Acid Base Disorders

Question 1

What is the relationship between h+ ions and ph

Answer 1

-inverse relationship
-low ph me and high concentration of h+

Question 2

What is the body’s ph

Answer 2

7.4 +/- 0.05

Question 3

Why does the body need to maintain ph

Answer 3

-alter structure and function of proteins(eg it can change the charges on the r groups on the amino acids)
-it can affect biological activity of ions such as cations
-affect movement of molecules within cells

Question 4

Sources of H+ ions in the body

Answer 4

1)Metabolic acids
-anaerobic glucose/fatty acid metabolism
-oxidation of sulphur containing amino acids and cationic amino acids and cationic amino acids

2)Respiratory acids
-co2

Question 5

What are the body’s mechanisms to control concentration of H+

Answer 5

1)Buffering systems such as carbonic acid-bicarbonate,protein,phosphate which has an immediate response

2)Respiratory system which is activated almost immediately

3)Renal system slowest mechanism to respond

Question 6

Renal regulation

Answer 6

-excretion of H+
-bicarbonate recovery
-bicarbonate regeneration

Question 7

Respiratory regulation

Answer 7

-expiration of CO2 Trough the lungs

Question 8

Renal regulation-Bicarbonate recovery

Answer 8

-in the glomerular filtrate bicarbonate ions join H+ in order to form carbonic acid which is then transformed by carbonic anhydrase to water and carbon dioxide as its an unstable molecule due to it being a weak acid.

-water then leaves the kidney through urine and carbon dioxide diffuses through the highly selective membrane into the proximal tubule cell

-carbon dioxide then joins water and forms carbonic acid(reaction due to the action of anhydrase)

-carbonic anhydrase then splits into bicarbonate ions and hydrogen ions.Bicarbonate can then diffuse into the blood stream and be recovered

Question 9

Renal regulation-Bicarbonate recovery

Answer 9

-in the glomerular filtrate bicarbonate ions join H+ in order to form carbonic acid which is then transformed by carbonic anhydrase to water and carbon dioxide as its an unstable molecule due to it being a weak acid.

-water then leaves the kidney through urine and carbon dioxide diffuses through the highly selective membrane into the proximal tubule cell

-carbon dioxide then joins water and forms carbonic acid(reaction due to the action of anhydrase)

-carbonic anhydrase then splits into bicarbonate ions and hydrogen ions.Bicarbonate can then diffuse into the blood stream and be recovered

Question 10

Bicarbonate regeneration

Answer 10

-Just as in recovery hydrogen ions leave the proximal tubule cell, then they join phosphate or ammonia to form either do hydrogen phosphate or ammonium which can be excreted in the urine

-there is a net loss of H+ from the body during bicarbonate recovery due to the urinary buffers

Question 11

Describe the partial pressures of gasses in peripheral tissues

Answer 11

-high partial pressure of of carbon dioxide
-low partial pressure of oxygen

Question 12

Describe the partial pressures of gasses in peripheral tissues

Answer 12

-high partial pressure of of carbon dioxide
-low partial pressure of oxygen

Question 13

Describe the partial pressures of gasses in the lungs

Answer 13

-Low partial pressure of carbon dioxide
-High partial pressure of oxygen

Question 14

Describes what happens to carbon dioxide in peripheral tissues

Answer 14

-co2 produced in the tissues is transported to the lungs as bicarbonate in blood plasma

-this is done when some of the carbon dioxide in the erythrocyte either 1)forms carbamine compounds with proteins such as heamologlobin forming carbaminoheamoglobim 2)dissolves im water 3)reacts with carbonic anhydrase to form carbonic acid which then dissociates into h+ which binds to Haemoglobin(h+hb) and bicarbonate which leaves into the plasma

Question 15

Describe the chloride shift that happens in erythrocytes

Answer 15

-chloride irons move into erythrocytes while bicarbonate moves out to the venous blood

-this is done by co2 diffusing into erythrocytes and being converted to bicarbonate by carbonic anhydrase

-the chloride shift mitigates the changes in ph

Question 16

Describe what happens to oxygen in the erythrocytes in the lungs

Answer 16

-oxygen enters erythrocytes and joins hydroxy Haemoglobin which dissociates into h+ which reacts with the bicarbonate ions from the plasma to form carbonic acid and hbo2
-carbonic anhydrase then splits carbonic acid into water and co2 which leaves the erythrocyte in order to be exhaled

Question 17

Blood gas analysis

Answer 17

• Arterial blood collected into syringe containing anticoagulant (eg heparin) and transported on ice(prevents glycolysis)
• Any air from syringe expelled before/after blood collection
• [H+] and pCO2 measured directly in arterial blood
• Blood gas analysers measure [H+] and pCO2 and are programmed to calculate bicarbonate

