| Catabolysis | |
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| A Vietnamese man, showing signs of starvation. | |
| Specialty | Endocrinology |
| Causes | Malnutrition |
 | This article needs additional citations for verification .(March 2012) |
Catabolysis is a biological process in which the body breaks down fat and muscle tissue in order to stay alive. Catabolysis occurs only when there is no longer any source of protein, carbohydrate, or vitamin nourishment feeding all body systems; it is the most severe type of malnutrition.
Due to the normal metabolic rate of humans catabolysis becomes life-threatening only after 1–2 months from the cessation of nutrition going into the body. After this time, the damage to muscles and organs can be permanent and can also eventually cause death, if left untreated. Catabolysis is the last metabolic resort for the body to keep itself — particularly the nervous system—functional.
Protein stores, especially in muscle tissue, provide the amino acids needed for the process. Amino acids are released into the blood and converted in the liver to alpha keto acids. Alpha keto acids can then be converted to glucose to maintain proper blood sugar levels.
The situation can become dire when one begins to lose muscle mass; this is a sign that the fat has been expended and the body is now metabolizing the muscle tissue. This results in muscle atrophy, a loss of strength and, ultimately, a depletion of muscular tissue completely. Muscle weakness is not necessarily a symptom of catabolysis: the muscles will normally feel fatigued when they are not receiving enough energy or oxygen. Ultimately, catabolysis can progress to the point of no return when the body's machinery for protein synthesis, itself made of protein, has been degraded to the point that it cannot handle any protein. At this point, attempts to correct the disorder by giving food or protein are futile.
The body has a natural store of fat (also called adipose tissue ) that stores reserve energy. One can still stay alive while the body breaks down the fatty tissue (hence people wasting away from starvation).
The person may, during catabolysis, have large amounts of lipids, proteins, and amino acids in the bloodstream, due to the muscle fibers and adipose tissues being broken down and sent to the nervous system and brain. One may also exhibit a fever, since the body is working hard to transfer the nutrients in the muscles and fat to the blood.
While catabolysis can be deadly over time, if the person is given medical treatment early enough, the effects of catabolysis can be reversed. However, the person may require intravenous nutrition, a blood transfusion, and/or oxygen replenishment. After that, it may be a few weeks to a few months before the person's muscle mass and fat deposits can build themselves up again; there is a possibility that they may never build back up, depending on the severity of the condition.
Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and metabolism. Over the last decades of the 20th century, biochemistry has become successful at explaining living processes through these three disciplines. Almost all areas of the life sciences are being uncovered and developed through biochemical methodology and research. Biochemistry focuses on understanding the chemical basis which allows biological molecules to give rise to the processes that occur within living cells and between cells, in turn relating greatly to the understanding of tissues and organs, as well as organism structure and function. Biochemistry is closely related to molecular biology, which is the study of the molecular mechanisms of biological phenomena.
The following is a glossary of diabetes which explains terms connected with diabetes.
Isoleucine is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group, an α-carboxylic acid group, and a hydrocarbon side chain with a branch. It is classified as a non-polar, uncharged, branched-chain, aliphatic amino acid. It is essential in humans, meaning the body cannot synthesize it, and must be ingested in our diet. Isoleucine is synthesized from pyruvate employing leucine biosynthesis enzymes in other organisms such as bacteria. It is encoded by the codons AUU, AUC, and AUA.
Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins. Leucine is an α-amino acid, meaning it contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −COO− form under biological conditions), and a side chain isobutyl group, making it a non-polar aliphatic amino acid. It is essential in humans, meaning the body cannot synthesize it: it must be obtained from the diet. Human dietary sources are foods that contain protein, such as meats, dairy products, soy products, and beans and other legumes. It is encoded by the codons UUA, UUG, CUU, CUC, CUA, and CUG.
Ketosis is a metabolic state characterized by elevated levels of ketone bodies in the blood or urine. Physiologic ketosis is a normal response to low glucose availability, such as low-carbohydrate diets or fasting, that provides an additional energy source for the brain in the form of ketones. In physiologic ketosis, ketones in the blood are elevated above baseline levels, but the body's acid–base homeostasis is maintained. This contrasts with ketoacidosis, an uncontrolled production of ketones that occurs in pathologic states and causes a metabolic acidosis, which is a medical emergency. Ketoacidosis is most commonly the result of complete insulin deficiency in type 1 diabetes or late-stage type 2 diabetes. Ketone levels can be measured in blood, urine or breath and are generally between 0.5 and 3.0 millimolar (mM) in physiologic ketosis, while ketoacidosis may cause blood concentrations greater than 10 mM.
Starvation is a severe deficiency in caloric energy intake, below the level needed to maintain an organism's life. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death. The term inanition refers to the symptoms and effects of starvation. Starvation may also be used as a means of torture or execution.
