130-424: Homosclerophorida is an order of marine sponges . It is the only order in the monotypic class Homoscleromorpha . The order is composed of two families: Plakinidae and Oscarellidae . Homoscleromorpha is phylogenetically well separated from Demospongiae . Therefore, it has been recognized as the fourth class of sponges. It has been suggested that Homoscleromorpha are more closely related to eumetazoans than to
260-593: A basal animal clade and a sister taxon of the diploblasts . They are sessile filter feeders that are bound to the seabed , and are one of the most ancient members of macrobenthos , with many historical species being important reef -building organisms. Sponges are multicellular organisms consisting of jelly-like mesohyl sandwiched between two thin layers of cells , and usually have tube-like bodies full of pores and channels that allow water to circulate through them. They have unspecialized cells that can transform into other types and that often migrate between
390-406: A common bile duct with the gallbladder. Bile is stored in the gallbladder for release when food is discharged into the duodenum and also after a few hours. The gallbladder is a hollow part of the biliary tract that sits just beneath the liver, with the gallbladder body resting in a small depression. It is a small organ where the bile produced by the liver is stored, before being released into
520-407: A monoglyceride . These are then absorbed by villi on the intestinal wall. If fats are not absorbed in this way in the small intestine problems can arise later in the large intestine which is not equipped to absorb fats. Bile also helps in the absorption of vitamin K from the diet. Bile is collected and delivered through the common hepatic duct . This duct joins with the cystic duct to connect in
650-584: A bone-like material called dentin , which is covered by the hardest tissue in the body— enamel . Teeth have different shapes to deal with different aspects of mastication employed in tearing and chewing pieces of food into smaller and smaller pieces. This results in a much larger surface area for the action of digestive enzymes. The teeth are named after their particular roles in the process of mastication— incisors are used for cutting or biting off pieces of food; canines , are used for tearing, premolars and molars are used for chewing and grinding. Mastication of
780-478: A branch of the facial nerve the chorda tympani , and the glossopharyngeal nerve . Taste messages are sent via these cranial nerves to the brain . The brain can distinguish between the chemical qualities of the food. The five basic tastes are referred to as those of saltiness , sourness , bitterness , sweetness , and umami . The detection of saltiness and sourness enables the control of salt and acid balance. The detection of bitterness warns of poisons—many of
910-531: A chemical that stops movement of other cells in the affected area, thus preventing the intruder from using the sponge's internal transport systems. If the intrusion persists, the grey cells concentrate in the area and release toxins that kill all cells in the area. The "immune" system can stay in this activated state for up to three weeks. Sponges have three asexual methods of reproduction: after fragmentation, by budding , and by producing gemmules . Fragments of sponges may be detached by currents or waves. They use
1040-445: A few carnivorous sponges have lost these water flow systems and the choanocytes. All known living sponges can remold their bodies, as most types of their cells can move within their bodies and a few can change from one type to another. Even if a few sponges are able to produce mucus – which acts as a microbial barrier in all other animals – no sponge with the ability to secrete a functional mucus layer has been recorded. Without such
1170-408: A more horizontal position, with its upper side functioning as part of the pharynx. In this manner it prevents food from going into the trachea and instead directs it to the esophagus, which is behind. During swallowing, the backward motion of the tongue forces the epiglottis over the glottis' opening to prevent any food that is being swallowed from entering the larynx which leads to the lungs; the larynx
1300-423: A mucus layer their living tissue is covered by a layer of microbial symbionts, which can contribute up to 40–50% of the sponge wet mass. This inability to prevent microbes from penetrating their porous tissue could be a major reason why they have never evolved a more complex anatomy. Like cnidarians (jellyfish, etc.) and ctenophores (comb jellies), and unlike all other known metazoans, sponges' bodies consist of
1430-406: A natural, semi-liquid form at all times. Hydrogen ions secreted from the inner lining of the gallbladder keep the bile acidic enough to prevent hardening. To dilute the bile, water and electrolytes from the digestion system are added. Also, salts attach themselves to cholesterol molecules in the bile to keep them from crystallising . If there is too much cholesterol or bilirubin in the bile, or if
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#17327986525651560-542: A non-living jelly-like mass ( mesohyl ) sandwiched between two main layers of cells. Cnidarians and ctenophores have simple nervous systems, and their cell layers are bound by internal connections and by being mounted on a basement membrane (thin fibrous mat, also known as " basal lamina "). Sponges do not have a nervous system similar to that of vertebrates but may have one that is quite different. Their middle jelly-like layers have large and varied populations of cells, and some types of cells in their outer layers may move into
1690-430: A plant's defences are of poisonous compounds that are bitter. Sweetness guides to those foods that will supply energy; the initial breakdown of the energy-giving carbohydrates by salivary amylase creates the taste of sweetness since simple sugars are the first result. The taste of umami is thought to signal protein-rich food. Sour tastes are acidic which is often found in bad food. The brain has to decide very quickly whether
1820-876: A root-like base. Sponges are more abundant but less diverse in temperate waters than in tropical waters, possibly because organisms that prey on sponges are more abundant in tropical waters. Glass sponges are the most common in polar waters and in the depths of temperate and tropical seas, as their very porous construction enables them to extract food from these resource-poor waters with the minimum of effort. Demosponges and calcareous sponges are abundant and diverse in shallower non-polar waters. The different classes of sponge live in different ranges of habitat: Sponges with photosynthesizing endosymbionts produce up to three times more oxygen than they consume, as well as more organic matter than they consume. Such contributions to their habitats' resources are significant along Australia's Great Barrier Reef but relatively minor in
1950-644: A study in 2007 found no evidence of this and concluded that they extract bacteria and other micro-organisms from water very efficiently (about 79%) and process suspended sediment grains to extract such prey. Collar bodies digest food and distribute it wrapped in vesicles that are transported by dynein "motor" molecules along bundles of microtubules that run throughout the syncytium . Sponges' cells absorb oxygen by diffusion from water into cells as water flows through body, into which carbon dioxide and other soluble waste products such as ammonia also diffuse. Archeocytes remove mineral particles that threaten to block
