Digestion is breaking large insoluble food molecules into small water-soluble food molecules so they can be absorbed into aqueous blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into the bloodstream. Digestion is a form of catabolism that is often divided into two processes based on how food is broken down: mechanical and chemical digestion. The term digestive mechanics refers to the physical damage of large pieces of food into smaller pieces which can then be accessed by digestive enzymes. In chemical digestion , enzymes break down food into small molecules that the body can use.
In the human digestive system, food enters the mouth and digestion of food mechanically begins with the act of chewing (chewing), a form of mechanical digestion, and the contact of saliva that wets. Saliva, a fluid secreted by the salivary glands, contains salivary amylases, an enzyme that initiates starch digestion in foods; saliva also contains mucus, which lubricates food, and hydrogen carbonate, which provides ideal conditions of pH (alkaline) for amylase to work. After undergoing mastication and starch digestion, the food will be a mass of small round slurry called a bolus. It will then run in the esophagus and into the abdomen by a peristaltic action. Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. Since both of these chemicals can damage the stomach wall, the mucus is secreted by the stomach, providing a slimy layer that acts as a shield against the damaging effects of chemicals. At the same time protein digestion occurs, mechanical mixing occurs by peristalsis, which is a wave of muscle contractions that move along the wall of the stomach. This allows the mass of food to mix further with digestive enzymes.
After some time (usually 1-2 hours in humans, 4-6 hours in dogs, 3-4 hours in the cat house), the resulting viscous liquid is called a chyme. When the pyloric sphincter valve opens, the chyme enters the duodenum where it mixes with the digestive enzymes of the pancreas and bile from the liver and then passes through the small intestine, where the digestion continues. When the chyme is fully digested, it is absorbed into the blood. 95% absorption of nutrients occurs in the small intestine. Water and minerals are absorbed back into the blood in the colon (colon) where the pH is slightly acidic around 5.6 ~ 6.9. Some vitamins, such as biotin and vitamin K (K 2 MK7) produced by bacteria in the colon are also absorbed into the blood in the colon. The waste material is removed from the rectum during bowel movements.
Video Digestion
Sistem pencernaan
The digestive system takes many forms. There is a fundamental difference between internal and external digestion. External digestion developed earlier in evolutionary history, and most fungi still depend on it. In this process, enzymes are secreted into the environment around the organism, where they break down organic matter, and some products propagate back into the organism. Animals have a tube (digestive tract) where internal digestion occurs, which is more efficient because more damaged products can be captured, and the internal chemical environment can be controlled more efficiently.
Some organisms, including almost all spiders, excrete only biotoxins and digestive chemicals (eg enzymes) into the extracellular environment before ingesting a consistent "soup". On the other hand, once a potential nutrient or food is present in the organism, digestion can be made into vesicles or structures such as a sac, through a tube, or through several specialized organs aimed at making nutrient absorption more efficient.
System secretion
Bacteria use multiple systems to get nutrients from other organisms in the environment.
Channel transport system
In the channel trans- system system, some proteins form adjacent channels that cross the inner and outer membranes of bacteria. It is a simple system, consisting of only three protein subunits: ABC protein, membrane fusion protein (MFP), and outer membrane protein (OMP). This secretion system transports various molecules, from ions, drugs, to proteins of various sizes (20 - 900 kDa). The secreted molecule varies in size from a small Escherichia coli colicin V peptide (10 kDa) to Pseudomonas fluorescens of LapA cell adhesion protein of 900 kDa.
Molecular syringe
The type III secretion system means that molecular syringes are used through which bacteria (eg certain types of Salmonella Shigella , Yersinia ) can inject nutrients into cells protista. One such mechanism was first discovered in Y. pestis and showed that toxins can be injected directly from the bacterial cytoplasm to the host cell cytoplasm rather than simply secreted into the extracellular medium.
Conjugation machine
Conjugate machines of several bacteria (and archella flagella) are capable of transporting both DNA and protein. It is found in Agrobacterium tumefaciens , which uses this system to introduce Ti plasmids and proteins into the host, which develops bile crowns (tumors). The VirB complex of Agrobacterium tumefaciens is a prototypic system.
