week 12 Flashcards
what is an acid?
any substance which can DONATE a H+ ion
what is a base?
any substance which can ACCEPT a H+ ion
how is acidity or alkalinity measured?
Acidity or Alkalinity of a solution is measured by
its pH
– pH is inversely proportional to the concentration of H+ ions
the more acidic a solution is …..
- The more acidic a solution is, the greater the
concentration of H+ ions - the lower its pH
- The more alkaline a solution is…..
- The more alkaline a solution is, the lower the
concentration of H+ ions - the higher the pH
what does pH affect?
pH affects all functional proteins and biochemical
reactions in the body, so pH is closely regulated
what is the Normal pH of body fluids:
– Arterial blood: pH 7.4
– Venous blood and interstitial fluid: pH 7.35
– Intracellular fluid: pH 7.0
what is Acidosis or acidemia?
Acidosis or acidemia: arterial pH <7.35
– the level of acidic compounds in the body rises or when the
level of alkaline compounds in the body falls
what is Alkalosis or alkalemia?
Alkalosis or alkalemia: arterial pH >7.45
– the level of alkaline compounds in the body rises or when the
level of acidic compounds in the body falls
what is most H+ produced by?
Most H+ is produced by metabolism.
Phosphorus-containing protein breakdown
releases phosphoric acid into extracellular fluid
– Lactic acid from anaerobic respiration of glucose
– Fatty acids and ketone bodies from fat metabolism
– H+ liberated when CO2 converted to HCO3
– in blood
what diets = more acid in blood.
Western diets are
generally high in
proteins
– Tends to acidify blood
by releasing more acids
during metabolism
what is Concentration of hydrogen ions regulated
sequentially by:
Chemical buffer systems and Physiological Buffering Systems
what is Chemical buffer systems and its effect?
Chemical buffer systems: rapid; first line of
defence
* minimises change in pH but does not remove acids or
bases from the body
what is physiological buffering systems and its effects?
Physiological Buffering Systems
* Respiratory mechanisms: act within 1–3 min
– removes carbon dioxide (which is acidic)
* Renal mechanisms: most potent, but require hours to
days to effect pH changes
– removes hydrogen (acid) and bicarbonate (base)
what happens to strong acids in water?
Strong acids dissociate
completely in water; can dramatically affect pH.
what happens to weak acids in water?
Weak acids dissociate
partially in water; are
efficient at preventing pH
changes
what happens to strong and weak bases in water?
Strong bases dissociate
easily in water; quickly tie
up H+. Weak bases accept H+
more slowly
Buffering a Solution diagram
what is a Chemical buffer?
system
of one or more
compounds that act to
resist pH changes when
strong acid or base is
added
– Bind H+ if pH drops;
release H+ if pH rises
what are some Chemical Buffer Systems?
- Bicarbonate buffer
system - Phosphate buffer system
- Protein buffer system
what does Bicarbonate Buffer System involve?
- Involves carbonic acid/H2CO3 (weak acid) and
bicarbonate/HCO3 (a weak base) - The major extracellular buffer system
what happens to bicarbonate buffer system if a strong acid is added?
- If strong acid added:
– HCO3
– (bicarbonate) ties up H+ and forms H2CO3 (carbonic acid)
– pH decreases only slightly
– HCO3
– concentration closely regulated by kidneys
what happens to bicarbonate buffer system If strong base added?
– It causes H2CO3 (carbonic acid) to dissociate and
donate H+ to form HCO3
– (bicarbonate)
– pH rises only slightly
Bicarbonate Buffer System equation
Bicarbonate Buffer System flowchart
what is the Phosphate Buffer System?
Action nearly identical to bicarbonate buffer
* Involves dihydrogen phosphate/H2PO4
– (weak acid)
and monohydrogen phosphate/HPO4
2– (a weak base)
* Effective buffer in urinary system and intracellular fluid,
where phosphate concentrations are high
what happens to Phosphate Buffer System if strong acid is added?
- If strong acid added:
- HPO4
2– (monohydrogen phosphate) ties up H+
and forms H2PO4
– (dihydrogen phosphate) - pH decreases only slightly
what happens to Phosphate Buffer System if strong base is added?
- If strong base added:
- It causes H2PO4
– (dihydrogen phosphate) to
dissociate and donate H+ to form HPO4
2–
(monohydrogen phosphate) - pH rises only slightly
Phosphate Buffer System equation
what does the Protein Buffer System include?
Intracellular proteins are most plentiful and powerful
buffers; plasma proteins also important
* Protein molecules are amphoteric (can function as
both weak acid and weak base)
– When pH rises (more alkaline), organic acid or carboxyl
(COOH) groups release H+
– When pH falls (more acidic), NH2 groups bind H+ to make
NH3 (Ammonia)
– Haemoglobin functions as intracellular buffer
What is physiological buffering systems?
- Chemical buffers cannot eliminate
excess acids and bases from the body - Respiratory and renal systems can
eliminate excess acids or bases from body
– Regulate amount of acid or base in body
– Act more slowly than chemical buffer systems
– Have more capacity than chemical buffer systems
What are some examples of Physiological Buffering Systems?
