Body Fluids & Acid-Base Balance - Tanta University PDF

The body fluids in clinically relevant conditions BY Dr. Nada Hashem Lecturer of Medical Biochemistry Tanta University  Objectives 1.Define acid ,base and alkali. 2.Understand the meaning of pH. 3.Explain the concepts of buffers and buffering system...

The body fluids in clinically relevant conditions BY Dr. Nada Hashem Lecturer of Medical Biochemistry Tanta University  Objectives 1.Define acid ,base and alkali. 2.Understand the meaning of pH. 3.Explain the concepts of buffers and buffering system. 4.Recognize the changes of acid base balance. 5.Utilize the resources of biomedical information including the available electronic facilities to update his/her knowledge.  Lecture Frame 1. Fluid compartments 2. Acid-Base 3. pH 4. Weak and strong acids 5. Buffer 6. Physiological Buffers 7. Respiratory and metabolic acidosis  Pre-class reading: Harper’s Illustrated Biochemistry Chapter 2 -p : 3-13 Pre- class movies: https://www.youtube.com/watch?v=DupXDD87oHc https://www.youtube.com/watch?v=ZLKEjXbCU30  Fluid Compartments Infants have 73% or more water- low body fat and muscle mass In old age, only about 45% of body weight is water healthy females have around 50% of body weight water. Fluid Compartments  Electrolyte Composition of Body Fluids They are substances which can be dissociated into ions in an electric field.e.g NaCl.  H+ Proton Proton donor acceptor Acid base  Acid – Base Acid: substance that ionizes in water to give H+ that associates with the solvent to increase H3O+ in solution. HCl H+ + Cl¯ CH3COOH CH3COO¯ + H+ H+ + H2O H3O+  Acid – Base Alkali: the substance which gives hydroxyl ions when dissolved in water NaOH Na+ + OH¯ N.B. All alkalies are bases , not all bases are alkalies  Acid = proton donor Base = proton acceptor HCl + H 2O H 3O + + Cl- strong acid Base conjugate acid conjugate base H2CO3 + H 2O H 3O + + HCO3- weak acid Base conjugate acid conjugate base NH3 + H 2O NH4+ + OH- Base acid conjugate acid conjugate base Note: water can act as an acid or a base. “amphiprotic” solvent  pH pH is the negative logarithm (base 10) of H+ concentration. i.e. pH = -log(H+) H2O H+ + OH¯ H+ = OH¯ =10-7 So, if the (H+) is 10-7 gram/ion/liter, the pH will be -log 10-7 = -(-7) = 7  pH = -log[H+] The pH of acidic solutions ranges from 0 – 7, The pH of neutral solutions is 7 and The pH of alkaline solutions ranges from 7 – 14.  Definitions Strong acid is any acid that ionizes completely in solutions. Strong base is a base that is completely dissociated in an aqueous solution. Weak base is a base that does not ionize fully in an aqueous solution. Weak acid is an acid that is partially dissociated into its ions in an aqueous solution or water HA H+ + A-, Ka = [H+][A-]/[HA] Ka is the acid dissociation constant pKa = -Log Ka  Buffers A buffer is an aqueous solution that resists changes in pH upon adding strong acids or alkalies. ❖ if we add 1 ml of HCl to pure water a buffer solution pH drops Significantly pH will drop slightly  Buffers Buffer solution consists of a mixture of a weak acid and its conjugate of strong base or a weak base and its conjugate of strong acid. e.g. acetic acid + sodium acetate Carbonic acid + sodium bicarbonate l  e.g buffer solution consists of acetic acid (weak acid) + sodium acetate (conjugate base). If strong alkali is added to solution it releases (OH-) which combines with acetic acid and so pH doesn’t rise. CH3COOH (aq) + OH-(aq) CH3COO-(aq) + H2O (aq) If a strong Acis added it releases H+ which combines with CH3COO- to form Weak acid so pH doesn’t dropid. CH3COO-(aq) + H+ (aq) CH3COOH (aq) You have an acetate buffer. You add sodium acetate (salt) to it. What happens to the pH? Problem: Which of the following solutions are buffers? a) KH2PO4/H3PO4 b) 0.30 mol CH3COOH/ 0.30 mol NaOH c) 0.20 mol CH3COOH/ 0.10 mol NaOH Solution: a) H3PO4 is a weak acid and KH2PO4 , a salt of its conjugate base H2PO4 1-, is a weak base. The system contains a conjugate acid-base pair and therefore is a buffer system  Physiologic buffer systems (in our body) They are important to keep the pH suitable for enzymatic reactions. They are important to keep the pH of blood within normal range (7.35 – 7.45) since any marked change in pH of blood is fatal. pH < 7.2 Acidosis pH > 7.6 Alkalosis Death if pH < 6.8 or > 7.8  Physiologic buffer systems (in our body) 1. Plasma proteins (amino acids in proteins are amphoteric ie contain basic NH3 group which can receive H+ and acidic COOH group which can lose H+ and become COO-). 2. Bicarbonate buffer system (H2CO3/NaHCO3). 3. Phosphate buffer system (NaH2PO4/Na2HPO4). 4. Haemoglobin (when it releases oxygen, H+ binds to NH3 in this protein) Amino Acids in Protein as Buffer Systems The Carbonic Acid–Bicarbonate Buffer System Figure 27–9 Buffer Systems in Body Fluids Figure 27–7 Respiratory Mechanism Respiratory Mechanism  Renal Mechanism Reabsorbtion of bicarbonate Respiratory acidosis  Metabolic acidosis Severe diarrhea Diabetes Mellitus strenuous exercise pH value of 7 indicates that the solution is Acidic Basic Neutral alkaline Which of the following pH value shown by bases 7 9 3 6  Complete: The pH of a solution decreases from 2 to 1. The concentration of H+ ions………….. decreases increases remains the same becomes zero In acid-base imbalance ,respiratory alkalosis is due to Decreased HCO3 - Decreased CO2 Increased HCO3 - Increased CO2 Buffers are mixture of: Strong acid and strong base Strong acid and weak base Weak acid and their conjugate base Weak base and weak acid  Define buffer Describe the difference between a strong acid and a weak acid.  GOOD LUCK & THANK YOU