Cvan finals

• Functions of the digestive system

  • Ingestion
  • Digestion
  • Absorption of food
  • Elimination of undigested food
• Parts of the digestive system

  • Digestive tubes (from mouth to anus)
  • Digestive glands
  • Accessory parts
• Digestive tract/tubes


  Starts from the oral cavity, pharynx, esophagus, stomach and small and large intestines
• Mouth


  • Anterior opening of the digestive tube, serves as an entrance for food
  • In agnathostomes, mouth is at the apex of the buccal funnel where the tongue projects
  • In gnathostomes, mouth varies depending on the size of the food being eaten
  • In fishes, opens in the oro-pharyngeal cavity and ends at the esophagus
  • In tetrapods, opens in the oral cavity and ends at the pharynx
  • In mammals, upper and lower borders are marked by lips covered with skin on the outside, lips and cheeks separated by the gums
  • In birds and turtles, mouth is bounded by horny beaks
• Oral/buccal cavity


  • Starts with the mouth and ends in the pharynx, bounded by the jaws anteriorly and laterally, palate superiorly, buccal floor and tongue inferiorly
• Tongue


  • Movable organ located at the floor of the oral cavity, serves as a sense organ and for food gathering
  • In cyclostomes, bears horny teeth on the surface for grasping
  • In fishes, a crescentic elevation on the floor of the pharynx that can be moved in narrow limits
  • In amphibians, the primary tongue fuses with the glandular field to form the definite tongue
  • In reptiles like turtles and crocodiles, tongue is not protrusile and lies only on the floor of the oral cavity, but in snakes and lizards it can be extended and retracted and also used for catching prey
  • In birds, tongue has no muscles and is a compounded definite type
  • In mammals, tongue is well developed, movable, fleshy and muscular except for whales, contains minute pointed elevations known as papillae that contain receptors not for taste
• Teeth


  • Accessory organs used for cutting, grinding and crushing of food
  • Epidermal teeth - cornified projections seen in cyclostomes, amphibians, larvae, platypus and sirenians
  • Dermal or true teeth - made up of a core dentine surmounted by a crown of enamel, found in the premaxillae, maxillae and mandible
  • Homodont - teeth are similar in form and shape
  • Heterodont - teeth are different in shapes and sizes
  • Monophyodont - with one set of teeth
  • Diphyodont - with two sets of teeth
  • Polyphyodont - with numerous sets of teeth
  • Acrodont - attached to the outer surface or summit of the jaw
  • Pleurodont - attached to the inner side of the jaw
  • Thecodont - occupy bony sockets or alveoli
• Pharynx


  • Tube which is common for both respiratory and digestive system, serves as a food catching device in tunicates, amphioxus and minute organisms
• Esophagus


  • A distensible muscular tube located posterior to the glottis that connects the pharynx and esophagus, length varies depending on the length of the neck
  • In fishes and amphibians, very short and lined with ciliated epithelium
  • In reptiles, long with longitudinal folds for distention
  • In birds, lined with horny papillae and widens into a large sac known as the crop
  • In mammals, length depends on the length of the neck
• Stomach/ventriculus


  • A spindle shape to sacciform enlargement with enzymes and acid secreting glands and thick muscular wall of smooth muscles
  • In fishes, straight, J or V shape with no distinction between the esophagus
  • In amphibians, a straight tube
  • In snakes and lizards, has a spindle stomach
  • In crocodiles, modified into a gizzard-like muscular region
  • In birds, has 2 parts - the anterior proventriculus and ventriculus or gizzard that aids in grinding of food
  • In mammals, larger in herbivores than carnivores, divided into rumen, reticulum, omasum and abomasum in herbivores
• Intestines


  • Usually consist of two main parts - small intestine and large intestine/colon, length varies depending on eating habits
  • In cyclostomes, usually straight
  • In fishes, wide but rather straight
  • In amphibians, small intestines slightly coiled and large intestine short, opens in the cloaca
  • In reptiles, small intestines coiled, elongated and fairly uniform in diameter, 1st vertebrate to have colic cecum
  • In birds, small intestine very long and straight, large intestine short, ends in the cloaca
  • In mammals, small intestine divided into duodenum, jejunum, ileum, large intestine divided into ascending, transverse, descending, sigmoid, rectum, ends in the anus
• Digestive glands


  • Oral glands
  • Liver
  • Pancreas
• Oral glands


  • Numerous multicellular glands in the walls of the oral cavity
  • Mucous secreting glands
  • Serous secreting glands
  • In amphibians, secrete adhesive properties to the tongue
  • In reptiles, upper labial glands secrete poisons
  • In birds except fish-eating birds, present
  • In mammals, small mucous glands - parotid, sublingual, submaxillary, infra-orbital
• Liver


  • Largest gland in the body, responsible for secretion of bile, storage of glycogen and excess sugar, production of urea, control of food and substances in the blood
  • In fishes, large, brownish, found anteriorly in the body cavity
  • In amphibians, large and lobed
  • In reptiles, lobed except in snakes, all have gallbladder
  • In birds, lobed, no gallbladder in many
• Pancreas


