H+
- Acidosis - increased levels of CO2 or H+
- Alkalosis - decreased levels of CO2 or H+ |
|
|
Term
| What ratio determines acidosis or alkalosis and the type? |
|
Definition
HCO3 / CO2
Decrease in ratio by increasing CO2 or decreasing bicarbonate causes acidosis |
|
|
Term
| What are normal amounts for pH, H+, CO2, and bicarbonate? |
|
Definition
pH - 7.4
H+ - 40 mEq/L
CO2 - 40 mm HG
HCO3 - 24mEq/L |
|
|
Term
| How do you determine the type of disorder |
|
Definition
1) pH - Acidosis or alkalosis?
2) CO2 levels - respiratory or compensatory
3) Bicarbonate levels |
|
|
Term
| What is respiratory acidosis? |
|
Definition
| An excess of CO2 caused by reduced expiration, CO2 > 40 --> decreased pH. Bicarbonate will slightly increase to compensate. |
|
|
Term
| What is respiratory alkalosis? |
|
Definition
| A decrease in CO2 below normal caused by hyperventilation --> increase in pH, compensatory decrease in bicarbonate. |
|
|
Term
| What is metabolic acidosis? |
|
Definition
Most common dysfunction of acid base
Low pH caused by loss of bicarbonate, buildup of acid. Measured by anion gap.
An increase in H+, may be a problem with AMMONIUM buffer. Increased CO2 ventilation to decrease CO2 levels as compensation |
|
|
Term
| What is metabolic alkalosis? |
|
Definition
| A basic condition caused by excess bicarbonate or loss of H+. Diuretics may cause/Aldosterone. Respiration decreases to retain CO2 |
|
|
Term
|
Definition
Evaluation tool for metabolic acidosis
Cations - positive ions
Anions - negative ions, bicarbonate
AG = Positive ions - Negative ions. A decrease in bicarbonate increases the gap
Normal AG = 13. Reduced bicarb increases. If Chlorine increases, AG may be normal. |
|
|
