Lecture 9 - Acid base balance

Question 1

Plasma pH

Answer 1

7.35 - 7.45

Question 2

H+ ion concentration

Answer 2

Low an tightly regulated

Question 3

pH greater than 7.45

Answer 3

Alkaemia

Question 4

pH lower than 7.35

Answer 4

Acidaemia

Question 5

Alkaemia

Answer 5

Lowers free calcium - dangerous

1. Less H+ ions bound to plasma proteins
2. More -vely charged sites are available on the plasma protein
3. Ionised free Ca2+ binds to plasma proteins (chelated) therefore less Ca2+ available
4. Ca2+ also binds to bone and leaves the ECF causing hypocalcaemia

Question 6

Hypocalcaemia

Answer 6

Increases neurone excitablity

• Tetany
• Paraesthesia

Question 7

pH 7.55

Answer 7

45% mortality

Question 8

pH 7.65

Answer 8

80% mortality

Question 9

Acideamia

Answer 9

Increases plasma K+ ion concentration - hyperkaleamia

Denatures proteins therefore impaired:

• muscle contraction
• glycolysis
• hepatic function

Question 10

pH 7.1

Answer 10

Severe effects and life threatening below 7.0

Question 11

Buffer system

Answer 11

CO2 + H20 –> H2CO3- –> H+ + HCO3-

Using carbonic anhydrase
pH dependent on how much CO2 is converted to H+

Question 12

Increased CO2

Answer 12

Pushes reaction to the right producing more H+

Question 13

Increased HCO3-

Answer 13

Pushes reaction to the left producing more CO2 which is breathed away

Question 14

What determines plasma pH

Answer 14

Determined by the HCO3- : pCO2 ratio (20:1)

HCO3- controlled by kidneys

Question 15

pCO2

Answer 15

Detected by chemoreceptors Controlled by ventilation

Disrupted by respiratory disease

Question 16

HCO3-

Answer 16

HCO3- made in RBC
Controlled by kidneys
Disturebed by metabolic and renal disease

Question 17

Kidneys

Answer 17

Produces and recovers HCO3-

Excretes H+

Question 18

Lungs

Answer 18

Alveloar ventilation diffuses CO2 out of blood to maintain concentration gradient

Question 19

HCO3- concentration in RBC

Answer 19

25 mmol/L

22-26 mmol/L
Can change to maintain pH

Question 20

HCO3- production and recovery

Answer 20

Kidneys recover all HCO3-

PCT makes 2HCO3- from glutamine and excreting NH4+ into urine

DCT makes 2 HCO3- from CO2 and H2O
(H+ bufffered by phosphate and ammonia in the urine)

Question 21

PCT HCO3- recovery

Answer 21

80 - 90% recovered by PCT

1. NHE excretes H+ into the lumen for every Na+ into the cell
2. HCO3- filtered in the glomerulus into the lumen binds to H+ to form CO2
3. CO2 diffuses into the cell transcellularly
4. CO2 is converted to H+ (which is excreted again) and HCO3-
5. HCO3- enters plasma via Na+/HCO3- co transporter therefore Na+dependent

Question 22

PCT HCO3- production

Answer 22

1. Glutamine is converted to alpha ketoglutarate and ammonium (NH4+)
2. Ammonium is converted to ammonia (NH3) which freely diffuses into the lumen and H+ which is secreted into the lumen using NHE
3. NH3 + H+ -> NH4 in lumen as ammonia acts as buffer
4. Alpha ketoglutarate produces 2 HCO3- molecules
5. HCO3- molecules diffuse into the blood via Na+/HCO3- channel

Question 23

DCT and CT

Answer 23

1. Alpha intercalated cells actively secret H+ into the lumen using H+ ATPase
2. Ammonia and hydrogen phosphate buffer the H+ in the lumen
3. CO2 and water (from metabolism) inside the intercalated cell produce HCO3-
4. HCO3- enters the blood via HCO3-/ Cl- antiporter therfore non Na+ dependent

Question 24

Increased acid load and low pH in healthy individual

Answer 24

Increased excretion of ammonium in urine as ammonia buffers H+

Ammonium generation from glutamine is increased in the PCT

NH3 freely moves in urine and interstitium as not charged

Question 25

NH4+ in thick ascending limb

Answer 25

Can be taken up by thick ascending limb where it travels to the collecting ducts. Dissociates into NH3 and H+ where it can be excreted into the lumen