Question 18

What readings does the blood gas analysis provide

Answer 18

Conc of h+
Partial pressure of carbon dioxide
Conc of bicarbonate

Question 19

Relationship between the 3 values provided by blood gas analysis

Answer 19

-if the change is due to the partial pressure of carbon dioxide it is a respiratory disorder

-if the change is due to the concentration of bicarbonate ions it is a metabolic acid

Question 20

Relationship between ph and concentration of bicarbonate

Answer 20

Directly proportional (if one goes up so does the other)

Question 21

Relationship between ph and partial pressure of carbon dioxide

Answer 21

Inversely related (if one goes up the other one goes down)

Question 22

Explain compensation

Answer 22

Is ph decreases so does the concentration of bicarbonate ions this means its a metabolic disorder so there will be respiratory compensation

If ph decreases co2 concentration increases meaning a respiratory disorder so metabolic compensation

Question 23

Causes of metabolic acidosis

Answer 23

1)Increased H+ formation
• Ketoacidosis (type 1 diabetes)
• Lactic acidosis
• Poisoning (e.g. salicylate, ethylene glycol)
• Inherited organic acidosis
2)decreased H+ excretion
• Renal tubular acidosis
• Acute renal failure
• Chronic renal failure
• Mineralocorticoid deficiency
3)Acid ingestion
4)loss of bicarbonate caused by eg diarrhea,pancreatic fistula

Question 24

Clinical presenation(symptoms) of metabolic acidosis

Answer 24

Hyperventilation (Kussmaul respiration)
Neuromuscular irritability: arrhythmias, cardiac arrest
CNS depression can go on and cause coma, lead to death

Question 25

Management of metabolic acidosis

Answer 25

-Treat underlying cause
-Administration of bicarbonate to correct severe acidosis (drip), careful only done in cases of severe acidosis. If you don’t get it right it can cause alkalosis

Question 26

Causes of metabolic alkalosis

Answer 26

1)Gastrointestinal loss of H+
Vomiting
Gastric aspiration
2)Renal loss of H+
• Conns syndrome (aldosterone)
• Cushing’s syndrome (cortisol, similar effect
to aldosterone)
3)Drugs eg carbenoxolone (to treat ulcers), similar action to aldosterone
• Thiazide diuretics (blood pressure)
4)Potassium depletion
5)Administration of alkali
• alkali ingestion
• Inappropriate treatment of acidosis

Question 27

Clinical presentation(symptoms) of metabolic alkalosis

Answer 27

Hypoventilation
Paraesthesia: pins and needles effect in hands and feet
Tetany: spasms of the muscles of face and hand due to changes in calcium
Muscle cramps

Question 28

Management of metabolic alkalosis

Answer 28

-Treat underlying cause
-Correct hypovolaemia (blood volume declined) if present

Question 29

Causes of respiratory acidosis

Answer 29

1)Airways obstruction
Chronic obstructive airway disease (bronchitis, emphysema) Bronchospasm (e.g. asthma)
2)Inhibition of respiratory centre
Some drugs will affect it anaesthetics, sedatives, cerebral trauma, tumours in brain
3)Neuromuscular disease: poliomyelitis, tetanus, neurotoxins, Guillain–
Barré syndrome
4)Pulmonary disease: pulmonary fibrosis, severe pneumonia, respiratory distress syndrome.
5)Acute: choking, bronchopneumonia, acute exacerbation of asthma
6)Chronic: chronic bronchitis, emphysema

Question 30

Clinical presentation(symptoms) of respiratory acidosis

Answer 30

Peripheral vasodilation
Headaches
CNS depression

Question 31

Management of respiratory acidosis

Answer 31

-Aim to improve alveolar ventilation and lower PCO2
-Maximise alveolar ventilation in chronic respiratory acidosis using physiotherapy
bronchodilators

Question 32

Causes of respiratory alkalosis

Answer 32

1)Hypoxia: high altitude, sever anaemia, pulmonary disease
2)Increased respiration: respiratory stimulants eg salicylates, primary hyperventilation syndrome, artificial hyperventilation
3)Pulmonary disease: pulmonary oedema, pulmonary embolism

Question 33

Clinical presentation of respiratory alkalosis

Answer 33

Confusion/ coma
Headaches/ dizziness

Question 34

Management of respiratory alkalosis

Answer 34

Treat underlying cause of hyperventilation
Acute: rebreathing

Question 35

3 rules when interpreting acid base disorders

Answer 35

1. Check [H+] (or pH)
2. Check PCO2 and [HCO3-] which is consistent with [H+]:
   metabolic or respiratory
3. Check the third component - any compensation (full or partial)