Acid base regulation

Biochemistry for nurses

Acid-Base Regulation The regulation of acid-base balance is concerning the proper balance

between chemical acids and bases in the extracellular fluids (which includes the blood plasma). Acid-Base regulation is also called Body Ph

The body is very sensitive to its extracellular pH level otherwise outside the acceptable range of pH, proteins are denatured and digested, enzymes lose their ability to function, and death may occur.

The body's acid–base balance is normally tightly regulated by buffering agents, the respiratory system, and the renal system, keeping the blood pH between 7.35 and 7.45.

Nurses require a good knowledge of the normal body mechanisms which regulate the Acid-Base balance because many ill patients have damaged respiratory, renal and/or metabolic functions.


Definitions

Acid: Acid is a substance which can donate a H+ or dissociate a H+

Base: Base is a substance which can accept a H+

Water (H2O) can be an acid or a base in same time

2 H2O H3O+ + OH-

Acid/Base pair: HCl / Cl-

NH4+ / NH3

H2O / OH-

H3O+ / H2O


pH: The term pH refers to the concentration of hydrogen ions (H+).

pH [H3O+]

[H3O+]pH

pH= - log [H3O+]

In water, the hydrogen ion (H+) is never free but always combined to

H2O to form H3O+ [H3O+] = [H+]


Buffer: Buffer is a mixture of weak acids and their conjugate bases.

The buffer has the ability to oppose changes (stabilize) in pH when acid or base are added to a solution.

As example: Buffer in Saliva HCO3- + H+

(conjugate base)H2CO3

(weak acid)

Bicarbonate (HCO3- )/Carbonic acid (H2CO3) acid buffer system

Salivary pH= 5.6 to 7.9 Below pH= 5.5 demineralization occurs (destruction of the tooth enamel) Carbonic anhydrase is present in saliva After diet, bacteria produce lactic acid which increases [H+] (pH decreases)

and attack teeth by producing caries (cavities).


Human blood pH is 7.4

In normal conditions, blood pH is between 7.35 and 7.45. To maintain constant the blood pH, two organs play an essential role:

1) LUNGS: breathing in removing carbon dioxide (CO2) has an effect on the blood pH

2) KIDNEYS: eliminating protons (H+) and retaining bicarbonate (HCO3-) has

an effect on the blood pHKidneys and Lungs contribute to the maintenance of acid-base balance of the body, but for various reasons, this balance can be broken (ACIDOSIS and ALKALOSIS).


An increased acidity in the blood and the other tissues.

The blood pH decreases below 7.35 MAJOR CAUSES: Diabete 1 (accumulation of ketoacids) Prolonged fasting (ketosis) Overdose of drugs and substances such as alcohols

and aspirin Lactic acidosis (accumulation of lactic acid as occurs

as a result of shock or use of certain drugs) Severe kidney disease Poisons such as ethylene glycol and methanol Lung disorders, severe asthma, pneumonia, or

pulmonary edema

Acidosis


A decreased acidity in the blood and the other tissues.

The blood pH increase above 7.45

MAJOR CAUSES: Anxiety or panic attacks Aspirin overdose Fever or infection Low levels of oxygen in the blood Loss of acid due to vomiting or drainage of the

stomach Overactive adrenal gland (due to Cushing syndrome

(excess secretion of cortisol) and some adrenal tumors)

Use of diuretics which increase production of urine (for example, thiazides, furosemide, ethacrynic acid) for treatment of high blood pressure, heart failure…

Alkalosis


Response to metabolic acidosis

Interactions among the carbonic acid/bicarbonate buffer system and compensatory mechanisms in the regulation of plasma pH


Response to metabolic alkalosis Pulmonary ventilation is slow and shallow

allowing carbon dioxide to accumulate in the blood

Kidneys generate H+ and eliminate bicarbonate from the body by urine

Education

Acid base regulation