Question 26

Minimum pH of urine

Answer 26

4.5 Due to H+ buffering system excreting H+ No HCO3- as also reabsorbed

Question 27

Hyperkalaemia

Answer 27

Caused by metabolic acidosis H+ moves into body cells and K+ moves out into blood In nephron cells, H+ is excreted into lumen and K+ is taken up Causes cardiac arrythmias

Question 28

Hypokalaemia

Answer 28

Caused by metaboloc alkalosis H+ moves out of cells and K+ moves in In distal nephron, H+ is absorbed and K+ is excreted

Question 29

Hypoventilation

Answer 29

Causes hypercapnia Increased CO2 Decreases pH Respiratory acidosis

Question 30

Hyperventilation

Answer 30

Causes hypocapnia Decreased CO2 High pH Respiratory alkalosis

Question 31

Compensation of respiratory acidosis and alkalosis

Answer 31

Acidosis - Kidneys produce more [HCO3-] Alkalosis - Kidneys decrease [HCO3-] Takes 2-3 days so gradual respiratory disease is well compensated but acute cases are not

Question 32

Metabolic acidosis

Answer 32

Tissues produce acid e.g. lactic acid and ketoacidosis Acids react with HCO3- decreasing the concentration Decreases pH

Question 33

Compensation of respiratory metabolic acidosis

Answer 33

Peripheral chemoreceptors detect pH drop in the carotid body Stimulates an increase in ventilation proportional to HCO3- loss

Question 34

Anion gap

Answer 34

([Na+] + [K+]) - ([Cl-] + [HCO3-]) Other anions are not measured e.g. proteins Gap increased if HCO3- is replaced by other anions e.g. lactate Tissues produce e.g. lactic acid in MI that reacts with HCO3- and replaces it with another anion. HCO3- decreases therefore the anion gap increases

Question 35

Renal cause of metabolic acidosis

Answer 35

Anion gap is unchanged As HCO3- produced less But Cl- produced instead

Question 36

metabolic alkalosis

Answer 36

Increase in HCO3- Cannot be compensated efficiently as body must preserve oxygen supply to brain so can't hypoventilate proportionally Therefore kidney excretes HCO3-

Question 37

Type 2 respiratory failure

Answer 37

Low O2 High pCO2 Compensated by increase of HCO3-

Question 38

Causes of type 2 resp failure

Answer 38

``` Hypoventilation Severe COPD Severe asthma Drug overdose Neuromuscular disease ```

Question 39

Conditions causing respiratory alkalosis

Answer 39

Hyperventilation Panic attacks Anxiety

Question 40

Type 1 respiratory failure

Answer 40

Low O2 Low CO2 Hyperventilation in repsonse to long term hypoxia Initial rise in pH Compensated for by fall in HCO3-

Question 41

Conditions causing metabolic acidosis with increased anion gap

Answer 41

- Ketoacidosis - diabetes - Lactic acidosis - exercise to exhaustion - Poor tissue perfusion - MI releases lactic acid - Uraemic acidosis - advanced renal failure causes a decrease in H+ secretion

Question 42

Uraemic acidosis

Answer 42

Build up in blood of : - phosphate - H+ - sulfate - urate

Question 43

Conditions causing metabolic acidosis with normal anion gap

Answer 43

Renal tubular acidosis - Type 1 - distal inability to pump out H+ - Type 2 - proximal problems with HCO3- reabsorption Severe persistant diarrhoea - loss of HCO3- replaced by Cl-

Question 44

Diabetic ketoacidosis

Answer 44

Normally get hyperkalaemia however, total body depletion of K+ - K+ moves out of body cells due to acidosis and lack of insulin - Osmotic diuresis due to less Na+ reabsorption means K+ lost in urine

Question 45

Conditions causing metabolic alkalosis

Answer 45

Vomiting - loss of H+ Mechanical drainage of stomach into duodenum - lack of secretion of HCO3- to neutralise H+ as no H+

Question 46

Volume deplete

Answer 46

Normally easy to correct metabolic alkalosis as downregulate NHE However, if volume deplete can't downregulate as need to retain water with Na+ absorption