Acid Base Balance

H+

• Hydrogen ion (lost an electron)

• Highly reactive

• Goal of cell/body: limit the amount of H+

Acid

• Any solute that dissociates in solution that releases H+ ions (proton donors)

• Strong acids - completely dissociate

  • Ex: HCl + H2O → H+ + Cl-

• Weak acids - do not dissociate completely; release fewer H+

  • Ex: CH3COOH (acetic acid) < - > CH3COO- + H+

Base

• Any solute that removes H+ (proton acceptors)

• Strong base

  • Ex: NaOH + H2O → Na+ + OH

• Weak base

  • Ex: NH3 (ammonia) < - > NH4+ + OH-

pH

• Power of hydrogen

• Measure the acidity of alkalinity of a solution; presented in a log scale

• 7 = neutral

• Less than 7 = acidic

• Greater than 7 = basic

pH scale

• pH = -log[H+]

Henderson -Hasselbalch equation

Importance of pH inside the cell

• pH of endosome → lysosome

• Low pH able to…

• Endosome → lysosome (pH = 4.7)

  • Low pH → able to degrade things

Importance of pH inside the digestive system

• Stomach has a low pH (1.5) to help breakdown food

Blood pH

• 7.35-7.45

• Acidosis: Less than 7.35

• Alkalosis: More than 7.45

Types of acids

• Fixed

• Organic

• Volatile

Fixed acids

• Do not leave solution, excreted via urination

• Cannot be excreted via the lungs

• Have to rely on kidney

• Ex: sulfuric acid (H2SO4) and phosphoric acid (H3PO4)

Organic acids

• Metabolic acids (produced via cellular metabolism)

• Ex: Lactic acid

• Cannot be excreted via the lungs

Voltailte acids

• Leaves the body via respiration

• Contributes the most to changes in pH

• Is excreted via the lungs

• Ex: carbonic acid (H2CO3)

How does your body maintain pH

• Buffer systems

• Breathing (respiratory compensation)

• Renal system

What are buffers

• Substances that help prevent a drastic shift in pH (decrease the amount of free H+ or OH- that is in the solution

• Blood is a natural buffer

Buffer systems

• What do they do

• Generally consists of

• 3 major buffer systems and where

• Buffers form chemical systems that absorb excess acids or bases and thus maintain a relatively stable pH

• Generally consists of a weak acid and weak base

• H < — > H+ + Y- (Y= anion that functions as a weak base)

• 3 major buffer systems:

  • Phosphate buffer system (ICF)

  • Protein buffer systems (ICF and ECF)

  • Carbonic acid - bicarbonate buffer system (ECF)

Phosphate buffer system

• Dihydrogen phosphate contributes to the phosphate buffering system to buffer the urine and intracellular fluid

Protein buffering system

• Amino acids contribute to the protein buffering system to buffer both intracellular and extracellular fluids

• Amino acids are used to stabilize the pH of the cell during metabolism to prevent damage to cellular organelles

Carbonic acid-bicarbonate buffering system

• Carbonic acid contributes to the carbonic acid-bicarbonate buffering system to buffer extracellular fluids to prevent changes to pH caused by metabolic acids and fixed acids

Buffers provide a __ solution to acid-base imbalance

• Temporary

• Ultimately, fluctuations in pH require compensation by both the lungs and the kidney

Respiratory mechanism

• Carbon dioxide reacts with water to be carried in the blood

• A change in rate of respiration can alter CO2 levels and drive changes in pH

When carbon dioxide levels increase

• More carbonic acid forms, additional hydrogen ions and bicarbonate ions are released, and the pH decreases

• Shift equation to the right

When carbon dioxide levels decrease

• The reaction runs in reverse

• Carbonic acid dissociates into carbon dioxide and water

• This removes H+ from the solution and increases the pH

• Shift equation to the left

Respiratory compensation

• In a state of acidosis: increase respiratory rate → decrease CO2 → increase pH (bicarbonate buffers extra H+)

• In a state of alkalosis: decrease respiratory rate → increase CO2 → decrease pH (generate more carbonic acid and H+)

Renal compensation - where does H+ secretion occur and what is needed

• H+ ions are secreted into the lumen in the proximal tubule, distal tubule, and collecting duct (exchanged for Na+ and Cl-)

• Eliminating large quantities of H+ ions requires the presence of buffers in the lumen

• Without buffers: kidneys could eliminate less than 1% of all H+ produced each day

• With buffers: kidneys can maintain homeostasis by eliminating large quantities of H+ ions

All buffering systems exist within…

• The kidney

Renal compensation - ammonia buffer system

• Bicarbonate and phosphate buffers are found in the renal tubule due to filtration resulting in excretion of H+

• Ammonia buffer system:

  • The proximal tubule generates ammonia via breakdown of glutamine

  • Ammonia can be used to buffer H+ in the lumen

  • Glutamine breakdown also generates HCO3-

• If acidosis: kidney increases production of ammonium ions, secretes H+, and reabsorbs bicarbonate (don’t want to lose bicarbonate in the urine)

• If alkalosis: kidney conserves H+ and secretes bicarbonate

Putting everything together - diagram

Acid/Base disorders can be…

• Respiratory

• Metabolic

Respiratory - acid/base disorders

• Acidosis: respiratory system cannot eliminate all of the CO2 generated by the tissues

  • Low respiratory rate (hypoventilation)

• Alkalosis: CO2 is below normal (hypocapnia)

  • Hyperventilation

Metabolic - acid/base disorders

• Acidosis: overproduction of acid; H+ release overwhelms the buffering system

  • Lactic acidosis or ketoacidosis - prolonged exercise generates lactic acid buildup; starving leads to the breakdown of lipids and ketone bodies

  • Impaired ability to excrete H+ by the kidneys

  • Loss of bicarbonate ions (cannot balance the H+)

• Alkalosis: elevated bicarbonate levels leading to the decrease in H+

  • Alkaline tide: after eating a meal, high production of HCl by the stomach leads to an increase in bicarbonate secretion into the blood

Acid/base disorder diagrams

Davenport diagram

Summary of acid and bases

• Normal pH

• pH is regulated by…

• Acidosis vs alkalosis

• Respiratory compensation

• Renal compensation

• Maintenance of fluid pH is critical to sustain life (7.35-7.45)

• pH is regulated by buffers, respiration, and urinary excretion

• Acidosis → decrease in pH

• Alkalosis → increase in pH

• Respiratory compensation involves the control of breathing rates, changing CO2 levels

• Renal compensation involves modifying H+ and CO2 excretion, ammonia production, bicarbonate reabsorption