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CPR 2 > Acid And Base 1 > Flashcards

Acid And Base 1 Flashcards

1
Q

What are acids?

A

Acids are compounds that can donate a hydrogen ion to a solution/accepts electron

  • Acidosis can be due to to addition of acid
  • Alkalosis can be due to loss of acid
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2
Q

What are bases?

A

Bases are compounds that accept hydrogen ions/donates electrons

  • Acidosis can be due to loss of a base
  • Alkalosis can be due to gain of base
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3
Q

Contrast strong and weak acids

A

Strong acids tend to dissociate completely in solution

Weak acids tend to dissociaate to a limited extent (function as better buffers)

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4
Q

How is pH calculated?

A

The negative log of [H+]; at a plasma pH = 7.4, the [H+] = 35- 45nmol/L

Nite that the [H+] abd pH are inversely related, and pH is a logarithmic scale

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5
Q

What is the Henderson-Hassalbach equation?

A

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

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6
Q

What is a buffer?

A

Buffers consists of a weak acid (HA) and it’s conjugate base(A-)

Conjugate pair= acid and base that differ by the presence of a proton

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7
Q

What is the function of Buffers?

A

These resist a change in pH (minimize a pH change), on addition of small quantities of acid (H+) or base (OH-)

Buffers can reversibly bind to H+

When pH of the solution is equal to pKa,

[weak acid]= [conjugate base]

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8
Q

What does buffering capacity depend on?

A

pKa(dissociation constant): buffers in body fluids require pKa around 7.4
Concentration of buffer: higher the concentration of buffer, higher 8s the buffering capacity

Usually effective when pH is pKa +/-1
-example: aceitic acid-acetate buffer is effective at a pH range of 3.8-5.8 (pK=4.8)

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9
Q

What are the examples of body buffers?

A

H2CO3- NaHCO3^-(bicarbonate buffers) ok=6.1
NaH2PO4^- Na2HPO4^2- (phosphate buffer) pk=6.8
NH4^+Cl NH3 (ammonia buffer) pk=9.2

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10
Q

What are the implications of the Henderson’s-hassalbach equation?

A

If pKa for a weak acid is known, H-H equation used to calculate the ratio of weak acid to conjugate base at any pH

At a pH of 1 unit below pKa, the ratio of [acid]:[base]=10:1

At a ph of 1 Unit ab9ve pKa, the ratio of [acid]:[base]= 1:10

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11
Q

Describe drug ionization of acidic medicine

A 
Uncharged forms (permanent forms) easily absorbed
-Cross lipid bilayermembrane
  • Acidic drugs (pK<7) present in uncharged form in stomach;
  • Acidic drugs are better excretedin alkaline urine

HA A-
RCOOH RCOO-

Basic drugs (pK>7) better in intestine, basic drugs better excreted in acidic urine

BHB

RNH3+R-NH2

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12
Q

Describe the absorption of acidic drugs like aspirin

A
  • Unchanged form (-COOH) in stomach(ph1.5), is absorbed in the stomach
  • pK of aspirin (Acetyl salicylic acid)=3.5

HAA-

In stomach,[Uncharged form; COOH]» [Charged form; COO-] —Hence absorbed in stomach

In intestine(pH=7.5], [Uncharged form; COOH] &laquo_space;[Charged form; COO-]

Calculate ratio of charged to uncharged forms in stomach and intestine

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13
Q

Describe absorption of basic drugs:morphine

A

Morphine (weak base) is charged in stomach (-NH3^+)

Uncharged form at intestinal pH (pH about 8), and mainly absorbed in intestine (pK morphine about 7.9)

(pH<7.9) R-NH3^+ R-NH2 (pH>7.9)(BH+B)

In stomach, [Charged form; -NH3^+]» [Uncharged form;NH2]
-Not as well absorbed in stomach

In intestine, [Unchsrged form;-NH2]>[Charged form;-NH3^+]
-Better absorbed in intestine (compared to stomach, [Uncharged form]> [Charged form] in intestine)

