“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
DR.M.RAVICHANDRA,M.SASST. PROFESSOR OF SURGERY RIMS ,SRIKAKULAM
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
Volatile acids: Can leave solution and enter the atmosphere. H2C03 (carbonic acid). Pco2 is most important factor in pH of body tissues. Pco2 is a measurement of tension or partial pressure of carbon dioxide in the blood. The normal arterial pCO2 is 4.1- 5.6 k Pa (31- 42 mmHg)
Fixed Acids: Acids that do not leave solution. Sulfuric and phosphoric acids.(H2SO4&H3PO4) Catabolism of amino acids, nucleic acids, and phospholipids.
Organic Acids: Byproducts of aerobic metabolism, during anaerobic metabolism and during starvation, diabetes. LACTIC ACID, KETONES ,PYRUVIC ACID
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
There are three primary systems that regulate the H+ concentration(1) the chemical acid-base buffer systems of the body fluids(2) the respiratory center(3) the kidneys
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.
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
Accomplished by converting: Strong acid Weak acid Strong base Weak base
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
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- THE RATIO OF BICARBONATE TO CARBONIC ACID IS NORMALLY 20:1 Alterations in the ratio alters Ph irrespective of absolute concetrations
NaOH + H2CO3 H2O + Na HCO3HCl + Na HCO3 NaCl + H2CO3
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
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
The main elements of the phosphate buffer system are H2PO4- and HPO4NaOH + NaH2PO4 H2O+ Na2HPO4HCl + Na2HPO4 NaCl + NaH2PO4
pK 6.8 8 % of the concentration of the bicarbonate buffer the total buffering power less than that of the bicarbonate buffering system.
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
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
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.
The buffer system buffers each other by shifting hydrogen from buffer to other
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
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
compensatory mechanisms in respiratory acidosis compensatory mechanisms in respiratory acidosis*Image via Bing
Inadequate ventilation of anaesthetized patient When the effects of muscle relaxants have not worn off or been fully reversed at the end of anaesthesia Risk increases when the patient has pre existing pulmonary disease like ch. Bronchitis or emphysema Thoracic & upper abdominal incisions
A CONDITION WHERE THE ARTERIAL PCO2 IS BELOW THE NORMAL RANGE LESS THAN 31 MM OF HG (OR) LESS THAN 5.6 KILO PASCALS
This is a calculated estimation of the undetermined or unmeasured anions in the blood This is some times used to establish the cause of metabolic acidosis ANIONGAP= (Na) _ (HCO3+Cl) NORMAL ANION GAP IS 10-16 mmol / L
RESPIRATORY- RETENTION OF CARBONDIOXIDE BY THE LUNGS RENAL – EXCRETION OF BICARBONATE BY THE KIDNEYS
Changes in Arteial Concentrations of H + , HCO 3 - & CO 2 in Acid-Base Disorders Primary HCO 3 Cause of HCO3- Cause of CO2 H + CO 2 Disorder - Change ChangeRespiratory Acidosis ↑ ↑ ↑ Renal Primary Compensation AbnormalityRespiratory Alkalosis ↓ ↓ ↓MetabolicAcidosis ↑ ↓ ↓ Reflex Primary Ventilatory AbnormalityMetabolic CompensationsAlkalosis ↓ ↑ ↑