ACID-BASE BALANCE IN FISHES :ACID-BASE BALANCE IN FISHES FEROSEKHAN S FISHERIES SCIENCE CIFE,MUMBAI


Introduction :Introduction Acid –base balance involves the maintenance of internal pH. Regulation of acid –base homeostasis is of critical importance to fishes. In order to achieve homeostasis, there must be a balance between the intake or production of hydrogen ions and the net removal of hydrogen ions from the body.


CONT…. :CONT…. A delicate balance of fluids, electrolytes, and acids and bases is required to maintain good health. This balance is called Homeostasis


pH Review :pH Review pH = - log [H+] H+ is really a proton Range is from 0 - 14 If [H+] is high, the solution is acidic; pH 7


Slide 5:Acids are H+ donors. Bases are H+ acceptors, or give up OH- in solution. Acids and bases can be: Strong – dissociate completely in solution HCl, NaOH Weak – dissociate only partially in solution Lactic acid, carbonic acid


Body Fluids :Body Fluids Intracellular fluid (ICF) found within the cells of the body constitutes 2/3 of total body fluid major cation is potassium Extracellular fluid (ECF) found outside the cells accounts of 1/3 of total body fluid major cation is sodium


The Body and pH :The Body and pH Homeostasis of pH is tightly controlled Intracellular fluid = 7.2 – 7.5 Blood pH = 7.7 – 8.0 8.5 death occurs Acidosis (acidemia) below 7.4 Alkalosis (alkalemia) above 8.3


pH of Fish Blood :7.7 8.0 Normal blood pH Alkalosis Acidosis 8.2 8.4 7.4 7.2 7.0 pH of Fish Blood


Small changes in pH can produce major disturbances :Small changes in pH can produce major disturbances Most enzymes function only with narrow pH ranges Acid-base balance can also affect electrolytes (Na+, K+, Cl-) Can also affect hormones


The body produces more acids than bases :The body produces more acids than bases Acids take in with foods Acids produced by metabolism of lipids and proteins Cellular metabolism produces CO2. CO2 + H20 ? H2CO3 ? H+ + HCO3-


How the Body defends against fluctuations in pH :How the Body defends against fluctuations in pH Three Systems in the body: 1.Buffers in the blood 2.Respiration through the gills 3.Excretion by the kidneys


Buffers in the Blood :Buffers in the Blood Buffers are substances that neutralize acids or bases Bicarbonate which is a base and carbonic acid in the body fluids protect the body against changes in acidity These buffer systems serve as a first line of defense against changes in the acid-base balance


Respiration through the gills :Respiration through the gills Carbon Dioxide which is formed during cellular metabolism forms carbonic acid in the blood decreasing the pH When the pH drops respiration rate increases this hyperventilation increases the amount of CO2 exhaled thereby lowering the carbonic acid concentration and restoring homeostasis


Excretion by the Kidneys :Excretion by the Kidneys The kidneys play the primary role in maintaining long term control of Acid-Base balance The kidney does this by selecting which ions to retain and which to excrete The kidneys adjust the body’s Acid-Base balance


Control of Acids :Control of Acids Buffer systems: Take up H+ or release H+ as conditions change Buffer pairs – weak acid and a base Results in a much smaller pH change


Cont… :Cont… 1. Extracellular buffer - Bicarbonate , Ammonia 2.Intracellular buffer - Protein, Phosphate


Bicarbonate buffer :Bicarbonate buffer Sodium Bicarbonate (NaHCO3) and carbonic acid (H2CO3) Maintain a 20:1 ratio : HCO3- : H2CO3 HCl + NaHCO3 ? H2CO3 + NaCl NaOH + H2CO3 ? NaHCO3 + H2O


Phosphate buffer :Phosphate buffer Major intracellular buffer H+ + HPO42- ? H2PO4- OH- + H2PO4- ? H2O + H2PO42-


Protein Buffers :Protein Buffers Non-bicarbonate buffers (Nbbs) – plasma proteins and hemoglobin. Includes hemoglobin, work in blood Carboxyl group gives up H+ Amino Group accepts H+


2. Respiratory mechanisms :2. Respiratory mechanisms Exhalation of carbon dioxide CO2 solubility in water is 25 times higher than that of oxygen ,so CO2 is easily lost to the envt. CO2 + H20 ? H2CO3 ? H+ + HCO3- Body pH can be adjusted by changing rate and depth of breathing.


3. Kidney excretion :3. Kidney excretion Can eliminate large amounts of acid Can also excrete base Can conserve and produce bicarb ions Most effective regulator of pH If kidneys fail, pH balance fails


Rates of correction :Rates of correction Buffers function almost instantaneously Respiratory mechanisms take several minutes to hours Renal mechanisms may take several hours to days


Acid-Base Imbalances :Acid-Base Imbalances pH 8.3 alkalosis The body response to acid-base imbalance is called compensation Partial compensation if range is still outside norms.


Compensation :Compensation If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation. If problem is respiratory, renal mechanisms can bring about metabolic compensation.


Slide 27:7–8.0


There are 4 Types of Acid-base Imbalances :There are 4 Types of Acid-base Imbalances 1.Respiratory Alkalosis 2.Respiratory Acidosis 3.Metabolic Alkalosis 4.Metabolic Acidosis


Respiratory Alkalosis :Respiratory Alkalosis Is a decrease in CO2, decrease in H+ (Hydrogen ions) and in increase in pH This condition can be caused by continuous fish movement or anxiety reaction The body compensates by the gills slowing the respiration rate and kidneys excreting more bicarbonate


Respiratory Acidosis :Respiratory Acidosis Is an increase in CO2, an increase in H+ and a decrease in pH This condition can be caused by , restrictive or obstructive gill diseases The body compensates by the gills increasing respiration rate and the kidneys by conserving bicarbonate ions and increasing renal net acid excretions


Metabolic Alkalosis :Metabolic Alkalosis Is a decrease in CO2, a decrease in H+ and an increase in pH This condition can be caused by , increased ingestion of alkali The body compensates by the gills creating a slow respiration rate and the kidneys excreting more bicarbonate


Metabolic Acidosis :Metabolic Acidosis Is an increase in CO2, and increase in H+ and a decrease in pH This condition can be caused by alkaline loss, excess acid production or ingestion The body compensates by the gills increasing respiration rate and the kidneys increasing renal net acid excretion


Conclusion :Conclusion Fishes are capable of regulating their internal pH using both internal buffering and transepithelial exchanges across the gills. Though their Pco2 and HCO3- are well below those found in mammals, they can tolerate a variety of acid-base challenges.


Slide 35:QUERIES ?