– Respiratory System
* Lungs eliminate volatile carbonic acid by eliminating CO2
– Renal System
* Kidneys eliminate nonvolatile acids produced by cellular metabolism
(phosphoric, uric, and lactic acids and ketones) to prevent metabolic
acidosis
* Kidneys also regulate blood levels of alkaline substances; renew
chemical buffers
Respiratory Regulation of H+: what happens during co2 unloading and loading
- During CO2 unloading (in the lungs), reaction shifts
to left (and H+ incorporated into H2O) - During CO2 loading (in the tissues), reaction shifts
to right (and H+ buffered by proteins)
what is Respiratory Regulation of H+?
Respiratory system eliminates CO2 (“acidic”)
* A reversible equilibrium exists in blood
Respiratory system impairment causes …
- acid-base imbalances
– Hypoventilation –> respiratory acidosis
– Hyperventilation –> respiratory alkalosis
what 2 types does Respiratory Regulation of H+ involve?
Hypercapnia (CO2 retention) and Hypocapnia (low CO2)
what does Hypercapnia (CO2 retention) involve?
– Rising plasma CO2 (which leads
to rises in H+ - acidosis) activates
peripheral chemoreceptors
–> Increased respiratory rate and
depth
–> More CO2 is removed from the
blood
–> H+ concentration is reduced
what does Hypocapnia (low CO2) involve?
Decreasing plasma CO2 (which
leads to decreases in H+ -
alkalosis) activates peripheral
chemoreceptors
–> decreased respiratory rate
and depth
–> More CO2 is retained in the
blood
–> H+ concentration increases
what are the Most important renal mechanisms of acid-base balance?
- Most important renal mechanisms:
– Conserving (reabsorbing) or generating new HCO3-
– Excreting HCO3-
what happens When the body is in alkalosis:
When the body is in alkalosis:
– Kidneys secrete HCO3-
– Reclaim H+ to acidify blood
what happens when the body is in acidosis:
– Kidneys secrete H+
– Reclaim HCO3- to increase the alkalinity of the blood
how does Rate of H+ secretion change with extracellular fluid
CO2 levels?
– ^ CO2 in peritubular capillary blood –> ^ rate of H+ secretion
– System responds to both rising and falling H+ concentrations
what are the Abnormalities of Acid-Base
Balance?
- Effects of Acidosis and Alkalosis.
what are the Effects of Acidosis and Alkalosis?
– Blood pH below 6.8 –> depression of CNS –> coma –> death
– Blood pH above 7.8 –> excitation of nervous system –>
muscle tetany, extreme nervousness, convulsions,
death often from respiratory arrest
what is Respiratory acidosis and alkalosis caused bu and what is it?
Respiratory acidosis and alkalosis
* Caused by failure of respiratory system to perform pHbalancing role
* Single most important indicator is blood PCO2
what is Metabolic acidosis and alkalosis?
- All abnormalities other than those caused by PCO2 levels in
blood; indicated by abnormal HCO3- levels
what is the most important indicator of adequacy of
respiratory function?
Most important indicator of adequacy of
respiratory function is PCO2 level (normally
35–45 mm Hg)
what does PCO2 above 45 mm Hg mean?
PCO2 above 45 mm Hg –> respiratory acidosis
* Common cause of acid-base imbalances
* Due to decrease in ventilation or gas exchange
* CO2 accumulates in blood
* Characterised by falling blood pH and rising PCO2
what does PCO2 below 35 mm Hg mean?
– PCO2 below 35 mm Hg–>respiratory alkalosis
* Common result of hyperventilation often due to stress or
pain
– CO2 eliminated faster than produced
what is Metabolic acidosis and what does it cause?
- Metabolic acidosis – low blood pH and HCO3
– Causes: - Ingestion of too much alcohol (–> acetic acid)
- Excessive loss of HCO3- (e.g., persistent diarrhea)
- Accumulation of lactic acid (exercise or shock), ketosis in
diabetic crisis, starvation, and kidney failure
what is Metabolic alkalosis and what does it cause?
Metabolic alkalosis (much less common than
metabolic acidosis)
– Indicated by rising blood pH and HCO3-
– Causes include vomiting of acid contents of stomach or
by intake of excess base (e.g., antacids)
what happens when there is a acid-base imbalance due to malfunction of
physiological buffer system?
If acid-base imbalance due to malfunction of
physiological buffer system, other one tries to
compensate
– Respiratory system attempts to correct metabolic
acid-base imbalances
– Kidneys attempt to correct respiratory acid-base
imbalances
* Respiratory system cannot compensate for
respiratory acid-base imbalances
* Renal system cannot compensate for acid-base
imbalances caused by renal problems
what does changes in respiratory rate and depth mean In renal metabolic acidosis?
– In metabolic acidosis:
* High H+ levels stimulate respiratory centres
* Rate and depth of breathing elevated
* Blood pH is below 7.35 and HCO3
– level is low
* As CO2 eliminated by respiratory system, PCO2 falls below
normal
what does changes in respiratory rate and depth mean In renal metabolic alkalosis?
– In metabolic alkalosis:
* Slow, shallow breathing
* Allows CO2 accumulation in blood
* Blood pH is over 7.45 and HCO3
– level is high
* As CO2 is retained, PCO2 rises to normal levels
what is the Renal Compensation for
Respiratory Acid-Base Imbalance.
- Hypoventilation causes elevated PCO2 and low
pH
– Respiratory acidosis
– Renal compensation: increases HCO3
– levels by
retaining HCO3
– and secreting H+ - Hyperventilation causes low PCO2 and high pH
– Respiratory alkalosis
– Renal compensation: decreases HCO3
– levels by
increasing the secretion of HCO3
– and retaining H+
