Lecture 4: Acids and Balance

acid base balance

The maintenance of the proper pH (7.35-7.45) in body fluids through the regulation of acid and base levels, crucial for homeostasis

arterial blood vs venous blood

arterial blood is sllighty more alkaline and venous blood is slightly more acidic

why is arterial blood more alkaline compared to venous blood

Arterial blood is more alkaline due to its higher oxygen content and lower carbon dioxide levels, which results in a higher pH compared to venous blood.

how does the body maintain acid base balance

buffering solutions (occur immediately) and organs (physiological mechanisms take longer)

buffering solutions

in both intra and extra cellular fluid and can include bicarbonate, hemoglobin, phosphate, and plasma proteins

which organs maintain acid base balance

lungs, kidneys, bone

how do lungs contribute to acid base balance

elimination or retention of CO2 - pretty quick, can act in a matter of minutes to change pH

how do kidneys contribute to acid base balance

reabsorption/elimnation of bicarbonate and the elimination of metabolic acids - slower, more in the range of days to change pH

how does bone contribute to acid base balance

exchange of calcium and release of carbonate - takes considerable amount of time to act

buffers

short term, immediate, solutions to pH imbalance - can absorb hydrogen and hydroxide ions located in both intra and extra cellular fluids

biggest buffering system in humans

carbonic acid-bicarbonate system

carbonic acid-bicarbonate system

primary defence is carbonate present in intra and extra cellular fluid, secondary defence is exhalation of CO2 from lungs, tertiary defence is renal reabsorption of bicarbonate

typical level of bicarbonate and carbonic acid

20 parts HCO3- to 1 part H2CO3

chemical symbol for bicarbonate

HCO3-

chemical symbol for carbonic acid

H2CO3

acidemia

blood pH of under 7.4

alkalemia

blood pH of over 7.4

volatile acids

can be eliminated via carbon dioxide in the blood (breathing) - not directly releasing an acid, but high levels carbon dioxide in the blood lead to production of carbonic acid, causing decreased pH

non-volatile acids

can be eliminated via urine (kidneys) - typically strong acids and include small amount of sulphuric, phosphoric and other organic acids

metabolic acidosis

occurs due to decreased levels of bicarbonate or from increased levels of non-carbonic acids; ratio of carbonate to carbonic acid shifts downwards; levels of carbonate in blood decrease to below 22mmol/L

how does metabolic acidosis occur

could be due to ketoacidosis, shock or acute ingestion of sort of toxin

early symptoms of metabolic acidosis

headache, lethargy, progresses to confusion and coma - death can result from dysrhythmias and hypotension

how can body respond to metabolic acidosis

typically through hyperventilation, decreasing amount of CO2 present

metabolic alkalosis

occurs due to increased retention of bicarbonate, decreased levels of certain metabolic acids (HCl, sometimes due to excessive vomiting)

why is there increased retention of bicarbonate in metabolic alkalosis?

due to lack of anions (Cl-) in extracellular fluid, signals to kidney to retain bicarbonate since it is an anion

clinical signs of metabolic alkalosis

weakness, muscle cramps, hyperactive reflexes, confusion - can lead to worse symptoms if untreated including convulsions and tachycardia

how can metabolic alkalosis be treated

through sodium chloride solution which helps replace the lost Cl which allows kidney to properly excrete bicarbonate

how does body respond to metabolic alkalosis

typically through hypoventilation, increasing the amount of CO2 present

respiratory acidosis

results from hypoventilation and leads to an excessive amount of carbon dioxide in blood - excess CO2 to hypercapnia to increase in carbonic acid concentration

how is respiratory acidosis diagnosed

through the measurement of partial pressure of CO2 of over 45mmHg and measurement of blood pH of under 7.35

normal partial pressure of CO2

38-42 mmHg

how does the body react to respiratory acidosis

attempts to compensate through retention of bicarbonate from the kidneys

respiratory alkalosis

results from hyperventilation which leads to drastic reduction of carbon dioxide in blood - lowered CO2 leads to hypocapnia which leads to decrease in carbonic acid concentration

how is respiratory alkalosis diagnosed

measurement of partial pressure of CO2 under 45mmHg and blood pH of over 7.45

how does body compensate for respiratory alkalosis

attempts to compensate through retention of H+ ions and excretion of bicarbonate from body

what are acids and bases

in solution, are either proton donors or acceptors, respectively

strong acids and bases

completely dissociate into their constituent components in water

weak acids and bases

do not completely dissociate in water - depending on how weak they are and their overall concentration, they can either negligibly affect or have significant effect on body function

K_a

the acid dissociation constant, a measure of the strength of an acid in solution - the larger the value, the stronger the acid - better represented by pK_a which is the negative logarithm of Ka - so the smaller the pK_a, the stronger the acid

K_w

the ion product constant of water, which is the product of the concentrations of hydrogen ions and hydroxide ions in water at a given temperature - at 25°C, Kw is 1.0 x 10⁻¹⁴ so the concentration of hydrogen ions and hydroxide ions are each 10^-7, making pH 7

K_w = [H+][A-]/[HA]

disassociation of acid equation

K_w = (ah)(aoh)/a_H2O = 10^-14

disassociation constant of water

pH = pKa + log ([A-]/[HA])

Henderson-Hesselbalch equation - useful for obtaining pH of solutions with weak acids

when to use quadratic equation

for figuring out concentrations of weak acids

pOH = pKb + log ([B+]/[BOH])

Henderson-Hesselbalch equation - useful for obtaining pH of solutions with weak bases

what does a lower pKa indicate

stronger acid

what does higher Ka indicate

stronger acid

what are buffers

compounds, when in solution, that work to resists the changes of pH; generally salts of an acid / weak base or weak acid / base

why can’t we use strong acids or strong bases to buffer

they dissociate entirely, no buffering capacity in water; can use these to change the pH of a solution but the solution already has to be buffered somehow