Gastrointestinal tract

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The layers are not truly longitudinal or circular, rather the layers of muscle are helical with different pitches. As the beak opens and closes, each movement propels the water droplet one step closer to the bird's mouth. Digestive systems take many forms. Many sharks have the ability to turn their stomachs inside out and evert it out of their mouths in order to get rid of unwanted contents perhaps developed as a way to reduce exposure to toxins. The taste buds of birds may be located in the upper beak epithelium, in the anterior mandible, and the mandibular epithelium posterior to the tongue.


Distention activates long and myenteric reflexes. This activates the release of acetylcholine , which stimulates the release of more gastric juices. As protein enters the stomach, it binds to hydrogen ions, which raises the pH of the stomach. Inhibition of gastrin and gastric acid secretion is lifted.

This triggers G cells to release gastrin , which in turn stimulates parietal cells to secrete gastric acid. Gastric acid is about 0. Acid release is also triggered by acetylcholine and histamine. The intestinal phase has two parts, the excitatory and the inhibitory. Partially digested food fills the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating sympathetic fibers causing the pyloric sphincter to tighten to prevent more food from entering, and inhibits local reflexes.

Protein digestion occurs in the stomach and duodenum in which 3 main enzymes, pepsin secreted by the stomach and trypsin and chymotrypsin secreted by the pancreas, break down food proteins into polypeptides that are then broken down by various exopeptidases and dipeptidases into amino acids. The digestive enzymes however are mostly secreted as their inactive precursors, the zymogens.

For example, trypsin is secreted by pancreas in the form of trypsinogen , which is activated in the duodenum by enterokinase to form trypsin. Trypsin then cleaves proteins to smaller polypeptides.

Digestion of some fats can begin in the mouth where lingual lipase breaks down some short chain lipids into diglycerides. However fats are mainly digested in the small intestine. In humans, dietary starches are composed of glucose units arranged in long chains called amylose, a polysaccharide. During digestion, bonds between glucose molecules are broken by salivary and pancreatic amylase , resulting in progressively smaller chains of glucose.

This results in simple sugars glucose and maltose 2 glucose molecules that can be absorbed by the small intestine. Lactase is an enzyme that breaks down the disaccharide lactose to its component parts, glucose and galactose. Glucose and galactose can be absorbed by the small intestine.

Approximately 65 percent of the adult population produce only small amounts of lactase and are unable to eat unfermented milk-based foods. This is commonly known as lactose intolerance. Lactose intolerance varies widely by ethnic heritage; more than 90 percent of peoples 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 the disaccharide sucrose , commonly known as table sugar, cane sugar, or beet sugar.

Sucrose digestion yields the sugars fructose and glucose which are readily absorbed by the small intestine. Some nutrients are complex molecules for example vitamin B 12 which would be destroyed if they were broken down into their functional groups. To digest vitamin B 12 non-destructively, haptocorrin in saliva strongly binds and protects the B 12 molecules from stomach acid as they enter the stomach and are cleaved from their protein complexes.

After the B 12 -haptocorrin complexes pass from the stomach via the pylorus to the duodenum, pancreatic proteases cleave haptocorrin from the B 12 molecules which rebind to intrinsic factor IF. These B 12 -IF complexes travel to the ileum portion of the small intestine where cubilin receptors enable assimilation and circulation of B 12 -IF complexes in the blood.

There are at least five hormones that aid and regulate the digestive system in mammals. There are variations across the vertebrates, as for instance in birds. Arrangements are complex and additional details are regularly discovered. For instance, more connections to metabolic control largely the glucose-insulin system have been uncovered in recent years.

Digestion is a complex process controlled by several factors. In the mouth, pharynx and esophagus, pH is typically about 6. Saliva controls pH in this region of the digestive tract. Salivary amylase is contained in saliva and starts the breakdown of carbohydrates into monosaccharides. Most digestive enzymes are sensitive to pH and will denature in a high or low pH environment. The stomach's high acidity inhibits the breakdown of carbohydrates within it. This acidity confers two benefits: In the small intestines, the duodenum provides critical pH balancing to activate digestive enzymes.

The liver secretes bile into the duodenum to neutralize the acidic conditions from the stomach, and the pancreatic duct empties into the duodenum, adding bicarbonate to neutralize the acidic chyme , thus creating a neutral environment. The mucosal tissue of the small intestines is alkaline with a pH of about 8. From Wikipedia, the free encyclopedia. For the industrial process, see anaerobic digestion. For the journal, see Digestion journal. A Catalina Macaw 's seed-shearing beak. This section needs expansion with: You can help by adding to it.