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14
Q

Explain the excretion of drugs

A
  • To increase excretion, it is important to prevent its Reabsorption from tubule
  • Adjust urine pH to ionize drug
  • As a result, drug will be “trapped” in tubule
  • Weak acids excreted better in alkaline urine (ionized at alkaline pH; R-COO-)
    • Salicylate (aspirin) poisoning treated by alkaline zing urine

Weak bases excretedbetter in acidic urine (Ionized form at acidic pH; R-NH3@^+)

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15
Q

Calculate the ratios of acids and bases

A

Aspirin: pk is 3.5
At stomach pH of 1.5, the difference is: 3.5-1.5=2
COOH: COO-=100:1
In the intestine pH of 7.5, the difference is: 7.5-3.5=4
COOH:COO-= 1:10000(10^4)
Urine pH is 6.5. Calculate ratio

Calculate using the pK of morphine =8
Assume, stomach pH is 2 the difference is 8-2=6
NH3+:NH2=1000000:1(10^6:1)
Intestine pH is 8, the difference is: 8-8=0
NH3+:NH2= 1:1= equal concentration of charged and uncharged forms
Urine pH is 6 calculate ratio

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16
Q

Explain the acid base balance if the body

A

Plasma pH=7.4(+/-0.05); [H+] = 35-45 mmol/L

Note logarithmic relation and inverse relation between pH and [H+]

Intracellular enzymes and protein functions are pH dependent

Metabolism produces several acids (about 20,000 mmol/day)

Three systems to regulate [H+]:

  • Buffers (first line)-immediate defense
  • Respiratiry system (second line)- regulates PCO2
  • Renal system (third line)-regulates HCO3- leveks
17
Q

What are the examples of volatile acids ?

A

Carbon dioxide- major metabolic acid (15,000-20,000 mEq/day)

-handled by lungs

18
Q

What are the nonvolatile acids?

A

50-100 mEq/day
-handled by kidneys
Inorganic acids
-Sulfric acid(H2SO4) formed by sulfur containing amino acid metabolism
-Phosphoric acid (H3PO4) formed by metabolism of phospholipids
Organic acids
-Ketone bodies (acetoacetic acid, 3-hydroxybutyric acid)
-Lactic acid (glycolysis under anaerobic conditions)

19
Q

How is plasma pH 34-45 mmol/L maintained despite addition of volatile and nonvolatile acids?

A

pH maintenance: Buffers, respiratory system and kidneys

  • On a mixed diet, production of acids (Sulfric, hydrochloric and phosphoric ) as a result of protein metabolism
  • Acids buffered by chemical buffer bases, ECF HCO3-
  • Respiratory system disposes off CO2
  • Kidneys eliminate H+ (combined with urinary buffers) and anions (sulfate/phosphate) in urine. They add new HCO3^- to ECF to replace HCO3^- consumed in buffering strong acids. They reabsorb filtered HCO3^-
20
Q

Explain the defenses against changes in proton concentration

A

Three primary systems to regulate H+:
1. Buffering systems (ECF and ICF):
IMMEDIATELY combine with acid/base to prevent large changes in [H+]

  1. Respiratory response:
    Within minutes to eliminate CO2(H2CO3)
  2. Renal response
    Slowest-hours/days to eliminate excess acid/base

MOST powerful regulatory system

21
Q

Explain body buffers as the first line of defense

A

Plasma pH is 7.35-7.45 and intracellular pH is about 7.1

Buffers minimize change in pH (does NOT prevent it) on addition of small quantity of acid or base

Major body buffer systems

  • Bicarbonate-carbonic acid buffer (ECF buffer)
  • Hemoglobin - due to histidine residues
  • Phosphate buffer (ICF buffer and renal tubular buffer)
  • Proteins(ICF and plasma)-due to histidine residues
  • Ammonia buffer (renal tubule)
22
Q

Explain the mechanism of bicarbonate buffer

A
  • CO2 + water forms carbonic acid (H2CO3)
  • Weak acid (H2CO3) and conjugate base (HCO3^-)
  • pKa bicarbonate buffer is 6.1 (close to plasma pH of 7.4)
  • High concentration in ECF
  • Carbonic anhydrase has different isoforms in RBC, renal tubule, parietal cells in stomaach
23
Q

Whaat is the impact of the bicarbonate buffer?

