4/5/2012 Avian digestion I. Introduction A. Shapes II. Taxonomy of food habits B. Grinding Function A. Herbivores C. Crop Milk B. Carnivores D. Other Functions A wonderful bird is the pelican, III. Mouth and Pharynx V. Stomach His bill will hold more than his belly can. A. Bill A. Proventriculus He can take in his beak B. Palate B. Ventriculus Food enough for a week, C. Tongue VI. Small Intestine But I'm damned if I see how the hell he D. Salivary Glands A. Duodenum can. IV. Esophagus and Crop B. Function A. Storage --Dixon Lanier Merritt (1879-?) The Pelican (1910) I. Introduction Digestive system needs to be as light as possible High metabolic rates require large extremely efficient amounts of fuel warbler might eat 80 percent of its body weight in a day! 1 4/5/2012 Loss of teeth and minimum jaw musculature Problem for birds – need to keep low body weight Thus, little fat storage need to locate, ingest, digest food as quickly and efficiently as possible Stellar’s Sea Eagle Major components of avian digestive system II. Taxonomy of food habits • oral cavity Many birds are generalists but many are also specialists • pharynx • esophagus (+ crop) Specializations are evident through the entire alimentary • stomach (proventriculus, canal. ventriculus) • small intestine • large intestine • cloaca 2 4/5/2012 As a group birds consume about any kind of food A. Herbivores ants nectar Granivores buds pollen Frugivores crustaceans roots Nectivores fish sap Folivores fruit snails grass wax insects etc. leaves B. Carnivores III. Mouth and Pharynx Raptors A. Bill Insectivores Function – seize, kill, prepare food for swallowing Piscivores Mollusc-eaters Correlation between food and food handling machinery is often obvious 3 4/5/2012 A. Bill Heron - Stabbing American Avocet - Forceps Blue-winged Teal – Filter Bill size can be important for “niche partitioning” A. Bill Structure – bony framework covered by tough layer of keratin (sheath) - rhamphotheca rhamphotheca continuously replaced as worn Bone 4 4/5/2012 edges of the bill are especially hard and Bill shape sharp and are called 'tomia', singular typically doesn’t 'tomium' vary between sexes B. Palate Rictal bristles – sensory function, Mouth roofed with hard palate prey capture Floor membranous choanal cleft no soft palate salivary glands taste buds 5 4/5/2012 C. Tongue Typically small, covered with a cornified epithelium, sharply pointed Parrots – very muscular •barbed Most species – few intrinsic muscles Poorly supplied with taste buds 6 4/5/2012 Tactile corpuscles widely • tubular distributed on tongues of •brushy woodpeckers and finches Parrots - high # on bill D. Salivary Glands Piscivores – few Serous – produce enzymes Granivores – dense Mucous – produce polysaccharides Woodpeckers Density of glands depends on diet Usually present in pharynx Also secrete amylase 7 4/5/2012 Swifts and Swallows Edible Swiftlet Hong Kong largest consumer of bird nests, http://news importing about a hundred tons every year, at a Many use dried saliva to cement their nests price of about U.S. $25 million. Suppliers are Indonesia, Malaysia, Myanmar, Singapore, southern parts of India, Sri Lanka, Thailand, and Vietnam. IV. Esophagus and Crop Salivary glands enlarge ~ 50x Esophagus – tube connecting oral cavity and stomach during nest-building • produces peristalsis • large in diameter (relative to other verts) Chimney Swift ~ 12x • usually provided with mucous glands and somewhat muscular Gray Jay – secrete sticky saliva • lined with heavy epithelium for caching food 8 4/5/2012 Large structure for food storage –Crop A. Storage Food can be stored ~ 1 day+ Seed-eating finches - side of esophagus has paired out - pockets for storage (swallowed or regurgitated for nestlings) If amylase in saliva some digestion occurs in crop Geese pack full of food B. Shapes C. Grinding Function Variable in shape across taxonomic groups Hoatzin – crop serves as grinding organ Muscular, numerous glands, contains bacteria Fusiform – Trochlidae, Emberizidae Bilobed – Columbiformes Single Sac – Falconiformes, House Sparrows 9 4/5/2012 D. Crop Milk Estrogen Æ Growth of lining Æ Prolactin Æ Shedding Provides food for young 25-35% lipid Stratified epithelial lining proliferates under effect estrogen 10-15% protein 70% water E. Other Functions Greater Prairie Chicken – anterior end modified Mourning Dove – as resonating chamber • proliferation of lining begins after 8 days incubation • sloughing 14 – 18 days Air forced into sac from trachea via pharynx • continues to 16 days after hatching 10 4/5/2012 Flamingoes and male Emperor Penguins Male E. Penguins incubate alone and Oily esophageal secretion females don’t return to nest ~ 7 days after hatching 59% protein 28% lipid Male has to provide some food Chicks double body weight on this