Week 3 Acid-Base Balance

Question 1

Physiologically what do we need hydrogen ions (acid) for

Answer 1

• Energy in mitochondria
• Protein conformation/function
• Metabolism

Question 2

How is hydrogen ion balance (homeostasis) acheived?

Answer 2

• Regulating production/excretion
• Buffering

Question 3

What are the different forms of hydrogen ion production in the body?

Answer 3

Question 4

What is a buffer solution?

Answer 4

A buffer solution resists changes in pH when and acid or base is added to it

Question 5

Types of buffer systems in the body?

Answer 5

• Bicarbonate system
• Haemoglobin
• Others (don’t need ot know the details of these) : phosphate, proteins, exchange of intracellular K+ for H+

Question 6

Basic equation of the bicarbonate buffering system

Answer 6

Question 7

Priciple of the haemoglobin buffering system?

Answer 7

CO2 can enter an RBC causing an increase in H+. H+ can actually bind to haemoglobin encouraging it to release oxygen. At the same time the left over HCO3- is exchanged for a Cl- ion outwitht he cell. This is another way CO2 and HCO3- can effect one another.

Question 8

In what way is the bicarbonate buffering system regulated?

Answer 8

It is open on both ends.

CO2 is excreted through the lungs and regenerated in respiration. On the other side H+ is excreted through the kidneys and HCO3- is regenerated through the kidneys.

Question 9

When end of the bicarb buffering system is the fastest?

Answer 9

The lung side

Question 10

What is the Hb buffering system an example of?

Answer 10

A protein buffering system

Question 11

Definition of acidosis/alkalosis

Answer 11

Question 12

Normal blood acidity (H+ concentration and pH)

Answer 12

Question 13

What is the [H+] relationship to [CO2] and [HCO3-]

Answer 13

Question 14

Fill in this table

Think about how each one occurs

Answer 14

Question 15

How does respiratory acidosis occur?

Answer 15

Respiration is decreased

pCO2 increases

H+ increases

Question 16

How does compensated respiratory acidosis occur?

Answer 16

In response to the acidosis more HCO3- is made resulting in a normal pH but with elevated CO2 levels

Question 17

How does respiratory alkalosis occur?

Answer 17

Respiration increases

pCO2 decreases

H+ decreases

Question 18

How does matabolic acidosis occur?

Answer 18

If there is a problem with your metabolism and your body is making too much H+.

You sense this acidosis and your body body responds by increasing respiration however this can only work so far.

Eventually you end up with high H+ and low pCO2

Question 19

How does metabolic alkalosis occur?

Answer 19

The body isn’t making enough acid either kidneys excrete too much or you have consumed to much alkaline medication.

Start breathing less to compensate. Can only do this so far until you need oxygen.

If it goes this far you end up with low H+ and high pCO2

Question 20

Biomarkers of acute, chronic & acute on chronic respiratory acidosis?

Answer 20

Question 21

Biomarkers of acute and chronic alkalosis

Answer 21

You get a small drop in bicarb as well because renal compensation of decreased H+ excretion also includes a decrease is bicarbonate generatio

Question 22

Examples of causes of matabolic acidosis

Answer 22

Question 23

Effects of metabolic acidosis

Answer 23

Question 24

Example causes of metabolic alkalosis

Answer 24

Question 25

Effects of metabolic alkalosis

Answer 25

Question 26

What's going on here?

Answer 26

This is metabolic acidosis. H+ raised but pCO2 lowered to compensate. Think renal failure, DKA (diabetic ketone acidosis), salicylate OD (found in plants, aspirin, acidosis caused by inhibtion os citric acid cycle and ultimately lactic acidosis), lactic acidosis. Would do a urine analysis to look for glucose, salicylate and lactate

Question 27

What's going on here?

Answer 27

pCO2 raised, H+ only slightly raised, pO2 low, pHCO3- raised Chronic compensated respritory acidosis. Most likely COPD

Question 28

Acid base disturbance cheat sheet just to look at

Answer 28

Question 29

What's going on here?

