2. water and PH measuring presentation.pptx

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1. 2. Water And PH •Water accounts for about 70% of a cell's weight, and most intracellular reactions occur in an aqueous environment. •Life therefore hinges on the properties of water. Properties of water – Polarity –Hydrogen bonding potential –Specific heat, heat of vaporization – Nucleophilic (electron rich) –Ionization –Water is an ideal biological solvent 1

2. Role of water in biological system • Water can dissolve most of biologically important molecules ( universal solvent ). •Water act as a medium for diffusion of molecules in the cell •Osmotic concentration of cell is maintained by water. •Water is the source for H+ ions for photosynthesis. • Oxygen is released by hydrolysis of water during photosynthesis. •Water act as a reactant in the hydrolysis reaction Water support aquatic plants and animals •Water cools the body by sweating process •Seed germination requires water •The main medium of blood and lymphatic system is water •Act as lubricant in the joints 2

3. CONT. •Hydrophilic and hydrophobic interactions of macromolecules permit formation and stabilization of cell membrane, conformation of proteins • Ice has less density than water • Water is transparent • Water can form buffers with acid and base • Due to the high heat capacity, water prevents the effect of temperature flu ctuations in the surrounding •In each water molecule (H2O) the two H atoms are linked to the O atom by covalent bonds •The two bonds are highly polar because the O is strongly attractive for electrons, whereas the H is only weakly attractive. 3

4. cont • Consequently, there is an unequal distribution of electrons in a water molecule, with a preponderance of positive charge on the two H atoms and of negative charge on the O •When a positively charged region of one water molecule (that is, one of its H atoms) approaches a negatively charged region (that is, the O) of a second water molecule, the electrical attraction between them can result in a weak bond called a hydrogen bond • These bonds are much weaker than covalent bonds and are easily broken by the random thermal motions due to the heat energy of the molecules, so each bond lasts only a short time 4

5. 5 Cont.

6. Cont. •Molecules, such as alcohols, that contain polar bonds and that can form hydrogen bonds with water dissolve readily in water. •Molecules carrying plus or minus charges (ions) likewise interact favorably with water. –Such molecules are termed hydrophilic, meaning that they are water-loving. •Water ionizes to form the hydronium (hydroxyl) ion and hydroxide ions •A large proportion of the molecules in the aqueous environment of a cell necessarily fall into this category including sugars, DNA, RNA, and most proteins. •Hydrophobic (water hating) molecules, by contrast, are uncharged and form few or no hydrogen bonds, and so do not dissolve in water . Eg : Hydrocarbons 6

7. Water D i str i but i on In Body & Regulat i on o f Water Metabol i sm All chemical reactions take place in aqueous medium in body, and all reactives are dissolved in body fluids. Water participates to many biochemical reactions, actively. Water plays an important role in absorption, transport, digestion, excretion & maintenance of body temperature. WATER BALANCE IN THE BODY Extracellular water osmolarity is maintained constant at 280-298 mOsm/L as a balance between water intake and water excretion. Under normal conditions approximately :- one half to two thirds of water intake is in the form of oral fluid intake, and one half to two thirds of water intake is in the form of oral intake of water in food . A small amount of water is produced by oxidative metabolism (150-300 ml/day) 7

8. Acıd- B ase Balance and Buffers 8 The end-products of the catabolism of carbonhydrates, lipids and proteins are generally acidic molecules in living organisms. In metabolic reactions, 22 000 mEq acid ( organic acids, inorganic acids and CO 2 ) is produced per day . H + is a direct participant for many reactions, and enzymes . increase d [ H + ] can easily alter the charges and functions of proteins, enzymes, nucleic acids, some hormones and membranes . Normal blood pH is 7 . 35-7 . 45 . Values < 6 . 8 ( Acidosis or acidemia ) or > 7 . 70 are toxic ( Alkalosis or alkalemia ) can result in coma, cardiac failure, and circulatory collapse. In living organisms, pH of the body fluids are tightly regulated by biological buffers and some organs ( lungs and kidneys ).

