Mouth and oral structures
When the pyloric sphincter valve opens, chyme enters the duodenum where it mixes with digestive enzymes from the pancreas and bile juice from the liver and then passes through the small intestine , in which digestion continues. An earthworm 's digestive system consists of a mouth , pharynx , esophagus , crop , gizzard , and intestine. Then they can illustrate the story and display them on the bulletin board. BO-luss toward the back of your throat and into the opening of your esophagus, the second part of the digestive tract. Liver The liver has many functions, but two of its main functions within the digestive system are to make and secrete bile, and to cleanse and purify the blood coming from the small intestine containing the nutrients just absorbed. Solids clump together to form the cud or bolus.
More on this topic for:
It is made up of the cecum, the ascending right colon, the transverse across colon, the descending left colon, and the sigmoid colon so-called for its "S" shape; the Greek letter for S is called the sigma , which connects to the rectum.
Stool, or waste left over from the digestive process, is passed through the colon by means of peristalsis contractions , first in a liquid state and ultimately in solid form as the water is removed from the stool. A stool is stored in the sigmoid colon until a "mass movement" empties it into the rectum once or twice a day. It normally takes about 36 hours for stool to get through the colon.
The stool itself is mostly food debris and bacteria. These bacteria perform several useful functions, such as synthesizing various vitamins , processing waste products and food particles, and protecting against harmful bacteria.
When the descending colon becomes full of stool, or feces, it empties its contents into the rectum to begin the process of elimination. The rectum Latin for "straight" is an 8-inch chamber that connects the colon to the anus. It is the rectum's job to receive stool from the colon, to let you know there is stool to be evacuated, and to hold the stool until evacuation happens. When anything gas or stool comes into the rectum, sensors send a message to the brain.
The brain then decides if the rectal contents can be released or not. If they can, the sphincters muscles relax and the rectum contracts, expelling its contents. If the contents cannot be expelled, the sphincters contract and the rectum accommodates, so that the sensation temporarily goes away. The anus is the last part of the digestive tract. It consists of the pelvic floor muscles and the two anal sphincters internal and external muscles.
The lining of the upper anus is specialized to detect rectal contents. It lets us know whether the contents are liquid, gas, or solid. The pelvic floor muscle creates an angle between the rectum and the anus that stops stool from coming out when it is not supposed to.
The anal sphincters provide fine control of stool. When the pyloric sphincter valve opens, chyme enters the duodenum where it mixes with digestive enzymes from the pancreas and bile juice from the liver and then passes through the small intestine , in which digestion continues. When the chyme is fully digested, it is absorbed into the blood. Water and minerals are reabsorbed back into the blood in the colon large intestine where the pH is slightly acidic about 5.
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. Waste material is eliminated from the rectum during defecation. Digestive systems take many forms. There is a fundamental distinction between internal and external digestion. External digestion developed earlier in evolutionary history, and most fungi still rely on it. Animals have a tube gastrointestinal tract in which internal digestion occurs, which is more efficient because more of the broken down products can be captured, and the internal chemical environment can be more efficiently controlled.
Some organisms, including nearly all spiders , simply secrete biotoxins and digestive chemicals e. In others, once potential nutrients or food is inside the organism , digestion can be conducted to a vesicle or a sac-like structure, through a tube, or through several specialized organs aimed at making the absorption of nutrients more efficient. Bacteria use several systems to obtain nutrients from other organisms in the environments.
In a channel transupport system, several proteins form a contiguous channel traversing the inner and outer membranes of the bacteria. It is a simple system, which consists of only three protein subunits: This secretion system transports various molecules, from ions, drugs, to proteins of various sizes 20 — kDa. The molecules secreted vary in size from the small Escherichia coli peptide colicin V, 10 kDa to the Pseudomonas fluorescens cell adhesion protein LapA of kDa.
A type III secretion system means that a molecular syringe is used through which a bacterium e. One such mechanism was first discovered in Y.
The conjugation machinery of some bacteria and archaeal flagella is capable of transporting both DNA and proteins. It was discovered in Agrobacterium tumefaciens , which uses this system to introduce the Ti plasmid and proteins into the host, which develops the crown gall tumor. The nitrogen fixing Rhizobia are an interesting case, wherein conjugative elements naturally engage in inter- kingdom conjugation. Such elements as the Agrobacterium Ti or Ri plasmids contain elements that can transfer to plant cells.
Transferred genes enter the plant cell nucleus and effectively transform the plant cells into factories for the production of opines , which the bacteria use as carbon and energy sources. Infected plant cells form crown gall or root tumors. The Ti and Ri plasmids are thus endosymbionts of the bacteria, which are in turn endosymbionts or parasites of the infected plant. The Ti and Ri plasmids are themselves conjugative. Ti and Ri transfer between bacteria uses an independent system the tra , or transfer, operon from that for inter-kingdom transfer the vir , or virulence , operon.
Such transfer creates virulent strains from previously avirulent Agrobacteria. In addition to the use of the multiprotein complexes listed above, Gram-negative bacteria possess another method for release of material: Vesicles from a number of bacterial species have been found to contain virulence factors, some have immunomodulatory effects, and some can directly adhere to and intoxicate host cells.
While release of vesicles has been demonstrated as a general response to stress conditions, the process of loading cargo proteins seems to be selective. The gastrovascular cavity functions as a stomach in both digestion and the distribution of nutrients to all parts of the body. Extracellular digestion takes place within this central cavity, which is lined with the gastrodermis, the internal layer of epithelium.
