BIOL125 Lecture Notes - Lecture 28: Vertebral Compression Fracture, Elastic Fiber, Renal Compensation
8 Jun 2018
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Changes across the lifespan
• 6.18. Acid-base balance
o Acids, bases and pH
• Acid
▪ Dissociates in solution and releases H+
▪ The more H+ released, the solution becomes more acidic
• Base
▪ Releases OH- in solution
▪ The more OH- released, solution becomes more basic/alkaline
• pH
▪ A scale for H+ concentration (logarithmic scale)
▪ Tells us whether substances are acids, bases or neutral
▪ pH of body fluids depends on dissolved:
• Acids
• Strong: completely dissociate
• HCl -> H+ + Cl-
• Weak: incomplete dissociation
• CO2 + H2O = H2CO3 = H+ + HCO3-
• Bases (strong/weak)
• Salts
▪ Importance
• pH of ECF
• Narrowly limited, usually 7.35-7.45
• Deviation of pH is dangerous
• Changes in H+ concentration affects membrane stability, enzyme
activity, plasma protein stability
• pH of blood below 7.35 = acidosis
• More common
• Due to acid production from normal metabolism
• Causes
• CNS deteriorated - comatose
• Cardiac contractions weak and irregular, heart failure
• Peripheral vasodilation, drop in BP, circulatory
collapse
• pH of blood above 7.45 = alkalosis
o Fluid distribution in the body
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o Types of acids in the body
• Fixed acids
▪ Remain in solution in body fluids until excreted by kidneys
▪ Produced in small amounts e.g. H3PO4
• Organic acids
▪ Role in cellular metabolism (reactants or products)
▪ Usually don't accumulate e.g. lactic acid, acetyl CoA
• Volatile acids
▪ Leave the body via the lungs e.g. H2CO3 leaves as CO2
o Carbonic acid - important volatile acid
CO2 + H2O = H2CO3 = H+ + HCO3-
• Spontaneously forms from water and CO2
• Process increased by carbonic anhydrase present in many cells e.g. RBC's, liver
and kidney cells
• A weak acid
• pCO2- is the most important factor affecting pH in body
• CO2 is usually converted to H2CO3 which then dissociates to H+ + HCO3-
• A rise in pCO2 means a drop in pH
• If high CO2, it is blown off via the lungs, so that H+ and HCO3- decrease and pH
rises
• CO2 transport in blood
▪ Formation of bicarbonate and carbonic acid is reversible
▪ In lungs, bicarbonate re-enters the RBC, recombines with H+ to form CO2
and water
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o Mechanisms of Acid-Base balance
• Long term management
▪ Excretion via the kidneys
• Secrete/reabsorb H+ into urine
• Secrete/reabsorb HCO3- into urine
• Controlling excretion of acids and bases
• Generate buffers that enter bloodstream
▪ Excretion via the lungs
• Affect pH balance through elimination of CO2 - breathing
• Short term/temporary management
▪ Buffers: temporarily neutralise acids/alkaline for homeostasis
o Buffers
• Dissolved compounds that stabilise and resist change to pH
• A substance appearing as a combination of its weak acid form and weak base
working together
• Weak acids donate H+ as pH rises
• Weak bases absorb H+ as pH rises
• Limitations
▪ Provide only temporary solution
▪ Don't eliminate H+ ions
▪ Supply of buffer molecules is limited
• 3 major buffer systems
▪ Protein buffer systems
• Help regulate pH in ECF and ICF
• Interact extensively with other buffer systems
• e.g. plasma proteins, Hb
▪ Phosphate buffer system
• Buffers pH of ICF and urine
▪ Carbonic acid-bicarbonate buffer system
• Most important in ECF
o Carbonic acid-bicarbonate buffer system
CO2 + H2O = H2CO3 = H+ + HCO3-
• Features
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Document Summary
Strong: completely dissociate: hcl -> h+ + cl, weak: incomplete dissociation, co2 + h2o = h2co3 = h+ + hco3, bases (strong/weak) Fixed acids: remain in solution in body fluids until excreted by kidneys, produced in small amounts e. g. h3po4, organic acids, role in cellular metabolism (reactants or products, usually don"t accumulate e. g. lactic acid, acetyl coa, volatile acids. Leave the body via the lungs e. g. h2co3 leaves as co2: carbonic acid - important volatile acid. Spontaneously forms from water and co2: process increased by carbonic anhydrase present in many cells e. g. rbc"s, liver and kidney cells. Is the most important factor affecting ph in body: a weak acid, pco2, co2 is usually converted to h2co3 which then dissociates to h+ + hco3, a rise in pco2 means a drop in ph. If high co2, it is blown off via the lungs, so that h+ and hco3 rises. Decrease and ph: co2 transport in blood.