2080-471: A third of the total mass of living tissue in some sponges, and some sponges gain 48% to 80% of their energy supply from these micro-organisms. In 2008, a University of Stuttgart team reported that spicules made of silica conduct light into the mesohyl , where the photosynthesizing endosymbionts live. Sponges that host photosynthesizing organisms are most common in waters with relatively poor supplies of food particles and often have leafy shapes that maximize
2210-738: Is biomineralized . The mesohyl functions as an endoskeleton in most sponges, and is the only skeleton in soft sponges that encrust hard surfaces such as rocks. More commonly the mesohyl is stiffened by mineral spicules , by spongin fibers or both. Spicules, which are present in most but not all species, may be made of silica or calcium carbonate, and vary in shape from simple rods to three-dimensional "stars" with up to six rays. Spicules are produced by sclerocyte cells, and may be separate, connected by joints, or fused. Some sponges also secrete exoskeletons that lie completely outside their organic components. For example, sclerosponges ("hard sponges") have massive calcium carbonate exoskeletons over which
2340-572: Is a neuter plural of the Modern Latin term porifer , which comes from the roots porus meaning "pore, opening", and -fer meaning "bearing or carrying". Sponges are similar to other animals in that they are multicellular , heterotrophic , lack cell walls and produce sperm cells . Unlike other animals, they lack true tissues and organs . Some of them are radially symmetrical, but most are asymmetrical. The shapes of their bodies are adapted for maximal efficiency of water flow through
2470-426: Is a form of chemoreception that takes place in the specialised taste receptors , contained in structures called taste buds in the mouth. Taste buds are mainly on the upper surface (dorsum) of the tongue. The function of taste perception is vital to help prevent harmful or rotten foods from being consumed. There are also taste buds on the epiglottis and upper part of the esophagus . The taste buds are innervated by
2600-417: Is also pulled upwards to assist this process. Stimulation of the larynx by ingested matter produces a strong cough reflex in order to protect the lungs. The pharynx is a part of the conducting zone of the respiratory system and also a part of the digestive system. It is the part of the throat immediately behind the nasal cavity at the back of the mouth and above the esophagus and larynx . The pharynx
2730-484: Is an important part of the body's digestive system. The muscular diaphragm separates the thoracic cavity from the abdominal cavity where most of the digestive organs are located. The suspensory muscle attaches the ascending duodenum to the diaphragm. This muscle is thought to be of help in the digestive system in that its attachment offers a wider angle to the duodenojejunal flexure for the easier passage of digesting material. The diaphragm also attaches to, and anchors
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#17327986525652860-420: Is closed at both ends, by the upper and lower esophageal sphincters . The opening of the upper sphincter is triggered by the swallowing reflex so that food is allowed through. The sphincter also serves to prevent back flow from the esophagus into the pharynx. The esophagus has a mucous membrane and the epithelium which has a protective function is continuously replaced due to the volume of food that passes inside
2990-402: Is constant, specimens 1 m (3.3 ft) wide must be about 5,000 years old. Some sponges start sexual reproduction when only a few weeks old, while others wait until they are several years old. Adult sponges lack neurons or any other kind of nervous tissue . However, most species have the ability to perform movements that are coordinated all over their bodies, mainly contractions of
3120-413: Is covered with a mucous membrane and there are taste buds on its lingual surface which faces into the mouth. Its laryngeal surface faces into the larynx. The epiglottis functions to guard the entrance of the glottis , the opening between the vocal folds . It is normally pointed upward during breathing with its underside functioning as part of the pharynx, but during swallowing, the epiglottis folds down to
3250-431: Is easiest. The fragile glass sponges , with " scaffolding " of silica spicules, are restricted to polar regions and the ocean depths where predators are rare. Fossils of all of these types have been found in rocks dated from 580 million years ago . In addition Archaeocyathids , whose fossils are common in rocks from 530 to 490 million years ago , are now regarded as a type of sponge. Although most of
3380-402: Is eaten. The stomach is half empty after an average of 1.2 hours. After four or five hours the stomach has emptied. In the small intestine, the pH becomes crucial; it needs to be finely balanced in order to activate digestive enzymes. The chyme is very acidic, with a low pH, having been released from the stomach and needs to be made much more alkaline. This is achieved in the duodenum by
3510-512: Is further helped by the lubrication provided by the saliva in its passage from the mouth into the esophagus. Also of importance is the presence in saliva of the digestive enzymes amylase and lipase. Amylase starts to work on the starch in carbohydrates , breaking it down into the simple sugars of maltose and dextrose that can be further broken down in the small intestine. Saliva in the mouth can account for 30% of this initial starch digestion. Lipase starts to work on breaking down fats . Lipase
3640-432: Is further produced in the pancreas where it is released to continue this digestion of fats. The presence of salivary lipase is of prime importance in young babies whose pancreatic lipase has yet to be developed. As well as its role in supplying digestive enzymes, saliva has a cleansing action for the teeth and mouth. It also has an immunological role in supplying antibodies to the system, such as immunoglobulin A . This
3770-466: Is its major pigment. Bile acts partly as a surfactant which lowers the surface tension between either two liquids or a solid and a liquid and helps to emulsify the fats in the chyme. Food fat is dispersed by the action of bile into smaller units called micelles . The breaking down into micelles creates a much larger surface area for the pancreatic enzyme, lipase to work on. Lipase digests the triglycerides which are broken down into two fatty acids and
3900-504: Is known about how they actually capture prey, although some species are thought to use either sticky threads or hooked spicules . Most carnivorous sponges live in deep waters, up to 8,840 m (5.49 mi), and the development of deep-ocean exploration techniques is expected to lead to the discovery of several more. However, one species has been found in Mediterranean caves at depths of 17–23 m (56–75 ft), alongside
4030-427: Is made up of three parts. The lower two parts—the oropharynx and the laryngopharynx are involved in the digestive system. The laryngopharynx connects to the esophagus and it serves as a passageway for both air and food. Air enters the larynx anteriorly but anything swallowed has priority and the passage of air is temporarily blocked. The pharynx is innervated by the pharyngeal plexus of the vagus nerve . Muscles in
