Module 5: Acid Base Balance

Question 1

what does Acid-Base Balance mean

Answer 1

In physiology, refers to the balance of body fluid hydrogen ions (H+)

Question 2

describe acids

Answer 2

Hydrogen-containing substances that dissociate into H+ and an anion (-ive ion) in solution; must be able to dissociate, some do not even with H+ (ex., glucose)
- Substances that release H+ in solution, ex., HCl (strong acid) vs. carbonic acid (weak)

Question 3

describe acid strength

Answer 3

The degree to which it dissociates into ions
- Strong Acid: Completely dissociates into free H+ and an anion (HCl)
- Weak Acid: Partially dissociates into free H+ and anion with original remaining
Ex., H2CO3 <-> H+ & HCO3-

Question 4

describe bases

Answer 4

Substances that will bind free H+ and remove it from solution

Question 5

describe base strength

Answer 5

The degree to which it binds with H+
- Strong Base: Ex., NaOH completely dissociates into Na+ and OH-, decreases free H+ concentration as it binds to any free H+ to form water
- Weak Base: Ex., ammonia; does not completely form OH-; like weak acids, will form equilibrium with the original substance and a basic form (NH3 <-> NH4+ & OH-)

Question 6

describe pH

Answer 6

“Power of Hydrogen”; expresses the concentration of [H+] in a more convenient way on a logarithmic scale (each step is a tenfold increase; log10(10) = 1, log10(100) = 2)

pH = -log10[H+] = log10(1/[H+]) ; [H+] = 10-pH

• Since H+ is the denominator, when H+ is high, pH is very low; high pH = basic
• pH scales are in changes of powers of 10; pH 7 = 10x less acidic than pH 6
• PURE WATER = pH 7
  
  • Anything above = basic; baking soda, soap, drain cleaner
  • Anything below = acidic; milk, bananas, acetic acid, lemons

Ex., pH of strong acid with 0.0025M -> log10(1/0.0025) = 2.60
Ex., calculate the H+ concentration with pH 6.6 -> 10-6.6 = 2.51*10-7 M [H+]
Ex., pH 6.6 vs. pH 2.6 -> 4 steps; 104 = 10,000x more acidic than 6.6

Question 7

describe how pH is highly regulated in the body (the numbers for arterial blood, venous blood, and blood avg)

Answer 7

arterial blood = 7.45, venous = 7.35, blood avg = 7.4

Question 8

what is acidosis

Answer 8

A blood pH of below 7.35; death occurs at 6.8

Question 9

what is alkalosis

Answer 9

A blood pH of above 7.45; death occurs at 8.0

Question 10

what are some associated changes with acidosis/alkalosis

Answer 10

1. Nerve/Muscle Function: Acidosis suppresses the CNS (disorientation, coma, death); Alkalosis makes the CNS/PNS overly excited (respiratory muscle spasms, convulsions, death)
2. Enzymatic Changes: Most body enzymes optimally function at pH 7.4; changes in pH can speed up, slow down enzymatic reactions and this is usually bad
3. Potassium Changes: H+ can substitute for K+ (NaKATPase) in acidosis; blood secretes more H+ and less K+ in kidneys, cause hyperkalemia, cells are more excitable, easily depolarize

Question 11

describe hydrogen production in the body

Answer 11

Near constant production or release of H+ into body fluids from metabolic activities

Question 11

describe carbonic acid formation

Answer 11

Carbonic Anhydrase (CA) converts CO2 + H2O (byproducts of cellular respiration) into H2CO3 (carbonic acid) which dissociates into H+ and HCO3- (bicarbonate)

CO2 + H2O <-CA-> H2CO3 <-> HCO3- + H+

Question 12

describe how hydrogen production, and CO2 (removal/production) can be driven in different directions with the lungs and tissues

Answer 12

Lungs: Removes CO2, so H+ content is reduced (basic) as equation shifts left
Tissues: Produces CO2, so H+ content increases (acidic) as equation shifts right

When respiration and metabolism are balanced, there is no net H+ change

Question 13

describe a chemical buffer

Answer 13

A mixture of two chemicals that interact to resist pH changes when an acid or base is added to the system (keeps the pH within narrow ranges for life)

Question 14

describe the buffer system, and how there are 4 distinct purposes

Answer 14

1. H2CO3:HCO3- Buffer System: Primary ECF against non-H2CO3 changes (non-resp)
2. Protein Buffer System: Primary ICF buffer (protein-rich), some ECF buffering
3. Haemoglobin Buffer System: Secondary ECF; for H2CO3 changes (resp)
4. Phosphate Buffer System: Only urinary buffer; some ICF buffering (phosphate-rich)

Question 15

describe the H2CO3: HCO3 Buffer System

Answer 15

Dissociates via: H2CO3 <-> HCO3- + H+
- Most important; buffers pH changes from everything except H2CO3/CO2 (itself) in the ECF
- H2CO3 and HCO3- are present in high quantities in the ECF; high capacity for buffering pH changes in the blood
- Both highly regulated by the body to keep concentrations stable
- Kidneys (HCO3-) and Lungs (CO2 -> regulates H2CO3)
- When base is added to the solution, it binds to the free H+ and reaction moves forward so more H+ dissociates to replace the loss
- When acid is added to the solution, the reaction moves backwards so less H+ dissociates
- Strong Acid + Unbuffered: ALL H+ is free, contributes to solution acidity, large changes
- Strong Acid + Buffered: Bicarb ions bind to H+, removes from solution, will not contribute to the acidity and changes are minor

Question 16

what are 2 specific scenarios that result in Buffer Pair Changes: CO2 + H2O <-> H2CO3 <-> HCO3- + H+

Answer 16

1. Intense Exercise: Forms lactic acid which drives higher [H+]; binds to HCO3- and causes a left shift -> acidity does not increase
2. Vomiting: Results in lower [H+] from losing gastric acid; H2CO3 dissociates as there is a right shift from the lost H+ -> acidity does not decrease (ECF will not become too basic)

Question 17

describe the protein buffer system

1. pH rise (basic)
2. pH drop (acidic)

Answer 17

Since proteins are composed of amino acids, they are great buffers
Acidic carboxylic acid group (COOH) and Basic amine group (NH2)
Important for protein-rich intracellular fluids (plasma proteins not significant vs. H2CO3)
1. pH Rise (Basic): The amino acid acts as an acid; releases H+ (COO-)
2. pH Drop (Acidic): The amino acid acts as a base; absorbs H+ (NH3+)