alone!!! V. S t o m a c h Birds possess two kinds of stomachs: Anterior glandular stomach Posterior muscular stomach 11 4/5/2012 A. Proventriculus Spindle-shaped glandular stomach – avian innovation Initial site of protein digestion Not found in reptiles • HCl (pH 0.2 – 1.2) •proteases Size related to bulk of food intake • chitinases Large – piscivores, frugivores, granivores B. Ventriculus Strong muscular organ (granivores) Fruit eaters – glands secrete mucous only, ventriculus has Prepares food for digestion (analog of teeth) appearance of proventriculus Mucous glands present in walls – secrete koilin lining 12 4/5/2012 Functions as principle barrier to indigestible material • In granivores may contain grit •feathers • lined with tough, abrasive, keratin layer (koilin) – cutica gastrica •hair •bone • teeth Seasonal change in in structure of stomachs corresponding to seasonal change in diet avian gastrointestinal tract - distinct reverse peristaltic movements (Duke Bearded Tits 1994). Winter diet – seeds, stomach 0.88 – 1.2g allows material in the gizzard to reenter Summer diet – insects, stomach 0.5 – 0.6g the proventriculus for additional treatment with acid and pepsin. 13 4/5/2012 VI. Small Intestine A. Duodenum Chief organ of digestion and absorption Histologically – not clearly differentiated from rest of stomach Once food enters intestine undergoes complete 1st loop after stomach chemical ateration via enzymes Contents mixed and absorbed by intestinal mucosa Anatomy Small intestine Receives – bile ducts, duodenal loop pancreatic ducts and ilium secretions from glands in mucosa generally shorter than mammals 14 4/5/2012 Secretions B. Function Amylase Saccharidases 1. Enzymatic activity – carbohydrases, lipases, proteases, and nucleases Peptidases 2. Primary site of absorption – by time product Lipase reaches large intestine it is completely absorbed Maltase, isomaltase Sucrase Enterokinase Secretin, CCK, vasoactive intestinal peptide 3. Length variable – varies with diet, 4. Retention time related to diet Long and tightly coiled– granivores, omnivores Long – granivores Short – carnivores, frugivores Short and slightly coiled – raptors, insectivores frugivores 15 4/5/2012 C. Lining Villi contain blood vessels, lymph vessels that absorb Lined with villi – projections that increase surface area nutrients for transport available for absorption. VII. Large Intestine Primary function is for water & electrolyte Contains minimum amount of non-digestable waste reabsorption • wastes voided as quickly as possible No relation between diet and structure • wastes sometimes voided in other ways Relatively short organ (e.g. pellets) 16 4/5/2012 VIII. Intestinal Caeca Has out-pockets called caeca Posterior end of intestine occur pair of caeca Size variable Large – Folivores (Cranes, ducks, geese) Small – Falcons, woodpeckers, insectivores, passerines, piscivores Absent - Parrots The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. 17 4/5/2012 IX. Cloaca Functions: A. Structure and Function 1. Absorption of water Receives waste from large intestine and materials from urinary and reproductive systems 2. Absorption of non-protein nitrogen 3. Digestion of carbohydrates and proteins 4. Microbial breakdown of cellulose 5. Microbial synthesis of vitamins(?) B. Bursa of Fabricus Divided into 3 sections Located on dorsal wall of cloaca • Coprodaeum – receives waste from large intestine Lymphatic pocket prominent in young birds but atrophied • Urodaeum – receives urine from kidneys (via in adults ureters), sperm and eggs from gonads • Proctodaeum – stores (temporarily) and ejects materials; closed posteriorly by muscular anus 18 4/5/2012 The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. Serves as the area where B – lymphocytes (wbc that produce antibodies) are generated. Once produced B – lymphocytes migrate to lymphoid tissue in other parts of body. Farmer and Breitenbach (1966) inoculated 2 wk old Now - Go take the Test! chickens with malaria ½ had Bursa Fabricus removed Controls recovered, but 11 of 15 bursectomized died 19 4/5/2012 Motility Food in the mouth stimulates salivation and swallowing Food in the esophagus or crop is directed by the gizzard contraction state Coordinated gastroduodenal contractions thin muscles-> duodenum-> thick muscles- > proventriculus about 3 cycles per minute Motility Regulation of feeding Refluxes of GI contents Body weight and age gizzard to proventriculus Environmental temperatures small intestine to gizzard Day Length cloaca to colon or rectum Activity Egestion Reproductive cycle Passage rate Food quality Water availability Food energy content 20 4/5/2012 Digestibility In birds, because of the combined urine and fecal excretion, metabolizability is usually determined rather than digestibility 21.