Flashcards
Acid-base physiology
Cards in this deck (71)
- 1What is the acid-base balance?The regulation of hydrogen ions
- 2What is pH proportional to?1/[H+]
- 3What is pH equal to?-log10[H+]
- 4What is the pH of water?7 - neutral
- 5What does doubling or halving [H+] do to the pH? What does this mean?1) Causes a shift of 0.3
2) Any movement along the pH equates to a large shift in [H+] - 6What is the [H+] when the pH is 6.4? 8.4?1) 400 nmol/L
2) 4 nmol/L - 7What is the pH of: 1) Lemon juice 2) Wine 3) Rain 4) Human blood 5) Baking soda 6) Detergent 7) Bleach1) 2.0
2) 4.0
3) 5.5
4) 7.5
5) 8.5
6) 10.0
7) 12.5 - 8What is the optimal pH range for most life?6.5-8.2
- 9What is the normal range of pH in the ECF?7.35-7.45
- 10What can movement outside the above ranges result in?Circulatory collapse, coma and death
- 11What is difference between acidemia and acidosis?1) Acidemia applies to the blood
2) Acidosis applies to the entire body - 12What are the four major metabolic sources of H+?1) Carbohydrates
2) Proteins
3) Fats
4) DNA - 13What is produced by metabolism of carbohydrates (glucose)? (2)1) Aerobic respiration - carbonic acid
2) Anaerobic respiration - lactic acid - 14How are proteins related to the production of H+?Oxidation of sulfur-containing amino acids results in the production of sulfuric acid
- 15How do fats contribute to the production of H+? When does this happen?1) The incomplete oxidation of fatty acids leads to the production of acidic ketone bodies.
2) If you haven't eaten for a while - body starts to use energy stores - 16How does DNA contribute to the production of H+?Hydrolysis of phosphoproteins and nucleic acid leads to the production of phosphoric acid,
- 17What are the three ways in which pH is maintained? Over what sort of time scales do these mechanisms work?1) Chemical buffers - very rapid (less than a second)
Excretion of acid:
2) Respiratory regulation - seconds to minutes
3) Renal regulation - minutes to hours - 18What are the three chemical buffer systems?1) Phosphate buffer system
2) Protein buffer system
3) Carbonic acid-bicarbonate buffer system - 19Where does the phosphate buffer system work?In the intracellular fluid
- 20What are the three components of the protein buffer system? Where does the protein buffer system work?1) Haemoglobin buffer system - red blood cells only (ICF)
2) Amino acid buffers - all proteins
3) Plasma proteins - ECF - 21Where does the carbonic acid-bicarbonate buffer system work?In the ECF
- 22Define a buffer solutionA solution which can maintain a nearly constant pH if it is diluted, or if strong acids or bases are added.
- 23What does a buffer solution consist of?A mixture of a weak acid and its conjugate base (or a weak base and its conjugate acid).
