Physiology 2130 Lecture 12: Module 12 Lecture
4 Jan 2021
School
Department
Course
Professor
PHYS 2130
July 20
Module 12
Module 12 Lecture: Acid/Base Balance
12.1 Objectives
●Define acid and base
●Describe pH, how it is calculated, and the normal pH of the body
●Describe and understand the relationship between free hydrogen ion concentration, acid, and pH
●Explain what a volatile acid is, what a nonvolatile acid is, and where they come from
●List the three ways the body regulates against increases in free hydrogen ions (H+)
●Explain how buffers work to help maintain pH when the levels of H+ change
●Explain how the respiratory system regulates the levels of volatile acids in the body
●Describe how the kidneys regulate pH by excreting H+ and reabsorbing bicarbonate ions
●Define alkalosis and acidosis
●Describe the types of alkalosis and acidosis and their causes
12.2 Introduction
●In this module, we will look at the relationship between hydrogen ions (H+) and acidity
●We will also define what acids and bases are, what a pH scale is, and why it is important to maintain H+ at
precise levels
●We will also look at the different mechanisms in the body for regulating H+ concentrations (and thus pH)
and we will also learn about some of the things that can alter the pH of the body
12.3 Why is this Important?
●Many chemical reactions take place in the body, and most of the machinery inside all the cells, are very
sensitive to the presence of hydrogen ions
●Hydrogen ions (H+) can alter the shape of proteins that act as enzymes that speed up chemical reactions
●As a result, any change in the concentration of H+ will affect the activity of almost every cell
●Therefore, it is essential that H+ concentration can be very carefully regulated
12.4 The Hydrogen Atom and the Hydrogen Ion
●The hydrogen atom
has a single proton, which is positively charger, and a single electron, which is
negatively charged. The result is an electrically neutral element
●A hydrogen ion
(H+) is a hydrogen ion that has lost its electron, leaving only the positively charged proton
●In some situations, the hydrogen ion may simply be called a proton
12.5 What Are Acids and Bases?
●An acid is any molecule that will release hydrogen ions
when put in a solution.
○I.e. HCl will break apart into free H+ and Cl-
○It is the presence of the free H+ that makes a solution acidic → the more free H+, the more acidic
the solution, and vice versa
○A strong acid will dissociate rapidly and release large amounts of H+ in solution (HCl is a strong
acid)
●A base is any molecule that will accept a hydrogen ion
○I.e. bicarbonate ions (HCO3-) will bind with H+ to form H2CO3
○Bases lower the concentration of free H+ in solution by combining with the H+
○With less free H+, the acidity of the solution will decrease and become more basic or alkaline
12.6 The pH Scale
●The pH scale is a way of quantifying the concentration of H+ in any solution
●The definition of pH is very complicated → pH is the logarithm (to the base 10) of the hydrogen ion
concentration
○Essentially, because it is a negative logarithm,
the more free H+, the lower the pH and vice versa
○The more free H+ there are in solution, the more acidic the solution and the lower the pH
12.7 The pH Scale (cont.)
●The pH scale goes from 0 to 14 with a neutral pH at 7
●A solution with a pH below 7 is considered acidic
●A solution with a pH above 7 is considered basic
●The normal pH of body fluids varies slightly between 7.35 and 7.45 and has an average of 7.4
○This is slightly basic
●Acidosis
is a term used body fluids when the pH is below 7.4, while alkalosis
occurs when the pH is above
7.4
●When the pH of body fluids is below 6.8 or above 7.8 for long periods of time, death will occur
12.8 The Source of Acid in the Body
●When cells in the body make energy (ATP) they will produce CO2 as a byproduct
●This CO2 can, with the help of the enzyme carbonic anhydrase, combine with water in RBCs to produce
carbonic acid (H2CO3)
●The carbonic acid will dissociate into free H+ and bicarbonate ions (HCO3-)
●In the lungs, the reaction will then reverse, carbonic acid will reform, it will convert to CO2 and H2O and
the CO2 will 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 CO2, which is then removed at the lungs, carbonic acid is known as
a volatile acid
●The metabolic breakdown of various proteins will produce a number of acids, including sulphuric acid,
phosphoric acid, lactic acid, and other organic acids
●The stomach is a large source of HCl
○These acids cannot be removed by the lungs and are called nonvolatile acids
○These acids are a significant source of free H+ and are constantly being produced throughout the
body
○As a result, they must be dealt with in order to maintain a constant pH
12.9 Regulation of Hydrogen Ion Concentration
●The body regulates free H+ concentration by three mechanisms → buffers, the respiratory system, and the
kidneys
●Buffers →
in body fluids (including the blood) bind free H+
○This system reacts almost immediately to sudden, brief changes in free H+, and, consequently, is
the body’s first line of defense
○It is very important to note that buffers do not directly remove H+ from the body nor do they alter
the pH
■Instead, they “bind up” free H+, stabilizing the pH, until balance can be re established by
the next two systems
●Respiratory system →
can regulate H+ concentration from volatile acids within seconds to minutes
Document Summary
Describe ph, how it is calculated, and the normal ph of the body. Describe and understand the relationship between free hydrogen ion concentration, acid, and ph. Explain what a volatile acid is, what a nonvolatile acid is, and where they come from. List the three ways the body regulates against increases in free hydrogen ions (h+) Explain how buffers work to help maintain ph when the levels of h+ change. Explain how the respiratory system regulates the levels of volatile acids in the body. Describe how the kidneys regulate ph by excreting h+ and reabsorbing bicarbonate ions. Describe the types of alkalosis and acidosis and their causes. In this module, we will look at the relationship between hydrogen ions (h+) and acidity. We will also define what acids and bases are, what a ph scale is, and why it is important to maintain h+ at precise levels.