The binding of nitrogen Rhizobia is an interesting case, where conjugate elements naturally engage in inter-royal conjugations. Elements such as Agrobacterium Ti or Ri plasmids contain elements that can transfer to plant cells. The transferred gene enters the nucleus of plant cells and effectively converts plant cells into factories to produce opine, which is used by bacteria as a source of carbon and energy. Infected plant cells form bile crowns or root tumors. The Ti and Ri plasmids are thus endosymbiated from bacteria, which in turn are the endosymbi (or parasite) of the infected plant.
The Ti and Ri plasmid are themselves conjugated. Ti and Ri transfer between bacteria using an independent system ( tra , or transfer, operon) from it for interregional transfer ( vir , or virulence, operon). Such transfers create a malignant strain of the previously avirulent Agrobacteria .
Release of external membrane vesicles
In addition to the use of the multiprotein complex listed above, Gram-negative bacteria have another method for the release of the material: the formation of the outer membrane vesicles. Part of the outer pinch membrane, forming a sphere structure made of a double layer of lipid lining the periplasmic material. Vesicles from a number of bacterial species have been found to contain virulence factors, some have immunomodulatory effects, and some may directly attach and intoxicate the host cell. While vesicle release has been shown to be a general response to stressful conditions, the process of loading cargo proteins appears to be selective.
Gastrovascular cavity
The gastrovascular cavity serves as the stomach in both digestion and distribution of nutrients to all parts of the body. Extracellular digestion occurs within this central cavity, which is coated with gastrodermis, the internal layer of the epithelium. This cavity has only one outer hole that functions both as the mouth and anus: undigested waste and matter are excreted through the mouth/anus, which can be described as incomplete gut.
In factories like Venus Flytrap that can make food by themselves through photosynthesis, it does not eat and digest its prey for the traditional purpose of harvesting energy and carbon, but prey mines primarily for essential nutrients (nitrogen and phosphor in particular) are short supply in boggy, acidic habitats.
Phagosome
Fagosomes are vacuoles that form around particles absorbed by phagocytosis. Vakuoles are formed by the fusion of cell membranes around the particles. Phagosomes are cellular compartments in which pathogenic microorganisms can be killed and digested. Phagosomes merge with lysosomes in the process of maturation, forming phagolisomas. In humans, Entamoeba histolytica can phagocytes red blood cells.
Organ and custom behavior
To help the digestion of food animals they evolve organs such as beak, tongue, teeth, plants, rempela, and others.
Beaks
Birds have specialized beak bones according to the bird's ecological niche. For example, macaws primarily feed on seeds, nuts, and fruit, using an impressive beak to open even the hardest seeds. First they scratched the thin line with the sharp tip of the beak, then they shifted open beans with the side of the beak.
The mouth of the squid is equipped with sharp horn beaks mainly made of cross linked proteins. It is used to kill and tear the prey into manageable parts. Its beak is very strong, but it contains no minerals, unlike teeth and jaws of many other organisms, including marine species. Its beak is the only part of the squid that can not be digested.
Tongue
The tongue is the skeletal muscle at the base of the mouth that manipulates the food to chew (chew) and swallow (deglutition). It is sensitive and is kept moist by saliva. The bottom of the tongue is covered with a fine mucous membrane. The tongue also has a sense of touch to find and position food particles that require further chewing. The tongue is used to roll the food particles into the bolus before being transported to the esophagus through the peristaltic.
The sublingual area below the front of the tongue is the location where the oral mucosa is very thin, and is based on the venous plexus. This is an ideal location to introduce certain drugs to the body. The sublingual route takes advantage of the highly vascular quality of the oral cavity, and allows rapid application of the drug into the cardiovascular system, through the gastrointestinal tract.
Dental
Teeth (single tooth) is a small whitish structure found in the jaws (or mouths) of many vertebrates used to tear, scrape, milk and chew food. Teeth are not made of bones, but rather from tissues of varying density and hardness, such as enamel, dentine, and cementum. Human teeth have a blood supply and a nerve that allows proprioception. This is the ability to sensation when chewing, for example if we bite something that is too hard for our teeth, like a broken plate mixed in food, our teeth send a message to our brain and we realize that it can not be chewed, so we stop trying.
The shape, size and number of different types of animal teeth are related to their diet. For example, herbivores have a number of molar used to grind plant material, which is difficult to digest. Carnivores have canine teeth used to kill and tear flesh.