9. Acid-base theory • According to the modern concept of Brönsted -Lowry: – acid donates protons(H+ ions). – bases accepts protons. • Strong acids dissociate nearly fully. • Weak acids only partially dissociate. 9

10. Cont The extent of ionization of a weak acid is a function of its acid dissociation constant pKa Acids with Ka < 1 are considered weak. Acids Ka for acetic acid is 1.76 x 10-5 -> difficult to work with so instead use log scale: pKa = -log Ka So the pKa of acetic acid is = -log 1.76 x 10 -5 = 4.75. The pH is a measure of acidity and the pKa is a measure of acid strength. 10

11. Definition of PH and pka pH is the (-) logarithm of [ H + ] PH = -log [ H + ] Scale ranges from 1 to 14. 1 means only H + are present, 14 means no H + present. pOH is the (-) logarithm of [ OH - ] pOH = -log [ OH - ] For water; [H+]=[OH-]=10 -7 M, pH=7 and pH+pOH=14 (calculated) A solution with PH<7 is acidic and A solution with PH>7 is basic Acids are [ H + ] donors Bases are [ H + ] acceptors 11

12. Buffers Buffer is a solution ( or a substance) that has the ability to maintain pH & bring it back to its optimal value by addition or removal of H + ; Buffer + H + H + Buffer Buffer tend to resist changes in pH when small amounts of strong acid [H + ] or strong base [OH - ] are added. A buffer system consists of :- a weak acid (the proton donor) and its conjugate base ( weak bases and their salts ). A mixture of equal concentrations of acetic acid and acetate ion is a buffer system . One can soak up excess protons (acid), the other can soak up excess hydroxide (base). When a strong acid (HCl) is added: CH3COO - + H Cl  CH3COOH + Cl - - When a strong base (NaOH) is added: CH 3 COO H +Na OH  CH3COO - + H 2 O + Na + 12

13. cont Buffering mechanism for weak base and its conjugate acid is also same. When the conjugate base and weak acid at equal concentrations, the buffer has the maximum buffering capacity and pH= pKa. A buffer system is maximally effective at a pH close to its pK a . 13

14. 14 1. Bicarbonate/carbonic acid buffer system 2. Protein buffer system 3. Hemoglobin buffer system 4. Phosphate buffer system Biological Buffering Systems

15. 15 The most important buffer of the plasma is the bicarbonate/carbonic acid buffer system The ratio of base to acid (HCO 3 -/H 2 CO 3 ) is nearly 20/1 in plasma under physiological conditions This buffer system is more complex than others, b/c carbonic acid (H 2 CO 3 ) is formed from dissolved CO 2 which produced in tissues and diffused to plasma . CO 2 + H 2 O H 2 CO 3 HCO 3 - + H + This reaction is slow in plasma but in erythrocytes, carbonic anhydrase increases the rate of this reaction. HCO 3 - /H 2 CO 3 = 20/1 when plasma pH=7 . 4 When hydrogen ion concentration increases in plasma, HCO 3 - ions bind H + forming H 2 CO 3 . H 2 CO 3 is converted to CO 2 + H 2 O . CO 2 is released to atmosphere by lungs . Bicarbonate/carbonic acid buffer system

16. Bicarbonate buffer Has the following limitations: Cannot protect the ECF from pH changes due to increased or depressed CO2 levels. Only functions when respiratory system & control centers are working normally. It is limited by availability of bicarbonate ions (bicarbonate reserve). 16

17. 17 The carboxyl & amino groups are what enable proteins to act as buffers . At neutral pH the carboxyl ion is present as COO- instead of COOH ( Acidic medium= becomes COOH Basic medium- becomes COO- ) while the amino group is actually-NH3+ (acidic medium) NH2 (Basic medium). In proteins, ionizable R groups (COOH groups of aspartate & glutamate, NH 2 groups of lysine, arginine & histidine) and N-terminale  -NH 2 groups of some amino acids are responsible for buffering. Proteins, especially albumin , account for the %95 of the non-bicarbonate buffer value of the plasma . Buffering effect of proteins is low in plasma Proteins are much more effective buffers in intracellular medium. The most important buffer groups of proteins in the physiological pH range are the imidazole groups of histidine which has a pKa value of 6.5 Each albumin molecule contains 16 histidines Protein buffer system

18. 18 Hemoglobin (Hb) is a protein which carries O 2 to tissues and CO 2 from tissues to lungs and is an effective buffer. The most important buffer groups of Hb are histidines . Each globin chain contains 9 histidine. %95 of CO 2 which is released from tissues to plasma is diffused into erythrocytes. In erythrocytes , carbonic anhydrase constitutes H 2 CO 3 from CO 2 and H 2 O and then HCO 3 - and H + are released by the ionization of H 2 CO 3 . Carbonic anhydrase CO 2 + H 2 O H 2 CO 3 HCO 3 - + H + Released protons take part in the formation of salt bridges between globin chains of Hb , and lead the change in the conformation of Hb molecule in tissue capillaries . Hemoglobin buffer system

