19- Regulation of [H+] in body fluids

Question 1

why is regulating H+ important?

Answer 1

-H+ affects protein function (enzymes, structurally)

• must be regulated within a narrow range and if it isn’t then…
• too little H+ increases excitability of neurons (seizures)
• too much H+ decreases excitability of neurons (comatose)

Question 2

relationship of H+ and seizures

Answer 2

too little H+ increases excitability of neurons

Question 3

relationship of H+ and comatose state

Answer 3

excess H+ decreases excitability of neurons

Question 4

arterial pH

Answer 4

7.4

Question 5

venous pH

Answer 5

7.35

Question 6

intracellular fluid pH

Answer 6

6.0 - 7.4

Question 7

cerebral spinal fluid pH

Answer 7

7.32

Question 8

urine pH

Answer 8

4.5 - 8.0

Question 9

acid vs base

Answer 9

acid
-compound which donates H+ or proton

base
-compound which accepts H+ or proton

Question 10

H+ in respiratory system

Answer 10

CO2 + H2O —> H2CO3 —> [H+] + HCO3-

Question 11

metabolic H+

Answer 11

H2PO4- —> H+ + HPO4

Question 12

H+ disorders

Answer 12

1. Respiratory acidosis
2. Respiratory alkalosis
3. meabolic acidosis
4. metabolic alkalosis

Question 13

respiratory acidosis

Answer 13

increased CO2
-hypoventilation

CAUSES

• depression of respiratory centers (anesthetics, sedatives, opioids, brain injury/disease, severe hypercapnia, hypoxia)
• neuromuscular disorders (spinal cord/phrenic nerve injury, polio, tetanus, myasthenia gravis, curare drugs, respiratory muscle disease)
• chest wall restriction (kyphoscoliosis, obesity)
• lung restriction (lung fibrosis, sarcoidosis, pneumothorax)
• pulmonary diseases (pneumonia, edema)
• airway obstruction (COPD, upper airway obstruction)

Question 14

respiratory alkalosis

Answer 14

decreased CO2
-hyperventilation

CAUSES

• origin in central nervous (anxiety, hyperventilation syndrome, encephalitis, meningitis, tumors)
• drugs or hormones (sacicylates, progesterone)
• bacteremias, fever
• pulmonary diseases (asthma, emboli)
• overventilation with mechanical ventilators
• hypoxemia, high altitude

Question 15

Metabolic acidosis

Answer 15

HCO3- decreased

CAUSES

• ingestion of toxic substances (methanol, ethanol, salicylates, ammonium chloride)
• loss of HCO3- (diarrhea, renal dysfunction)
• lactic acidosis (hypoxemia, anemia, shock severe exercise, acute respiratory distress syndrome)
• ketoacidosis (diabetes, alcoholism, starvation)
• renal dysfunction

Question 16

Metabolic alkalosis

Answer 16

HCO3- increased

CAUSES

• loss of H+ (vomiting, gastric fistulas, diuretic therapy)
• treatment with or overproduction of steroids (aldosterone)
• ingestion of excess HCO3- or other bases (antacids_

Question 17

if you have an arterial blood sample, how do you tell if its acidosis or alkalosis

Answer 17

pH
<7.4 = acidosis
>7.4 = alkalosis

Question 18

if you have an arterial blood sample with a pH of <7.4, how can you tell whether its metabolic or respiratory?

Answer 18

Metabolic acidosis has a HCO3- < 24mEq/L

Respiratory acidosis has a PCO2 > 40mmHg

Question 19

if you have an arterial blood sample with a pH of >7.4, how can you tell whether its metabolic or respiratory?