Crop
Plants, or croup, are a thin-walled portion of the gastrointestinal tract used for food storage before digestion. In some birds it is a muscular, expanded pouch near throat or throat. In adult pigeons and pigeons, plants can produce plant milk to feed newly hatched birds.
Certain insects may have an esophagus that grows or enlarges.
Abomasum
Herbivores have evolved cecums (or abomasum in cases of ruminants). Ruminants have a frontal stomach with four chambers. These are the rumen, reticulum, omasum, and abomasum. In the first two rooms, rumen and reticulum, food is mixed with saliva and separates into a layer of solid and liquid material. Solids collect to form cud (or bolus). The mother then vomited, chewed gently to completely mix it with saliva and break down the particle size.
Fiber, especially cellulose and hemi-cellulose, is primarily broken down into volatile fatty acids, acetic acid, propionic acid and butyric acid in these chambers (reticulo-rumen) by microbes: (bacteria, protozoa, and fungi). In the omasum, water and many elements of inorganic minerals are absorbed into the bloodstream.
Abomasum is the fourth and final stomach compartment in ruminants. This is equivalent to a monogastric abdomen (for example, in humans or pigs), and digesta is processed here in the same way. It serves primarily as a site for the hydrolysis of microbial protein and food proteins, preparing this protein source for digestion and further absorption in the small intestine. Digesta is eventually transferred to the small intestine, where digestion and absorption of nutrients occur. Microbes produced in the reticulo-rumen are also digested in the small intestine.
Special behavior
Regurgitation has been mentioned above under abomasum and plants, referring to plant milk, secretions of pigeons and pigeons where parents feed their children with regurgitation.
Many sharks have the ability to turn their stomach out and remove it from their mouths to get rid of unwanted content (probably developed as a way to reduce exposure to toxins).
Other animals, such as rabbits and rodents, practice coprophagia behavior - eating special faeces to re-digest food, especially in the case of fiber. Capybara, rabbits, hamsters and other related species do not have a complex digestive system as well as, for example, ruminants. Instead they extract more nutrients from the grass by feeding them through the intestines. Soft pellet pellets from digested foods are partially excreted and are generally consumed immediately. They also produce normal impurities, which are not eaten.
Young elephants, pandas, koalas and hippos eat their mother's excrement, perhaps to get the bacteria needed to digest vegetation properly. When they are born, their intestines do not contain these bacteria (they are completely sterile). Without them, they will not be able to get the nutritional value of many plant components.
In earthworm
The earthworm digestive system consists of mouth, pharynx, esophagus, plant, rempela, and intestine. The mouth is surrounded by a strong lips, which act like a hand to pick up dead grass pieces, leaves, and weeds, with pieces of soil to help chew. Lips break the food into smaller pieces. In pharynx, food is lubricated by mucus secretions to facilitate travel. The esophagus adds calcium carbonate to neutralize the acid formed by the decay of the foodstuff. Temporary storage occurs in plants where food and calcium carbonate are mixed. The strong muscles of the gizzard shake and mix the mass of food and dirt. When stirring is complete, the glands in the wall of the stomach add enzymes to the viscous paste, which helps break down the organic chemistry. With peristaltic, the mixture is sent to the intestine where the friendly bacteria continue to break down the chemical. It releases carbohydrates, proteins, fats, and various vitamins and minerals for absorption into the body.
Maps Digestion
Overview of vertebrate digestion
In most vertebrates, digestion is a multistage process in the digestive system, starting from the consumption of raw materials, most often other organisms. Ingestion usually involves some kind of mechanical and chemical processing. Digestion is separated into four steps:
- Ingestion: putting food into the mouth (ingestion of food in the digestive system),
- Mechanical and chemical disturbances: mastication and blending of bolus produced with water, acids, bile and enzymes in the stomach and intestines to break down complex molecules into simple structures,
- Absorption: nutrients from the digestive system to the circulatory and lymphatic capillaries through osmosis, active transport, and diffusion, and
- Egestion (Excretion): Eliminates digested ingredients from the gastrointestinal tract through a bowel movement.
Underlying this process is muscle movement throughout the system through swallowing and peristalsis. Each step in the digestion requires energy, and thus imposes an "overhead charge" on the energy available from the absorbed substance. The difference in overhead costs is an important influence on lifestyle, behavior, and even physical structure. Examples can be seen in humans, which differ greatly from other hominids (lack of hair, smaller jaws and muscles, different teeth, intestine length, cooking, etc.).
