ACID-BASE BALANCE

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• Acid-Base Balance• The body's maintenance of a healthy pH

range for blood and tissues that is slightly basic (pH between 7.35 - 7.45).

• This balance is achieved through the use of systems in the blood (which help to minimize pH changes) and by the lungs and kidneys, which eliminate excess amounts of acids or bases from the body.

• Normally because of metabolic, there is daily a hug amount of

H ion 40 mmoles/day and CO2 15,000 mmoles/day, which should be effectively deal with in order to maintain normal acid – base state .

• A buffer solution • is an aqueous solution consisting of a

mixture of a weak acid and its conjugate base or a weak base and its conjugate acid.

• It has the property that it resist the change in pH when a small amount of strong acid or base is added to it.

• Buffers found in all body fluids .

• Strong acids are poor buffers because they make the system more acid .

• Weak acids good buffers since they can tilt a reaction in the other direction .

• Function• Maintains pH homeostasis .• Maintenance of H+ concentration .

• Why do we need Buffer Systems ?• If the acids produced in the body from the

catabolism of food and other cellular processes are not removed or buffered, the body’s pH would drop

• Significant drops in pH interferes with cell enzyme systems.

• Change in PH below 6.8 or above 8.0 may result in death .

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

The most important buffer for maintaining acid-base balance in the blood is the carbonic-acid-bicarbonatebuffer.

As shown in the above equation, the pH of the buffered solution (i.e., the blood) is dependent only on the ratio of theamount of CO2 present in the blood to the amount of HCO3- (bicarbonate ion) present in the blood (at a giventemperature, so that pK remains constant). This ratio remains relatively constant, because the concentrations ofboth buffer components (HCO3- and CO2) are very large, compared to the amount of H+ added to the bloodduring normal activities and moderate exercise .

This figure shows the major organsthat help control the bloodconcentrations of CO2 and HCO3-, andthus help control the pH of the blood.Removing CO2 from the blood helpsincrease the pH.Removing HCO3- from the blood helpslower the pH.

• The major buffers system in man Four Major Buffer Systems1 - Bicarbonate-carbonic acid Buffer.• H2CO3 H+ + HCO3¯(major ) 2 - Phosphate Buffer system ( Major intracellular buffer )

H2PO4 H+ + HPO4 ¯2

Protein Buffer systems3 - Hemoglobin Buffer system .

HPr H+ + Pr¯4 - Amino acids NH4

+ H++ NH3

Buffer Systems in Body Fluids

Figure 27.7

• Phosphate Buffer System

• Has a major role in the elimination of H+ via the kidney• Assists in the exchange of sodium for

hydrogen• It participates in the following reaction

• HPO-24 + H+ H2PO –

4

• Essential within the erythrocytes .

• Protein Buffer System Roles• Originates from amino acids .• ALBUMIN- primary protein due to high

concentration in plasma .• Buffer both hydrogen ions and carbon

dioxide .

• Hemoglobin Buffer System Roles• Binds CO2 .• Binds and transports hydrogen and

oxygen .• Participates in the chloride shift .• Maintains blood pH as hemoglobin

changes from oxyhemoglobin to deoxyhemoglobin .

Bicarbonate/carbonic acid buffer

system Function almost instantaneously Cells that are utilizing O2, produce CO2,

which builds up. Thus, more CO2 is found in the tissue cells than in nearby blood cells. This results in a pressure (pCO2).

Diffusion occurs, the CO2 leaves the tissue through the interstitial fluid into the capillary blood .

CO2 transport in the blood

Regenerate of bicarbonate by the kidny

Excretion of H ion by the kidny 1-Ammonium buffer

2- Phosphate buffer

• Acid – Base disorder • 1-Metabolic acidosis• 2- Metabolic alkalosis• 3-Respiratory acidosis• 4-Respiratory alkalosis

• metabolic acidosis is a condition that occurs when the body produces too much acid or when the kidneys are not removing enough acid from the body. If unchecked, metabolic acidosis leads to acidemia, i.e., blood pH is low (less than 7.35) due to increased production of hydrogen by the body or the inability of the body to form bicarbonate (HCO3-) in the kidney. Its causes are diverse, and its consequences can be serious, including coma and death.

• Causes :• A – Increase H+ production :• 1 - Diabetic ketoacidosis .• 2 - Alcoholic ketoacidosis .• 3 - Starvation ketoacidosis .• B – Decreased H+ excretion :• 1 - Renal Failure .• 2 - Renal tubular acidosis .• 3 - Carbonic anhydrase inhibitors .• C – Lose of HCO3_ ( GIT Causes ) :• 1- Severe diarrhea .• 2- Small bowel fistula .

• Biochemical features

• PCO2 H+ HCO3¯• Befor compensation N • After compensation

• ℎ𝑖𝑔ℎ 𝑛𝑜𝑟𝑚𝑎𝑙• Compensation is done by the lungs by

Increased ventilation .

• Metabolic alkalosis is a metabolic condition in which the pH of tissue is elevated beyond the normal range ( 7.35-7.45 ).

• This is the result of decreased hydrogen ion concentration, leading to increased bicarbonate, or as a direct result of increased bicarbonate concentrations.

• Bicarbonate excess • Causes:• Excess vomiting = loss of stomach acid .• Excessive use of alkaline drugs .• Certain diuretics .• Endocrine disorders .• Heavy ingestion of antacids .• Severe dehydration .

• Biochemical features• PCO2 H+ HCO3¯• Befor compensation N • After compensation

• low 𝑛𝑜𝑟𝑚𝑎𝑙• Compensation is done by the lungs by

decreased ventilation .

• Respiratory alkalosis • is a condition marked by low levels of

carbon dioxide in the blood due to lung disease that leads to shortness of breath can also cause respiratory alkalosis(breathing excessively ).

• Causes• Primary cause is hyperventilation .• Oxygen deficiency at high altitudes .• Pulmonary disease and Congestive heart failure –

caused by hypoxia .• Acute anxiety .• Fever, anemia .• Cirrhosis .• Gram-negative sepsis .

• Biochemical features• PCO2 H+ HCO3¯• Befor compensation ↓ ↓ ↓N

• or slightly lower

• After compensation ↓ ↑ ↓𝑜𝑟• low 𝑛𝑜𝑟𝑚𝑎𝑙• Compensation is done by Kidneys which conserve

hydrogen ion and excrete bicarbonate ion .

Respiratory acidosis is a medical condition in which decreased ventilation (hypoventilation) causes increased blood carbon dioxide concentration and decreased pH .

• Causes :• Chronic conditions:• Depression of respiratory center in brain

that controls breathing rate – drugs or head trauma .

• Paralysis of respiratory or chest muscles .• Emphysema .• Pulmonary edema .• Pneumothorax .

Biochemical features

• PCO2 H+ HCO3¯• Befor compensation ↑ ↑ ↑N • or slightly

higher

• After compensation ↑ ↑𝑜𝑟 ↑• high 𝑛𝑜𝑟𝑚𝑎𝑙• Compensation is done by Kidneys which eliminate

hydrogen ion and retain bicarbonate ion .

• Normal value• HCO3¯ 24 -28 mmol / l• H+ 35 – 46 nmol/l• PCO2 35 – 45 mmHg • PH ( Blood ) ---- 7.36 – 7.44