Human Biology and Health. Scientific American Library, New York. Living at Micro Scale , p. Harvard University Press, Cambridge, Mass. Secretory Mechanisms and Role in Pathogenesis. A Molecular Approach , 2nd ed. Journal of General Microbiology. Inspiration for design of robust organic composites".

Levi Publishing Co, Inc. US National Library of Medicine. US National Institutes of Health. Retrieved 27 June Physiology of the gastrointestinal system. Submucous plexus Myenteric plexus. Segmentation contractions Migrating motor complex Borborygmus Defecation. Retrieved from " https: Pages with unresolved properties CS1 maint: Views Read View source View history. In other projects Wikimedia Commons Wikiquote.

This page was last edited on 20 April , at By using this site, you agree to the Terms of Use and Privacy Policy. Anatomical terminology [ edit on Wikidata ].

Library resources about Digestive system. Birds use their momentum to travel underwater at an average descent rate of 2. After chasing prey, birds developed an upward momentum before gliding passively back to the surface, making use of their buoyancy to complete the dive at the lowest possible energy cost.

Check the Gannet videos at ARKive. Aerial insectivores -- Swifts depend on flying efficiently and maintaining high speed. Hawking insectivores, like flycatchers , depend on perches located near prey, but they must be able to accelerate rapidly and be very maneuverable. Swallows combine these two strategies; they are fast, maneuverable and able to accelerate when necessary Warrick Although not part of the digestive system in an anatomical sense, some birds, like hawks and owls , use their feet and talons to capture prey.

Typically, raptor prey are killed by the talons of the contracting foot being driven into their bodies; if required, the hooked bill is used to kill prey being held by the talons. The raptor digital tendon locking mechanism -- Digital tendons form a mechanical-locking mechanism in many birds that must maintain a degree of grip force, including perching, hanging, tree-climbing, and raptorial species. In raptors, powerful hindlimb muscles produce a strong grasp, and a tendon locking mechanism TLM helps sustain grip force.

The components of the digital TLM include a 'textured' pad on the ventral surface of each flexor tendon that contains thousands of minute, rigid, well-defined projections called tubercles see figure below.

The neighboring portion of the surrounding tendon sheath contains a series of transversely running plicae folds that often have a proximal slant i. When the flexor tendons are pulled taut, and the digits flexed, the tubercle pad moves proximally over the stationary plicae on the sheath. When resistance to digital flexion is met, the locking elements intermesh and engage and the friction produced prevents slippage of the tendons.

This permits digital flexion to be maintained with little or no muscular involvement E inoder and Richardson Action of the avian digital TLM: This shows the movement of the talon a , flexor e and extensor d tendons, ungual phalanx b , and the movement of the ventrally located tubercle pad f relative to the stationary plicated sheath g and phalangeal bone c From: Einoder and Richardson Each raptor has a unique force production, along with a different time of activity, that would allow for a degree of prey specialization.

Great Horned Owl foot. B Great Horned Owl. The relation between rate of success and direction of movement for a food item that was pulled forward a , backward b and sideways c. Direction of prey progression — dotted arrow 1 , direction of owl flight — dashed arrow 2 , and direction to which the owl had to move its head or trunk — solid arrow 3. Owl picture from Knudsen Movement and direction of prey affect raptor success rate -- Shifferman and Eilam tested a novel idea, that rather than maximizing their distance from a predator during close-distance encounters, prey species are better off moving directly or diagonally toward the predator in order to increase the relative speed and confine the attack to a single available clashing point.

They used two tamed Barn Owls Tyto alba to measure the rate of attack success in relation to the direction of prey movement. A dead mouse or chick was used to simulate the prey, pulled to various directions by means of a transparent string during the owl's attack. This failure to catch prey that move sideways may reflect constraints in postural head movements in aerial raptors that cannot move the eyes but rather move the entire head in tracking prey.

So far there is no evidence that defensive behavior in terrestrial prey species takes advantage of the above escape directions to lower rates of predator success. However, birds seem to adjust their defensive tactics in the vertical domain by taking-off at a steep angle, thus moving diagonally toward the direction of an approaching aerial predator. These preliminary findings warrant further studies in Barn Owls and other predators, in both field and laboratory settings, to uncover fine predator head movements during hunting, the corresponding defensive behavior of the prey, and the adaptive significance of these behaviors.