The main part of digestion occurs in the small intestine. The large intestine serves primarily as a place for the fermentation of substances digested by intestinal bacteria and for resorption of water from digesting before excretion.
In mammals, the preparation for digestion begins with a cephalic phase in which saliva is produced in the mouth and digestive enzymes are produced in the stomach. Mechanical and chemical digestion begins in the mouth where food is chewed, and mixed with saliva to start the starch enzymatic process. The stomach continues to break food mechanically and chemically through stirring and mixing with acids and enzymes. Absorption occurs in the stomach and gastrointestinal tract, and the process is completed with a bowel movement.
Human digestive process
Human digestive tract about 9 meters in length. Food digestion physiology varies between individuals and on other factors such as food characteristics and food size, and the digestive process usually takes between 24 and 72 hours.
Digestion begins in the mouth with salivary secretions and digestive enzymes. The food is formed into a bolus by mechanical mastication and ingested into the esophagus from which it enters the stomach through peristaltic action. Gastric juice contains hydrochloric acid and pepsin which will damage the walls of the stomach and mucus secreted for protection. In the stomach further the release of the enzyme breaks down the food further and this is combined with stirring stomach action. Partially digested food enters the duodenum as a thick, semi-liquid chyme. In the small intestine, large parts of the digestion occur and this is aided by secretions of bile, pancreatic and intestinal juices. The intestinal wall is lined with villi, and their epithelial cells are covered with many microvilli to improve nutrient absorption by increasing the surface area of ​​the intestine.
In the large intestine, food passes more slowly to allow fermentation by intestinal flora to take place. Here the water is absorbed and the waste material is stored as impurities which must be removed by bowel movements through the anal and anal canals.
Mechanism of nerve and biochemical control
Different digestive phases occur including: cephalic , gastric phase phases, and intestinal phases .
The cephalic phase occurs in vision, mind and smell of food, which stimulates the cerebral cortex. Stimulus and odor stimuli are sent to the hypothalamus and medulla oblongata. Once this is passed through the vagus nerve and the release of acetylcholine. Gastric secretion in this phase increases up to 40% of the maximum level. The acidity in the stomach is not supported by food at this point and thus acts to inhibit the parietal (acid secret) and G cells (secrete gastrin) activity through cell secretion D from somatostatin.
The stomach phase takes 3 to 4 hours. It is stimulated by gastric distention, the presence of food in the stomach and a decrease in pH. Distension activates long reflex and myenteric. This activates the release of acetylcholine, which stimulates the release of more gastric juices. When the protein enters the stomach, the protein binds hydrogen ions, which increase the pH of the stomach. Inhibition of gastrin and secretion of stomach acid is removed. This triggers G cells to release gastrin, which in turn stimulates parietal cells to secrete stomach acid. Gastric acid is about 0.5% hydrochloric acid (HCl), which lowers the pH to the desired pH 1-3. Acid release is also triggered by acetylcholine and histamine.
The intestinal phase has two parts, excitability and inhibition. Partially digested foods fill the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflexes inhibit vagus nuclei, activating the sympathetic fibers causing the puffer sphincter to tighten to prevent more food from entering, and inhibiting local reflexes.
Detailed nutrition
protein digestion
Protein digestion occurs in the stomach and duodenum where 3 major enzymes, pepsin secreted by the stomach and trypsin and chymotrypsin secreted by the pancreas, break down food proteins into polypeptides which are then broken down by various exopeptidases and dipeptidase into amino acids. However, digestive enzymes are mostly secreted as inactive precursors, zymogens. For example, trypsin is secreted by the pancreas in the form of trypsinogen, which is activated in the duodenum by enterokinase to form trypsin. Trypsin then cuts the protein into smaller polypeptides.
Fat digestion
The digestion of some fats can begin in the mouth where lingual lipase breaks down several short chain lipids into diglycerides. But the fat is mainly digested in the small intestine. The presence of fat in the small intestine produces hormones that stimulate the release of pancreatic lipase from the pancreas and bile from the liver which helps in fat emulsification for the absorption of fatty acids. The perfect digestion of one fat molecule (triglycerides) produces a mixture of fatty acids, mono and di-glycerides, as well as some undigested triglycerides, but no free glycerol molecules.
