Respiratory Acid base balance by Dr. Samreena

Respiratory regulation of Acid-Base Balance

DR. SUMREENA MANSOOR

ASSISTANT PROF OF BIOCHEMISTRY

DEPT OF BIOCHEMISTRY & MOLECULAR BIOLOGY

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

pH Review


The Body and pH


Acids are H+ donors. Bases are H+ acceptors, or give up OH- in

solution. Acids and bases can be:

Strong – dissociate completely in solution

HCl, NaOH Weak – dissociate only partially in

solution Lactic acid, carbonic acid


Types of Acids in the Body

Volatile acids: Can leave solution and enter the

atmosphere. H2C03 (carbonic acid). Pco2 is most important factor in pH of

body tissues.



Fixed Acids: Acids that do not leave solution. Sulfuric and phosphoric acid. Catabolism of amino acids, nucleic

acids, and phospholipids.



Organic Acids: Byproducts of aerobic metabolism,

during anaerobic metabolism and during starvation, diabetes.

Lactic acid, ketones.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Small changes in pH can produce major disturbances

Most enzymes function only with narrow pH ranges

Acid-base balance can also affect electrolytes (Na+, K+, Cl-)

Can also affect hormones


The body produces more acids than bases

Acids take in with foods Acids produced by metabolism of

lipids and proteins Cellular metabolism produces CO2. CO2 + H20 ↔ H2CO3 ↔ H+ +

HCO3-


Henderson-Hasselbalch Equation


APPLICATIONS OF HH EQUATION Analysis of dissociation of the alanine

in the same way as described for acetic acid

Use to calculate how pH of a physiologic solution responds to changes in the concentration of a week acid and/or it’s corresponding salt form.

Example Bicarbonate buffer system (How HCO3 and CO2 Influence pH)


APPLICATIONS OF HH EQUATION Useful for calculating ionic forms of

acidic and basic drugs. Acidic drug HA H++A-

Example: Aspirin Basic drug BH+ B+H+

Example: Morphine Drug can readily pass through the

membrane if it is uncharged


APPLICATIONS OF HH EQUATION

How much drug is found on either

side of a membrane that separates

two compartments that differ in

pH, for example, the stomach (pH

1.0-1.5) and blood plasma (pH 7.4)


Buffer Systems

Provide or remove H+ and stabilize the pH.

Include weak acids that can donate H+ and weak bases that can absorb H+.

Change in pH, after addition of acid, is less than it would be in the absence of buffer.


Chemical Buffers

Act within fraction of a second. Protein. HCO3

-. Phosphate.


Proteins

COOH or NH2. Largest pool of buffers in the body. pKa close to plasma. Albumin, globulins such as Hb.


Protein Buffers Includes hemoglobin, work in blood Carboxyl group gives up H+ Amino Group accepts H+

Glutamate, aspartate, histidine, arginine, lysine Additional potentially charged groups in side

chain


Bicarbonate buffer Sodium Bicarbonate (NaHCO3) and

carbonic acid (H2CO3) Maintain a 20:1 ratio : HCO3

- : H2CO3

HCl + NaHCO3 ↔ H2CO3 + NaCl

NaOH + H2CO3 ↔ NaHCO3 + H2O


HCO3-

pk= 6.1

Most important ECF buffer.

Present in large quantities.

Respiratory and renal systems act

on this buffer system.


Phosphate buffer Major intracellular buffer H+ + HPO4

2- ↔ H2PO4-

OH- + H2PO4- ↔ H2O + HPO4

2-

pk = 6.8

Better buffer in ICF (kidneys and bone)


Rates of correction

Buffers function almost

instantaneously

Respiratory mechanisms take several

minutes to hours

Renal mechanisms may take several

hours to days


Respiratory System

2nd line of defense. Acts within min. maximal in 12-24 hrs. H2CO3 produced converted to CO2, and

excreted by the lungs. Powerful, but works with volatile acids Exhalation of carbon dioxide. CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3

-

Body pH can be adjusted by changing rate and depth of breathing


Renal system

Can eliminate large amounts of acid

Can conserve and produce

bicarbonate ions

Most effective regulator of pH

If kidneys fail pH balance fails


Urinary Buffers

Urine pH = 4.5

H+ secreted into the urine tubule

and combines with HPO4-2 or NH3.

HPO4-2 + H+ H2PO4

-2

NH3 + H+ NH4+


Acid-Base Imbalances pH< 7.35 acidosis

pH > 7.45 alkalosis

The body response to acid-base imbalance is

called compensation

May be complete if brought back within

normal limits

Partial compensation if range is still outside

norms.


Compensation

If underlying problem is metabolic,

hyperventilation or hypoventilation

can help : respiratory

compensation

If problem is respiratory, renal

mechanisms can bring about

metabolic compensation


Acidosis Principal effect of acidosis is depression of the

CNS through ↓ in synaptic transmission

Generalized weakness

Deranged CNS function the greatest threat

Severe acidosis causes

Disorientation

Coma

Death


Alkalosis

Alkalosis can cause

It can cause :

Nervousness

Muscle spasms or tetany

Convulsions

Loss of consciousness

Death


Respiratory Acidosis

Carbonic acid excess caused by blood levels of CO2 above 45 mm Hg

Hypercapnia – High levels of CO2 in blood

Chronic conditions: Depression of respiratory center in brain

that controls breathing rate – drugs or head trauma

Paralysis of respiratory or chest muscles Emphysema


Respiratory Acidosis

Acute conditions:

Adult Respiratory Distress Syndrome

Pulmonary edema

Pneumothorax


Compensation for Respiratory Acidosis

Kidneys eliminate hydrogen ion and retain

bicarbonate ion

Acute respiratory failure:

pH low,[HCO-3] high normal, or slightly raised

Chronic respiratory failure:

pH normal or low depending upon chronicity,

[HCO-3] raised


Signs and Symptoms of Respiratory Acidosis

Breathlessness Restlessness Lethargy and disorientation Tremors, convulsions, coma

Respiratory rate rapid then gradually

depressed

Skin warm and flushed due to

vasodilatation caused by excess CO2


Treatment of Respiratory Acidosis

Restore ventilation Treat underlying dysfunction or

disease


Respiratory Alkalosis

Carbonic acid deficit

pCO2 less than 35 mm Hg

(hypocapnea)

Primary cause is hyperventilation


Respiratory Alkalosis Conditions that stimulate respiratory

center: Hysterical over breathing (overrides normal

respiratory control) Raised ICP (Which stimulate respiratory

centre) Hypoxia Pulmonary edema Lobar pneumonia Pulmonary collapse or fibrosis Excessive artificial ventilation


Compensation of Respiratory Alkalosis

Compensatory fall in plasma [HCO-3] tends to

correct the pH

Pco2 always reduced

[HCO-3] low normal or low

pH raised (uncompensated or partly

compensated) or normal (fully compensated)


Treatment of Respiratory Alkalosis

Treat underlying cause

IV Chloride containing solution – Cl-

ions replace lost bicarbonate ions


THANKS

Respiratory Acid base balance by Dr. Samreena

Health & Medicine

Transcript of Respiratory Acid base balance by Dr. Samreena