Acid-Base Balance 1 Flashcards
Define what an Acid is
Molecules containing hydrogen atoms that can release hydrogen ions (H+) into solution (e.g. H2CO3)
Define what a Base is
an ion or a molecule that can accept a H+
ion (e.g. HCO3−is a base because it can combine with H+ to form H2CO3 )
Differentiate between a strong and a weak acid and base
Strong acid: Rapidly dissociates, releasing large amounts of H+ ions into solution (e.g. HCl)
Weak acids: less likely to dissociate their ions,releasing small amounts of H+ ions into solution (e.g. H2CO3)
Strong base: reacts rapidly and strongly with H+ and, quickly removes H+ from a solution (e.g. OH− , reacts with H+ to form H2O
Weak base: Binds with H+ much more weakly (e.g. HCO3−)
Define the concept of pH
pH is the abbreviation for the potential of hydrogen
Formula: pH = -log[H+]-This means pH is the negative base 10 logarithm (“log” on a calculator) of the hydrogen ion concentration of a solution
The pH of any fluid is the measure of its hydrogen ion [H+] concentration relative to that of a given standard solution (measure of the acidity or alkalinity of a fluid)
Normal [H+ ] = 40 nEq/L or (0.00000004 Eq/L)
Normal pH = −log[H+] = -log [0.00000004] = 7.4 (arterial blood)
Venous blood and interstitial fluids is about 7.35 due to extra amounts of carbon dioxide (CO2 ) released from the tissues to form H2CO3 in these fluids
A high [H+ ] corresponds to a low pH and vice versa
A pH >7.4 → alkalosis
A pH <7.4 → acidosis
Define what a buffer is
Any substance that can reversibly bind H+. Found in the fluids, and react rapidly to minimize a change in pH concentration.
A buffer is a solution containing either a weak acid and its conjugate base (salt) or a weak base and its conjugate acid (salt)
Resistant to changes in pH
Used to maintain a stable pH in a solution, by neutralizing small quantities of additional acid or base
The amount of acid or base that can be added to a buffer before changing its pH is called its buffer capacity
A buffer is any substance that can reversibly bind H+
General form of the buffering reaction is :
Buffer + H+ ↔ HBuffer
Source of Hydrogen
Carbonic acid formation-The major source of H+
is from metabolically produced CO2
Inorganic acid produced during nutrient breakdown-Dietary proteins contain a large quantity of sulfuric acid and phosphoric acid
Organic acid resulting from intermediary metabolism-Lactic acid and fatty acids
80 mEq of H+ is either ingested or produced each
day by metabolism, without buffering, the daily
production and ingestion of acids would cause
lethal changes in body fluid [H+]
What is the aim of the acid-base balance mechanism of the Body
To maintain the pH (H+ concentration) homeostasis in the ECF & ICF.
Why is Hydrogen ion homeostasis important
The activities of almost all enzyme system of the body are influenced by the
[H+]. Changes can alter nearly all cell & body functions.
The primary systems defending against changes in the hydrogen ion and the mode of action for each one.
Chemical Buffer: Immediately :Bind H+/OHNo elimination
Respiratory System: Minutes :Handles CO2 (H2CO3)
Kidneys: Hours - days :Excretes acid/bases
Chemical Buffers
The first line of defence:
- Bicarbonate Buffer system-Primary ECF buffer system
- Protein Buffer System-Primary ICF
- Phosphate Buffer system-Plays an important role in the urinary system
What does the bicarbonate Buffer consists of?
It consists of a weak acid(H2CO3) and a bicarbonate salt(HCO3-)
When a strong acid (HCl ) is added to the bicarbonate buffer solution, the increased H+ released from the acid (HCl → H+ + Cl−) is buffered by HCO3−
The excess CO2 greatly stimulates respiration, which eliminates the CO2 from the ECF
When a strong base (NaOH), is added to the bicarbonate buffer solution, NaOH combines
with H2CO3 to form additional HCO3−
The [H2CO3 ] decreases (because it reacts with NaOH), causing more CO2 to combine with
H2O to replace the H2CO3
CO2 levels in blood decrease, decreases rate of expiration, rise in blood
Bicarbonate Buffer system equation
CO2 + H2O H2CO3 H+ + HCO3-
Sources of Carbonic Anhydrase in the body
Lung alveoli endothelium
Renal tubular cells
Red blood cells
Stomach epithelium (parietal cells)
Brain (epithelium of choroid plexus)
Phosphate Buffer
The phosphate buffer system plays a much greater role in the intracellular than the extracellular fluid compartment.
It is also an important buffer of the glomerular filtrate.
The main elements of the phosphate buffer system are H2PO4− and HPO4 2-
When a strong acid (HCl) is added to the buffer system, the H+ is accepted by the base HPO4
2- and converted to H2PO4−
When a strong base (NaOH), is added to the buffer system, the OH− is buffered by the H2PO4−
to form additional amounts of HPO42- + H2O
Phosphate buffer equation
HPO_42- + H+ H-2PO_4-
