NURS1004 Week 12 Lecture 1 Acid Base Balance Prepared by Didy Button

Transcription

1 NURS1004 Week 12 Lecture 1 Acid Base Balance Prepared by Didy Button The Role of Amino Acids in Protein Buffer Systems

2 2-7 ph and Homeostasis ph The concentration of hydrogen ions (H + ) in a solution Neutral ph A balance of H + (Hydrogen ions) & OH (Hydronium ions) Pure water = 7.0

3 2-7 ph and Homeostasis Acidic ph Lower Than 7.0 High H + concentration Low OH concentration Basic (or alkaline) ph Higher Than 7.0 Low H + concentration High OH concentration ph of Human Blood Ranges from 7.35 to 7.45

4 2-7 ph and Homeostasis ph Scale Has an inverse relationship with H + concentration More H + ions mean lower ph, less H + ions mean higher ph

5 Figure 2-10 ph and Hydrogen Ion Concentration 1 mol/l hydrochloric acid Stomach acid Beer, vinegar, wine, Tomatoes, pickles grapes Urine Saliva, milk Blood Ocean Pure water water Eggs Household bleach Household ammonia 1 mol/l sodium hydroxide Oven cleaner Extremely acidic Increasing concentration of H + Neutral Increasing concentration of OH Extremely basic ph 0 [H + ] 10 0 (mol/l)

6 2-8 Inorganic Compounds Acid A solute that adds hydrogen ions to a solution Proton donor Strong acids dissociate completely in solution Base A solute that removes hydrogen ions from a solution Proton acceptor Strong bases dissociate completely in solution Weak Acids and Weak Bases Fail to dissociate completely Help to balance the ph

7 2-8 Inorganic Compounds Salts Solutes that dissociate into cations (+ve charged ions) Charged and anions ( -ve charged ions) other than hydrogen ions and hydroxide ions

8 2-8 Inorganic Compounds Buffers and ph Control Buffers Weak acid/salt compounds Neutralize either strong acid or strong base Sodium bicarbonate (NaHCO 3 ) is very important in humans Antacids Basic compounds that neutralize acid and form a salt Alka-Seltzer, Quick-Eze, Tums, Mylanta, etc.

9 27-1 Fluid, Electrolyte, and Acid Base Balance Acid Base Balance Precisely balances production and loss of hydrogen ions (ph) The body generates acids during normal metabolism Tends to reduce ph

10 Acid Base Balance ph of body fluids is altered by addition or deletion of acids or bases Acids and bases may be strong or weak Strong acids and strong bases Dissociate completely in solution Weak acids or weak bases Do not dissociate completely in solution Some molecules remain intact Liberate fewer hydrogen ions Have less effect on ph of solution

11 Table 27-3 A Review of Important Terms Relating to Acid Base Balance

12 Carbonic Acid Is a weak acid In ECF at normal ph: Equilibrium state exists H 2 CO 3 H + + HCO 3

13 The Importance of ph Control ph of body fluids depends on dissolved: Acids Bases Salts ph of ECF Is narrowly limited, usually

14 Acidosis Physiological state resulting from abnormally low plasma ph Acidemia plasma ph < 7.35 Alkalosis Physiological state resulting from abnormally high plasma ph Alkalemia plasma ph > 7.45

15 Acidosis and Alkalosis Affect all body systems Particularly nervous and cardiovascular systems Both are dangerous But acidosis is more common Because normal cellular activities generate acids

16 Types of Acids in the Body 1. Fixed acids 2. Organic acids 3. Volatile acids

17 Fixed Acids Are acids that do not leave solution Once produced they remain in body fluids Until eliminated by kidneys Sulfuric acid and phosphoric acid Are most important fixed acids in the body Are generated during catabolism of: Amino acids Phospholipids Nucleic acids

18 Organic Acids Produced by aerobic metabolism Are metabolized rapidly Do not accumulate Produced by anaerobic metabolism (e.g., lactic acid) Build up rapidly

19 Carbonic Acid A volatile acid that can leave solution and enter the atmosphere At the lungs, carbonic acid breaks down into carbon dioxide and water Carbon dioxide diffuses into alveoli