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4160-433: Is much greater than that of the canals, water flow through chambers slows to 3.6 cm per hour , making it easy for choanocytes to capture food. All the water is expelled through a single osculum at about 8.5 cm per second , fast enough to carry waste products some distance away. In zoology a skeleton is any fairly rigid structure of an animal, irrespective of whether it has joints and irrespective of whether it
4290-434: Is probably most common, where larvae with vertically transmitted symbionts also acquire others horizontally). There are four types of larvae, but all are lecithotrophic (non-feeding) balls of cells with an outer layer of cells whose flagella or cilia enable the larvae to move. After swimming for a few days the larvae sink and crawl until they find a place to settle. Most of the cells transform into archeocytes and then into
4420-459: Is seen to be key in preventing infections of the salivary glands, importantly that of parotitis . Saliva also contains a glycoprotein called haptocorrin which is a binding protein to vitamin B 12 . It binds with the vitamin in order to carry it safely through the acidic content of the stomach. When it reaches the duodenum, pancreatic enzymes break down the glycoprotein and free the vitamin which then binds with intrinsic factor . Food enters
4550-455: Is the jejunum and the third is the ileum ). The duodenum is the first and shortest section of the small intestine. It is a hollow, jointed C-shaped tube connecting the stomach to the jejunum. It starts at the duodenal bulb and ends at the suspensory muscle of duodenum . The attachment of the suspensory muscle to the diaphragm is thought to help the passage of food by making a wider angle at its attachment. Most food digestion takes place in
4680-402: Is the largest lymphoid organ in the body but has other functions. It breaks down both red and white blood cells that are spent . This is why it is sometimes known as the 'graveyard of red blood cells'. A product of this digestion is the pigment bilirubin , which is sent to the liver and secreted in the bile . Another product is iron , which is used in the formation of new blood cells in
4810-482: Is the longest part of the GI tract. The largest part of the GI tract is the colon or large intestine . Water is absorbed here and the remaining waste matter is stored prior to defecation . There are many specialised cells of the GI tract. These include the various cells of the gastric glands, taste cells , pancreatic duct cells , enterocytes and microfold cells . Some parts of the digestive system are also part of
4940-601: Is the only skeleton in soft sponges that encrust such hard surfaces as rocks. More commonly, the mesohyl is stiffened by mineral spicules , by spongin fibers, or both. 90% of all known sponge species that have the widest range of habitats including all freshwater ones are demosponges that use spongin; many species have silica spicules, whereas some species have calcium carbonate exoskeletons . Calcareous sponges have calcium carbonate spicules and, in some species, calcium carbonate exoskeletons, are restricted to relatively shallow marine waters where production of calcium carbonate
5070-430: Is the rhythmic contraction of muscles that begins in the esophagus and continues along the wall of the stomach and the rest of the gastrointestinal tract. This initially results in the production of chyme which when fully broken down in the small intestine is absorbed as chyle into the lymphatic system . Most of the digestion of food takes place in the small intestine. Water and some minerals are reabsorbed back into
5200-536: The bone marrow . Medicine treats the spleen solely as belonging to the lymphatic system , though it is acknowledged that the full range of its important functions is not yet understood. The liver is the second largest organ (after the skin ) and is an accessory digestive gland which plays a role in the body's metabolism . The liver has many functions some of which are important to digestion. The liver can detoxify various metabolites ; synthesise proteins and produce biochemicals needed for digestion. It regulates
5330-421: The duodenum via the pyloric canal , contains countless glands which secrete digestive enzymes including gastrin. After an hour or two, a thick semi-liquid called chyme is produced. When the pyloric sphincter , or valve opens, chyme enters the duodenum where it mixes further with digestive enzymes from the pancreas, and then passes through the small intestine, where digestion continues. The parietal cells in
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5460-451: The epithelia of more complex animals, they are not bound tightly by cell-to-cell connections or a basal lamina (thin fibrous sheet underneath). The flexibility of these layers and re-modeling of the mesohyl by lophocytes allow the animals to adjust their shapes throughout their lives to take maximum advantage of local water currents. The simplest body structure in sponges is a tube or vase shape known as "asconoid", but this severely limits
5590-408: The excretory system , including the large intestine. The mouth is the first part of the upper gastrointestinal tract and is equipped with several structures that begin the first processes of digestion. These include salivary glands, teeth and the tongue. The mouth consists of two regions; the vestibule and the oral cavity proper. The vestibule is the area between the teeth, lips and cheeks, and
5720-413: The gastrointestinal tract plus the accessory organs of digestion (the tongue , salivary glands , pancreas , liver , and gallbladder ). Digestion involves the breakdown of food into smaller and smaller components, until they can be absorbed and assimilated into the body. The process of digestion has three stages: the cephalic phase , the gastric phase , and the intestinal phase . The first stage,
5850-456: The genus Chondrocladia uses a highly modified water flow system to inflate balloon-like structures that are used for capturing prey. Freshwater sponges often host green algae as endosymbionts within archaeocytes and other cells and benefit from nutrients produced by the algae. Many marine species host other photosynthesizing organisms, most commonly cyanobacteria but in some cases dinoflagellates . Symbiotic cyanobacteria may form
5980-470: The mesohyl and form spermatic cysts while eggs are formed by transformation of archeocytes , or of choanocytes in some species. Each egg generally acquires a yolk by consuming "nurse cells". During spawning, sperm burst out of their cysts and are expelled via the osculum . If they contact another sponge of the same species, the water flow carries them to choanocytes that engulf them but, instead of digesting them, metamorphose to an ameboid form and carry
6110-463: The pinacocytes , squeezing the water channels and thus expelling excess sediment and other substances that may cause blockages. Some species can contract the osculum independently of the rest of the body. Sponges may also contract in order to reduce the area that is vulnerable to attack by predators. In cases where two sponges are fused, for example if there is a large but still unseparated bud, these contraction waves slowly become coordinated in both of
6240-411: The thorax and enters the stomach through a hole in the thoracic diaphragm —the esophageal hiatus , at the level of the tenth thoracic vertebra (T10). Its length averages 25 cm, varying with an individual's height. It is divided into cervical, thoracic and abdominal parts. The pharynx joins the esophagus at the esophageal inlet which is behind the cricoid cartilage . At rest the esophagus
