pH of BLOOD, ITS REGULATION, ACIDOSIS & ALKALOSIS.

MAY.13.2010

BASICS

• Acid-base balance is a dynamic relationship which reflects

the concentration of hydrogen ions (H+) in the body.

• Hydrogen ions are acids which must be maintained within strict limits

• Any deviation from the norm affects biochemical events.

• Acid-base relationship is measured in a logarithm (pH) which is inversely proportional to the hydrogen ion concentration.

pH (power of H)

pH = Negative log10 of the hydrogen ions concentration expressed in mol/L

pH= - log10 [H+]

High H+ ion concentration = low pH

Low H+ ion concentration = high pH

BASICS

THE pH SCALE

• Scale ranges from 1 to 14

1 means only hydrogen ions are present

14 means no hydrogen ions present

The pH of water is 7.0 which is neutral

The normal range of the human body is 7.35 - 7.45

Basic

pH neutral

Acidic

Death

Normal and abnormalpH ranges of blood

pH’s of commonsubstances

Death

Acidosis

Normal

Alkalosis

8.00

7.45

7.35

6.8

Battery acid

Concentrated lye

Water

Gastric juiceLemon juice

Vinegar

Household ammonia

Baking soda

Pancreatic juiceBlood

MilkUrine

Coffee

Orange juice

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

pH OF BLOOD [7.35-7.45]

Alteration outside these boundaries affects all body systems

• Can result in coma, cardiac failure, and circulatory collapse.

• Normal pH of body fluids– Arterial blood is 7.4– Venous blood and interstitial fluid is 7.35– Intracellular fluid is 7.0

• Alkalosis or alkalemia – arterial blood pH rises above 7.45

• Acidosis or acidemia – arterial pH drops below 7.35

ACID AND BASES

ACID: Protons (hydrogen ions H+) donors.

BASES: Protons (hydrogen ions H+) acceptors.

(Cation= positive, Anion=negative)

Weak acid: Partially dissociate. (not completely break apart)

Strong acid: completely dissociate into anions and cation.

STRONG AND WEAK ACID

ACID

Strong Acid Sulfuric acid

Weak acid Carbonic acid

Lactic acid

Pyruvic acid

Citric acid

Acetatoacetic acid

β-hydroxybutyric acid

Acetic acid

Dihydrogen Phosphate

Ammonium ion

MAJOR SOURCES

Dietary sulfate and S-containing amino acids. (Cystine, Methionine.)

CO2 from TCA cycle

Anaerobic glycolysis

Glycolysis

TCA cycle and diet(e.g., citric fruits)

Fatty acid oxidation to ketone bodies

Fatty acid oxidation to ketone bodies

Ethanol metabolism

Dietary organic phosphates

Dietary nitrogen-containing compounds

ACID IN THE BODY OF A HEALTHY INDIVIDUAL

SOURCES OF HYDROGEN IONS

• Most hydrogen ions originate from cellular metabolism.

Breakdown of phosphorus-containing proteins releases phosphoric acid into the ECF.

Anaerobic respiration of glucose produces lactic acid.

Fat metabolism yields organic acids and ketone bodies.

Transporting carbon dioxide as bicarbonate releases hydrogen ions.

BODY REGULATION OF ACID-BASE

• The body constantly produces acids through metabolism.

• These acids must be constantly eliminated from the body.

• Three systems perform this task – Buffer system– Respiratory system– Renal system

BUFFER SYSTEMS IN BODY FLUIDS

BUFFER SYSTEM

• Buffers: – if pH rises, buffers bind H+;

– if pH falls, buffers release H+

• Protein buffer: Intracellular and plasma proteins absorb H+. Provide ¾ of buffering in body. E.g., hemoglobin.

• Bicarbonate buffering system: Important in plasma• Phosphate buffer system: important as an

intracellular buffer The fastest performer, works in seconds.

• Bicarbonate ions combine with excess hydrogen ions to form carbonic acid in a dynamic relationship.

THE CARBONIC ACID-BICARBONATE BUFFER SYSTEM

CARBONIC ACID-BICARBONATE BUFFER SYSTEM IN REGULATIOIN OF pH

THE CENTRAL ROLE OF CARBONIC ACID-BICARBONATE SYSTEM IN REGULATION

OF pH

AMINO ACID BUFFER

• For every molecule of carbonic acid, there are 20 molecules of bicarbonate.

• Any change in the this 20:1 ratio is immediately corrected to maintain pH.

• An increase H+ causes an increase in H2CO3.