20 Carbon Dioxide In solution in peripheral tissues: Interacts with water to form carbonic acid Carbonic acid dissociates to release: Hydrogen ions Bicarbonate ions

21 Carbonic Anhydrase Enzyme that catalyzes dissociation of carbonic acid Found in: Cytoplasm of red blood cells Liver and kidney cells Parietal cells of stomach Other cells

22 CO 2 and ph Most CO 2 in solution converts to carbonic acid Most carbonic acid dissociates P CO2 is the most important factor affecting ph in body tissues P CO2 and ph are inversely related

23 CO 2 and ph When CO 2 levels rise: H + and bicarbonate ions are released ph goes down At alveoli: CO 2 diffuses into atmosphere H + and bicarbonate ions in alveolar capillaries drop Blood ph rises

24 Figure 27-9 The Basic Relationship between P CO2 and Plasma ph P CO mm Hg HOMEOSTASIS If P CO2 rises H 2 O + CO 2 H 2 CO 3 HCO 3 H + + When carbon dioxide levels rise, more carbonic acid forms, additional hydrogen ions and bicarbonate ions are released, and the ph goes down.

25 Figure 27-9 The Basic Relationship between P CO2 and Plasma ph HOMEOSTASIS ph If P CO2 falls H + + HCO 3 H 2 CO 3 H 2 O + CO 2 When the P CO2 falls, the reaction runs in reverse, and carbonic acid dissociates into carbon dioxide and water. This removes H + ions from solution and increases the ph.

26 Mechanisms of ph Control To maintain acid base balance: The body balances gains and losses of hydrogen ions And gains and losses of bicarbonate ions

27 Hydrogen Ions (H + ) Are gained At digestive tract Through cellular metabolic activities Are eliminated At kidneys and in urine At lungs Must be neutralized to avoid tissue damage Acids produced in normal metabolic activity Are temporarily neutralized by buffers in body fluids

28 Buffers Are dissolved compounds that stabilize ph By providing or removing H + Weak acids Can donate H + Weak bases Can absorb H +

29 Buffer System Consists of a combination of: A weak acid And the anion released by its dissociation The anion functions as a weak base In solution, molecules of weak acid exist in equilibrium with its dissociation products

30 Three Major Buffer Systems 1. Protein buffer systems Help regulate ph in ECF and ICF Interact extensively with other buffer systems 2. Carbonic acid bicarbonate buffer system Most important in ECF 3. Phosphate buffer system Buffers ph of ICF and urine

31 Figure Buffer Systems in Body Fluids Buffer Systems occur in Intracellular fluid (ICF) Extracellular fluid (ECF) Phosphate Buffer System The phosphate buffer system has an important role in buffering the ph of the ICF and of urine. Protein Buffer Systems Protein buffer systems contribute to the regulation of ph in the ECF and ICF. These buffer systems interact extensively with the other two buffer systems. Hemoglobin buffer system (RBCs only) Amino acid buffers (All proteins) Plasma protein buffers Carbonic Acid Bicarbonate Buffer System The carbonic acid bicarbonate buffer system is most important in the ECF.

32 Protein Buffer Systems Depend on amino acids Respond to ph changes by accepting or releasing H + If ph rises: Carboxyl group of amino acid dissociates Acting as weak acid, releasing a hydrogen ion Carboxyl group becomes carboxylate ion

33 Protein Buffer Systems At normal ph ( ) Carboxyl groups of most amino acids have already given up their H + If ph drops: Carboxylate ion and amino group act as weak bases Accept H + Form carboxyl group and amino ion

34 Protein Buffer Systems Carboxyl and amino groups in peptide bonds cannot function as buffers Other proteins contribute to buffering capabilities Plasma proteins Proteins in interstitial fluid Proteins in ICF

35 Figure The Role of Amino Acids in Protein Buffer Systems Neutral ph If ph rises If ph falls In alkaline medium, amino acid acts as an acid and releases H + Amino acid In acidic medium, amino acid acts as a base and absorbs H +

36 The Hemoglobin Buffer System CO 2 diffuses across RBC membrane No transport mechanism required As carbonic acid dissociates: Bicarbonate ions diffuse into plasma In exchange for chloride ions (chloride shift) Hydrogen ions are buffered by hemoglobin molecules Last Slide.