Answer 19

Metabolic alkalosis has a HCO3- >24mEq/L

Respiratory alkalosis has a PCO2 <40mmHg

Question 20

How to make up for respiratory acidosis and alkalosis

Answer 20

Renal Compensation

acidosis: HCO3- >24mEq/L
alkalosis: HCO3- <24mEq/L

Question 21

How to make up for metabolic acidosis and alkalosis

Answer 21

Respiratory compensation

acidosis: PCO2 <40mmHg
alkalosis: HCO3- >40mmHg

Question 22

CO2 hydration reaction

Answer 22

CO2 + H2O —> [H+] + HCO3-

Question 23

Respiratory acidosis

Answer 23

CO2 is above normal

Question 24

Metabolic acidosis

Answer 24

CO2 is below normal

Question 25

physical-chemical buffering is a result of

Answer 25

compounds in a solution minimize the charge in H+ in the solution when a strong acid or base are added to the solution NaOH --> Na+ + OH ---> NaHCO3 + H2O

Question 26

ion contents of extracellular fluid

Answer 26

HCO3- HPO4 Proteins

Question 27

ion contents of intracellular fluid

Answer 27

HPO4 | Proteins

Question 28

isohydric principle

Answer 28

when H+ is altered in a solution all buffer pairs will be affected

Question 29

determinants of H+ buffering

Answer 29

- concentration or amount of the buffer pair in the solution | - pK of the buffer pair relative to the pH of the solution

Question 30

pH and pK buffering

Answer 30

pH solution = pK buffer pair equal amounts of - H+ - acid - base when adding an acid or base, conditions are optimal for buffering around 6ish

Question 31

Physiologic H+ regulation

Answer 31

processes in the body that can alter the amount of the physical-chemical buffers 1. transmembrane exchange 2. pulmonary ventilation

Question 32

transmembrane exchange

Answer 32

- Intracellular fluid - High concentration of physical- chemical buffers Example: Respiratory or Metabolic Acidosis Extracellular Fluid Buffering of H+ is through movement of H+ into cells in exchange for Na or K+.

Question 33

pulmonary ventilation

Answer 33

-H+ buffering through HCO3- - H2CO3 buffer pair Example: During metabolic acidosis such as lactacidosis, the following reaction occurs: lactic acid --> lactate + H+ --> H+ + HCO3- --> H2CO3 --> H2O + CO2 and the CO2 is eliminated by the respiratory system *each CO2 that comes out takes care of one of the H+ ions made by the anaerobic cycle

Question 34

renal regulation of H+

Answer 34

1. excretion of titratable acid 2. reabsorption of bicarbonate 3. HCO3- regeneration -sulfuric acid -phosphoric acid -lactic acid -other Results in buffering -H+ by HCO3- -forming H2CO3- -dissociates into H2O and CO2 -eliminated by the lungs

Question 35

how does the brain regulate H+ concentrations

Answer 35

blood-brain barrier

Question 36

blood-brain barrier

Answer 36

-restricts charged particles movement (such as H+) - systemic metabolic acidosis and alkalosis - -cerebrospinal fluid [H+] changes only 10% (of the change in the blood [H+]) - but its ineffective in buffering of respiratory acidosis and alkalosis - -glial cells in the brain increase production of NH3 and lactic acid during respiratory acidosis and alkalosis respectively

Question 37

On admission a patient was lethargic, but 7 hours after correcting arterial pH with HCO3 infusion, he became comatose. There was no further treatment, but 22 hours later he was wide awake. explain this

Answer 37

the coma was due to too much H+ in the system after the HCO3 infusion but once everything settled and more CO2 and H2O were produced from the HCO3 the person woke up and was fine the brain was eventually able to correct itself with time (between 7 and 22 hours) Between 7 and 24 hours after treatment, CSF pH and HCO3- both increased as a result of HCO3- crossing the blood brain barrier or generation of HCO3- in the brain.

Question 38

H+ buffering or regulating mechanisms

Answer 38

Respiratory Component - rapid-acting - limitedbyHCO3-availability Transmembrane Exchange - slightlyslower - limited by phosphate sites Renal - slow to respond - minimal limitations in a healthy human - -in patient with renal dysfunction limited capability for excreting the acid

Question 39

clinical use of anion gap

Answer 39

Anions and Cations - Must be equal to maintain electrical neutrality - Clinically Na+ (144mM) is the only cation usually measured - Only anions measured are Cl- (108 mM/L and HCO-3 (24 mM/L). - Difference between anions and cations is 12mM/L - During metabolic acidosis, HCO-3 is decreased, but there is an increase in some anion such as lactate- to maintain electrical neutrality. - A clinically useful term to assess the degree of acidosis is the anion gap which in metabolic acidosis increases.