6370-427: The uvula . The surface of the hard palate allows for the pressure needed in eating food, to leave the nasal passage clear. The opening between the lips is termed the oral fissure, and the opening into the throat is called the fauces . At either side of the soft palate are the palatoglossus muscles which also reach into regions of the tongue. These muscles raise the back of the tongue and also close both sides of
6500-455: The " Siamese twins ". The coordinating mechanism is unknown, but may involve chemicals similar to neurotransmitters . However, glass sponges rapidly transmit electrical impulses through all parts of the syncytium , and use this to halt the motion of their flagella if the incoming water contains toxins or excessive sediment. Myocytes are thought to be responsible for closing the osculum and for transmitting signals between different parts of
6630-611: The 1950s, though, these had been overfished so heavily that the industry almost collapsed, and most sponge-like materials are now synthetic. Sponges and their microscopic endosymbionts are now being researched as possible sources of medicines for treating a wide range of diseases. Dolphins have been observed using sponges as tools while foraging . Sponges constitute the phylum Porifera, and have been defined as sessile metazoans (multicelled immobile animals) that have water intake and outlet openings connected by chambers lined with choanocytes , cells with whip-like flagella. However,
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#17327986525656760-523: The Caribbean. Many sponges shed spicules , forming a dense carpet several meters deep that keeps away echinoderms which would otherwise prey on the sponges. They also produce toxins that prevent other sessile organisms such as bryozoans or sea squirts from growing on or near them, making sponges very effective competitors for living space. One of many examples includes ageliferin . Digestive system The human digestive system consists of
6890-521: The Mediterranean Sea, 82% of the species in this taxon can be found in caves, and 41% of them are found nowhere else. This article about a demosponge is a stub . You can help Misplaced Pages by expanding it . Sponge Parazoa /Ahistozoa ( sans Placozoa ) Sponges or sea sponges are members of the metazoan phylum Porifera ( / p ə ˈ r ɪ f ər ə ˌ p ɔː -/ pər- IF -ər-ə, por- ; meaning 'pore bearer'),
7020-414: The addition of bile from the gall bladder combined with the bicarbonate secretions from the pancreatic duct and also from secretions of bicarbonate-rich mucus from duodenal glands known as Brunner's glands . The chyme arrives in the intestines having been released from the stomach through the opening of the pyloric sphincter . The resulting alkaline fluid mix neutralises the gastric acid which would damage
7150-475: The amount of sunlight they collect. A recently discovered carnivorous sponge that lives near hydrothermal vents hosts methane-eating bacteria and digests some of them. Sponges do not have the complex immune systems of most other animals. However, they reject grafts from other species but accept them from other members of their own species. In a few marine species, gray cells play the leading role in rejection of foreign material. When invaded, they produce
7280-523: The approximately 5,000–10,000 known species of sponges feed on bacteria and other microscopic food in the water, some host photosynthesizing microorganisms as endosymbionts , and these alliances often produce more food and oxygen than they consume. A few species of sponges that live in food-poor environments have evolved as carnivores that prey mainly on small crustaceans . Most sponges reproduce sexually , but they can also reproduce asexually. Sexually reproducing species release sperm cells into
7410-430: The bile and pancreatic juice can act on the chyme that is released from the stomach into the duodenum. Aqueous pancreatic secretions from pancreatic duct cells contain bicarbonate ions which are alkaline and help with the bile to neutralise the acidic chyme that is churned out by the stomach. The pancreas is also the main source of enzymes for the digestion of fats and proteins. Some of these are released in response to
7540-402: The biliary tract via the cystic duct , which then joins the common hepatic duct to form the common bile duct. At this junction is a mucosal fold called Hartmann's pouch , where gallstones commonly get stuck. The muscular layer of the body is of smooth muscle tissue that helps the gallbladder contract, so that it can discharge its bile into the bile duct. The gallbladder needs to store bile in
7670-444: The blood in the colon of the large intestine . The waste products of digestion ( feces ) are defecated from the rectum via the anus . There are several organs and other components involved in the digestion of food. The organs known as the accessory digestive organs are the liver , gall bladder and pancreas . Other components include the mouth , salivary glands , tongue , teeth and epiglottis . The largest structure of
7800-432: The blood sugar is low; glucagon allows stored sugar to be broken down into glucose by the liver in order to re-balance the sugar levels. The pancreas produces and releases important digestive enzymes in the pancreatic juice that it delivers to the duodenum. The pancreas lies below and at the back of the stomach. It connects to the duodenum via the pancreatic duct which it joins near to the bile duct's connection where both
7930-418: The body. Sponges contain genes very similar to those that contain the "recipe" for the post- synaptic density, an important signal-receiving structure in the neurons of all other animals. However, in sponges these genes are only activated in "flask cells" that appear only in larvae and may provide some sensory capability while the larvae are swimming. This raises questions about whether flask cells represent
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#17327986525658060-430: The bowel or the gut. The lower GI starts at the pyloric sphincter of the stomach and finishes at the anus. The small intestine is subdivided into the duodenum , the jejunum and the ileum . The cecum marks the division between the small and large intestine. The large intestine includes the rectum and anal canal . Partially digested food starts to arrive in the small intestine as semi-liquid chyme , one hour after it
8190-467: The bulk of lipoproteins. The liver is located in the upper right quadrant of the abdomen and below the diaphragm to which it is attached at one part, the bare area of the liver. This is to the right of the stomach and it overlies the gall bladder. The liver synthesises bile acids and lecithin to promote the digestion of fat. Bile produced by the liver is made up of water (97%), bile salts , mucus and pigments , 1% fats and inorganic salts. Bilirubin
8320-477: The center. The larvae then leave their parents' bodies. The cytological progression of porifera oogenesis and spermatogenesis ( gametogenesis ) is very similar to that of other metazoa. Most of the genes from the classic set of meiotic genes, including genes for DNA recombination and double-strand break repair, that are conserved in eukaryotes are expressed in the sponges (e.g. Geodia hentscheli and Geodia phlegraei ). Since porifera are considered to be
