Acid- Base Balance

Question 1

Normal H+ concentration

Answer 1

40 nEq/ L

NOTE: In extreme conditions the H+ concentration can vary between 10 and 160 nEq/L, without causing death

Question 2

What are the normal arterial and venous pH, respectively?

Answer 2

Arterial= 7.4

Venous= 7.35

NOTE: pH is lower, i.e. acidity is higher in venous blood because of the presence of dissolved carbon dioxide, which forms carbonic acid.

Question 3

A human being can survive for a few hours if the pH is ________ or _______ survival below or above these limits is impossible

Answer 3

6.8; 8.0

Question 4

What is Gastric pH so low (0.8)?

Answer 4

Because of the parietal cells releasing HCl

Question 5

How does the body primarily regulate the H+ concentration?

Answer 5

• Chemical Acid- Base buffer systems of body fluids
• Respiratory system
• Kidneys

NOTE: Buffer systems act quickly but the kidneys respond slowly.

Question 6

The respiratory systems regulates removal of _______.

Answer 6

CO2 (and therefore H2CO3)

Question 7

A_______ is any substance that can reversibly react with G+.

Answer 7

Buffer

Question 8

Where is carbonic anhydrase located?

Answer 8

• Lining of alveoli
• Epithelial cells of kidneys

NOTE: Carbonic anhydrase is expressed on both apical and basolateral membranes.

Question 9

If a strong acid is added to bicarbonate, it is converted to a ___________. However, if a strong base is added to bicarbinate, it is converted to a _________.

Answer 9

Weak acid; Weak base

Question 10

Increased HCO3- is compensated by increased excretion of HCO3- by the _____________

Answer 10

kidney tubules

Question 11

Concentration of un-dissociated H2CO3 cannot be measured. Why?

Answer 11

Because it dissociates immediately into CO2 and H20 or to H+ and HCO3-

Question 12

Bicarbonate Buffer System Titration Curve

Answer 12

Question 13

When is the pH the same as the pK?

Answer 13

When each component (HCO3- and CO2) consitutes 50% of the total buffer system

Question 14

When is the buffer system most effective?

Answer 14

In the central part of the curve

NOTE: The buffer system is effective for ± 1.0, beyond which the buffering capacity rapidly decrease

Question 15

Bicarbonate buffer system is the best buffer in the body. Why?

Answer 15

Because the [HCO3-] and [CO2] are constantly regulated by the kidneys and lungs respectively

Question 16

Henderson-Hasselbalch equation

Answer 16

pH=6.1+log⁡[HCO3-/(0.03∗PCO2)]

Question 17

Impaired regulation by kidneys result in ________ acidosis and alkalosis.

Answer 17

metabolic

Question 18

Impaired regulation by lungs result in ________ acidosis and alkalosis.

Answer 18

respiratory

Question 19

What are the main elements of the phosphate buffer system?

Answer 19

H2PO4− and HPO4

NOTE: The phosphate buffer system is important in buffering intracellular pH.

Question 20

The phosphate buffer system is especially important in _________

Answer 20

Tubular fluids

NOTE: The pH in tubular fluid is lower than ECF

Question 21

The diffusion of elements of the ____________ buffer system causes the pH in intracellular fluid to change when there are changes in extracellular pH.

Answer 21

Bicarbonate

*This means that preventing change in pH inside the cells may take hours

Question 22

________% of chemical buffering in cells occurs through proteins.

Answer 22

60-70

Question 23

The pK of proteins is closer to _________ (intracellular/extracelular) pH.

Answer 23

Intracellular

*This makes proteins ideal for intracellular buffering, unlike the bicarbonate buffering system

Question 24

Isohydric principle

Answer 24

The phenomenon whereby multiple acid/base pairs in solution will be in equilibrium with one another, tied together by their common reagent: the hydrogen ion and hence, the pH of solution.

NOTE: Change in [H+] in ECF would cause change in the balance of all buffer systems at the same time

Question 25

What is the mechanism by which CO2 is removed from the body?

Answer 25

1. CO2 is formed metabolically in the body 2. It diffuses into the interstitial fluids 3. It is transported to the lungs 4. Removed by pulmonary ventilation

Question 26

About ______ mol/L of dissolved CO2 normally are in the extracellular fluid, corresponding to a PCO2 of 40 mmHg.

Answer 26

1.2

Question 27

An _____ (increase/decrease) in metabolic formation of CO2 increases the PCO2 of the extracellular fluid.

Answer 27

Increase \*Conversely, a decreased metabolic rate lowers the PCO2

Question 28

Decreasing the pH from 7.4 to 7.0, icreases alveolar ventilation rate by about _________ times the normal.

Answer 28

4-5 \*The opposite is true for increased pH

Question 29

Reduction in pH produces a marked increase in ventilation. Increased pH is not effective. Why?

