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Chapter 12

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Physiology 1021
Tom Stavraky

Why is th+s Important?  H can alter the shape of proteins that act as enzymes that speed up chemical reactions  any change in the concentration of H will affect the activity of almost every cell The Hydrogen Atom and Hydrogen Ion  H has a single proton, which is positively charged, and a single electron, which is negatively charged  results in an electrically neutral element +  H is a H atom that has lost its electron, leaving only the positively charged proton What Are Acids and Bases?  acid is any molecule that will release H+ when put in a solution + +  presence of the free H that makes a solution acidic—the more free + , the more acidic  strong acid will dissociate rapidly and release large amounts of H in solution  base is any molecule that will accept a hydrogen ion + +  bases lowe+ the concentration of free H in solution by combining with the H  less free H , the acidity of the solution will decrease and become more basic or alkaline The pH Scale +  a way of quantifying the concentration of H in any solution  pH is the negative logarithm (to the base 10) of the hydrogen ion concentration  the more free H , the lower the pH  0 to 14 with neutral pH at 7  below 7 is considered acidic  above 7 is alkaline or basic  normal pH of body fluids varies slightly between 7.35 and 7.45 and has an average of 7.4  Note that this is slightly alkaline. Arterial blood has a pH of 7.45 while venous blood has a pH of 7.35  acidosis is a term used to describe body fluids when the pH is below 7.4  alkalosis occurs when the pH is above 7.4  pH of body fluids is below 6.8 or above 7.8 for long periods of time, death will occur The Source of Acid in the Body  when cells in the body make energy (ATP) they will produce CO as a2byproduct  Respiratory System this CO c2n, with the help of the enzyme carbonic anhydrase, combine with water in red blood cells to produce carbonic acid, H 2O . 3he carbonic + − acid will dissociate into free H and bicarbonate ions, HCO .3In the lungs, the reaction will then reverse—carbonic acid will reform, it will convert to CO 2nd H O2and the CO 2ill be removed and exhaled. As a result, there is generally no NET increase in free H in the plasma. Because the carbonic acid reforms into CO , which is then removed at 2 the lungs, carbonic acid is known as a volatile acid.  metabolic breakdown of various proteins will produce a number of acids including sulphuric acid, phosphoric acid, lactic acid, and other organic acids  stomach is a large source of hydrochloric acid  these acids cannot be removed by the lungs and are therefore called nonvolatile acids  these acids are a significant source of free H and are constantly being produced throughout the body Regulation of H Concentration—Buffers +  a buffer is any molecule that can reversibly bind (or release) free H  buffers bind free H , and thereby reduce the amount of free H in solution  they help to stabilize the pH +  general reaction between a buffer and a free H is:  This reaction shows that the buffer, called “X,” combines with free H to make XH  buffers do not +revent the pH from changing; they only help to minimize any pH change until the free H can be removed from the body by either the lungs or kidneys  buffers we have already seen include bicarbonate ions and hemoglobin (Hb) +  free H can bind with buffers in both the intracellular and extracellular fluid  intracellular buffers include phosphates (which won’t be covered here) and intracellular proteins, such as hemoglobin (Hb) inside red blood cells −  most powerful extracellular buffer is the bicarbonate ion, HCO 3  Hb can reversibly bind with free H to help stabilize the acidity inside the RBCs o can also bind CO to reduce the potential acidity should the CO combine with 2 2 H + to form carbonic acid, H CO2 3 Regulation of H Concentration—Respiratory System  involves detection of this gas by central and peripheral chemoreceptors  when CO l2vels increase, both of these receptors detect the change and cause an increase in ventilation  increased ventilation causes more CO to be removed at the lungs, which will then return
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