  • 2nd largest digestive gland, located behind the liver in the loop between the stomach and duodenum, has islets of Langerhans that produce insulin
  • In cyclostomes and amphioxus, have pancreatic tissues instead of a pancreas
  • In fishes, diffused and almost unrecognizable in many teleosts and dipnoi
  • In amphibians like frogs, present and opens directly to the duodenum and indirectly towards the bile duct
  • In mammals, well developed with a ventral duct that opens into the bile duct and a dorsal duct that enters the duodenum
• All animals need oxygen in their cells and must get rid of carbon dioxide. This is the sole function of the respiratory system. It serves as a route for gaseous exchange between the tissues and the surrounding environment of the body.
• Ways animals obtain oxygen

  • From water or air through a moist surface directly in the body (e.g. earthworm)
  • From air or water through the thin body wall to the blood vessels (e.g. leeches)
  • From water to gill surface to blood vessels (fishes)
  • From air to the moist lung surfaces to the blood vessels
• Phases of respiration


  • External respiration - exchange of gases between the blood and the environment through the respiratory organs
  • Internal respiration - exchange of gases between the blood and the tissue or cells of the body
• Respiratory organs in vertebrates

  • Gills
  • Skin
  • Lungs
• Nasal passages


  • In petromyzontiformes/lamprey, an unpaired nasal canal connected to the nostrils and olfactory sac
  • In fishes, no connection between nostrils and mouth cavity, in elasmobranchs the oronasal groove forms a channel connecting the olfactory pit and mouth, in teleosts water drawn to the mouth passes through the gill slits
  • In amphibians, short and well developed with external and internal nares
  • In reptiles, lower nasal passages with paired palatine folds, in crocodiles the two sets meet at the median line forming a secondary palate
  • In birds, short with external nares at the base of the beak, secondary palate incomplete compared to reptiles
  • In mammals, elongated, large and more complicated, nostrils located in the nose anteriorly, divided into vestibular, respiratory and olfactory regions, have Jacobson's organ as an accessory olfactory device
• Gills


  • Thin walled extensions of the epithelial surface made up of feather-like filaments or gill lamellae rich in capillaries
  • External gills - developed from the epithelium covering the outer surface of the visceral arches
  • Internal gills - developed from the epithelium lining the inner surface of the visceral arches
• Nasal passages in mammals

  • Elongated, large and more complicated compared to lower forms of animals
  • Nostrils located in the nose anteriorly
• Regions of nasal passages in mammals

  • Vestibular region
  • Respiratory region
  • Olfactory region
• Jacobson's organ or vomeronasal organ


  Accessory olfactory device in the recognition of food
• Jacobson's organ first appeared in amphibians and is well developed in lizards and snakes
• Gills


  • Thin walled extensions of the epithelial surface made up of feather like filaments or gill lamellae rich with capillaries
• Types of gills


  • External gills
  • Internal gills
• External gills


  • Developed from the epithelium covering the outer surface of the visceral arches, covered with ectoderm
• Internal gills


  • Series of gill filaments borne on one side or both sides of the interbranchial septum
  • Lamellar type (elasmobranch) with well developed interbranchial septum and rigid comblike gill rakers
  • Filamental type (teleosts) with reduced interbranchial septum and covered operculum
• Amphibian larval gills


  • Integumentary gills with tufts of filaments extending externally, covered with ciliated epithelium
• Swim bladder


  Gas filled diverticulum that arises from the pharyngeal or esophageal region, may be single or bilobed, and may open into the digestive tract dorsally, ventrally or not at all
• Physostomous swim bladders


  Always open
• Physoclistous swim bladders


  Completely closed
• Functions of swim bladder

  • Respiratory organ for fishes in shallow waters
  • Hydrostatic organ
  • Sound production
• Larynx in amphibians


  • Paired cartilage bounding the glottis
  • Upper paired cartilage Arytenoids
  • Lower paired Cricoid
  • Vocal cords
  • Lower rim of vocal cords vibrates as air passes causing sound
  • Male anurans have larger larynx with vocal sacs that act as a resonator
• Larynx in reptiles


  • Not well developed
  • Supported with arytenoids and incomplete cricoid
  • Crocodiles have 3 types of cartilage: cricoid, arytenoid and thyroid
  • Most reptiles cannot produce sound except some lizards like geckos
• Trachea in reptiles


  • Varies in length depending on neck length
  • Left lungs of snakes and lizards are smaller
• Lungs in reptiles


  • Similar to mammalian lungs in crocodiles
• Larynx in birds


  • Not capable of producing sound, the lower end of the trachea (syrinx) is the sound producing organ
• Parts of the syrinx

  • Tracheal syrinx
  • Bronchotracheal syrinx (has a resonating chamber)
  • Bronchial syrinx (found between and enters lung)