Answer 29

The reason for this phenomenon is that as the alveolar ventilation rate decreases, as a result of an increase in pH (decreased H+ concentration), the amount of oxygen added to the blood decreases and the partial pressure of oxygen (Po2) in the blood also decreases, which stimulates the ventilation rate.

Question 30

**True or False.** Respiratory control is slow and it takes hours to achieve the 50-75% correction.

Answer 30

False. \*The respiratory control is _fast_ and can achieve 50-75% correction in _3-12 mins._

Question 31

In cases of emphysema, there is a buildup of CO2 leading to respiratory __________ (acidosis/alkalosis).

Answer 31

Acidosis **NOTE:** In cases of emphysema, the ability to respond to metabolic acidosis is decreased due to blunted ventilation. This leaves the kidneys as the sole remaining mechanism to regulate acid-base balance.

Question 32

What is the main role of the kidneys in acid-base balance in cases of acidosis and alkalosis, respectively?

Answer 32

**_Acidosis_** * Reabsorb bicarbonate * Excrete H+ **_Alkalosis_** * Excrete more bicarbonate * Decrease H+ excretion

Question 33

What are the three mechanism of control by kidneys?

Answer 33

* Secretion of H+ * Reabsorption of filtered HCO3- * Production of new HCO3- **NOTE:** For each HCO3- reabsorbed, there must be a H+ secreted.

Question 34

Kidneys eliminate _________ acids.

Answer 34

Non-volatile Such as: H2SO4, H3PO4

Question 35

What are possible causes of metabolic acidosis? By what mechanism?

Answer 35

* **Aspiring poisining** * increases H+ intake * **Diabetes mellitus** * increases H+ production * **Diarrhea** * HCO3- loss * **Renal tubular acidosis** * Decreased H+ secretion * Decreased HCO3- reabsorbsion * **Carbonic anhydrase inhibitors** * Decreases H+ secretion

Question 36

Causes of respiratory acidosis

Answer 36

* Brain damage * Pneumonia * Emphysema * Other lung disorders

Question 37

Causes of metabolic alkalosis

Answer 37

* Increased base intake * Vomiting gastric acid * Mineralocorticoid excess * Overuse of diuretics (_except_ carboic anhydrase inhibitors)

Question 38

By what mechanism can an increase in aldosterone cause metabolic alkalosis?

Answer 38

Increase in aldosterone causes: * increase in tubular K+ secretion * Increase in H+ secretion * Increase in HCO3 reabsorbtion * Increase in new HCO3 production

Question 39

By what mechanism can an overuse of diuretics cause metabolic alkalosis?

Answer 39

* Decrease extracellular volume * Increases angiotensin II, which increases aldosterone * K+ depletion

Question 40

What are causes of respiratory acidiosis?

Answer 40

* High altitude * Psychic (fear, pain,etc.)

Question 41

Anion gap

Answer 41

Na+ - Cl^- - HCO3^-

Question 42

Normal anion gap

Answer 42

8-16 mEq/L

Question 43

Most of bicarbonate is reabsorbed by ________ tubules.

Answer 43

Proximal

Question 44

ABG provides information regarding what three condition about a patient?

Answer 44

* Ventilation * Oygenation * Acid-base status

Question 45

In what cases of metabolic acidosis is there a change in anion gap?

Answer 45

Diabetes mellitus Lactic acidosis Aspirin poisoning Methanol Poisining Starvation

Question 46

How do you determine if the condition is acute or chronic?

Answer 46

**FOR PRIMARY RESPIRATORY CONDITION** * Calculate the change in pH that would occur if the change in PCO2 were **acute** 0.08 pH units/10 mmHg PCO2 or for **chronic**, 0.03/10 mmHg PCO2. **FOR PRIMARY METABOLIC CONDITION** * The last two digits of the PaCO2 should approximate the pH value (e.g. 7.25 should relate to a PCO2 of 25 mmHg).

Question 47

AaDO2

Answer 47

Alveolar- Arterial Pressure Difference

Question 48

Normal AaDO2

Answer 48

\<15 mmHg **NOTE:** Value for AaDO2 increases 3 mmHg per decade of life

Question 49

Normal Anion Gap Acidiosis

Answer 49

**U**reterostomy **S**mall Bowel Fistula **E**xtra Chloride **D**iarrhea **C**arbonic anhydrase inhibitor (acetazolamide) **A**drenal Insufficiency **R**enal Tubular acidosis **P**ancreatic fistula

Question 50

High anion gap acidosis

Answer 50

**M**enthol **U**remia (Chronic renal failure) **D**iabetic ketoacidosis **P**araldehyde **I**ron, isoniazid **L**actic Acid **E**thanol, ethylene glycol **S**alicylates (Aspirin poisoning)