8450-415: The central cavity, where the water deposits nutrients and then leaves through a hole called the osculum . The single-celled choanoflagellates resemble the choanocyte cells of sponges which are used to drive their water flow systems and capture most of their food. This along with phylogenetic studies of ribosomal molecules have been used as morphological evidence to suggest sponges are the sister group to
8580-423: The cephalic phase of digestion, begins with secretions from gastric glands in response to the sight and smell of food. This stage includes the mechanical breakdown of food by chewing , and the chemical breakdown by digestive enzymes , that takes place in the mouth . Saliva contains the digestive enzymes amylase , and lingual lipase , secreted by the salivary and serous glands on the tongue. Chewing, in which
8710-497: The cheeks, inner surfaces of the lips , and floor of the mouth, and the mucin produced is highly protective against tooth decay . The roof of the mouth is termed the palate and it separates the oral cavity from the nasal cavity. The palate is hard at the front of the mouth since the overlying mucosa is covering a plate of bone ; it is softer and more pliable at the back being made of muscle and connective tissue, and it can move to swallow food and liquids. The soft palate ends at
8840-597: The cross-section area of the choanocyte-lined regions is much greater than that of the intake and outlet channels. This makes the flow slower near the choanocytes and thus makes it easier for them to trap food particles. For example, in Leuconia , a small leuconoid sponge about 10 centimetres (3.9 in) tall and 1 centimetre (0.39 in) in diameter, water enters each of more than 80,000 intake canals at 6 cm per minute . However, because Leuconia has more than 2 million flagellated chambers whose combined diameter
8970-424: The digestion of proteins . As these two chemicals would damage the stomach wall, mucus is secreted by innumerable gastric glands in the stomach, to provide a slimy protective layer against the damaging effects of the chemicals on the inner layers of the stomach. At the same time that protein is being digested, mechanical churning occurs through the action of peristalsis, waves of muscular contractions that move along
9100-413: The digestive system is the gastrointestinal tract (GI tract). This starts at the mouth and ends at the anus , covering a distance of about nine metres (30 ft). A major digestive organ is the stomach . Within its mucosa are millions of embedded gastric glands . Their secretions are vital to the functioning of the organ. Most of the digestion of food takes place in the small intestine which
9230-401: The digestive process, and mainly contains hydrochloric acid and sodium chloride . A peptide hormone , gastrin , produced by G cells in the gastric glands , stimulates the production of gastric juice which activates the digestive enzymes. Pepsinogen is a precursor enzyme ( zymogen ) produced by the gastric chief cells , and gastric acid activates this to the enzyme pepsin which begins
9360-420: The duodenum. Here, the partially digested food is mixed with a number of enzymes produced by the pancreas. Digestion is helped by the chewing of food carried out by the muscles of mastication , the tongue, and the teeth , and also by the contractions of peristalsis , and segmentation . Gastric acid, and the production of mucus in the stomach, are essential for the continuation of digestion. Peristalsis
9490-448: The earliest divergent animals, these findings indicate that the basic toolkit of meiosis including capabilities for recombination and DNA repair were present early in eukaryote evolution. Sponges in temperate regions live for at most a few years, but some tropical species and perhaps some deep-ocean ones may live for 200 years or more. Some calcified demosponges grow by only 0.2 mm (0.0079 in) per year and, if that rate
9620-406: The enzymes; which avoids the onset of pancreatitis caused by autodegradation. Once released in the intestine, the enzyme enteropeptidase present in the intestinal mucosa activates trypsinogen by cleaving it to form trypsin; further cleavage results in chymotripsin. The lower gastrointestinal tract (GI), includes the small intestine and all of the large intestine . The intestine is also called
9750-429: The esophagus. During swallowing, food passes from the mouth through the pharynx into the esophagus. The epiglottis folds down to a more horizontal position to direct the food into the esophagus, and away from the trachea . Once in the esophagus, the bolus travels down to the stomach via rhythmic contraction and relaxation of muscles known as peristalsis . The lower esophageal sphincter is a muscular sphincter surrounding
9880-423: The fact that growth in any direction increases the number of choanocyte chambers enables them to take a wider range of forms, for example, "encrusting" sponges whose shapes follow those of the surfaces to which they attach. All freshwater and most shallow-water marine sponges have leuconid bodies. The networks of water passages in glass sponges are similar to the leuconid structure. In all three types of structure
10010-462: The fat is absorbed, the bile is also absorbed and transported back to the liver for reuse. The pancreas is a major organ functioning as an accessory digestive gland in the digestive system. It is both an endocrine gland and an exocrine gland . The endocrine part secretes insulin when the blood sugar becomes high; insulin moves glucose from the blood into the muscles and other tissues for use as energy. The endocrine part releases glucagon when
10140-547: The fauces to enable food to be swallowed. Mucus helps in the mastication of food in its ability to soften and collect the food in the formation of the bolus. There are three pairs of main salivary glands and between 800 and 1,000 minor salivary glands, all of which mainly serve the digestive process, and also play an important role in the maintenance of dental health and general mouth lubrication, without which speech would be impossible. The main glands are all exocrine glands , secreting via ducts. All of these glands terminate in
10270-535: The first outgroup to branch off the evolutionary tree from the last common ancestor of all animals , with fossil evidence of primitive sponges such as Otavia from as early as the Tonian period (around 800 Mya ). The branch of zoology that studies sponges is known as spongiology . The term sponge derives from the Ancient Greek word σπόγγος spóngos . The scientific name Porifera
10400-422: The food is mixed with saliva, begins the mechanical process of digestion. This produces a bolus which is swallowed down the esophagus to enter the stomach . The second stage, the gastric phase, happens in the stomach. Here, the food is further broken down by mixing with gastric acid until it passes into the duodenum , the first part of the small intestine . The third stage, the intestinal phase, begins in
10530-493: The food should be eaten or not. It was the findings in 1991, describing the first olfactory receptors that helped to prompt the research into taste. The olfactory receptors are located on cell surfaces in the nose which bind to chemicals enabling the detection of smells. It is assumed that signals from taste receptors work together with those from the nose, to form an idea of complex food flavours. Teeth are complex structures made of materials specific to them. They are made of
