Renal 7

Question 1

State the normal pH of the blood. How does the pH change in a patient with acidosis or alkalosis?

Answer 1

• Normal pH of blood: 7.4
  
  • pH decreases with acidosis (an increase in H+ concentration of ECF)
  • pH increases with alkalosis (a decrease in H+ concentration of ECF)

Question 2

Describe how the ventilation rate (and thus PCO2) changes with changes in pH.

Answer 2

• As ventilation increases, PCO2 is released and there is less acid in the ECF. Hyperventilaiton can lead to respiratory alkalosis and hypoventilation can lead to respiratory acidosis
• The medulla oblongota can compensate: if pH low  increase ventilation and vice-versa
• Respiratory compensation cannot eliminate metabolic acidosis/alkalosis but can help

Question 3

Define the following terms:

• Respiratory acidosis
• Respiratory alkalosis
• Metabolic acidosis
• Metabolic alkalosis
• Acidemia
• Alkalemia

Answer 3

• Respiratory acidosis: disease from decreased ventilation that results in lower pH
• Respiratory alkalosis: disease from increased ventilation that results in increased pH
• Metabolic acidosis: bicarbonate concentration in body fluids from accumulation of acids or abnormal loss of bases from body
• Metabolic alkalosis: resulting from hydroge-ion loss or excessive intake of alkaline substances
• Acidemia: pH lower than 7.35
• Alkalemia: pH higher than 7.45

Question 4

Describe how the kidneys compensate for metabolic or respiratory acidosis or alkalosis.

Answer 4

• If alkalosis, kidney will excrete alkaline urine containing a high concentraion of bicarbonate (HCO3-)
  
  • If acidosis, kindey will excrete an acidic urine by reabsorbing the bicarbonate that was filtered

Question 5

Describe the effect of a chemical buffer when a strong acid or strong base is added to a body fluid.

Answer 5

• Buffers help prevent large changes in pH during the lag time between a transient accumulation of acid or base and the compensating response.
• When concentration of H+ increases (from strong acid)  an increasing amount of H+ will bind to buffer as long as there is buffer available (Buffer + H+  H-Buffer)
  
  • If a strong acid like HCl was added, it would completely dissociate. If there was no buffer (NaHCO3), the H+ would decrease pH substantially
• When concentraion of H+ decreases (from strong base)  H+ is released from buffer thus increasing H+ concentration and bringing pH back to original value
  
  • If stong base was added (NaOH), it would completely dissociate into –OH…to avoid a high pH, we have carbonic acid which will provide a H+ to offset the –OH.

Question 6

Briefly describe the important buffer systems of the body. Where is each most useful? (ECF, ICF, in the kidney tubules)

Answer 6

• Bicarbonate buffer system: Useful in the ECF
  - Carbonic acid is the weak acid (Buffer-H) and bicarbonate is the conjugate base
  - CO2 + H20  H2CO3 (Carbonic Acid)  HCO3- (Bicarbonate) + H+
  - Reaction aboved catalyzed by Carbonic Acid
  
  • Phosphate buffer system: Useful in ICF and urine
• In kidney tubulues, phosphate can take up a lot of H+ because phosphates become concentrated in the tubulesand pH there is lower than thatof the ECF
• Ex) HCl + Na2HPO4-  NaH2PO4 + NaCl
  NaOH + NaH2PO4  Na2HPO4 + H20
• Protein Buffer system: Important in intracellular buffers. Hemoglobin and plasma proteins in blood also. Not part of the normal compensatory response to acid-base changes.
• Ammonia Buffer system: Body’s major response to an acid load. In proximal tubule cell of kidney, glutamine is metabolized to bicarbonate which is added to blood and ammonuim ion which is added to tubule. Essentially the Glutamine is broken down into base and acid (base brought to blood and acid excreted)

Question 7

Describe the process of bicarbonate reabsorption. What is secreted in this process? Is it excreted? How can this process compensate for acidosis? Alkalosis?

Answer 7

• If acidosis, proximal tubule will reabsorb 90% and collecting duct will reabsorb 10% of bicarbonate.
  
  • If alkalosis the kidney would excrete bicarbonate.
• H+ from secretion joins filtered bicarbonate in the tubule  carbonic acid  CO2 and H20. The CO2 diffuses into the renal tubule cell where it combines with H20 to make carbonic acid again  H+ and HCO3-. The HCO3- then moves down its concentration gradient across the basolateral membrane via carrier mediated diffusion.
• So for every H+ secreted into the tubular lumen, a bicarbonate ion enters the blood. The H+ that was secreted is leaves the body as H20.

Question 8

Describe phosphate buffering in respiratory acidosis.

Answer 8

• Often used in severe acidosis because the bicarbonate buffer system is saturated.
• Secreted H+ will combine with filtered NaHPO4-  NaH2PO4 that will be excreted. More CO2 will enter tubular cell thru basolateral membrane  combine with H20  carbonic acid  bicarbonate and H+. The Bicarbonate is newly added to the blood and the H+ is secreted out to be removed with the phosphate.

Question 9

Describe glutamine-NH4+ buffering in severe respiratory acidosis.

Answer 9

• Utilized when all of the bicarbonate and phosphate buffers are used up.
• In the proximal tubule cell, glutamine is metabolized to bicarbonate and ammonium ion. Bicarbonate is given to the blood and ammonium ion is excreted in the urine.

Question 10

10. Sketch a Davenport diagram and label the x and y axis. Put in the 40 PaCO2 line and show where it intercepts the line for normal pH. 11. If given a Davenport diagram label the sections where a patient would be in metabolic acidosis, metabolic alkalosis, respiratory acidosis and respiratory alkalosis.12. If given a Davenport diagram be able to match points on the diagram with clinical scenarios (e.g. patient in uncompensated and compensated respiratory acidosis or alkalosis , metabolic acidosis or alkalosis)

Answer 10

davenport diagram gives a visual representation of acid base distrubances