4/3/2023 0 Comments Cellular respiration overview![]() While oxygen is being dropped off at cells, carbon dioxide is being picked up and transported from tissue cells to the lungs. Oxygen rich blood is transported by the circulatory system from lung capillaries to body cells and tissues. At the same time, carbon dioxide diffuses in the opposite direction (from the blood to lung alveoli) and is expelled. Oxygen within the lungs diffuses across the thin epithelium of lung alveoli (air sacs) into surrounding capillaries containing oxygen depleted blood. This includes contraction and relaxation of the diaphragm and accessory muscles, as well as breathing rate.Ä®xternal respiratory processes explain how oxygen is obtained, but how does oxygen get to body cells? Internal respiration involves the transportation of gases between the blood and body tissues. External respiration in mammals encompasses the mechanical processes related to breathing. In the human body, oxygen is taken into the lungs by inhalation and carbon dioxide is expelled from the lungs by exhalation. Humans and other mammals have a respiratory system with specialized respiratory organs ( lungs) and tissues. ![]() Insects and spiders have respiratory organs called tracheae, while fish have gills as sites for gas exchange. In organisms such as nematodes (roundworms), gases and nutrients are exchanged with the external environment by diffusion across the surface of the animals body. Others either have organs specialized for gas exchange or have a complete respiratory system. Animals that lack specialized organs for respiration rely on diffusion across external tissue surfaces to obtain oxygen. In animal organisms, the process of external respiration is performed in a number of different ways. One method for obtaining oxygen from the environment is through external respiration or breathing. Wetcake/DigitalVision Vectors/Getty Images External Respiration ![]() When exhaling the diaphragm relaxes and the lungs contract, moving the chest back down. If oxygen is not available ( anaerobic conditions ) then pyruvate undergoes fermentation in the cytoplasm of the cell.When inhaling, the diaphragm contracts and the lungs expand, pushing the chest upwards. If oxygen is available ( aerobic conditions ), pyruvate molecules progress into the citric acid cycle. This occurs in both glycolysis and the citric acid cycle. The hydrogen ions and electrons are passed to the electron transport chain on the inner mitochondrial membrane. Äehydrogenase enzymes remove hydrogen ions and electrons from intermediates of this cycle, which are passed to the coenzyme NAD (forming NADH). This breakdown of glucose into pyruvate therefore results in a net gain of ATP molecules in this energy payoff stage. More ATP molecules are then regenerated than were used in the production of other intermediates. ![]() Phosphorylation of glucose and these intermediates requires ATP molecules in an energy investment stage. ![]() The production of pyruvate from glucose involves the production of several intermediate molecules. This process does not require oxygen (it is anaerobic ). Glycolysis is the breakdown of glucose into two pyruvate molecules. ![]()
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