Answer 29

* H+ lowered - alkalosis * pCO2 lowered - correlates therefore cause * HCO3- normal - no metabolic compensation Acute respiratory alkalosis

Question 30

What's going on here? Any changes you might expect over the next few days?

Answer 30

* H+ raised - acidosis * pCO2 raised - correlated therefore cause * HCO3- normal - no metabolic response Acute respiratory acidosis After a couple days you would expect the HCO3- to increase as metabolic compensation. However in accidents it is common to also have renal impairement leading to further acidosis.

Question 31

What is going on here?

Answer 31

* H+ lowered - alkalosis * pCO2 raised - opposite so respiratory compensation * HCO3- raised - metabolic cause Chronic metabolic alkalosis with respiratory compensation The vomitting leads to a loss of acid in the system thus lowering overall H+. In order to replenish this stomach acid you end up with HCO3- getting pumped into the blood further increasing the alkalosis.

Question 32

What's going on here?

Answer 32

* H+ raised - acidosis * pCO2 lowered - respiratory response * HCO3- lowered - metabolic cause * AG (anion gap) raised - anions taken up by H+ Metabolic acidosis with respiratory compensation DKA - diabetic ketone acidosis. Without insulin the liver begins to break down fats for fuel resulting in a build up of acidic ketones

Question 33

What's going on here?

Answer 33

* H+ raised - acidosis * pCO2 lowered - respiratory response * HCO3- lowered - metabolic cause * AG (anion gap) raised - anions taken up by H+ Metabolic acidosis with full respiratory compensation Aspirin is broken down into salicylic acid

Question 34

What's going on here?

Answer 34

* H+ raised - acidosis * pCO2 lowered - respiratory response * HCO3- lowered - metabolic cause * AG (anion gap) raised - anions taken up by H+ Metabolic acidosis with respiratory compensation Carbon monoxide poisoning. CO bind to haemoglobin blocking oxygen and causing a left shift of the oxygen dissociation curve reducing haemoglobin's ability to give up the oxygen it does have. This reduces delivery to tissues causing them to produce lactic acid from anaerobic respiration resulting in acidosis

Question 35

Put these causes of metabolic acidosis into different categories based on anion gap salicylate (aspirin) overdose ethylene glycol / methanol poisoning severe diarrhoea DKA high intestinal fistula output renal tubular acidosis lactic acidosis renal failure

Answer 35

Question 36

What is the reason why some form of metabolic acidosis cause an anion gap and others don't?

Answer 36

AG = [Na⁺] – ([Cl⁻] + [HCO₃⁻]) For any type of acidosis that is caused by the gain of a complete acid e.g. for a ketone body you have H+Ketone-. The H+ is buffered by HCO₃⁻ hence HCO₃⁻ drops and the anion gap rises. Electrical neutrality is maintained as there are now unmeasurable anions present (e.g. Ketone-). For any time of acidosis where there is either pure H+ gain or HCO₃⁻ loss then in order to maintain electrical neutrality Cl- absorbtion is increased hence the anion gap doesn't change.

Question 37

What blood result is often a sign of metabolic alkalosis vs respiratory alkalosis?

Answer 37

Hypokalaemia

Question 38

Why do you get hypokalaemia in metabolic alkalosis?

Answer 38

In the kidneys Na+ is absorbed in exchange for K+ secretion but also H+ secretion. Hyperaldosteronism can result in increased H+ and K+ secretion in exchange for Na+ absorption leading to alkalosis with hypokalaemia. In alkalosis due to vomiting: 1. Volume Depletion → RAAS Activation Aldosterone ↑ → promotes Na⁺ reabsorption at the expense of K⁺ and H⁺ secretion in the kidneys. Result: Hypokalaemia and worsening alkalosis. 2. In metabolic alkalosis, H⁺ shifts out of cells to buffer the high blood pH. To maintain electrical neutrality, K⁺ shifts into cells → further ↓ serum potassium.