chapter 27 lecture 3 is acid-base balance and buffer systems the acid-base balance of body is mainly controlled by controlling the hydrogen ion concentration the body fluids especially those outside the cells the homeostasis the hydrogen ion concentration is extremely important because proteins can be denatured their tertiary or three-dimensional structure can be denatured that's one of the things remember that happens in the stomach normal plasma ph has to be maintained between 7.35 and 7.45 so that's slightly alkaline remember 7 is neutral and it's a pretty narrow range so we have to keep it within that range otherwise if it's too alkaline if it goes above 7.45 you could have big problems same thing if it goes below 7.35 different things tend to to acidify the blood including high protein diets also things like we learned before which is breaking down fat using fat or that as a an energy source in lieu of sugar that can cause keto ketone bodies to build up and when they build up in the blood you have ketoacidosis so we have three major mechanisms that help to regulate ph the buffer systems exhalation of carbon dioxide and excretion of hydrogen ions from the kidneys buffer systems work to prevent drastic changes in ph and so they can change either a strong acid or a strong base into a weak acid or base which doesn't impact the ph as much buffer systems work extremely fast we have three different ones that we have in our body we have a protein buffer system carbonic acid bicarbonate buffer system and the phosphate buffer system the protein buffer system is mostly intracellular but plasma proteins can do it as well the protein molecules are what we call amphoteric amphoteric means that they can act as both a weak acid and a weak base weak acids and bases don't change the ph very much strong acids and bases do so if we can convert those strong acids and bases into weak ones we'll stay within the normal range more easily so when the ph rises that means it becomes more alkaline the organic acid or the carboxyl group remember carboxyl is it is can also be called carboxylic acid because it's an acid so when the ph goes up and it becomes more alkaline the carboxylic acid group or an organic acid releases hydrogen ions and the hydrogen ions then bind to whatever the alkaline substance is and decrease the ph when the ph goes down the amino group which is alkaline binds to hydrogen ions because when the ph falls is because hydrogen ions have increased and this will bind that up the bicarbonate buffer system is probably the most important buffer system in our body it helps to buffer the ph of blood when we make atp we produce carbon dioxide and water as waste products they combine together to form carbonic acid carbonic acid is a weak acid and weak acids dissociate and we have a hydrogen ion and bicarbonate so this acts as a base and this acts as an acid these travel this is how it travels back and forth in the blood between carbonic acid and bicarbonate when it gets to the lungs it recombines and it is excreted as carbon dioxide and water vapor it's also going to be the bicarbonate can be excreted by the kidney if you have too much if your blood is too alkaline it'll excrete some of this the kidneys can also excrete the hydrogen ions so they can selectively excrete one or the other of these two compounds or ions the reversible reaction is important in the extracellular fluid so here we're going to release hydrogen ions to lower the ph if the reaction goes in the other direction and the bicarbonate turns into carbonic acid it binds up hydrogen ions so it decreases the ph so that raises the ph okay so if it gets too acidic or if it gets too alkaline it releases hydrogen ions to decrease it if it gets too acidic it binds up hydrogen ions to make it more alkaline as i said it works with the respiratory and urinary systems in order to lower ph the kidneys can selectively excrete bicarbonate to make the ph more acidic and to raise it to make it more alkaline the kidneys can excrete hydrogen ions and the lungs excrete carbon dioxide the phosphate buffer system is important in plasma with plasma and erythrocytes and in this case we have phosphate plus water gives us h3o plus and the we go from the dihydrogen phosphate to a monohydrogen phosphate so any acid is going to react with the mono hydrogen phosphate to form the dihydrogen phosphate so when it's acidic when you have acidic conditions this is going to bind up hydrogen ions if it's basic conditions this will release hydrogen ions so it just goes back and forth either releasing or gaining hydrogen ions between the mono and dihydrogen phosphate forms so our first line of defense against ph shift is going to be one of these buffer systems if they become overwhelmed if they're not functioning properly or they can't keep up with the ph change then our second line of defense is going to be these physiological systems that work as buffers the respiratory system and the renal system the respiratory system is going to help with buffering by excreting co2 and the renal system the kidneys are going to excrete hydrogen ions when we exhale um the more carbon dioxide is going to be released and then by doing that we decrea we increase the ph so by exhalation we make our blood more alkaline so the ph body fluids can be adjusted by a change in the rate and depth of respiration and that takes about one to three minutes now remember the buffer systems work in seconds so this takes a little longer a decrease in respiration rate and depth means less carbon dioxide is exhaled and it causes the blood ph to decrease to become more acidic so the ph is also going to affect the rate of breathing the kidneys excrete hydrogen ions and they're going to reabsorb bicarbonate to help with maintaining the ph so something some stimulus disrupts homeostasis by decreasing blood ph which increases hydrogen ion concentration this is detected by chemoreceptors and they send information to the inspiratory area in the medulla and the diaphragm contracts more forcefully and frequently so more carbon dioxide is exhaled and then you form less carbonic acid and there are fewer hydrogen ions present and blood ph increases so which is equal to the hydrogen ion content decreasing and then it brings the ph back to normal in the kidney hydrogen ions are excreted the excretion of hydrogen ions in the urine is the only way to eliminate a large amount of them the kidneys can make new bicarbonate safe filtered bicarbonate if you have renal failure your kidneys aren't working it can cause death pretty quickly because of not being able to combat acidosis so cells in the proximal convoluted tubule the collecting ducts secrete hydrogen ions in the proximal convoluted tubule there's sodium hydrogen ion antiporters that secrete hydrogen reabsorbs sodium some of the intercalated cells have proton pumps and remember a hydrogen ion is it's is generally called a proton because it doesn't have an electron it only has one proton so proton pumps are going to move hydrogen ions so there's hydrogen these are going to secrete hydrogen ions into the tubular fluid uh bicarbonate antiporters reabsorb bicarbonate other intercalated cells have proton pumps in their membranes and chloride and bicarbonate antiporters and their apical membranes and so they're going to excrete excess hydrogen when the ph is too low or excrete excess bicarbonate when the ph is too high the normal ph of the systemic arterial blood is between 7.35 and 7.45 if you go below 7.35 you have acidosis and the principal effect of that is going to be to depress the central nervous nervous system by depressing or slowing down synaptic transmissions alkalosis is above 7.45 and that is going to have the opposite effect instead of depressing and you're going to have over excitability the goals for lecture 3 are describe each of the following protein buffer system phosphate buffer system carbonic acid bicarbonate buffer system and describe how the lungs and kidneys can help maintain proper ph levels in the body what is meant by acidosis alkalosis