- 24Describe the equation for the phosphate buffer system. Where is this important?1) [H+] + [HPO4^2-] ----- [H2PO^4-]
2) Minor relevance in the ECF but is important as part of the renal regulation mechanism/in the urine - 25What is the mechanism of protein buffer systemsAcidic and basic side chains can give up or take up H+:
If the pH rises (i.e. solution becomes more alkaline) the carboxyl group of amino acid can donate a H+. If the pH falls (the solution become more acidic) the amine group can act as a weak base and accept an H+. - 26Why can proteins have quite a big effect on pH despite only behaving as weak acids/bases?As there are so many proteins
- 27What is the equation which describes the haemoglobin buffer system? What does it buffer? Why is it useful?1) [H+] + [Hb] ---- [HHb]
2) Buffers changes in H+ caused by CO2 levels
3) Can be carried to an excretion mechanism - 28Describe how haemoglobin can help buffer H+ in tissues?In the tissues:
CO2 + H20 --- H20CO3 ---- H+ + HCO3-
H+ + Hb --- HHb
This can then be carried to the lungs where HHb releases H+ and takes up O2
H+ + HCO3- ---- H2CO3 ----- H20 + CO2
and the CO2 is exhaled - 29What is the bicarbonate/carbon dioxide buffer system useful for?CO2 + H20 --- H2CO3 --- H+ + HCO3
Can buffer H+ from any OTHER source than CO2 e.g. lactic acid, salicylic acid but CANNOT buffer CO2 retention due to a respiratory problem (A system cannot buffer itself... If the change in acidity it due to a respiratory problem, i.e. something is dysfunctional, then the system will not be able to correct itself. Moreover changes in HCO3- happen over a long time from kidney regulation and cannot adapt to an acute problem). - 30What are the systems which buffer H+ in the blood?1) Bicarbonate
2) Phosphate
3) Plasma protein
4) Haemoglobin - 31What is the buffer capacity (in Mmoles H+ L^-1) of: 1) Bicarbonate 2) Haemoglobin 3) Protein 4) Phosphate What therefore is the total blood buffer capacity?1) 18
2) 8
3) 1.7
4) 0.3
4) 28 - 32How do the lungs help regulate acid-base balance? What may this alter? What is the normal level of plasma CO2?1) By eliminating or retaining CO2
2) May alter the rate and depth of respirations
3) 35 to 45mmHG = 4.7-6.0kPA - 33How do the kidneys help regulate acid-base balance? How long does this take? What is the normal level of plasma bicarbonate?1) Through renal retention or excretion of H+/CO3-
2) May take hours or days to correct pH
3) 22 to 26 mEq/L - 34How does the respiratory acid-base regulation compare to that of the renal system? (2)1) Much faster
2) Much smaller clearance ability - 35How is pH buffered in the kidney tubules?Bicarbonate is reabsorbed by a complex method, involving sodium transport. Hydrogen ions excreted, buffered by ammonia and phosphate. Balance of acid/alkaline urine regulates ECF acid-base balance.
- 36What is the Henderson-Hasselbach equation?H20 + CO2 --- H2CO3 ---K2/K1--- H+ + HCO3^-1
- 37What is the equilibrium constant?ka = k2/k1 = [H+][HCO^3-]/[H2CO3]
- 38What is acidity proportional to?[HCO^3-]/[CO2]
- 39How is an acid-base imbalance diagnosed? (3)1) Clinical history
2) Physical examination
3) Arterial blood gas analysis - 40Why is heparin used when a blood sample is taken?To reduce bleeding
- 41What causes respiratory acid base disorders?When abnormal respiratory function causes a rise in CO2 in ECF
- 42What is the basis of metabolic acid-base disorders?Generation of organic or fixed acids - anything which affects the concentration of bicarbonate ions in ECF
- 43What is measured in an arterial gas printout? (3)1) pO2
2) pCO2
3) pH - 44What is HbO2% and how is it calculated?Hb saturation - calculated from pO2 (from O2 dissociation curve; assumes normal p50 and no abnormal Hb)
- 45For the following, state the normal arterial blood gas values: pH PaO2 PaCO2 Bicarbonate Base excess1) 7.35-7.45
2) >11 kPA or 80-100 mmHg
3) 4.7-6.0 kPa or 35-45 mmHg
4) 22-26 mmol/L
5) +/- 2 mEq/l - 46What are the mechanisms behind respiratory acidosis? (2)1) Hypoventilation
2) Excess CO2 production - 47What are the different possible etiologies of respiratory acidosis? (6)1) COPD
2) Neuromuscular disease
3) Respiratory center depression
4) Late ARDS
5) Inadequate mechanical ventilation
6) Sepsis or burns - 48What will you see with respiratory acidosis? (4)1) CO2 retained
2) H+ and bicarbonate generated