Barred Owl primary - leading edge below and trailing edge above. The silent flight of owls -- Noise is generated by vortices produced when air flows over a bird's wing and larger vortices produce more noise.

Wings with small saw-toothed projections vortex generators , like those on the leading edge of owl wings, generate many small vortices instead of large vortices and produces less aerodynamic noise. In addition, the fringe feathers at the trailing edge of the wing with fewer hooklets at the ends of the barbs help to break up the sound waves that are generated as air flows over the top of their wings and forms downstream wakes, and the soft down feathers located elsewhere on the wings and legs of owls absorb the remaining sound frequencies above 2, hertz and make owls completely silent to their prey.

As a bonus, with high angles of attack and at slow speeds, vortex generators stick out of the stagnant air near the surface of the wing, and into the freely moving air outside the boundary layer.

This surface layer is typically quite thin, but dramatically reduces speed of the airflow towards the rear of the wing. The vortex generators mix the free stream with the stagnant air to get it moving again, providing considerably more airflow at the rear of the wing and helping to prevent stalling. This process is referred to as 're-energizing the boundary layer.

Unpredictable predators -- The use of space by predators in relation to their prey is a poorly understood aspect of predator-prey interactions.

Classic theory suggests that predators should focus their efforts on areas of abundant prey, that is, prey hotspots, whereas game-theoretical models of predator and prey movement suggest that the distribution of predators should match that of their prey's resources. If, however, prey are spatially anchored to one location and these prey have particularly strong antipredator responses that make them difficult to capture with frequent attacks, then predators may be forced to adopt alternative movement strategies to hunt behaviorally responsive prey.

Roth and Lima examined the movement patterns of bird-eating Sharp-shinned Hawks Accipiter striatus in an attempt to shed light on hotspot use by predators. Their results suggest that these hawks do not focus on prey hotspots such as bird feeders but instead maintain much spatial and temporal unpredictability in their movements. Hawks seldom revisited the same area, and the few frequently used areas were revisited in a manner consistent with unpredictable returns, giving prey little additional information about risk.

But why wouldn't Sharp-shinned Hawks focus their hunting on the areas with the most potential prey bird feeders? One possibility is that behaviorally responsive prey diminish the "hotspot" quality of feeders. Although feeder hotspots are sources of abundant prey, the individuals at such feeders generally benefit from group vigilance as a result of these higher densities. As a result, the vulnerability of the prey may actually be lower at feeders than at other locations.

In addition, unpredictable movement may reflect a sort of "prey management" by predators, whereby predators spread their hunting activity over multiple areas in an effort to avoid inflating the antipredator behavior of their prey. This hunting strategy may be effective when prey are anchored to high-resource areas such as feeders and use antipredator behaviors, such as high vigilance, that reduce a predator's attack success if it attacks frequently and predictably.

Seabirds are choking on ocean plastic video. The tongues of cormorants and other fish-eating species are small because these species swallow prey whole and tongues are not needed to manipulate or position food in the oral cavity. Dorsal view of the surface of the lower bill of a Great Cormorant Phalacrocorax carbo. Arrow shows the tongue with sharpened tip. Scale bar, 12 mm. Lateral view of the cormorant tongue. The tongue and the small anterior and posterior areas of the mucosa of the bill are covered by white keratinized epithelium.

Black arrow shows short base of the tongue. White arrow shows the median crest on the dorsal surface of the tongue. A, anterior; B, posterior. Scale bar, 3 mm Source: Detailed view of the horny tip left of the Guadeloupe Woodpecker tongue in vivo position Villard and Cuisin Dorsal view of the tongue of the Spotted Nutcracker Nucifraga caryocatactes.

Arrows show two elongated processes of the apex. A, apex, B, body, R, root, LP, laryngeal prominence. Scale bar, 3 mm. Lateral view of the tongue of the nutcracker. Arrow shows elongated processes, pointed diagonally, B, body, R, root. Hummingbird tongues are fluid traps, not capillary tubes -- Hummingbird tongues pick up a liquid, calorie-dense food that cannot be grasped, a physical challenge that has long inspired the study of nectar-transport mechanics.

Existing biophysical models predict optimal hummingbird foraging on the basis of equations that assume that fluid rises through the tongue in the same way as through capillary tubes. Rico-Guevara and Rubega found that hummingbird tongues do not function like a pair of tiny, static tubes drawing up floral nectar via capillary action.