10660-399: The food with the help of saliva and mucus results in the formation of a soft bolus which can then be swallowed to make its way down the upper gastrointestinal tract to the stomach. The digestive enzymes in saliva also help in keeping the teeth clean by breaking down any lodged food particles. The epiglottis is a flap of elastic cartilage attached to the entrance of the larynx . It
10790-486: The fundus of the stomach, produce a glycoprotein called intrinsic factor which is essential for the absorption of vitamin B12 . Vitamin B12 (cobalamin), is carried to, and through the stomach, bound to a glycoprotein secreted by the salivary glands – transcobalamin I also called haptocorrin, which protects the acid-sensitive vitamin from the acidic stomach contents. Once in the more neutral duodenum, pancreatic enzymes break down
10920-437: The gallbladder does not empty properly the systems can fail. This is how gallstones form when a small piece of calcium gets coated with either cholesterol or bilirubin and the bile crystallises and forms a gallstone. The main purpose of the gallbladder is to store and release bile, or gall . Bile is released into the small intestine in order to help in the digestion of fats by breaking down larger molecules into smaller ones. After
11050-581: The genera Oscarella and Pseudocorticium . These sponges are massive or encrusting in form and have a very simple structure with very little variation in spicule form (all spicules tend to be very small). Reproduction is viviparous and the larva is an oval form known as an amphiblastula . This form is usual in calcareous sponges but is less common in other sponges. Homoscleromorpha are exclusively marine sponges that tend to encrust on other surfaces at shallow depths. These sponges typically inhabit shady locations, under overhangs and inside caves. In
11180-404: The immune system) against microbes in food, when it makes contact with these glands on the tongue tissue. Sensory information can stimulate the secretion of saliva providing the necessary fluid for the tongue to work with and also to ease swallowing of the food. Saliva moistens and softens food, and along with the chewing action of the teeth, transforms the food into a smooth bolus . The bolus
11310-425: The intestines (the majority being in the small intestine). They are unusual cells in that they have villi on their surface which in turn have innumerable microvilli on their surface. All these villi make for a greater surface area, not only for the absorption of chyme but also for its further digestion by large numbers of digestive enzymes present on the microvilli. The chylomicrons are small enough to pass through
11440-414: The lining of the intestine. The mucus component lubricates the walls of the intestine. When the digested food particles are reduced enough in size and composition, they can be absorbed by the intestinal wall and carried to the bloodstream. The first receptacle for this chyme is the duodenal bulb . From here it passes into the first of the three sections of the small intestine, the duodenum (the next section
11570-410: The liver at its bare area . The esophagus enters the abdomen through a hole in the diaphragm at the level of T10 . The stomach is a major organ of the gastrointestinal tract and digestive system. It is a consistently J-shaped organ joined to the esophagus at its upper end and to the duodenum at its lower end. Gastric acid (informally gastric juice ), produced in the stomach plays a vital role in
11700-412: The living tissue is suspended like a cobweb that contains most of the cell types. This tissue is a syncytium that in some ways behaves like many cells that share a single external membrane , and in others like a single cell with multiple nuclei . Most sponges work rather like chimneys : they take in water at the bottom and eject it from the osculum at the top. Since ambient currents are faster at
11830-447: The lower part of the esophagus. The gastroesophageal junction between the esophagus and the stomach is controlled by the lower esophageal sphincter, which remains constricted at all times other than during swallowing and vomiting to prevent the contents of the stomach from entering the esophagus. As the esophagus does not have the same protection from acid as the stomach, any failure of this sphincter can lead to heartburn. The diaphragm
11960-406: The main cell layers and the mesohyl in the process. They do not have complex nervous , digestive or circulatory systems . Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes, usually via flagella movements of the so-called " collar cells ". Believed to be some of the most basal animals alive today, sponges were possibly
12090-409: The manipulation of food (and speech ); the range of manipulation is optimally controlled by the action of several muscles and limited in its external range by the stretch of the frenum. The tongue's two sets of muscles, are four intrinsic muscles that originate in the tongue and are involved with its shaping, and four extrinsic muscles originating in bone that are involved with its movement. Taste
12220-436: The middle layer and change their functions. A sponge's body is hollow and is held in shape by the mesohyl , a jelly-like substance made mainly of collagen and reinforced by a dense network of fibers also made of collagen. 18 distinct cell types have been identified. The inner surface is covered with choanocytes , cells with cylindrical or conical collars surrounding one flagellum per choanocyte. The wave-like motion of
12350-448: The mobility of their pinacocytes and choanocytes and reshaping of the mesohyl to re-attach themselves to a suitable surface and then rebuild themselves as small but functional sponges over the course of several days. The same capabilities enable sponges that have been squeezed through a fine cloth to regenerate. A sponge fragment can only regenerate if it contains both collencytes to produce mesohyl and archeocytes to produce all
12480-434: The more usual filter-feeding sponges. The cave-dwelling predators capture crustaceans under 1 mm (0.039 in) long by entangling them with fine threads, digest them by enveloping them with further threads over the course of a few days, and then return to their normal shape; there is no evidence that they use venom . Most known carnivorous sponges have completely lost the water flow system and choanocytes . However,
12610-409: The mouth continues as the thin mucosa which lines the bases of the teeth. The main component of mucus is a glycoprotein called mucin and the type secreted varies according to the region involved. Mucin is viscous, clear, and clinging. Underlying the mucous membrane in the mouth is a thin layer of smooth muscle tissue and the loose connection to the membrane gives it its great elasticity. It covers
12740-424: The mouth where the first stage in the digestive process takes place, with the action of the tongue and the secretion of saliva. The tongue is a fleshy and muscular sensory organ , and the first sensory information is received via the taste buds in the papillae on its surface. If the taste is agreeable, the tongue will go into action, manipulating the food in the mouth which stimulates the secretion of saliva from
12870-423: The mouth. The largest of these are the parotid glands —their secretion is mainly serous . The next pair are underneath the jaw, the submandibular glands , these produce both serous fluid and mucus. The serous fluid is produced by serous glands in these salivary glands which also produce lingual lipase . They produce about 70% of the oral cavity saliva. The third pair are the sublingual glands located underneath
