 In this video, I will describe the pH buffer systems in the body and their importance for pH homeostasis. The pH of human blood is typically about 7.4. The optimal blood pH range is between 7.35 and 7.45. If blood pH falls outside of this range, it can lead to disruption of organ functions. Blood pH below 7.35 is known as acidosis and leads to disruption of the nervous system functions, specifically depression of the central nervous system causing headache, disorientation, and in extreme cases can lead to loss of consciousness or even death. You can see other organ systems are also affected. The respiratory system can be disrupted by acidosis leading to shortness of breath or coughing. The cardiovascular system can be disrupted leading to arrhythmia of the heart or an increase in heart rate. The skeletal muscular system can be disrupted leading to seizures or weakness. The digestive system can be affected by acidosis causing nausea, vomiting, or diarrhea. Blood pH greater than 7.45 is known as alkalosis. Alkalosis leads to disruption of the nervous system functions as well, leading to over-excitability of the nervous system which causes abnormal tingling sensations, muscular twitches and spasms, lightheadedness, anxiety, confusion, and in extreme cases, alkalosis can lead to loss of consciousness or even death. You can see the effects of alkalosis also include effects on the digestive system that can cause nausea and vomiting. There is a lot of overlap in the symptoms associated with acidosis and alkalosis, including disruption of the nervous system functions and nausea and vomiting. These symptoms are largely related to disruption in the structure of proteins at the molecular level that results from a blood pH outside of the optimal range. Disrupting the structure of proteins will disrupt the function of proteins and then this will disrupt the function of cells, tissues, organs, and organ systems, ultimately leading to the symptoms observed at the level of the organism. A pH buffer is a chemical system that prevents rapid changes in the pH of a solution by dampening the change in hydrogen ion concentration that occurs as acid or base is introduced into the solution. One of the pH buffering systems in the body is shown in the illustration here, the amino acid buffering system. The amino acids can accept hydrogen ions from solution in order to prevent a decrease in blood pH. Similarly, amino acids can contribute a hydrogen ion to solution in order to help prevent blood pH from becoming too high. While there are some free amino acids found inside the cytosol in cells and in the extracellular fluids and blood plasma, most amino acids in the body are found bound together in polypeptides and proteins, and the protein buffering system accounts for about two thirds of the blood buffering capacity. The most abundant protein in blood plasma is albumin, and hemoglobin is the most abundant protein found within cells in the blood within the erythrocytes. So, albumin and hemoglobin contribute to the pH buffering capacity of blood, as the amino acids within these proteins are able to function as buffers, either absorbing hydrogen ions or releasing hydrogen ions in order to stabilize the pH of the solution. The phosphate buffering system resulting from sodium monohydrogen phosphate and sodium dihydrogen phosphate is another important pH buffer in the blood. Sodium monohydrogen phosphate functions as a weak base to accept hydrogen ions from solution, preventing a decrease in the blood pH. The bicarbonate buffering system is another important pH buffer in the body. Bicarbonate is a weak acid that can accept a hydrogen ion to form carbonic acid. This system accounts for the majority of the pH buffering capacity of the extracellular fluids, which have a relatively low protein concentration, but the bicarbonate buffering system is also very important for the ability of the respiratory and urinary systems to regulate the pH balance of the body, because carbonic acid can be converted to water and carbon dioxide. The enzyme carbonic anhydrase catalyzes this chemical reaction that converts carbonic acid to water and carbon dioxide, as well as the reverse reaction where carbon dioxide and water can be converted to carbonic acid. This is very important because the respiratory system can remove carbon dioxide from the body in the process of external respiration. The urinary system can remove excess hydrogen ions and bicarbonate ions from the body, and so the bicarbonate buffering system is an important place where the respiratory and urinary systems will be able to have an effect to regulate the pH balance of the body by either removing carbon dioxide or removing bicarbonate or hydrogen ions. The respiratory and urinary systems can shift the bicarbonate buffering system either towards bicarbonate or further towards carbonic acid.