Anaerobic Respiration - Podcast Version TeachMePhysiology 0:00 / 0:00 1x 0.25x 0.5x 0.75x 1x 1.25x 1.5x 1.75x 2x Anaerobic respiration is the process of ATP synthesis without adequate oxygen delivery to tissues. Sometimes the body cannot supply the muscles with the oxygen it needs to create energy, for example during intense exercise. Without the process of anaerobic respiration, there would be no energy supplied to muscles in these times of high demand. This article will consider the process of anaerobic respiration and its clinical significance. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Process of Anaerobic Respiration Without oxygen, the electron transport chain (ETC) cannot continue as there is no terminal electron acceptor. Therefore, the usual number of ATP molecules cannot be created. Cessation of the ETC leads to reduced activity of the reactions before this step, such as the TCA cycle and glycolysis. The anaerobic pathway utilises pyruvate, the final product of glycolysis. Without the functioning ETC there is an excess of NADH and pyruvate. Pyruvate is subsequently reduced to lactate (lactic acid) by NADH, yielding NAD+. This reaction is catalyzed by the enzyme lactate dehydrogenase. By recycling NAD+, the process of glycolysis is able to continue as the supply of NAD+ has been replenished. Glycolysis produces 2 net ATP molecules, which can be used for energy. By CNX OpenStax (https://commons.wikimedia.org/wiki/File:Figure_07_05_02.png) [CC BY 4.0 (http://creativecommons.org/licenses/by/4.0)], via Wikimedia Commons Fig 1Diagram showing the process of anaerobic respiration. While these 2 ATP molecules are much less than would be produced by aerobic respiration, without anaerobic respiration there would be no other method of ATP production. Anaerobic glycolysis happens faster than aerobic because less energy is produced for every molecule of glucose broken down (2ATP vs 32ATP), so more glucose must be broken down at a faster rate to meet energy demands. In situations where cells’ oxygen demands increase above supply (i.e. ischaemia), glycolysis will quickly occur, producing lactic acid. This may occur physiologically, such as in the muscles during intense exercise, or pathologically, for example in ischaemic heart disease or when a malignant tumour outgrows its blood supply. Removal of lactate The lactate produced as a result of anaerobic respiration must be removed from the blood as it is acidic. There are two main ways to do this: Lactate is transported to metabolically active cells, such as in the heart and brain. Here it is converted back to pyruvate, which is then utilised in the TCA cycle. Lactate is transported to the liver and converted to pyruvate. Pyruvate is then used in the process of gluconeogenesis to create more glucose Clinical Relevance Lactic acidosis Excessive production of lactate can lead to lactic acidosis, a sub-type of metabolic acidosis. This is where the pH of the blood has become more acidic due to rising levels of lactate within the body. There are a number of causes for lactic acidosis but broadly it is caused by the body being unable to respire aerobically. Some causes include: Diabetes mellitus Enzyme deficiencies – for example, pyruvate dehydrogenase deficiency Drugs – for example, metformin and isoniazid Haemorrhage Sepsis Mitochondrial disorders Symptoms typical of metabolic acidosis include nausea, vomiting, muscle weakness and rapid breathing. Treatment is difficult, as there is little evidence to support the use of sodium bicarbonate solutions (to balance the pH) or direct removal of lactate (via haemofiltration). Treatment is therefore supportive and would depend on the aetiology; if medication is the cause it may need to be withdrawn and certain mitochondrial disorders may require adapted diets. Do you think you’re ready? Take the quiz below Pro Feature - Quiz Anaerobic Respiration Question 1 of 3 Submitting... Skip Next Rate question: You scored 0% Skipped: 0/3 More Questions Available Upgrade to TeachMePhysiology Pro Challenge yourself with over 2100 multiple-choice questions to reinforce learning Learn More Frequent questions What is anaerobic respiration? Anaerobic respiration is the process of ATP production that occurs without sufficient oxygen. It enables the body to generate energy, particularly during intense physical activity when oxygen supply is limited. How does anaerobic respiration lead to lactate production? During anaerobic respiration, pyruvate, the end product of glycolysis, is converted to lactate by the enzyme lactate dehydrogenase. This process recycles NAD+, allowing glycolysis to continue and produce ATP even in the absence of oxygen. What are the clinical implications of lactic acidosis? Lactic acidosis occurs when excessive lactate production results in a decrease in blood pH, indicating metabolic acidosis. It can arise from conditions that impair aerobic respiration, such as sepsis, diabetes, or certain drug effects. How is lactate removed from the body after anaerobic respiration? Lactate is primarily cleared from the bloodstream by being transported to metabolically active tissues, like the heart and brain, where it is converted back to pyruvate. It can also be sent to the liver for gluconeogenesis to produce glucose. Why is anaerobic respiration faster than aerobic respiration? Anaerobic respiration is quicker because it produces less ATP per glucose molecule—only 2 ATP compared to 32 ATP in aerobic respiration. This allows for rapid energy production to meet immediate demands when oxygen is scarce. 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