8 - Acid Base 1

Question 1

What is the definition of pH

Answer 1

pH = -log10 (H+) where H+ is mol/L
(H+) = 10-pH

Question 2

What is the normal ECF pH

Answer 2

7.4 (7.35-7.45)

Crucial for enzyme and organ function

Question 3

ph below 7.35

Answer 3

acidaemia

Question 4

ph above 7.45

Answer 4

alkalaemia

Question 5

Difference between alkalaemia/acidaemia and alkalosis/acidosis

Answer 5

alkalaemia/acidaemia is that STATE of the blood pH while alkalosis/acidosis are PATHOLOGICAL processes that CHANGE pH

Question 6

Acidosis

Answer 6

ph is usually an acidaemia i.e. less than 7.35 (but may not be if more than 1 acid-base disorder is present), 7.2 is severe acidosis and less than 6.9 is incompatible with life

Question 7

What is a buffer

Answer 7

A buffer minimises pH changes due to either the addition or removal of H+ ions temporarily (the H+ is NOT eliminated)

Question 8

When does the pK of a buffer = the pH

Answer 8

When the conc of A- and HA are equal as

pH = pK +log(A-/HA)

Question 9

What are some buffers that are present in the blood?

Answer 9

1. Bicarbonate: H+ + HCO3- > H20 + CO2

2. Proteins (albumin, HB): H+ + A- > HA

Question 10

How do proteins act as buffers?

Answer 10

H+ is added onto the COO- and/or the NH3

Question 11

With the bicarbonate buffer system how is pH determined>

Answer 11

Henderson Hasselbach equation

pH = 6.74 + log(HCO3-/pCO2)

Question 12

What is the respiratory control of pCO2

Answer 12

metabolism creates a lot of co2, and the ventilation rate controls the pCO2. Low pH stimulates ventilation to increase excretion of CO2

Question 13

Incr pco2 causes … decreased pco2 causes…

Answer 13

AcidOSIS and alkalosis

Question 14

How are blood gas measurements made and what do they measure

Answer 14

• venous or arterial blood collection
• pH, pCO2, pO2 measured directly via blood gas analyser
• can then calculate HCO3- and base excess

Question 15

What is normal HCO3- and pCO2?

Answer 15

HCO3- : 24

pCO2= 5.3

Question 16

What are the 2 urinary buffers

Answer 16

1. Phorphoric acid
2. Ammonium ions
   > allow H+ to be excreted

Question 17

example of a resp acidosis

Answer 17

Severe asthma attack where can’t excrete co2

Question 18

example of resp alkalosis

Answer 18

Panic attack/hyperventilation (also most asthma attacks)

Question 19

Example of metabolic acidosis

Answer 19

Increase in acid load that exceeds the kidney’s ability to excrete acid and so HCO3- tries to buffer it and is depleted.

Question 20

3 causes of metabolic acidosis

Answer 20

1. Increased acid producion
   - lactic acidosis (hypoxia, anaerobic metabolism, poor perfusion due to hypotension or ischaemia, CO/cyanide poisoning
   - diabetic ketoacidosis due to beta-hydroxybutyric acids and acetoacetic acids
2. Decreased acid secretion due to renal failure or renal tubular acidosis
3. Low HCO3-
   - vomiting, severe diarrhoea, ileostomy

Question 21

Why may you see a reduction in pCO2 despite ph being low and hco3- being low?

Answer 21

Degree of compensation for the metabolic acidosis

Question 22

Describe resp compensation seen in metabolic acidosis

Answer 22

The low pH stimulates ventilation which lowers pCO2 (acidotic breathing)

Question 23

Breathing symptoms can be a sign of what 2 things

Answer 23

Either the primary problem or compensation

Question 24

Role of kidney in the acid-base balance?

Answer 24

• can generate new HCO3-
• reabsorbs HCO3-
• gets rid of acid by attaching it to ammonia or phosphoric acid

Question 25

Why do kidneys excrete acid

Answer 25

To balance the non-volatile (non-CO2) acid that is generated through metabolism.

Question 26

Net Acid Secretion by the kidneys

Answer 26

= urinary ammonium + urinary titratable acid - urinary HCO3- (NONE in normal state) x volume

Question 27

What are the 3 main renal processes in acid-base balance

Answer 27

1. HCO3- reabs
2. generation of new HCO3-
3. H+ secretion in the DT and CD primary by NH4+ and H3PO4

Question 28

1. Bicarbonate reabsorption?

Answer 28

• Most (80%) is reabsorbed in the PT

- na+ follows to maintain osmol

Question 29

2. New HCO3- generation?

Answer 29

CO2 from the ECF enters the cell and is converted by carbonic anhydrase in the cytoplasm and brush border of PT cells > H2CO3 > HCO3 + H+
The HCO3- is then released into the ECF and the H+ is secreted in to the lumen/urine

Question 30

What is Acetazolamide

Answer 30

CA inhibitor and so causes metabolic acidoses

Question 31

Via what 2 pumps is H+ actively excreted?

Answer 31

H+ ATPase and Na/H+ exchanger

Question 32

How is new HCO3- generated?

Answer 32

CO2 from the blood is converted via CA into HCO3- + H+. HCO3- is reabsorbed while the H+ is either directly secreted or combined with titratable acids i.e. phosphate or ammonia

Question 33

What drives H+ excretion in the DISTAL tubule and CD?

Answer 33

ALDOSTERONE drives expression of ENaC channels on the lumenal surface. This causes Na to be reabsorbed from the lumen into the blood and in exchange you get SECRETION of both K+ and H+

Question 34

Renal handling of NH4+?

Answer 34

• ammonium is generated from glutamine metabolism in PT cells and secreted into the lumen and 2 HCO3- are also made and reabsorbed
• most is reabsorbed in the TAH
• in the CD diffusion trapping occurs where H+ combines with NH3 to secrete NH4+

Question 35

What is the kidneys response to acidosis?

Answer 35

1. Increased HCO3- and H+ transport along the nephron
2. Increased ammoniagenesis
3. Increased availability of urinary buffers

> increased acid secretion of which most is driven by NH4+

Question 36

What renal compensation do you see in resp acidosis?

Answer 36

See a gradual increase in HCO3- reabsorption and generation over a couple of days.
Also excrete more acid primarily through ammonia