Gastrointestinal tract

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In adult doves and pigeons, the crop can produce crop milk to feed newly hatched birds. Aerial insectivores -- Swifts depend on flying efficiently and maintaining high speed. American Journal of Anatomy In the pharynx, the food is lubricated by mucus secretions for easier passage. Owl picture from Knudsen


For example, low pH ranging from 1 to 4 of the stomach is fatal for many microorganisms that enter it. Beneficial bacteria also can contribute to the homeostasis of the gastrointestinal immune system. For example Clostridia , one of the most predominant bacterial groups in the GI tract, play an important role in influencing the dynamics of the gut's immune system.

This is due to the production of short-chain fatty acids during the fermentation of plant-derived nutrients such as butyrate and propionate. Basically, the butyrate induces the differentiation of Treg cells by enhancing histone H3 acetylation in the promoter and conserved non-coding sequence regions of the FOXP3 locus, thus regulating the T cells , resulting in the reduction of the inflammatory response and allergies.

The large intestine hosts several kinds of bacteria that can deal with molecules that the human body cannot otherwise break down.

These bacteria also account for the production of gases at host-pathogen interface , inside our intestine this gas is released as flatulence when eliminated through the anus. However the large intestine is mainly concerned with the absorption of water from digested material which is regulated by the hypothalamus and the re absorption of sodium , as well as any nutrients that may have escaped primary digestion in the ileum.

Health-enhancing intestinal bacteria of the gut flora serve to prevent the overgrowth of potentially harmful bacteria in the gut. These two types of bacteria compete for space and "food," as there are limited resources within the intestinal tract. Enzymes such as CYP3A4 , along with the antiporter activities, are also instrumental in the intestine's role of drug metabolism in the detoxification of antigens and xenobiotics.

There are many diseases and conditions that can affect the gastrointestinal system, including infections , inflammation and cancer. Various pathogens can cause gastroenteritis an inflammation of the stomach and small intestine. These can include those organisms that cause foodborne illnesses. Gastroenteritis is the most common disease of the GI tract. Diverticular disease is a condition that is very common in older people in industrialized countries.

It usually affects the large intestine but has been known to affect the small intestine as well. Diverticulosis occurs when pouches form on the intestinal wall.

Once the pouches become inflamed it is known as diverticulitis. Inflammatory bowel disease is an inflammatory condition affecting the bowel walls, and includes the subtypes Crohn's disease and ulcerative colitis. While Crohn's can affect the entire gastrointestinal tract, ulcerative colitis is limited to the large intestine.

Crohn's disease is widely regarded as an autoimmune disease. Although ulcerative colitis is often treated as though it were an autoimmune disease, there is no consensus that it actually is such. Functional gastrointestinal disorders the most common of which is irritable bowel syndrome. Functional constipation and chronic functional abdominal pain are other functional disorders of the intestine that have physiological causes, but do not have identifiable structural, chemical, or infectious pathologies.

Gastrointestinal surgery can often be performed in the outpatient setting. In the United States in , operations on the digestive system accounted for 3 of the 25 most common ambulatory surgery procedures and constituted 9. Various methods of imaging the gastrointestinal tract include the upper and lower gastrointestinal series:. Animal intestines have multiple uses. From each species of livestock that is a source of milk , a corresponding rennet is obtained from the intestines of milk-fed calves.

Pig and calf intestines are eaten, and pig intestines are used as sausage casings. Calf intestines supply calf-intestinal alkaline phosphatase CIP , and are used to make goldbeater's skin. Many birds and other animals have a specialised stomach in the digestive tract called a gizzard used for grinding up food.

Another feature not found in the human but found in a range of other animals is the crop. In birds this is found as a pouch alongside the esophagus. Other animals including amphibians , birds , reptiles , and egg-laying mammals have a major difference in their GI tract in that it ends in a cloaca and not an anus. From Wikipedia, the free encyclopedia. Redirected from Digestive tract. For other uses, see Guts disambiguation.

Esophagus , Stomach , and duodenum. Development of the digestive system. Duct of gland outside tract 7: Gland in mucosa 8: Glands in submucosa Meissner's submucosal plexus Areolar connective tissue Auerbach's myenteric plexus Oral mucosa and Gastric mucosa. Serous membrane and Adventitia. This section discusses related diseases, medical associations with the gastrointestinal tract, and use in surgery. Gastrointestinal disease and Gastroenterology. Ruminant and Methanogens in digestive tract of ruminants.

This article uses anatomical terminology; for an overview, see Anatomical terminology. Invertebrate Zoology 7 ed. Surgical and Radiologic Anatomy. Factor in achieving total enteroscopy? H; Fava, F; Hermes, G. M; Hold, G; Quraishi, M. G; Hart, A A new clinical frontier". The Neglected Endocrine Organ". Introduction to Behavioral Endocrinology.

Retrieved 2 September Oxford textbook of medicine: 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.

The abomasum is the fourth and final stomach compartment in ruminants. It is a close equivalent of a monogastric stomach e. To evenly distribute load and cut down on vibration, like the hyoid, they added a rubber layer. Woodpecker's head inspires shock absorbers. The unequal length of the upper and lower parts of woodpecker beaks the lower being longer directs the force of impact downwards, away from the brain, when it hits the tree red coloration indicates the greatest force or stess; blue indicates the least force or stress.

Time after impact proceeds from upper left 0. The hyoid of woodpeckers loops over top of the skull to completely surround their skulls. The hyoid helps direct the stress of impact below and around the skull and brain and also acts like a 'safety belt', helping to keep the brain in place. It is the movement of the brain inside the skull during impact, more than the blow itself, that causes concussions. If the brain is held in place, injury risks are greatly reduced.

As in the above figure, time after impact proceeds from upper left to lower right Figures from Wang et al. Built to peck - Segment 2. Built to peck - Segment 4. Built to peck - Segment 5. Built to peck - Segment 6. Built to peck - Segment 7. The capillary ratchet mechanism. Surface tension transport of prey by feeding shorebirds: They peck at the surface, picking up droplets of water with prey inside.

Because their beaks point downward when feeding, gravity must be overcome to get those droplets from the tip of the bird's long beak to its mouth.

This feeding strategy depends on surface tension. As the beak opens and closes, each movement propels the water droplet one step closer to the bird's mouth. Specifically, when the beak closes, the drop's leading edge moves toward the mouth, while the trailing edge stays put. In this stepwise ratcheting fashion, the drop travels along the beak at a speed of about 1 meter per second.

The efficiency of the process, called the "capillary ratchet," depends on beak shape, and long, narrow beaks, like those of phalaropes, are best suited to this mode of feeding.

Serin Serinus serinus with a seed positioned in its bill. Note how the tongue is used to hold the seed in position From: Their data provide the first detailed description of this highly specialized foraging technique. They recorded no or a very low deceleration when Gannets entered the water, which underlines the remarkable streamlining of this large bird.

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.