This cavity has only one opening to the outside that functions as both a mouth and an anus: In a plant such as the Venus Flytrap that can make its own food through photosynthesis, it does not eat and digest its prey for the traditional objectives of harvesting energy and carbon, but mines prey primarily for essential nutrients nitrogen and phosphorus in particular that are in short supply in its boggy, acidic habitat.
A phagosome is a vacuole formed around a particle absorbed by phagocytosis. The vacuole is formed by the fusion of the cell membrane around the particle. A phagosome is a cellular compartment in which pathogenic microorganisms can be killed and digested. Phagosomes fuse with lysosomes in their maturation process, forming phagolysosomes. In humans, Entamoeba histolytica can phagocytose red blood cells. To aid in the digestion of their food animals evolved organs such as beaks, tongues , teeth, a crop, gizzard, and others.
Birds have bony beaks that are specialised according to the bird's ecological niche. For example, macaws primarily eat seeds, nuts, and fruit, using their impressive beaks to open even the toughest seed. First they scratch a thin line with the sharp point of the beak, then they shear the seed open with the sides of the beak. The mouth of the squid is equipped with a sharp horny beak mainly made of cross-linked proteins.
It is used to kill and tear prey into manageable pieces. The beak is very robust, but does not contain any minerals, unlike the teeth and jaws of many other organisms, including marine species. The tongue is skeletal muscle on the floor of the mouth that manipulates food for chewing mastication and swallowing deglutition.
It is sensitive and kept moist by saliva. The underside of the tongue is covered with a smooth mucous membrane. The tongue also has a touch sense for locating and positioning food particles that require further chewing. The tongue is utilized to roll food particles into a bolus before being transported down the esophagus through peristalsis.
The sublingual region underneath the front of the tongue is a location where the oral mucosa is very thin, and underlain by a plexus of veins. This is an ideal location for introducing certain medications to the body. The sublingual route takes advantage of the highly vascular quality of the oral cavity, and allows for the speedy application of medication into the cardiovascular system, bypassing the gastrointestinal tract.
Teeth singular tooth are small whitish structures found in the jaws or mouths of many vertebrates that are used to tear, scrape, milk and chew food. Teeth are not made of bone, but rather of tissues of varying density and hardness, such as enamel, dentine and cementum.
Human teeth have a blood and nerve supply which enables proprioception. This is the ability of sensation when chewing, for example if we were to bite into something too hard for our teeth, such as a chipped plate mixed in food, our teeth send a message to our brain and we realise that it cannot be chewed, so we stop trying. The shapes, sizes and numbers of types of animals' teeth are related to their diets. For example, herbivores have a number of molars which are used to grind plant matter, which is difficult to digest.
Carnivores have canine teeth which are used to kill and tear meat. A crop , or croup, is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion. In some birds it is an expanded, muscular pouch near the gullet or throat. In adult doves and pigeons, the crop can produce crop milk to feed newly hatched birds. Certain insects may have a crop or enlarged esophagus. Herbivores have evolved cecums or an abomasum in the case of ruminants.
Ruminants have a fore-stomach with four chambers. These are the rumen , reticulum , omasum , and abomasum. In the first two chambers, the rumen and the reticulum, the food is mixed with saliva and separates into layers of solid and liquid material. Solids clump together to form the cud or bolus. The cud is then regurgitated, chewed slowly to completely mix it with saliva and to break down the particle size. Fibre, especially cellulose and hemi-cellulose , is primarily broken down into the volatile fatty acids , acetic acid , propionic acid and butyric acid in these chambers the reticulo-rumen by microbes: In the omasum, water and many of the inorganic mineral elements are absorbed into the blood stream.
When you swallow a small ball of mushed-up food or liquids, a special flap called the epiglottis say: If you've ever drunk something too fast, started to cough, and heard someone say that your drink "went down the wrong way," the person meant that it went down your windpipe by mistake.
This happens when the epiglottis doesn't have enough time to flop down, and you cough involuntarily without thinking about it to clear your windpipe. Once food has entered the esophagus, it doesn't just drop right into your stomach.
Instead, muscles in the walls of the esophagus move in a wavy way to slowly squeeze the food through the esophagus. This takes about 2 or 3 seconds. Your stomach, which is attached to the end of the esophagus, is a stretchy sack shaped like the letter J. It has three important jobs:. The stomach is like a mixer, churning and mashing together all the small balls of food that came down the esophagus into smaller and smaller pieces.
It does this with help from the strong muscles in the walls of the stomach and gastric say: GAS-trik juices that also come from the stomach's walls. In addition to breaking down food, gastric juices also help kill bacteria that might be in the eaten food. The small intestine say: If you stretched out an adult's small intestine, it would be about 22 feet long 6. The small intestine breaks down the food mixture even more so your body can absorb all the vitamins, minerals, proteins, carbohydrates , and fats.
PAN-kree-uss , liver, and gallbladder. Those organs send different juices to the first part of the small intestine. These juices help to digest food and allow the body to absorb nutrients. The pancreas makes juices that help the body digest fats and protein. A juice from the liver called bile helps to absorb fats into the bloodstream. And the gallbladder serves as a warehouse for bile, storing it until the body needs it.
Your food may spend as long as 4 hours in the small intestine and will become a very thin, watery mixture. It's time well spent because, at the end of the journey, the nutrients from your pizza, orange, and milk can pass from the intestine into the blood. Once in the blood, your body is closer to benefiting from the complex carbohydrates in the pizza crust, the vitamin C in your orange, the protein in the chicken, and the calcium in your milk.