13000-442: The number of choanocytes and hence in pumping capacity enables syconoid sponges to grow up to a few centimeters in diameter. The "leuconoid" pattern boosts pumping capacity further by filling the interior almost completely with mesohyl that contains a network of chambers lined with choanocytes and connected to each other and to the water intakes and outlet by tubes. Leuconid sponges grow to over 1 m (3.3 ft) in diameter, and
13130-691: The organic matter forms a thin layer with choanocyte chambers in pits in the mineral. These exoskeletons are secreted by the pinacocytes that form the animals' skins. Although adult sponges are fundamentally sessile animals, some marine and freshwater species can move across the sea bed at speeds of 1–4 mm (0.039–0.157 in) per day, as a result of amoeba -like movements of pinacocytes and other cells. A few species can contract their whole bodies, and many can close their oscula and ostia . Juveniles drift or swim freely, while adults are stationary. Sponges do not have distinct circulatory , respiratory , digestive , and excretory systems – instead,
13260-432: The ostia, while those at the base of the animal are responsible for anchoring it. Other types of cells live and move within the mesohyl: Many larval sponges possess neuron-less eyes that are based on cryptochromes . They mediate phototaxic behavior. Glass sponges present a distinctive variation on this basic plan. Their spicules, which are made of silica , form a scaffolding -like framework between whose rods
13390-539: The ostia, transport them through the mesohyl and generally dump them into the outgoing water current, although some species incorporate them into their skeletons. In waters where the supply of food particles is very poor, some species prey on crustaceans and other small animals. So far only 137 species have been discovered. Most belong to the family Cladorhizidae , but a few members of the Guitarridae and Esperiopsidae are also carnivores. In most cases, little
13520-661: The other cell types. A very few species reproduce by budding. Gemmules are "survival pods" which a few marine sponges and many freshwater species produce by the thousands when dying and which some, mainly freshwater species, regularly produce in autumn. Spongocytes make gemmules by wrapping shells of spongin, often reinforced with spicules, round clusters of archeocytes that are full of nutrients. Freshwater gemmules may also include photosynthesizing symbionts. The gemmules then become dormant, and in this state can survive cold, drying out, lack of oxygen and extreme variations in salinity . Freshwater gemmules often do not revive until
13650-659: The other sponge groups, rendering sponges paraphyletic. This view has not been supported by later work using larger datasets and new techniques for phylogenetic inference, which tend to support sponges as monophyletic, with Homoscleromorpha grouping together with Calcarea . On the basis of molecular and morphological evidence, the two families Plakinidae and Oscarellidae have been reinstated. There are 117 species in this group divided into 9 genera. The spiculate genera in this group are Aspiculophora , Corticium , Placinolopha , Plakina , Plakinasterella , Plakortis and Tetralophophora . The aspiculate species are
13780-402: The pharynx push the food into the esophagus. The pharynx joins the esophagus at the oesophageal inlet which is located behind the cricoid cartilage . The esophagus , commonly known as the foodpipe or gullet, consists of a muscular tube through which food passes from the pharynx to the stomach. The esophagus is continuous with the laryngopharynx. It passes through the posterior mediastinum in
13910-582: The predecessors of true neurons or are evidence that sponges' ancestors had true neurons but lost them as they adapted to a sessile lifestyle. Sponges are worldwide in their distribution, living in a wide range of ocean habitats, from the polar regions to the tropics. Most live in quiet, clear waters, because sediment stirred up by waves or currents would block their pores, making it difficult for them to feed and breathe. The greatest numbers of sponges are usually found on firm surfaces such as rocks, but some sponges can attach themselves to soft sediment by means of
14040-590: The production of cholecystokinin in the duodenum. (The enzymes that digest polysaccharides, by contrast, are primarily produced by the walls of the intestines.) The cells are filled with secretory granules containing the precursor digestive enzymes. The major proteases , the pancreatic enzymes which work on proteins, are trypsinogen and chymotrypsinogen . Elastase is also produced. Smaller amounts of lipase and amylase are secreted. The pancreas also secretes phospholipase A2 , lysophospholipase , and cholesterol esterase . The precursor zymogens , are inactive variants of
14170-419: The protective glycoprotein. The freed vitamin B12 then binds to intrinsic factor which is then absorbed by the enterocytes in the ileum. The stomach is a distensible organ and can normally expand to hold about one litre of food. This expansion is enabled by a series of gastric folds in the inner walls of the stomach. The stomach of a newborn baby will only be able to expand to retain about 30 ml. The spleen
14300-416: The pumping capacity that supplies food and oxygen depends on the area covered by choanocytes. Asconoid sponges seldom exceed 1 mm (0.039 in) in diameter. Some sponges overcome this limitation by adopting the "syconoid" structure, in which the body wall is pleated . The inner pockets of the pleats are lined with choanocytes, which connect to the outer pockets of the pleats by ostia. This increase in
14430-402: The rest is the oral cavity proper. Most of the oral cavity is lined with oral mucosa , a mucous membrane that produces a lubricating mucus , of which only a small amount is needed. Mucous membranes vary in structure in the different regions of the body but they all produce a lubricating mucus, which is either secreted by surface cells or more usually by underlying glands. The mucous membrane in
14560-648: The rest of animals. A great majority are marine (salt-water) species, ranging in habitat from tidal zones to depths exceeding 8,800 m (5.5 mi), though there are freshwater species. All adult sponges are sessile , meaning that they attach to an underwater surface and remain fixed in place (i.e., do not travel). While in their larval stage of life, they are motile . Many sponges have internal skeletons of spicules (skeletal-like fragments of calcium carbonate or silicon dioxide ), and/or spongin (a modified type of collagen protein). An internal gelatinous matrix called mesohyl functions as an endoskeleton , and it
14690-428: The salivary glands. The liquid quality of the saliva will help in the softening of the food and its enzyme content will start to break down the food whilst it is still in the mouth. The first part of the food to be broken down is the starch of carbohydrates (by the enzyme amylase in the saliva). The tongue is attached to the floor of the mouth by a ligamentous band called the frenum and this gives it great mobility for