A
  • Addition of H+, forms H2CO3–> CO2 that is lost via lungs
  • In clinical setting, applying H-H equation for bicarbonate buffer
  • pKa of bicarbonate buffer is 6.1

Plasma pH of 7.4, ratio of [Base]/[Acid] is 20:1
Normal [HCO3^-]=22-26 mEq/L(24 mEq/L)
Arterial PaCO2= 38-42 mmHg. (40mmHg)

24
Q

What is the ratio of bicarbonate buffer?

A

Plasma pH of 7.4, ratio of [Base]/[Acid] (24:1.2)=20.1

25
Q

How are bicarbonate and. PaCO2 levels regulated?

A

Bicarbonate levels-renal system

PaCO2 levels -respiratory system

Bicarbonate levels and PCO2 levels independently regulated by two different systems (open system)

Assess acid-base status: measure blood pH, PaCO2 and HCO3^-

26
Q

What is the central message of the H-H equation?

A

Plasma pH= simple function of the HCO3^-: aPaCO2 ratio

Increased (HCO3^-: aPCO2)= alkalosi; could be due to HCO3^- increase or PCO2 decrease

Decreased (HCO3^-:aPCO2)= acidosis; could be due to HCO3^- decreased or PCO2 increase

27
Q

Explain the handling of volatile acid CO2

A

Daily CO2 production about 15,000- 20,000 mEq/day

CO2 lost via the lungs (volatile acid)

Respiratory system regulates PaCO2 (acid component) of bicarbonate buffer system

  • CO2 produced by carbohydrate, fat and amino acid metabolism
  • Hemoglobin (non-bicarbonate buffers) buffers and accepts H+ formed during CO2 transport from tissues
  • About 75% of CO2 transported as HCO3^-
    • HCO3^- in venous blood higher than in arterial blood

Carbonic anhydrase is rich in RBC

28
Q

How is CO2 transported from tissues to lungs?

A
  1. Oxygen dissociates from hemoglobin to form deoxyhemoglobin
  2. CO2 diffuses from tissues into blood
  3. Formation of carbonic acid in presence of carbonic anhydrase
  4. Carbonic acid (weak acid) dissociation
  5. Hydrogen ions formed buffered by hemoglobin (histidine)
29
Q

Describe CO2 in the lungs

A
  1. Oxygen diffuses from alveoli into RBC and binds to Hb to form OxyHb
  2. H+ released from histidine residues from Hb
  3. H+ associate with HCO3^- to form carbonic acid (H2CO3^-)
  4. CO2 formed from carbonic acid by carbonic anhydrase
  5. CO2 diffuses into the alveoli and is lost by expiration
30
Q

What are functions of chemoreceptors in regulating CO2 and pH?

A

Chemoreceptors: increased PaCO2–> increases proton concentration which stimulates respiratory center increasing respiration -hyperventilation

Control centers respond by increasing /decreasing ventilation to keep PaCO2 near 40 mmHg(-ve feedback controller)

31
Q

What leads to respiratory acid base disorders?

A
  • When CO2 production= CO2 loss via expiration, arterial PaCO2 is maintained constant
  • Disorders which decrease rate of ventilation result in CO2 accumulation (respiratory acidosis) and increase in PaCO2

Increased CO2 + H2O H2CO increased H+ + HCO3^-

Disorders wh8ch increase rate of ventilation result in washout of CO2 (respiratory alkalosis ) and a fall in PaCO2

Decreaded CO2 + H2O H2CO3 decreased H+ + HCO3^-

32
Q

What is the role of Respiratory center in pH in regulation?

A

-Respiratiry center responds to changes in pH

When blood pH falls(metabolic acidosis), stimulates respiratory center—> increased rate and depth of respiration (hyperventilation). Increased CO2 washout, lowers PaCO2(compensatory response)

When blood pH increases (metabolic alkalosis), inhibits respiratory center—> decrease in respiratory rate (hypoventilation). Increased CO2 retention, increases PaCO2 (compensatory response)

Respiratory system regulates PaCO2 (ac8d) components of bicarbonate buffer

CPR 2 (32 decks)

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