Acid-Base Balance

Question 1

What is an acid?

Answer 1

A molecule capable of releasing a hydrogen ion

Question 2

What are sources of acid?

Answer 2

Carbonic acid - altered by breathing
Non-carbonic - buffered in body and excreted by kidneys
Metabolism
In complete fat and carbohydrate metabolism
Mixed diet of meat and veg

Question 3

What is a base?

Answer 3

Molecule capable of combining a hydrogen ion

Question 4

Why maintain acid-base balance?

Answer 4

Maintenance is essential for normal metabolic reactions - affect enzymes and chemical reactions

Question 5

What pH does the body keep blood close to?

Answer 5

7.4
ECF - 7.35-7.45
ICF - 7.0 - 7.2

Question 6

What are the 3 mechanisms controlling blood pH?

Answer 6

Buffers
Respiratory
Renal

Question 7

What are pH buffer systems?

Answer 7

Combinations of a weak acid and a weak base that exist in balance under normal pH conditions

Question 8

How do pH buffer systems maintain acid-base balance?

Answer 8

Chemically minimize changes in pH by adjusting proportion of acid and base
1st to act

Question 9

What are the 2 most important pH buffers?

Answer 9

Bicarbonate/carbonic acid
Haemoglobin

Question 10

How does bicarbonate maintain the acid-base balance?

Answer 10

Acidic: HCO3- is reduced to neutralize pH
Alkaline: H+ is consumed to neutralize pH = more HCO3- produced from H2CO3 dissociation

Question 11

What is the HCO3-/CO2 buffer system most important for?

Answer 11

Blood and ECF

Question 12

What is most carbon dioxide converted to?

Answer 12

Carbonic acid -> dissociates into H+ and a bicarbonate ion

Question 13

What does the carbonic acid-bicarbonate buffer system prevent?

Answer 13

Changes in pH caused by organic acids and fixed acids in ECF

Question 14

What 3 things is the carbonic acid-bicarbonate buffer limited by?

Answer 14

Availability of bicarbonate ions
Functions only when respiratory system is working normally
Cannot protect pH against elevated or depressed levels of CO2

Question 15

What is haemoglobin important in?

Answer 15

In the role of carbonic acid buffering
35% of H+ buffering

Question 16

What is the MoA of the Hemoglobin buffer system?

Answer 16

CO2 diffuses across RBC membrane
Bicarbonate ions diffuse into plasma in exchange for chloride ions

Question 17

What compartment does the hemoglobin buffer system maintain?

Answer 17

Intracellular buffer system with a direct effect on ECF pH
Prevents pH changes when plasma PCO2 is rising or falling

Question 18

What are 2 other buffers?

Answer 18

Plasma proteins (10%)
Phosphate (5%)

Question 19

What are 4 characteristics of the respiratory acid-base control mechanisms?

Answer 19

Eliminate or retain CO2
Change in pH are rapid
Occurs within in minutes
PCO2 proportional to VCO2/VA

Question 20

What happens to the alveolar minute ventilation?

Answer 20

Altered to remove or retain CO2 from the lungs

Question 21

What part of the brain reacts to low pH?

Answer 21

Medullary respiratory centre

Question 22

What does the brain do to breathing when pH falls?

Answer 22

Increases speed and depth of breathing - more CO2 excreted

Question 23

What happens to breathing when pH increases?

Answer 23

Rate and depth of ventilation declines - less CO2 excreted

Question 24

What are 3 characteristics of the renal acid-base control?

Answer 24

Movement of bicarbonate
Retention/excretion of acids
Generating additional buffers

Question 25

What is the MoA of kidneys in acid-base balance?

Answer 25

Directly secrete H+ into urine - directly regulate body pH
preservation of body’s bicarbonate stores

Question 26

What is the preservation of body’s bicarbonate stores accomplished by?

Answer 26

Reabsorption of 99.9% of filtered bicarbonate
Regeneration of titrated bicarbonate by excretion

Question 27

What does H+ ions in the nephron lumen react with?

Answer 27

Bicarbonate ions, phosphate ions and ammonia