14820-468: The same species but different individuals can join forces to form one sponge. Some gemmules are retained within the parent sponge, and in spring it can be difficult to tell whether an old sponge has revived or been "recolonized" by its own gemmules. Most sponges are hermaphrodites (function as both sexes simultaneously), although sponges have no gonads (reproductive organs). Sperm are produced by choanocytes or entire choanocyte chambers that sink into
14950-402: The size of the animal. The body structure is characterized by a stalk-like spongocoel surrounded by a single layer of choanocytes. If it is simply scaled up, the ratio of its volume to surface area increases, because surface increases as the square of length or width while volume increases proportionally to the cube. The amount of tissue that needs food and oxygen is determined by the volume, but
15080-480: The small intestine. Segmentation contractions act to mix and move the chyme more slowly in the small intestine allowing more time for absorption (and these continue in the large intestine). In the duodenum, pancreatic lipase is secreted together with a co-enzyme , colipase to further digest the fat content of the chyme. From this breakdown, smaller particles of emulsified fats called chylomicrons are produced. There are also digestive cells called enterocytes lining
15210-425: The small intestine. Bile flows from the liver through the bile ducts and into the gall bladder for storage. The bile is released in response to cholecystokinin (CCK), a peptide hormone released from the duodenum. The production of CCK (by endocrine cells of the duodenum) is stimulated by the presence of fat in the duodenum. It is divided into three sections, a fundus, body and neck. The neck tapers and connects to
15340-444: The sperm through the mesohyl to eggs, which in most cases engulf the carrier and its cargo. A few species release fertilized eggs into the water, but most retain the eggs until they hatch. By retaining the eggs, the parents can transfer symbiotic microorganisms directly to their offspring through vertical transmission , while the species who release their eggs into the water has to acquire symbionts horizontally (a combination of both
15470-504: The sponges, for example as temperatures drop, many freshwater species and a few marine ones produce gemmules , "survival pods" of unspecialized cells that remain dormant until conditions improve; they then either form completely new sponges or recolonize the skeletons of their parents. The few species of demosponge that have entirely soft fibrous skeletons with no hard elements have been used by humans over thousands of years for several purposes, including as padding and as cleaning tools. By
15600-443: The starch content into maltose. There are other serous glands on the surface of the tongue that encircle taste buds on the back part of the tongue and these also produce lingual lipase . Lipase is a digestive enzyme that catalyses the hydrolysis of lipids (fats). These glands are termed Von Ebner's glands which have also been shown to have another function in the secretion of histatins which offer an early defense (outside of
15730-422: The stomach wall. This allows the mass of food to further mix with the digestive enzymes. Gastric lipase secreted by the chief cells in the fundic glands in the gastric mucosa of the stomach, is an acidic lipase, in contrast with the alkaline pancreatic lipase. This breaks down fats to some degree though is not as efficient as the pancreatic lipase. The pylorus , the lowest section of the stomach which attaches to
15860-427: The storage of glycogen which it can form from glucose ( glycogenesis ). The liver can also synthesise glucose from certain amino acids . Its digestive functions are largely involved with the breaking down of carbohydrates. It also maintains protein metabolism in its synthesis and degradation. In lipid metabolism it synthesises cholesterol . Fats are also produced in the process of lipogenesis . The liver synthesises
15990-399: The temperature drops, stays cold for a few months and then reaches a near-"normal" level. When a gemmule germinates, the archeocytes round the outside of the cluster transform into pinacocytes , a membrane over a pore in the shell bursts, the cluster of cells slowly emerges, and most of the remaining archeocytes transform into other cell types needed to make a functioning sponge. Gemmules from
16120-412: The tongue and their secretion is mainly mucous with a small percentage of saliva. Within the oral mucosa, and also on the tongue, palates, and floor of the mouth, are the minor salivary glands; their secretions are mainly mucous and they are innervated by the facial nerve ( CN7 ). The glands also secrete amylase a first stage in the breakdown of food acting on the carbohydrate in the food to transform
16250-409: The top, the suction effect that they produce by Bernoulli's principle does some of the work for free. Sponges can control the water flow by various combinations of wholly or partially closing the osculum and ostia (the intake pores) and varying the beat of the flagella, and may shut it down if there is a lot of sand or silt in the water. Although the layers of pinacocytes and choanocytes resemble
16380-489: The types appropriate for their locations in a miniature adult sponge. Glass sponge embryos start by dividing into separate cells, but once 32 cells have formed they rapidly transform into larvae that externally are ovoid with a band of cilia round the middle that they use for movement, but internally have the typical glass sponge structure of spicules with a cobweb-like main syncitium draped around and between them and choanosyncytia with multiple collar bodies in
16510-670: The walls of the ostia. Bacteria-sized particles, below 0.5 micrometers, pass through the ostia and are caught and consumed by choanocytes . Since the smallest particles are by far the most common, choanocytes typically capture 80% of a sponge's food supply. Archaeocytes transport food packaged in vesicles from cells that directly digest food to those that do not. At least one species of sponge has internal fibers that function as tracks for use by nutrient-carrying archaeocytes, and these tracks also move inert objects. It used to be claimed that glass sponges could live on nutrients dissolved in sea water and were very averse to silt. However,
16640-493: The water flow system supports all these functions. They filter food particles out of the water flowing through them. Particles larger than 50 micrometers cannot enter the ostia and pinacocytes consume them by phagocytosis (engulfing and intracellular digestion). Particles from 0.5 μm to 50 μm are trapped in the ostia, which taper from the outer to inner ends. These particles are consumed by pinacocytes or by archaeocytes which partially extrude themselves through
16770-402: The water to fertilize ova released or retained by its mate or "mother"; the fertilized eggs develop into larvae which swim off in search of places to settle. Sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. Some species reproduce by budding. When environmental conditions become less hospitable to
16900-458: The whip-like flagella drives water through the sponge's body. All sponges have ostia , channels leading to the interior through the mesohyl, and in most sponges these are controlled by tube-like porocytes that form closable inlet valves. Pinacocytes , plate-like cells, form a single-layered external skin over all other parts of the mesohyl that are not covered by choanocytes, and the pinacocytes also digest food particles that are too large to enter
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