Stoelting Study 16 Acid Base

Front 1

1. What is the importance of maintaining a physiologic acid-base status?

Back 1

1. A physiologic acid-base status ensures the optimal function of enzymes, the proper distribution of electrolytes, optimal myocardial contractility, and an optimal saturation of hemoglobin with Olygen. The acid-base balance is representative of a balance between the production of hydrogen ions and the excretion of hydrogen ions. There are two types of acids produced by the body. One is carbonic acid, which is produced by the hydration of carbon dioxide and is eliminated by alveolar ventilation. The other acids are metabolic acids, which I are primarily eliminated by the kidneys. Deviations from normal levels of each of these ions results in acid-base abnormalities. In general, a deviation of carbonic acids from normal results from respiratory causes and a deviation of metabolic acids from nonna! results from metabolic causes.

Front 2

I 2. What is the normal plasma H+ concentration? What is the normal plasma HC03 concentration?

Back 2

2. The normal plasma H + concentration is 36 to 44 nmol/L. The normal plasma HC03 - concentration is about 24 mEqlL

Front 3

3. What is the normal arterial pH of blood?

Back 3

3. The normal arterial pH of blood is between 7.36 and 7.44.

Front 4

4. How is normal arterial pH maintained?

Back 4

4. Normal arterial pH is maintained through the buffer systems, ventilatory responses, and renal responses. The ventilatory respome involves alterations in alveolar ventilation and therefore the blood and tissue carbon dioxide concentI1tions. The kidneys allow for near-complete restoration of the arterial pH through the reabsorption of bicarbonate ions and the secretion of hydrogen ions by the renal tubule

Front 5

5. What are some of the buffering systems in the blood? Which buffering system has the greatest contribution to the total buffering capacity of blood?

Back 5

5. When there is a disturbance in the concentration of acid in the blood, buffering systems in the blood help to decrease the degree of disturbance in the pH. A buffer is defined as a solution !hat maintains its hydrogen ion concentration when a strong acid or base is added to the solution. The buffering systems in the blood include bicarbonate, hemoglobin, phosphate, and plasma proteins. The bicarbonate buffering system I responsible for about 50% of the total buffering capacity of the body. Hemoglobin is responsible for about 35% of the total buffering capacity, and the remainder is by phosphate and the plasma proteins.

Front 6

6. How does the bicarbonate buffering system work? What enzyme facilitates this reaction?

Back 6

6. The bicarbonate buffering sy.tem works by hydrating carbon dioxide in the plasma and in the erythrocytes. In erythrocytes the enzyme carbonic anhydrase facilitates this reaction. The hydration of carbon dioxide results in HZC03. which spon1aneously dissociates to form H+ and HeOl -. The W that is formed is buffered by the hemoglobin, whereas the He03 - that is formed enters the plasma to function as a buffer. With the entry of HC03 - in the plasma to act as a buffer, chloride ions enter the erythrocytes to maintain electrical neutrality. This is termed a chloride shift,

Front 7

7. How does hemoglobin act as a buffer?

Back 7

7. Hemoglobin exists as a weak acid and a salt in erythrocytes, allowing it to serve as a buffer. It acts as a buffer through its reduced form binding with the hydrogen ion. Carbon dioxide can also be transported by hemoglobin, forming carbaminohemoglobin and further contributing to its buffering

Front 8

8. How quickly does the buffering system of the blood respond to changes in arterial pH?

Back 8

8. The buffering system of the blood responds to changes in arterial pH almost instantly.

Front 9

9. How quickly does alveolar ventilation respond to changes in arterial pH?

Back 9

9. Compensatory changes in alveolar ventilation in response to changes in arterial pH occur within minutes.

Front 10

10. How quickly do the kidneys respond to changes in arterial pH?

Back 10

10. Compensatory changes by the kidneys in response to :hanges in arterial pH require 12 to 48 hours to complete.

Front 11

58. What are some events that shift the oxyhemoglobin dissociation curve to the right? What does a rightward shift of the curve reflect physiologically?

Back 11

58. The oxyhemoglobin dissociation curve shifts to the right in response to acidosis, · hypercapnia, hyperthermia, and an increased 2,3-diphosphoglycerate value, as can occur with chronic arterial hypoxemia or anemia, and during exercise. A rightward shift of the curve ~eflects a decreased affinity of hemoglobin for oxygen at a given partial pressure, such that the unloading of oxygen at the tissues is facilitated

Front 12

59. What are some events that shift the hemoglobin dissocition curve to the left? What does a leftward shift of the curve reflect physiologically?

Back 12

59. The oxyhemoglobin dissociation curve shifts to the left in response to alkalosis, hypocapnia, hypothermia, a decreased 2,3-diphosphoglycerate value, as can 1 occur with the transfusion of old bank blood or in diabetic ketoacidosis, and I carbon monoxide poisoning. A leftviard shift of the curve reflects an increased affinity of hemoglobin for oxygen at a given partial pressure, such that a lower partial pressure of oxygen is required to saturate the hemoglobin. This results ! in the necessity of a lower oxygen concentration in the tissues for the oxygen to llnload from hemoglobin