Question

Case Study Section 1 – pH

Based on “The Case of the Mortified Mom: Acids, pH and Buffers” by Terry Platt (National Center for Case Study Teaching in Science)

The Patient:

Paramedics were called to the home of the Mathews family because their 3-year old daughter, Molly, had gotten into the medicine cabinet and consumed a large number of aspirin tablets. When the paramedics arrived Molly had vomited several times, with bits of undissolved tablets visible, but seemed sleepy, almost lethargic. She was rushed to the nearest Emergency Room. When she reached the hospital she was unarousable and was breathing rapidly and deeply. She was examined and lab samples were obtained.

Above is the structure of aspirin, or acetylsalicylic acid, which is a weak acid with a pKa of 3.5. The active, and toxic at high doses, form is the protonated form.

Blood pH can be impacted by the carbonic acid/bicarbonate system, which utilizes the following formula:

                  CO₂ + H₂O « H₂CO₃ « HCO₃^- + H⁺

Question 1:

Under normal conditions the carbonic acid/bicarbonate system functions to:

A.              Maintain blood pH near physiological pH.

B.              Remove excessive H⁺ generated during metabolism.

C.              Transport CO₂ from the tissues to the lungs for exhalation.

D.             All of the above.

Normal blood bicarbonate levels should be 22 – 26 mM.

Question 2:

Which of the following conditions would you expect to be the situation in Molly’s case?

A.              Blood bicarbonate above normal.

B.              Blood bicarbonate within the normal range.

C.              Blood bicarbonate below normal.

The physician intubated Molly’s trachea and carried out hyperventilation, which he explained to the family was “to avoid hypoventilation and a worsening of her metabolic acidosis.” They also administered activated charcoal through a nasogastric tube and IV bicarbonate.

Question 3:

What is the purpose of the activated charcoal?

A.              Absorb the residual aspirin to prevent it from entering her bloodstream.

B.              Increase the rate of absorption of the aspirin to shorten the duration of the overdose.

C.              Increase the pH of the stomach.

D.             Settle her stomach after the vomiting.

Question 4:

What effect would the IV bicarbonate have on the carbonic acid/bicarbonate reaction above?

A.              Shift it to the left.

B.              Shift it to the right.

C.              Settle it closer to equilibrium.

D.             No effect.

A few hours later Molly was breathing more regularly and her blood pH was returning to normal.

Question 5:

What would be the consequence(s) of lower than normal blood pH?

A.              Cause proteins to denature

B.              Decrease in enzyme activities

C.              Limit hemoglobin’s ability to transport oxygen

D.             All of the above

E.              None of the above

Question 6:

Bicarbonate was an effective buffer in Molly’s situation, what else could/does serve as buffers in the body?

A.              Free amino acids

B.              Phosphate compounds

C.              Proteins

D.             Urea

E.              All of the above

F.              None of the above

Answer 1

1).Under normal condition bicarbonate system functions all the above actions given:They maintain the PH,remove excessive H+ ions and remove carbon dioxide by exhalation.

Answer is 'D'

2). Low level of bicarbonate in the blood may cause a condition called metabolic acidosis, or too much acid in the body. A wide range of conditions, including diarrhea, kidney disease, and liver failure, can cause metabolic acidosis.

Hence answer is 'C'

3). Answer is 'A', activated charcoal absorb toxic materials from gut preventing it to enter in to the body

4). Decreasing the bicarbonate concentration will shift the equation to the left and increase H+ ion concentration and generate acidosis. This process is called metabolic acidosis.

So the answer is 'A'

5). The glycolytic enzyme phosphofructokinase is pH dependent as its activity decreases with decreasing pH.

Decreasing the pH by adding an acid converts the –COO- ion to a neutral -COOH group.In each case the ionic attraction disappears, and the protein shape unfolds.

As blood reaches the lungs, the carbon dioxide concentration decreases, causing an increase in PH. This increase in pH increases hemoglobin's affinity for oxygen through the

So the a answer is all the above ie 'D'

6). All the given components can be serve as a buffer. So answer is 'E'