acid base balance

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Slide 1: 

“If one advances confidently in the direction of his dreams, he will meet with a success unexpected in common hours --Henry David Thoreau "Shoot for the moon.  Even if you miss it, you will land among the stars….!" - Les Brown

Acid-Base Balance : 

Acid-Base Balance

Slide 3: 

A hydrogen ion is a single free proton released from a hydrogen atom Acids.. Molecules containing hydrogen atoms that can release hydrogen ions in solutions -hydrochloric acid (HCl) ,carbonic acid (H2CO3) A base…. an ion or a molecule that can accept an H+ -HCO3-,HPO4=,The proteins ,hemoglobin

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Strong and Weak Acids and Bases A strong acid ..rapidly dissociates and releases large amounts of H+ in solution….HCl Weak acids ..less tendency to dissociate their ions … is H2CO3 A strong base … reacts rapidly and strongly with H+ and quickly removes these from a solution…OH- A typical weak base is HCO3- Most of the acids and bases in the extracellular fluid that involved in normal acid-base regulation are weak acids and bases

Types of Acids in the body : 

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.

Types of Acids in the body : 

Types of Acids in the body Fixed Acids: Acids that do not leave solution. Sulfuric and phosphoric acid. Catabolism of amino acids, nucleic acids, and phospholipids.

Types of Acids in the body : 

Types of Acids in the body Organic Acids: Byproducts of aerobic metabolism, during anaerobic metabolism and during starvation, diabetes. Lactic acid, ketones.

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Normal Hydrogen Ion Concentration and pH of Body Fluids the blood H+ concentration is normally maintained within tight limits around a normal value of about 0.00004 mEq/L (40 nEq/L) Ph= log 1/H= -log [H] Ph=7.4

Slide 9: 

pH = pK + log HCO3 CO2

Defenses Against Changes in Hydrogen Ion Concentration : 

Defenses Against Changes in Hydrogen Ion Concentration There are three primary systems that regulate the H+ concentration the chemical acid-base buffer systems of the body fluids (2) the respiratory center (3) the kidneys

Buffer Systems : 

Buffer Systems a buffer system is a combination of two compounds that minimizes pH changes when acid or base is added to a solution A pair of substance is involved: one substance yield H+ ion when PH is increased the other binds with H+ ion when pH is decreased.

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Chemical buffer system Combination of weak acid and weak base Binds to H+ as H+ concentration rises Releases H+ as H+ concentration falls Can restore normal pH almost immediately Three major chemical buffer systems Bicarbonate system Phosphate system Protein system

buffers : 

buffers Accomplished by converting: Strong acid ? Weak acid Strong base ? Weak base


BODY BUFFER SYSTEMS bicarbonate/carbonic acid major plasma buffer phosphate: H2PO4- / HPO42- major urine buffer ammonium: NH3 / NH4+ also used to buffer the urine proteins: important in ICF Hb: is the main buffer against CO2 changes

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BICARBONATE BUFFER SYSTEM Carbonic acid (H2CO3) Weak acid Bicarbonate ion (HCO3-) Weak base CO2 + H20 ? H2CO3 ? H+ + HCO3- Works along with respiratory and urinary system These systems remove CO2 or HCO3-

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NaOH + H2CO3 H2O + Na HCO3 HCl + Na HCO3 NaCl + H2CO3

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pK 6.1 the concentrations of CO2 and HCO3 not great. the most powerful extracellular buffer in the body the two elements of the buffer system are regulated by the kidneys and the lungs

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PHOSPHATE BUFFER SYSTEM Dihydrogen phosphate ion (H2PO4-) Weak acid Monohydrogen phosphate ion (HPO42-) Weak base H2PO4- ? H+ + HPO42- More important in buffering kidney filtrate than in tissue

Phosphate Buffer System : 

Phosphate Buffer System The main elements of the phosphate buffer system are H2PO4- and HPO4 NaOH + NaH2PO4 H2O+ Na2HPO4 HCl + Na2HPO4 NaCl + NaH2PO4

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pK 6.8 8 % of the concentration of the bicarbonate buffer the total buffering power less than that of the bicarbonate buffering system.

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the phosphate buffer is important in the tubular fluids of the kidney for two reasons (1) phosphate concentrated in the tubules (2) the tubular fluid has lower pH than the extracellular fluid does - bringing the operating range of the buffer closer to the pK (6.8) of the system important in buffering intracellular fluid because the concentration of phosphate in this fluid is many times that in the extracellular fluid

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PROTEIN BUFFER SYSTEM Proteins are more concentrated than bicarbonate and phosphate buffers Accounts for ~75% of all chemical buffering of body fluids Buffering ability due to certain functional groups of amino acid residues

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except for the red blood cells, the slowness with which H+ and HCO3 move through the cell membranes often delays the maximum ability of the intracellular proteins to buffer extracellular acid-base abnormalities. the pKs of many of these protein systems close to 7.4.

Isohydric buffer system : 

Isohydric buffer system The buffer system buffers each other by shifting hydrogen from buffer to other

2. Respiratory mechanisms : 

2. Respiratory mechanisms Exhalation of carbon dioxide Powerful, but only works with volatile acids Doesn’t affect fixed acids like lactic acid CO2 + H20 ? H2CO3 ? H+ + HCO3- Body pH can be adjusted by changing rate and depth of breathing

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the overall buffering power of the respiratory system is one to two times as great as the buffering power of all other chemical buffers in the ECF combined

Renal Control of Acid-Base Balance : 

Renal Control of Acid-Base Balance Alkalosis ??urinary HCO3- Acidosis ??urinary HCO3- new HCO3- production

Acid-Base Imbalances : 

Acid-Base Imbalances pH< 7.35 acidosis pH > 7.45 alkalosis

Compensation for Metabolic Acidosis : 

Compensation for Metabolic Acidosis Increased ventilation Renal excretion of hydrogen ions if possible K+ exchanges with excess H+ in ECF ( H+ into cells, K+ out of cells)

Clinical Causes of Acid-Base Disorders : 

Respiratory Acidosis; ?PCO2 & [H+] Respiratory Alkalosis; ?PCO2 & [H+] Metabolic Acidosis ; compensatory reflex hyperventilation ? ?PCO2 Tubular acidosis; ?HCO3- reabsorption & H+ secretion Diarrhea & Vomiting(intestinal); ?HCO3- Diabetes Mellitus; ?acetoacetic acid (ketone body) Ingestion of acids; aspirin, methyl alcohol Chronic renal failure; ?acid excretion Hypoxia (severe exercise); ?lactic acid Clinical Causes of Acid-Base Disorders

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Metabolic Alkalosis ; compensatory reflex hypoventilation ? ?PCO2 Diuretics; ?distal tubule flow ??Na+ reabsorption & H+ secretion Excess Aldosterone; ?H+ secretion Vomiting; ?H+ (upper gastric content) Ingestion of alkaline drugs; sodium bicarbonate

Analysis of Acid-Base Disorders : 

Analysis of Acid-Base Disorders