Instead, the tongue tip is a dynamic liquid-trapping device that dynamically traps nectar by rapidly changing their shape during feeding. In addition, the tongue—fluid interactions are identical in both living and dead birds, demonstrating that this mechanism is a function of the tongue structure itself, and therefore highly efficient because no energy expenditure by the bird is required to drive the opening and closing of the trap. These results rule out previous conclusions from capillarity-based models of nectar feeding and highlight the necessity of developing a new biophysical model for nectar intake in hummingbirds.

Hummingbird tongue tips twist to trap nectar. How the hummingbird tongue really works with videos. Close encounters with possible prey. You want to live 10—20 years. You are peering under leaves, poking into rolled ones, searching around stems, exploring bark crevices and other insect hiding places. Abruptly an eye appears, 1—5 cm from your bill. The eye or a portion of it is half seen, obstructed, shadowed, partly out of focus, more or less round, multicolored, and perhaps moving.

Now, a safe few meters away, are you going to go back to see whether that was food? Associated body patterns often suggest other head and facial features, which in turn enhance the eye-like nature of the spots.

None of these patterns exactly matches the eyes or face of any particular species of predator; but, even when quickly and partially glimpsed, all give the illusion of an eye or face. These false eyes are mimicking the eyes and faces of such predators of insect-eating birds as snakes, lizards, other birds, and small mammals, as perceived at close range by the insectivorous birds in their natural world.

Note the distended throat of this American Kestrel. Pigeons generally lay two eggs one day apart, which hatch 18 days after they are laid. A similar substance is produced by flamingos and male Emperor Penguins. The normal function of the crop is food storage. Pigeon 'milk' also contains IgA antibodies and antioxidants carotenoids. The avian stomach is divided into 2 parts:.

Photomicrograph 50X of a cross section through the proventriculus showing folds of mucous membrane P ; deep proventricular glands GP ; capsule connective tissue around the glands arrow head ; muscle layer m ; serosa connective tissue with blood vessels S , and the lumen L From: Photomicrograph X of longitudinal section of the gizzard showing folds of mucous membrane lined by simple prismatic epithelium P ; simple tubular glands Gs in the lamina propria constituted by connective tissue Lp ; secretion of glands S that are continuous with the cuticle or koilin ; C , part of muscle layer m , interpersed with bundles of connective tissue Tc From: Photomicrograph X of the koilin of an Eclectus Parrot Eclectus roratus.

Note the regular, columnated structure of the koilin layer K and its association with the glandular epithelium E of the ventriculus From: De Voe et al. A, koilin, B, crypts, C, glands that secrete koilin, D, epithelial surface, E, desquamated epithelial cells, 2 Mucosa of the gizzard. A, koilin, B, secretion in gland lumens and crypts, and 3 Koilin layer. A, secretion column, B, koilin-layer surface, C, horizontal stripe indicating a 'pause' in secretion of the koilin, D, cellular debris.

Eglitis and Knouff Vultures of the seas -- Animals are primarily limited by their capacity to acquire food, yet digestive performance also conditions energy acquisition, and ultimately fitness. Optimal foraging theory predicts that organisms feeding on patchy resources should maximize their food loads within each patch, and should digest these loads quickly to minimize travelling costs between food patches.

GPS-tracking of 40 Wandering Albatrosses from the Crozet archipelago during the incubation phase confirmed foraging movements of between — km, giving the birds access to a variety of prey, including fishery wastes. Using miniaturized, autonomous data recorders placed in the stomach of three birds, the first-ever measurements of gastric pH and temperature in procellariformes were obtained. Such low stomach pH gives Wandering Albatrosses a strategic advantage because it allows a rapid chemical breakdown of ingested food and rapid digestion.

This is useful for feeding on patchy, natural prey, but also on fishery wastes, which might be an important additional food resource for Wandering Albatrosses. It is likely that this physiological characteristic evolved as a response to a diet largely composed of squid, and to a patchy distribution of this food resource resulting in large, infrequent meals.

The strategy of Wandering Albatrosses is to cover long distances rapidly and at low costs to increase the probability of encountering dispersed prey patches whose distribution is unpredictable. Knots with large gizzards consumed far more molluscs with shells than the birds with smaller gizzards.

Birds with smaller gizzards simply couldn't feed fast enough. By allowing them to crush more shell per gizzard-full, larger gizzards gave birds the edge. Thus, even though it is energetically costly for the knots to maintain a larger gizzard, when the bird needs to get the most out of its crunchy diet, it's a price worth paying. So, the birds' gizzards enlarge as they fatten for migration. Because the molluscs' shells stay the same size as the molluscs shrink, the amount of shell a bird must process to eat its fill also increases.