• A decrease in H+ causes a decrease in H2CO3.

BUFFER SYSTEM

• Carbonic acid is a weak, volatile acid which must be eliminated.

• The enzyme carbonic anhydrase causes the carbonic acid to convert to carbon dioxide and water.

• The CO2 and the H2O are easily eliminated by the lungs and kidneys.

• The system also works in reverse.

BUFFER SYSTEM

RESPIRATORY SYSTEM

• Works in minutes

• The lungs eliminate excess CO2 by increasing respirations,

causing a decrease in H+ and an increase in pH.

• The lungs can retain more CO2 by slowing respirations,

causing an increase in H+ and a decrease in pH.

• Respiratory center: – if pH rises, respiratory rate decreases; – if pH falls, respiratory rate increases.

ACID- acid- increaseAlkali- alkali-lower

RESPIRATORY ACID-BASE REGULATION

RESPIRATORY ACID-BASE REGULATION

RENAL SYSTEM

• Can take hours to days to work• Kidneys can retain bicarbonate ion, causing a decrease in

H+ and an increase in pH

• Kidneys can excrete bicarbonate ion, causing an increase in

H+ and a decrease in pH.• Kidneys

– if pH rises, distal tubule decreases H+ secretion into the urine and decreases HCO3

- absorption into the blood (more H2CO3 will dissociate into H+ and HCO3

-);

– if pH falls, distal tubule increases H+ secretion into the urine and increases HCO3

- absorption into the blood

KIDNEY TUBULES AND pH REGULATION

KIDNEY TUBULES AND pH REGULATION

ACID-BASE DISORDERS

• Respiratory acid base disorders– Result when abnormal respiratory function causes rise or fall

in CO2 in ECF

• Metabolic acid-base disorders– Generation of organic or fixed acids– Anything affecting concentration of bicarbonate ions in ECF

ACID-BASE DISORDERS

ACIDOSIS AND ALKALOSIS• Acidosis: pH body fluids below 7.35

– Respiratory: Caused by inadequate ventilation- reduced elimination of CO2, asthma, damage to respiratory center in brain, emphysema.

– Metabolic: Results from all conditions other than respiratory that decrease pH- diarrhea, vomiting, ingesting overdose of aspirin, untreated diabetes mellitus, anaerobic respiration.

• Alkalosis: pH body fluids above 7.45

– Respiratory: Caused by hyperventilation, high altitude (reduced partial pressure of O2)

– Metabolic: Results from all conditions other than respiratory that increase pH- severe vomiting, too much aldosterone, ingestion of substances like bicarbonate of soda.

• Results from excessive levels of CO2 in body fluids.

RESPIRATORY ACIDOSIS

• Relatively rare condition• Associated with hyperventilation

RESPIRATORY ALKALOSIS

• Major causes are:

– Depletion of bicarbonate reserve

– Inability to excrete hydrogen ions at kidneys

– Production of large numbers of fixed / organic acids

– Bicarbonate loss due to chronic diarrhea

METOBOLIC ACIDOSIS

• Occurs when HCO3- concentrations become elevated

– Caused by repeated vomiting.

METOBOLIC ALKALOSIS

THE RESPONSE TO METABOLIC ACIDOSIS

THE RESPONSE TO METABOLIC ALKALOSIS

ACID-BASE AND POTASSIUM IMBALANCE

• Acidosis– H+ diffuses into cells and drives out K+, elevating K+

concentration in ECF• H+ buffered by protein in ICF, causes membrane

hyperpolarization, nerve and muscle cells are hard to stimulate; CNS depression may lead to death

Acidosis Hyperkalemia

• Alkalosis

– H+ diffuses out of cells and K+ diffuses in, membranes depolarized, nerves over-stimulate muscles causing spasms, tetany, convulsions, respiratory paralysis

ACID-BASE AND POTASSIUM IMBALANCE

Alkalosis Hypokalemia

• Diagnostic blood tests (Arterial Blood Gases) ABG– Blood pH

– PCO2

– Bicarbonate levels

DETECTION OF ACIDOSIS AND ALKALOSIS

INCREASED IN BLOOD pH

DECREASED IN BLOOD pH

POINTS TO REMEMBER

pH= - log10 [H+]

High H+ ion concentration = low pH

Low H+ ion concentration = high pH

Normal pH OF BLOOD [7.35-7.45]

Regulation of acid-base balance by 3 systems.

Acid-base disorders.

Regulation of acidosis and alkalosis.

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