Avian Anatomy Readings PDF

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Avian Respiratory System 1. Compared to mammals, respiratory system of birds contains a simpler larynx, a syrinx, only 4 orders or generations of conducting airways, compact spongy lung, and air sacs 2. Highly efficient avian respiratory system comprises lung tissue positioned between conducting airways and air sacs 3. During inspiration, air is drawn into nasal cavity and through lung tissue to the air sacs a. During expiration, the reverse occurs 4. Birds breathe more slowly and deeply than mammals and lung volume of birds remains relatively constant while the volume of their air sacs changes during ventilation 5. Nasal cavity is lined by epithelia similar to those of mammals with stratified squamous epithelium rostrally, olfactory epithelium dorsocaudally, and respiratory epithelium lining most of the remaining areas a. In respiratory epithelium, groups of goblet cells form intraepithelial glands b. Large air spaces, the paired infraorbital sinuses, are often clinically involved in respiratory infections i. These drain into nasal cavity and are lined by respiratory epithelium 6. Larynx is devoid of vocal folds and produces little sound 7. Trachea is similar in structure to mammals, except that the tracheal cartilages form complete rings encircling the airway a. Cartilage rings overlap and interlock with adjacent rings b. Trachealis muscle is absent and intraepithelial mucous glands are numerous c. Trachea does not undergo phasic changes in diameter during breathing 8. Vocalization occurs in avian syrinx, a specialized region of tracheobronchial junction with considerable species-dependent structural variation a. Intrasyringeal (tympaniform) membranes vibrate during sound production and are lined by stratified squamous epithelium 9. Lungs comprise primary, secondary, and tertiary bronchi, atria, and air capillaries a. Extrapulmonary primary bronchi continue as intrapulmonary primary bronchi or mesobronchi, each of which terminates by opening into an abdominal air sac b. Epithelium of the primary bronchi is similar to that of the trachea c. Bronchial cartilages are incomplete medially in proximal portion of bronchi and are patchlike more distally d. Secondary bronchi arise from each intrapulmonary primary bronchus and many open into other air sacs e. Tertiary bronchi, AKA parabronchi, interconnect the secondary bronchi f. Epithelium varies from respiratory epithelium in secondary bronchi to simple cuboidal or squamous epithelium in the tertiary bronchi g. Network of spiraling bundles of smooth muscle occurs in the lamina propria of secondary and tertiary bronchi h. Numerous small air spaces, AKA atria, open into tertiary bronchi i. Projecting tips of interatrial septa contain smooth muscle and are lined by squamous cells 10. Gas exchange occurs between blood and air capillaries a. Capillaries open into atria

b. Simple squamous epithelium lines the greater portion of the atria and air capillaries c. Epithelial portion of gas exchange area consists of both type I and type II cells similar to those of mammals i. Biphasic fluid lining layer, similar to surfactant, is also observed in birds 11. Terminal air sacs are lined by simple squamous to cuboidal epithelium a. Epithelial surfaces adjacent to bronchi are ciliated Avian Respiratory System 1. Oral cavity is lined throughout by a keratinized stratified squamous epithelium 2. Propria-submucosa contains diffuse lymphatic tissue and salivary glands 3. Tongue is covered by a keratinized stratified squamous epithelium and contains bundles of skeletal muscle, lingual salivary glands, and a bone- the entoglossal bone a. Taste buds are found only on the base of the tongue and floor of the oral cavity b. All salivary glands are branched tubular mucous glands with openings into a common cavity from which an excretory duct leads to the oral cavity 4. Esophagus is similar in structure both cranial and caudal to the crop a. Thick, keratinized stratified squamous epithelium b. Lamina propria is a loose CT containing large mucous glands c. Lamina muscularis consists of longitudinally arranged smooth muscle fibers d. Submucosa consists of a thin layer of loose CT e. Tunica muscularis is composed of a thick inner circular layer and a thin outer longitudinal layer of smooth muscle 5. Crop is a saclike diverticulum of the esophagus a. Storage organ where the ingested food is moistened by the mucous secretions of the esophageal glands b. Glands are restricted to an area near its junction with the esophagus 6. Bird does not have a glandular stomach similar to that of mammals but instead has 2 separate organs between the esophagus and duodenum a. Proventriculus= glandular stomach b. Ventriculus= muscular stomach i. Both perform many of the functions of the mammalian stomach 7. Mucosa of the proventriculus is characterized by macroscopic papillae with numerous macroscopic folds (plicae) a. Plicae are of varying heights and arranged concentrically around the single duct opening at the apex of each papilla b. Simple columnar epithelium covers the plicae and continues into 3 generations of ducts of the proventricular glands c. Glands are lined by simple cuboidal to low columnar epithelium in which the adjacent cells are in direct contact only on their basal half, giving a serrated appearance to the luminal surface d. One cell type is identifiable- the oxynticopeptic cell i. Produces both pepsinogen and hydrochloric acid e. Lamina propria is loose CT

f.

Lamina muscularis is split into a very thin layer and a thick outer layer by the proventricular glands g. Typical 2 layered tunica muscularis consisting of entirely smooth muscle underlies loose CT of very thin submucosa h. Proventriculus is covered by a typical serosa 8. Ventriculus (gizzard) is highly muscular and responsible for grinding and macerating the ingesta a. Lining is referred to as the cuticle or koilin membrane i. Koilin- secretory product produced by mucosal glands and surface epithelial cells 1. NOT a stratum corneum 2. Glands form hard koilin rod clusters, which enter the membrane and are separated by soft koilin produced by the surface epithelial cells b. Surface epithelium is simple columnar while surface epithelium of simple, branched tubular mucosal glands is simple cuboidal c. Lamina of the glands are filled with secretory product, which stains bright red with keratohyalin stains d. Lamina propria and submucosa are both loose CT e. Lamina muscularis is discontinuous f. Tunica muscularis is s single thick layer of parallel smooth muscle cells that spread from 2 aponeuroses at the center of the organ i. Criss-crossed by bands of dense CT ii. Outermost tunic is a typical serosa 9. Small intestine is similar to mammals histologically a. Lamina propria submucosa contain large amounts of diffuse and nodular lymphatic tissue i. Submucosal glands of duodenum are generally absent b. Tunica muscularis is composed of inner circular and outer longitudinal layers of smooth muscle c. Outermost tunic is typical serosa 10. 2 ceca open into digestive tract at the junction of the ileum and rectum a. Proximal portion contains prominent villi i. In adult birds, large masses of diffuse and nodular lymphatic tissue infiltrate the lamina propria and submucosa, forming grossly visible cecal tonsils b. In middle region, villi are shorter and broader and mucosal folds are present c. Distal ceca are devoid of villi d. Surface epithelium of mucosa is simple columnar with goblet cells 11. Rectum is part of the large intestine a. Extends from ileum to coprodeum of the cloaca b. Resembles small intestine in that villi are present c. Scattered diffuse and nodular lymphatic tissues occur in the lamina propria and submucosa

12. Cloaca- divided into 3 parts a. Coprodeum, urodeum, and proctodeum are separated by transverse folds b. All 3 parts have similar structure c. Villi are present d. Epithelium of mucosa is simple columnar e. Cloacal bursa opens into proctodeum 13. Liver, gallbladder, and exocrine pancreas are similar to that of mammals...