But with their larger gizzards, the birds can still make the most of even the crunchiest winter diet! Within 14 days, they showed a doubling of the size of their gizzards. Red Knots have strong muscular gizzards for feeding on molluscs.

A shift back to a mussel diet induced about a doubling in gizzard mass in just a few days. As the knots were fed progessively smaller mussels day 22 to day 46 that are easier to crush, gizzard mass again declined. A switch back to a soft food pellet diet caused a further decline in gizzard mass. Finally, a switch back to a mussel diet again cause a rapid increase in gizzard mass From: Piersma and Drent Ostrich Struthio camelus stomach. Note how particle size of material in the gizzard ventriculus is smaller than in the proventriculus due to the grinding action of the muscular walls plus small pebbles gastroliths.

The capacity to reduce particle size is related to the metabolic demands of a species. Therefore, particle size reduction is often considered the key digestive difference between ecto- and endotherms that allows endotherms to rely on shorter digesta retention times without losing digestive efficiency, and hence facilitate the high level of food intake necessary to meet their increased metabolic requirements.

In contrast, adaptations for chewing intrinsically increase the weight of the head. The use of the gizzard system has the potential advantages that intake rate is not limited by chewing, that no investment in dental tissue is necessary, and that dental wear is not a determinant of senescence as observed in mammals.

The absence of age-dependent tooth wear might even be a contributing factor to the slower onset of senescence in birds as compared to mammals. On the other hand, the use of a gizzard requires the intake of suitable grit or stones—an action that represents, in the few studies where this has actually been quantified in birds, a relevant proportion of feeding time Fritz et al. Gastrointestinal tracts of a carnivorous hawk, an omnivorous chicken, and 4 herbivorous birds. Note larger size of crop in omnivore and herbivores, and particularly in hoatzin.

Ceca are small in hawks and relatively large in grouse. Although ceca are relatively small in Hoatzins , Emus, and Ostriches, an expanded foregut Hoatzins , a much longer midgut Emus , or a much longer colon Ostriches compensates for this From: Stevens and Hume This section discusses related diseases, medical associations with the gastrointestinal tract, and use in surgery.

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Science of everyday things: The Journal of Biological Chemistry. Agency for Healthcare Research and Quality. Journal of Clinical Investigation. Retrieved 19 May Human systems and organs. Fibrous joint Cartilaginous joint Synovial joint.

Skin Subcutaneous tissue Breast Mammary gland. Myeloid Myeloid immune system Lymphoid Lymphoid immune system. Genitourinary system Kidney Ureter Bladder Urethra. Anatomy of the mouth. Vermilion border Frenulum of lower lip Labial commissure of mouth Philtrum.

Hard palate Soft palate Palatine raphe Incisive papilla. Parotid gland duct Submandibular gland duct Sublingual gland duct. Oropharynx fauces Plica semilunaris of the fauces Uvula Palatoglossal arch Palatopharyngeal arch Tonsillar fossa Palatine tonsil.

Anatomy of the gastrointestinal tract , excluding the mouth. Muscles Spaces peripharyngeal retropharyngeal parapharyngeal retrovisceral danger prevertebral Pterygomandibular raphe Pharyngeal raphe Buccopharyngeal fascia Pharyngobasilar fascia Piriform sinus. Sphincters upper lower glands. Suspensory muscle Major duodenal papilla Minor duodenal papilla Duodenojejunal flexure Brunner's glands.

Ileocecal valve Peyer's patches Microfold cell. Ascending colon Hepatic flexure Transverse colon Splenic flexure Descending colon Sigmoid colon Continuous taenia coli haustra epiploic appendix. Retrieved from " https: Abdomen Digestive system Endocrine system Routes of administration. Pages with unresolved properties All articles with unsourced statements Articles with unsourced statements from March Articles with unsourced statements from May Articles with unsourced statements from October Views Read Edit View history.

In other projects Wikimedia Commons. This page was last edited on 7 September , at By using this site, you agree to the Terms of Use and Privacy Policy. Diagram of stomach, intestines and rectum. Tractus digestorius mouth to anus , canalis alimentarius esophagus to large intestine , canalis gastrointestinales stomach to large intestine. Anatomical terminology [ edit on Wikidata ]. Esophagus, Stomach, Duodenum 1st and 2nd parts , Liver, Gallbladder, Pancreas, Superior portion of pancreas Note that though the Spleen is supplied by the celiac trunk , it is derived from dorsal mesentery and therefore not a foregut derivative.

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