3) pH may fall
4) Organic base (calculated 'base excess' may increase to compensate) - 49What is respiratory alkalosis calculated with?Hyperventilation
- 50What are the homeostatic responses to decreased pCO2 (as a result of hyperventilation)?1) Respiratory alkalosis which causes:
a) Renal compensation
b) Buffer system other than the carbonic system to release H+ ions
c) Inhibition of arterial and CSF chemoreceptors which leads to:
i) Respiratory compensation (decreased respiratory rate) and increase pCO2 - 51What are the risk factors and etiology of respiratory alkalosis? (5)Hyperventilation due to:
1) Extreme anxiety, stress or pain
2) Elevated body temperature
3) Overventilation with ventilator
4) Hypoxemia (emphysema or pneumonia)
5) CNS trauma or tumor - 52What will you see in association with respiratory alkalosis? (3)1) CO2 falls
2) Law of mass action - H+ and bicarbonate become depleted
3) pH may rise - 53What are the major causes of metabolic acidosis? (2)1) Excess acid production or retention
2) Bicarbonate loss - 54Why might there be an excess of acid production or retention? (2)1) Inability to excrete hydrogen ions via kidney
2) Production of large numbers of fixed/organic acids - 55What may cause bicarbonate loss?Could be due to chronic diarrhea
- 56What are the homeostatic mechanisms which occur in response to metabolic acidosis? (3)1) Buffer systems other than carbonic acid-bicarbonate system absorb H+ ions
2) Renal compensation - increased H+ secretion, increased HCO3- generation
3) Increased pCO2 - respiratory compensation (increased respiratory rate) - decreased PO2 - 57What are the risk factors/etiology of metabolic acidosis? (4)1) Conditions which increase acids in the blood
2) Prolonged diarrhea
3) Toxins (Antifreeze or aspiring)
4) Carbonic anhydrase inhibitors - 58What are the four conditions which may increase acids in the blood? (4)1) Renal failure
2) DKA
3) Starvation
4) Lactic acidosis - 59What would you expect to see in association with metabolic acidosis? (5)1) Unwell patient
2) H+ generated
3) Law mass action - H+ combines with bicarbonate, which falls
4) Extra CO2 generated, rapid expiration by patient to excrete, so pCO2 falls
5) pH falls (effects on various - includes cardiac function) - 60When does metabolic alkalosis occur (and why)?When HCO3- concentrations become elevated
1) Caused by retention of carbohydrate
2) Loss off organic acid - eg repeated vomiting - 61What is the homeostatic response to metabolic alkalosis?1) Increased HCO3- leads to renal compensation (increased H+ and HCO3- secretion)
2) The increased pH leads to buffer systems (other than the carbonic acid system) donating H+ ions and respiratory compensation (decreased respiratory rate) and therefore increased pCO2 - 62What are the risk factors of/etiology behind metabolic alkalosis? (3)1) Acid loss
2) Loss of potassium
3) Antacids - 63What might cause acid loss? (2)1) Vomiting
2) Gastric suction - 64What might cause a loss of potassium? (2)1) Steroids
2) Diuresis - 65What will you see with metabolic alkalosis? (4)1) Bicarbonate rises
2) Law of mass action - H+ combines with bicarbonate so H+ falls
3) pCO2 may rise until body has time to correct
4) pH rises - 66See handout for fall homeostatic flow chartX
- 67What is the anion gap?Contribution of unmeasured anions to acidosis - difference between the total of sodium and potassium ion concentration, minus the total of chloride and bicarbonate concentration. Measure of the difference between unestimated anions - phosphate, acetate and ketones - and cations
- 68What is the equation for the anion gap?AG = [K+] + [Na+] - [Cl-] + [HCO3-] (plasma concentrations)
- 69What is the normal range for the anion gap?8-12 mmol/L
- 70What does a high anion gap indicated?Indicates a loss of HCO3- without concurrent increase in Cl-. Electroneutrality maintained by elevated levels of anions like lactate, beta-hydroxybutyrate and acetoacetate, PO4- and SO4- - these anions are not part of the anion-gap calcultaion and therefore a high anion gap results
- 71XIn a normal blood test you measure K+ and Na+ as well as Cl- and HCO3-. The anion gap is all the other ions (usually lactate, ketones and phosphates etc.) which make you electrically neutral (difference between negative and positive ions). If the gap increases it is filled by the above.