[MUSIC] Hello everyone, welcome back to my Coursera class, Biochemical Principles of Energy Metabolism. And Beginning of second week, so during five sessions. I'm about to introduce the basic functions for metabolic organs. And for the second session, I'm going to start the biochemical and or physiological basis of bioenergetics. So I'm going to begin with the how we feel about hunger, and what's the basis of feeding behavior. In the very, very beginning of bioenergetics, I'm going to introduce the carbohydrate digestion. And in the middle of carbohydrate metabolism, I'm about to review the basic principles of enzymes and their actions. Finally, the session will be ended up by introducing the molecule basis of carbohydrate absorption. All right, so I'm going to repeatedly use the word homeostasis during the entire, this Coursera class. So homeostasis is one of seven key features of life. Basically by definition homeostasis is the body's ability to detect change and activate a series of mechanisms that oppose or sometimes enhance, Our body functions. So as a result we can maintain relatively, this is the point, stable internal conditions. So in this context, in our bodies, multiple organs are involve in terms of coordinating homeostatic mechanisms. So organ is a group of tissues that perform a specific function. So tissues means basically those four different tissues, like epithelial tissues, connective tissues, the nervous tissues, and muscular tissues. A combination of those four different tissues can lead to the formation of an organ and each organ performs it's own functions. The context of homeostatic regulation. So there are many context of homeostatic responses. As I said previously, during the first week, we're about to study energy homeostasis. So again, I will recapitulate the definition of energy homeostasis. A complex biological process that involved multiple organs to coordinate homeostatic regulation of this is the point energy intake and energy expenditure. How chemical energies in a form of nutrient can be transformed and can be digested and can be utilized to drive the formation of ATP. And how those ATP molecules can be used, and then how those chemical waste can be released out of our body. So living organisms have sustained to utilize different types of nutrients carbohydrates, fats, and even proteins. And the catabolic reactions and anabolic reactions are tightly linked in multiple organs involved in nutrient sensing. And nutrient digestion and the homeostatic regulation of energy expenditure. Let me begin with metabolic organs one by one. So number one organ, I want to introduce is pancreas. Pancreas is located along the internal curvature of duodenum. Duodenum is the beginning of small intestine and right downstream of stomach. So pancreas, okay, on your left you are looking at the pancreas structure over here. And the pancreatic tissues contained different types of cells. And this purple, Quite concentrated collection of cells are so called that the islets of Langerhans. So islets of Langerhans is the main side of insulin and glucagon hormone production. So based on these two major insulin and glucagon hormone production, pancreas can be considered as an endocrine system. And this insulin and glucagon are two major hormones are involved in glucose homeostasis. And I'm about to present about chemical details later during this course. On top of this, pancreas also can be considered as exocrine cell. So that means, this pancreatic tissue and cells can synthesize and produce a series of enzymes to facilitate the digestion of food, carbohydrates, protein, and lipids. Second organ, second system is liver and gallbladder. Apparently, I believe you know the main function of liver. One of key physiologic help in terms of metabolic reactions in human body, in particular glycogen synthesis and degradation. This glycogen means glucose, Polymer, Is kind of storage molecule of our energy source glucose. And sometimes during the prolonged fasting condition, our liver can synthesize and can produce glycogen. And even glucose, and glucose producing biochemical reaction is so called gluconeogenesis. And liver is primary site of organ in terms of producing glucose molecules. So other then that, fatty acid uptake and trafficking and even bile production can be done in liver tissue. So what about gallbladder? Gallbladder is sort of storage organ for bile. And bile is involved in the fat digestion and the absorption. So I'm going to show the bile structure and how bile acid can function in terms of fatty acid digestion processes, later during this Coursera class. Next one is adipose tissue, also called fat tissue. So this is a loosely bound connective tissue basically composed of adipocytes. Adipocytes means fat cells simply speaking. So adipose organ or adipose tissue is a major organ for storing energy in the form of fat. And physically our adipose tissue can function in cushioning or insulating our body. And most importantly dynamic influx or outflux of fatty acids across adipose tissue can regulate whole body energy homeostasis. And I am going to clearly explain why the fat and fatty acid are so called efficient macromolecule in terms of energy metabolism. Well the next one is muscle. In particular, skeletal muscle is the primary organ of insulin stimulated glucose uptake. It's a major organ for taking care of glucose uptake. This is very important in terms of regulating blood glucose. And the major fuels sources for muscle are glucose or sometimes fatty acid and ketone bodies. So ketone bodies is a product from the fatty [INAUDIBLE] and I'm going to explain very clear, very clearly later in this class. And on top of this extra glucose, extra glucose can be polymerize in a form of glycogen. And 75% of entire glycogen, actually indeed stored inside your muscle. And in response to fasting, fasting conditions, that means energy deficient condition. Skeletal muscles can even release amino acids. Amino acid means building blocks for proteins in particular, alanine or glutamine. So those amino acids can be released out of your muscle. And those macro molecules, sorry about that, those nutrients can be utilized to maintain internal stable blood glucose levels throughout the liver assisted by the chemical actions. And one more piece of information is unlike skeletal muscles, your heart muscles, cardiac muscles can function aerobically. And has no capacity in terms of glycogen storage, right? So next one is brain, next one is brain. So you might be very curious about brain function in terms of energy homeostasis. Obviously brain is one of major, major organ responsible for bioenergetics in terms of regulating food intake. And energy expenditure processes to keep our bodies maintaining energy balance. So in particular, hypothalamus is part of our brain. And this hypothalamic region of human brain and mammalian brain can monitor changes in the energy status, By directly sensing the biochemical changes in your blood levels of hormones and nutrients. So there is a specialized neural circuit, a collection of neuronal cells and synaptic relays in your brain. In particular hypothalamic regions are involved in the coordination of metabolically very important adaptive responses in food intake and in top of that energy expenditure. Upon the different types of metabolic stimuli, for example, starvation or after meal sort of condition. Lastly, gastrointestinal tract, so that means stomach or intestines. Those digestive systems obviously are very important in terms of ingestion and digestion of foods. And absorption and finally excretion of a remaining waste. More importantly gastrointestinal tract are major, one of major organs for hormone secretion. So there is a series of gastrointestinal hormones. They are secreted by the sometimes stomach epithelial cells or intestinal epithelial cells, and there are some examples over here. So my point is I hope you could understand gastrointestinal cells, and the tissues are not just important in terms of mutual digestion processes. But also play a critical function in the whole body homeostasis throughout those hormone of production and secretion. So I'm not going to explain each GI hormone one by one. You can just take a look at this table and gastrin, for instance stimulate gastric acid secretion and so on.