19. 19 The binding of proton and CO 2 is conversly related to binding of oxygen. In tissue capillaries proton and CO 2 binding decreases the oxygen binding capacity of Hb so that oxygen is released by Hb. This effect of pH and CO 2 concentration on the binding and release of oxygen by Hb is called the Bohr Effect . Because of the accumulation of HCO 3 - formed by ionization of H 2 CO 3 within erythrocytes , there is a concentration gradient for HCO 3 - between plasma and erythrocytes . In that case, HCO 3 - ions rapidly move from erythrocytes to plasma , and Cl - ions move from plasma to erythrocytes to provide electrochemical balance . This shift of Cl - is referred to as the chloride shift.

20. 20 All those phenomenons occur in capillaries of peripheral erythrocytes conversely change in capillaries of lungs . When Hb reaches the lungs, the high oxygen concentration promotes binding of oxygen and release of protons from broken salt bridges. Protons associate with HCO 3 - and H 2 CO 3 forms. H 2 O and CO 2 form by the reaction catalyzed by carbonic anhydrase H 2 CO 3 Carbonic anhydrase CO 2 + H 2 O This phenomenon is referred as Haldane Effect. H 2 O and CO 2 are excreted to atmosphere by respiration.

21. 21 Main elements of phosphate buffer system- H 2 PO 4 - & HPO 4 2- . is most effective in intracellular medium, especially inkidneys . Phosphoric acid has 3 ionization steps : H 3 PO 4 H 2 PO 4 - + H + pK1= 1.9 H 2 PO 4 - HPO 4 2- + H + pK2= 6.8 HPO 4 2- PO 4 3- + H + pK3= 12.4 When Hb reaches the lungs , the high oxygen concentration promotes binding of oxygen and release of protons from broken salt bridges . Protons associate with HCO 3 - and H 2 CO 3 forms. H 2 O and CO 2 form by the reaction catalyzed by carbonic anhydrase H 2 CO 3 Carbonic anhydrase CO 2 + H 2 O This phenomenon is referred as Haldane Effect. H 2 O and CO 2 are excreted to atmosphere by respiration . Phosphate buffer system

22. 22 Among the 3 ionization steps, H 2 PO 4 - / HPO 4 2- is an efficient/good buffer b/c of its pK a value (6 . 8) which is close to physiological pH (7 . 4). HPO 4 2- / H 2 PO 4 - = 4 at the pH (7 . 4). Phosphate buffer system is not effective in plasma (ECF) , because phosphate ion concentrations are low but more in ICF . However it is important in the renal tubules of kidneys for excretion of acids in the urine. H + secrected into the tubular lumen by the Na + –K + exchanger react with HPO 4 2- to form H 2 PO 4 - . Some organic phosphates (2,3 diphosphoglycerate in erythrocytes) has also buffering capacity .

23. 23 Lungs and kidneys have an important role for regulation of acid-base balance . Lungs Lungs provide O 2 /CO 2 exchange between blood and atmosphere . O 2 and CO 2 are transported between lungs and peripheral tissues by Hb within erythrocytes . CO 2 carried with either carbaminoHb form or H + form in the salt bridges between globin chains is excreted by respiration. Respiratory center senses and responds to the pH of blood and the source of pulmonary control. Both O 2 and CO 2 partial pressures influence the center. REGULATION OF ACID-BASE BALANCE

24. 24 A decrease in pH results in an increased respiratory rate and deeper breathing. A decrease in respiratory rate leads to accumulation of CO 2 and decrease in pH. Pulmonary response is rapid (max. at 3-6 h) while renal compensation is relatively slower. Kidneys The kidneys secrete protons through 3 mechanisms: 1. Reabsorbsion of HCO 3 - 2. Na + /H + exchange 3. Production of ammonia and excretion of NH 4 +

25. 25 The proximal tubule is responsible for reabsorbsion of HCO 3 - filtered through glomeruli. In tubuler cells CO 2 reacts with H 2 O to form H 2 CO 3 HCO 3 - derived from dissociation of H 2 CO 3 is reabsorbed to plasma 1. Reabsorbsion of HCO 3 -