Carbohydrate digestion
In humans, diet starch consists of glucose units arranged in long chains called amylose, polysaccharides. During digestion, bonds between glucose molecules are broken down by salivary amylases and pancreas, resulting in smaller glucose chains. It produces simple sugar and maltose (2 molecules of glucose) that can be absorbed by the small intestine.
Lactase is an enzyme that breaks down disaccharide lactose into its component parts, glucose and galactose. Glucose and galactose can be absorbed by the small intestine. About 65 percent of the adult population produces only a small amount of lactase and can not eat non-fermented milk-based foods. This is commonly known as lactose intolerance. Lactose intolerance varies greatly according to ethnic heritage; more than 90 percent of people of east Asian descent are lactose intolerant, in contrast to about 5 percent of people of northern European descent.
Sucrase is an enzyme that breaks down disaccharide sucrose, commonly known as table sugar, cane sugar, or beet sugar. Digestive sugar produces fructose and glucose sugars that are easily absorbed by the small intestine.
Digestion of DNA and RNA
DNA and RNA are broken down into mononucleotides by nucleation of deoxyribonuclease and ribonuclease (DNase and RNase) from the pancreas.
Non-destructive digestion
Some nutrients are complex molecules (eg vitamin B 12 ) that will be destroyed if they are broken down into their functional groups. In order to digest non-destructive vitamin B 12 , haptocorrin in saliva strongly binds and protects B 12 molecules from stomach acid as they enter the stomach and are cleaved from the protein complex.
After the complex B 12 -haptocorrin passes from the stomach through the pylorius to the duodenum, the pancreatic protease divides the haptocorrin from a molecule B 12 that emigrates to the intrinsic factor (IF). This complex B 12 -IF runs into the ileal portion of the small intestine where cubilin receptors allow the assimilation and complex circulation of B 12 -IF in the blood.
Digestive hormone
There are at least five hormones that help and regulate the digestive system in mammals. There are variations across vertebrates, such as in birds. The setup is complicated and additional details are regularly found. For example, more connections to metabolic control (most glucose-insulin systems) have been found in recent years.
- Gastrin - is in the stomach and stimulates the gland to secrete pepsinogen (inactive form of pepsin enzyme) and hydrochloric acid. Gastrin secretion is stimulated by food that enters the stomach. Secretion is hampered by low pH.
- Secretin - is in the duodenum and signifies the secretion of sodium bicarbonate in the pancreas and stimulates the secretion of bile in the liver. This hormone responds to the acidity of chyme.
- Cholecystokinin (CCK) - is in the duodenum and stimulates digestive enzyme release in the pancreas and stimulates bile discharge in the gallbladder. This hormone is secreted in response to fat in the chyme.
- Gastric inhibition peptide (GIP) - is in the duodenum and lowers the turbulent stomach in turn slows the emptying in the abdomen. Another function is to induce insulin secretion.
- Motilin - is in the duodenum and increases the myocortical complex component of gastrointestinal motility migration and stimulates pepsin production.
Significance of pH
Digestion is a complex process that is controlled by several factors. pH plays an important role in the normal functioning gastrointestinal tract. In the mouth, pharynx and esophagus, the pH is usually about 6.8, very sour weak. Saliva controls the pH of the region in the gastrointestinal tract. Salivary amylase is contained in saliva and initiates the breakdown of carbohydrates into monosaccharides. Most digestive enzymes are sensitive to pH and will change properties in high or low pH environments.
High gastric acidity inhibits breakdown of carbohydrates in it. This acidity conferes two benefits: it nourishes proteins for further digestion in the small intestine, and provides non-specific immunity, damage or eliminate pathogens.
In the small intestine, the duodenum provides a critical pH balance to activate the digestive enzymes. The liver releases the bile into the duodenum to neutralize the acidic condition of the stomach, and the pancreatic duct empties into the duodenum, adding bicarbonate to neutralize the acid chyme, thus creating a neutral environment. The small bowel mucosal tissue is alkaline with a pH of about 8.5.
See also
- Gastropod digestive system
- Digestive system of humpback whales
- Erepsin
- Gastroesophageal reflux disease
- The discovery and development of proton pump inhibitors
References
External links
- Human Physiology - Digestion
- NIH guidance for the digestive system
- Digestive System
- How does the Digestive System work?
Source of the article : Wikipedia
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