OBJECTIVES : 1) explain the importance of acid – base balance. 2) explain the rule of hydrogen ion excretion. 3) Define pH and state the normal pH range of blood.
OBJECTIVES : 4) state the role of the most important of these in the maintenance of acid- base balance. 5) mechanisms of buffers, lungs, kidneys in maintaining homeostasis. 6) Define :Metabolic acidosis, alkalosis Respiratory acidosis, alkalosis
Let’s remember these concepts : Hydrogen ion concentration – determine acidity and alkalinity in a solution. pH range (1 to 14). Physiological pH = 7.4 Inverse relationship between pH & H+
Acid – Base Balance what is acid-base balance? metabolic function can occur only if the body cells & their surrounding envi are kept relatively constant. So regulation of both fluid and electrolyte balance, acid–base balance is very important. Acid-base balance refers to: the homeostasis or balance of the hydrogen ion concentration in body fluids.
Acid – Base Balance Importance of acid-base balance: Disturbance in acid base balance leads to cellular dysfunction. metabolic activities - …+ e.g enzymes activity membrane transport process, ionic state, chemical reaction – all depend on pH
Since many end – products of the body’s metabolic rxns are acidic the body produces a large excess of acid under normal physiological conditions. If acids were allowed to accumulate, the effect on pH, tissue fluid, intracellular fluid would be dramatic. As a result, it is very important to regulate pH
How to regulate pH ? Elimination of the excess hydrogen ions from the body. Prevention of pH changes in the blood while transporting hydrogen ions to the organs to be excreted. Accomplished by : Each of these systems shares the responsibility of maintaining the hydrogen ion concentration [H+] and the blood pH Renal system. Respiratory system. Buffer system.
An acid – base buffer is a chemical solution which prevents excessive change in pH & [H+] when either 1) a weak acid and its alkali salt 2) or weak base and its acid salt. In the body, the buffers of physiological importance are mixture of weak acids and their alkali salts.
How Does Buffer Work? If excess base is added to the solution, the weak acid part of the buffer reacts to neutralize it and vise versa. In this way, the body’s buffers can be regarded as chemical sponges soaking up surplus H+ or releasing them as required.
These buffers are responsible for maintaining a normal blood pH (7.35 – 7.45) during hydrogen ion transport to the lungs & kidneys. Bicarbonate / carbonic acid buffer system. Phosphate buffer system. Hemoglobin buffer system. Proteins buffer system. Main Buffer Systems
The Bicarbonate/Carbons Buffer System is the major buffer system for fixed acids in the blood. It buffers ≈0.7 (70%) of the fixed acids in the plasma and ≈0.3 (30%) of the fixed acids in the RBCs. It is quantitatively the largest buffer system in the body, and so is the most important overall in regulating pH.
This buffer system can be regulated via lungs & kidneys : 1) Carbonic acid can be retained or exhales as carbon dioxide 2) Bicarbonate can be retained or excreted by the kidney tubules as required by the body In the blood, the normal ratio of HCO 3 - /H 2 CO 3 is 20/1, so this system is heavily weighted towards buffering against excess acid production
Respiratory System The lungs are responsible for the regulation of the levels of volatile acids in the body fluids. The term “ volatile” indicates that these compounds can be “breathed off”, i.e. excreted as gases (carbon dioxide in the major end-product of metabolism).
Mechanism CO2 concentration is roughly inversely proportional to the alveolar ventilation CO2 produced by metabolic rxns dissolves in blood H2CO3 it’s buffered transported to the lungs CO2 reformation CO2 diffuses to the alveoli exhaled out of the body
Respiratory System : loss of CO2, and increase pH. increase the rate and depth of respiration, These neurons then send a signal to the respiratory control centers in the medulla, Changes in blood [CO2] and pH modulate respiration by acting on chemosesnitive neurons in the medulla.
Important to know the following about respiratory system mechanisms : Ventilation: In fact, the ventilation can be reduced to 0 or increased to more than 10 times normal. Hyperventilation: Ventilation which are increased in rate and/or depth resulting in a loss of CO2 from the body Hypoventilation: Ventilation which are decreased in rate and/or depth resulting in a retention of CO2 from the body
Respiratory system is very rapid, but has only 50% - 75% efficiency rate. Beyond that, the lungs alone can not return the pH to its normal level because as the [H+ ]approaches normal, the stimulus to the respiratory center is lost. And so, kidneys and the buffering systems must act to restore the balance.
Renal System Kidneys are responsible for the regulation of the levels of nonvolatile or fixed acids (cannot be breathed off ) e.g. lactic acid, H2SO4, H3PO4 and ketone bodies …etc. Kidneys regulate the pH by varying the amounts of H+ they excrete in the urine. HCO 3 - they reabsorb.
Renal System If the body needs to eliminate the excess acid ( pH low ), the kidney excrete more H+ and retain HCO 3 – ion to neutralize the excess acid. If pH becomes two alkaline, the kidneys respond by retaining H+ and excrete HCO3- ions. Elimination of H+ ions.
Reabsorbtion of filtrated HCO3-. This response is quite slow ( takes hours ) in comparison to that of the respiratory system. The kidneys have 100% efficiency rate. Kidney failure causes metabolic acidosis or alkalosis. Renal System :
Acid Base Disturbance When acid base balance is disturbed due to dse, for example, lungs & kidneys regulate acid base homeostasis Remember that pH depends on [CO3-] / [H2CO3] At normal condition this ratio equals 20:1 when this ratio changes it leads to pH or acidosis / pH or alkalosis
The body tends to tolerate acidosis much better than alkalosis. Respiratory or metabolic acidosis/alkalosis : Any acid – base disturbance involving a loss of [HCO3-] is classified as metabolic acidosis increasing of [HCO3-] as metabolic alkalosis Any acid – base disturbance involving an increase in [ H2CO3] as CO2 retention is classified as respiratory acidosis increasing of [H2CO3] or loss of CO2 as respiratory alkalosis >>> hypoxia, PCO2
Exercise 1 You have the following values for a patient : pH 7.5 / PCO2 25 mmHg / [HCO3-] 22 mmol/L PO2 90 mmHg Is it alkalosis or acidosis? Is it respiratory or renal? What is the main reason that may cause it?
Exercise 2 You are given the following values: pH 7.3 / PCO2 40 mmHg / [HCO3-] 15 mmol/L PO2 90 mmHg Is it alkalosis or acidosis? Is it respiratory or renal? What is your prognosis?