26. 26 H + secreted into the tubules in exchange for Na + from the tubular fluid by Na + /H + -ATPase combines with HCO 3 - to form CO 2 and water. The CO 2 diffuses into the tubular cells where it is rehydrated to H 2 CO 3 by carbonic anhdydrase. H 2 CO 3 dissociates to HCO 3 - and H + .The HCO 3 - is reabsorbed and diffuses into the blood stream. K + ions compete with H + for Na + /H + exchange. When K + ions excretion increase in urine, excretion of H + ions decreases. Na + /H + exchange may also be coupled to formation of H 2 PO 4 - from HPO 4 2- in the lumen. 2. Na + /H + exchange

27. 27 These disorders are classified according to their cause: 1. Metabolic acidosis 2. Respiratory acidosis 3. Metabolic alkalosis 4. Respiratory alkalosis pH is lower than 7.37 in acidosis , higher than 7.44 in alkalosis . DISORDERS OF ACID-BASE BALANCE

28. 28 It is detected by decreased plasma bicarbonate. Causes : 1. Production of organic acid that exceeds the rate of elimination (e.g.,lactic acid acidosis) 2. Reduced excretion of acids resulting an accumulation of acid that consumes bicarbonate (e.g., renal failure, some renal tubular acidosis) 3.Excessive loss of bicarbonate due to increased renal excretion or excessive loss of duodenal fluid Total anions in plasma must equal total cations 1. Metabolic acidosis

29. 29 Anion gap: - It is unmeasured anions (phosphate, sulfate, proteins) in plasma and it is calculated as the difference between measured cations and measured anions. Anion gap=  Na +  +  K +    Cl -    HCO 3 -  - It is equal 12  4 mEq/L under physiological conditions. - Anion gap is generally high in metabolic acidosis.

30. 30 Renal failure Renal tubular acidosis Diabetic ketoacidosis Lactic acidosis Hypoxia Increased acid intake Hyperthyroidism Hyperparathyroidism Carbonic anhydrase inhibitors Salicylate overdose Causes of metabolic acidosis

31. 31 Respiratory acidosis is characterized by accumulation of CO 2 , rise in pCO 2 , decreases in bicarbonate concentration and pH. It may result from central depression of respiration or from pulmonary disease Plasma K + concentration may increase because of its competition with H + for Na + /H + exchange. Plasma Cl - concentration may decrease because of chloride shift (Cl - also accompanies the renal excretion of NH 4 + ). Urine is much more acidic than usual. Acute respiratory acidosis is compensated by kidneys. However renal compensation is not enough in the case of chronic respiratory acidosis. The primary goal of treatment is to remove the cause of the distributed ventilation. 2. Respiratory acidosis

32. 32 Narcotic or barbiturate overdose - drug Trauma Infection Cerebrovascular accident Asthma, obstructive lung diseases Causes of R espiratory Ac idosis

33. 33 Metabolic alkalosis is characterized by elevated plasma bicarbonate level. It may result from administration of excessive amount of alkali or vomiting which causes loss of H + and Cl - . Plasma level of bicarbonate is high, K + and Cl - are low, urine is much more alkaline than usual. When pH> 7.55 many of anions bind the Ca 2+ ions so that ionized Ca 2+ concentration decreases in plasma. This leads the cramps and convulsions. Metabolic alkalosis is compensated by lungs and kidneys. Respiratory rate is decreased by lungs as a result of depression of respiratory center by high pH, therefore CO 2 is kept . Renal compensation involves decreased reabsorbtion of bicarbonate, Na + /H + exchange and NH 4 + formation which lead formation of alkaline urine. 3. Metabolic alkalosis

34. 34 Loss of hidrogen ions from GIS K + deficiency Hyperaldosteronism Cushing syndrome Antiacids, diüretics, corticosteroids Causes of metabolic alkalosis

35. 35 Respiratory alkalosis occurs when the respiratory rate increases abnormally and leads to decrease in P CO2 and rise in blood pH . Hyperventilation occurs in hysteria, pulmonary irritation and head injury with damage to respiratory center. The increase in blood pH is buffered by plasma bicarbonate buffer system. Renal compensation seldom occurs because this type of alkalosis is usually transitory. The increase in blood pH is buffered by plasma bicarbonate buffer system. 4. Respiratory alkalosis