Carnitine is a quaternary ammonium compound involved in metabolism in most mammals, plants, and some bacteria. In support of energy metabolism, carnitine transports long-chain fatty acids into mitochondria to be oxidized for energy production, and also participates in removing products of metabolism from cells. Given its key metabolic roles, carnitine is concentrated in tissues like skeletal and cardiac muscle that metabolize fatty acids as an energy source. Healthy individuals, including strict vegetarians, synthesize enough L-carnitine in vivo to not require supplementation.
Lipolysis is the metabolic pathway through which lipid triglycerides are hydrolyzed into a glycerol and three fatty acids. It is used to mobilize stored energy during fasting or exercise, and usually occurs in fat adipocytes. The most important regulatory hormone in lipolysis is insulin; lipolysis can only occur when insulin action falls to low levels, as occurs during fasting. Other hormones that affect lipolysis include glucagon, epinephrine, norepinephrine, growth hormone, atrial natriuretic peptide, brain natriuretic peptide, and cortisol.
Carbohydrate metabolism is the whole of the biochemical processes responsible for the metabolic formation, breakdown, and interconversion of carbohydrates in living organisms.
Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular endothelial cells and a variety of immune cells such as adipose tissue macrophages. Adipose tissue is derived from preadipocytes. Its main role is to store energy in the form of lipids, although it also cushions and insulates the body. Far from being hormonally inert, adipose tissue has, in recent years, been recognized as a major endocrine organ, as it produces hormones such as leptin, estrogen, resistin, and cytokines. In obesity, adipose tissue is also implicated in the chronic release of pro-inflammatory markers known as adipokines, which are responsible for the development of metabolic syndrome, a constellation of diseases including, but not limited to, type 2 diabetes, cardiovascular disease and atherosclerosis. The two types of adipose tissue are white adipose tissue (WAT), which stores energy, and brown adipose tissue (BAT), which generates body heat. The formation of adipose tissue appears to be controlled in part by the adipose gene. Adipose tissue – more specifically brown adipose tissue – was first identified by the Swiss naturalist Conrad Gessner in 1551.
Basal metabolic rate (BMR) is the rate of energy expenditure per unit time by endothermic animals at rest. It is reported in energy units per unit time ranging from watt (joule/second) to ml O2/min or joule per hour per kg body mass J/(h·kg). Proper measurement requires a strict set of criteria to be met. These criteria include being in a physically and psychologically undisturbed state and being in a thermally neutral environment while in the post-absorptive state (i.e., not actively digesting food). In bradymetabolic animals, such as fish and reptiles, the equivalent term standard metabolic rate (SMR) applies. It follows the same criteria as BMR, but requires the documentation of the temperature at which the metabolic rate was measured. This makes BMR a variant of standard metabolic rate measurement that excludes the temperature data, a practice that has led to problems in defining "standard" rates of metabolism for many mammals.
Fatty acid metabolism consists of various metabolic processes involving or closely related to fatty acids, a family of molecules classified within the lipid macronutrient category. These processes can mainly be divided into (1) catabolic processes that generate energy and (2) anabolic processes where they serve as building blocks for other compounds.
Beta-ketothiolase deficiency is a rare, autosomal recessive metabolic disorder in which the body cannot properly process the amino acid isoleucine or the products of lipid breakdown. Along with SCOT deficiency, it belongs to a group of disorders called ketone utilisation disorders.
A branched-chain amino acid (BCAA) is an amino acid having an aliphatic side-chain with a branch. Among the proteinogenic amino acids, there are three BCAAs: leucine, isoleucine, and valine. Non-proteinogenic BCAAs include 2-aminoisobutyric acid.
Absorptive state is the period in which the gastrointestinal tract is full and the anabolic processes exceed catabolism. The fuel used for this process is glucose.
Refeeding syndrome is a metabolic disturbance that occurs as a result of reinstitution of nutrition in people and animals who are starved, severely malnourished, or metabolically stressed because of severe illness. When too much food or liquid nutrition supplement is eaten during the initial four to seven days following a malnutrition event, the production of glycogen, fat and protein in cells may cause low serum (blood) concentrations of potassium, magnesium and phosphate. Cardiac, pulmonary and neurological symptoms can be signs of refeeding syndrome. The low serum minerals, if severe enough, can be fatal.
Sports nutrition is the study and practice of nutrition and diet with regards to improving anyone's athletic performance. Nutrition is an important part of many sports training regimens, being popular in strength sports and endurance sports. Sports nutrition focuses its studies on the type, as well as the quantity of fluids and food taken by an athlete. In addition, it deals with the consumption of nutrients such as vitamins, minerals, supplements and organic substances that include carbohydrates, proteins and fats.
Starvation response in animals is a set of adaptive biochemical and physiological changes, triggered by lack of food or extreme weight loss, in which the body seeks to conserve energy by reducing the amount of calories it burns.
The Randle cycle, also known as the glucose fatty-acid cycle, is a metabolic process involving the competition of glucose and fatty acids for substrates. It is theorized to play a role in explaining type 2 diabetes and insulin resistance.
Adiposopathy is a proposed cardiovascular disease (CVD) which may explain the anatomical and/or functional changes to fat cells which may indirectly increase other CVD risk, and may be a contributor to the metabolic syndrome.
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