Acids, Bases + Buffers

Question 1

What is an acid?

Answer 1

H+ donor

Question 2

What is a base?

Answer 2

H+ acceptor

Question 3

What is a strong acid?

Answer 3

A compound that ionises completely in solution to form hydrogen ions and a base

Question 4

What is a weak acid?

Answer 4

Compounds that are only partially ionised in solution

Question 5

What is the function of a buffer?

Answer 5

Resists changes in PH when small quantities of strong acid or base are added.

Question 6

What is the ideal PH of blood?

Answer 6

7.4

Question 7

Give the Henderson-Hasselbach equation.

Answer 7

PH = pKa + log([HCO3-]/[CO2])

Question 8

How are most of the H+ ions produced in the body?

Answer 8

As a result of CO2 release from aerobic metabolism. CO2 rapidly reacts with water forming carbonic acid that dissociates into H+ and HCO3-

Question 9

Give the equation of CO2 - H+

Answer 9

CO2 + H20 > H2CO3 > HCO3- + H+

Question 10

Which enzyme catalyses the conversion of CO2 to H+?

Answer 10

Carbonic anhydrase

Question 11

Which three systems work to ensure PH remains in range?

Answer 11

1. Blood and tissue buffering
2. Excretion of CO2 by lungs
3. Renal excretion of H+ and regeneration of HCO3-

Question 12

Name the most important buffer system of the body.

Answer 12

Bicarbonate

Question 13

How is the bicarbonate buffer efficiency improved (think lungs and kidneys)?

Answer 13

1. CO2 is removed by lungs

2. Bicarbonate is regenerated at the kidneys

Question 14

Proteins form buffers as well. Name a protein that is part of this system.

Answer 14

Albumin

Question 15

How do proteins work as a buffer?

Answer 15

The protein matrix of bone buffers large amounts of H+ ion

Question 16

How is haemoglobin a buffer?

Answer 16

It binds to both CO2 and H+, removing these from the blood.

CO2: CO2 diffuses into red cells down their concentration gradient.. It binds with haemoglobin reversibly to form carbaminohaemoglobin or with water to form carbonic acid.

H+: CO2 in red cells combines with water to form carbonic acid. This dissociates into bicarbonate and H+ ions. H+ ions bind to reduced haemoglobin to form HHb. HCO3- ions pass back into the plasma in exchange for Cl- ions.

Question 17

Which state of haemoglobin has the strongest affinity for CO2 and H+?

Answer 17

Deoxygenated haemoglobin

Question 18

In the lungs, what mathematical relationship is between arterial partial pressure of CO2 and the alveolar ventilation?

Answer 18

Arterial partial pressure is inversely proportional to alveolar ventilation - i.e. if alveolar ventilation falls, PaCO2 rises.

Question 19

What is alkalosis in terms of PH?

Answer 19

PH > 7.45

Question 20

What is acidosis in terms of PH?

Answer 20

PH < 7.35

Question 21

Name the types of alkalosis and acidosis.

Answer 21

Respiratory and metabolic.

Question 22

What is acidaemia?

Answer 22

Too many hydrogen ions in plasma

Question 23

What is alkalaemia?

Answer 23

Too few hydrogen ions in plasma

Question 24

What causes respiratory acidosis?

Answer 24

Common: Decreased alveolar ventilation, causes decreased excretion of CO2.

Less common: Excessive production of CO2 by aerobic metabolism, can be caused by fever.

Question 25

What is the PaCO2 in respiratory acidosis?

Answer 25

>6kPa

Question 26

What causes respiratory alkalosis?

Answer 26

Excessive excretion of CO2. Caused by severe asthma and pulmonary embolism

Question 27

What is the PaCO2 in respiratory alkalosis?

Answer 27

<4.5kPa

Question 28

List the causes of metabolic acidosis.

Answer 28

1. Excess H+ production from the excessive production of organic acids as a result of anaerobic metabolism. 2. Low perfusion 3. Reduced ability to use oxygen as a substrate e.g. in sepsis 4. Renal tubular dysfunction leads to inadequate excretion of H+ 5. Diabetic ketoacidosis - unable to use glucose, resulting in the production of ketone bodies which releases H+ 6. Crohn's disease where excessive diarrhoea results in large amounts of bicarbonate being lost

Question 29

List the causes of metabolic alkalosis.

Answer 29

1. Excess H+ loss from prolonged vomiting | 2. Excessive reabsorption of bicarbonates as a result of chloride loss through prolonged vomiting

Question 30

Which type of acidosis and alkalosis has a greater effect on the body and why?

Answer 30

Metabolic. This is because compensation is much slower in metabolic processes than respiratory, resulting in a delayed response.

Question 31

What is the anion gap?

Answer 31

The difference in serum concentration of cations (positive) and anions (negative).

Question 32

Which ions aren't included when considering the anion gap?

Answer 32

K+, PO4-, SO4-

Question 33

What is the normal value of the anion gap?

Answer 33

Between 3-11 mEq/mol

Question 34

How does the anion gap help to diagnose the cause of metabolic acidosis?

Answer 34

If there is a high anion gap, it can be used to see if the cause is due to excessive loss of bicarbonate or excess H+ production