Transcript digestive
Consisting of two main parts : 1. The alimentary canal or digestive tract. 2. The digestive glands. It consists of several organs: Mouth, vestibule, buccal cavity, pharynx, oesophagus, stomach, small intestine, large intestine and anus. • vestibule and buccal cavity – lined with ectoderm, constitute the stomodaeum. • Posterior part of large intestine (rectum) – lined with ectoderm and forms the proctodaeum. • The rest – lined with endoderm and form the mesodaeum and mesenteron. Subterminal, bound by two soft, movable, hairy lips: upper and lower. The upper lip - hare lip, has a vertical cleft at its middle. Narrow space - Lined by abundant mucous glands. Bounded above by the palate, below by the throat, on sides by the jaws. Anterior part of palate strengthened by bony processes of jaw bones (premaxillae, maxillae, palatines) – called hard palate. Bears transverse ridges – rugae. anterior end - nasopalatine canals. Posterior end – smooth and fleshy – called soft palate. Contains two important structures: tongue and teeth. A highly muscular organ. Filiform papillae all over (Dorsal). Circumvallate papilla (at the base) – Single & large . fungiform papillae (anterior) part. All papillae contain taste buds. Organ of taste, helps in chewing the food under the teeth and swallowing. Bears mucuous glands. Teeth on both the jaws. Homodont (in sockets). Monophyodont - Permanent set (single). Heterodont – two types (incisors – cutting and molars – grinding). Wide toothless space – Diastema. Dental formula – i1/1, c0/0, pm0/0, m3/3 = 16 OR 1003/1003 = 16. V.S of mammalian tooth Alimentary canal of rat With liver and pancreas Tooth – three regions: crown, neck embedded in gum and root. Dentine – covers the greater part, presence of canaliculi and odontoblasts. Pulp cavity – with pulp canal at base has pulp (persistent) with BV, lymph channels and NF. Enamel – shining white top cover. Nasopharynx (upper) – common internal naris at roof, a pair of openings - eustachian tubes on sides. Oropharynx – recieves buccal cavity – leads posteriorly to oesophagus (dorsal), voicebox or larynx (ventral). Opening – glottis – with bilobed cartilage epiglottis. Long straight tube – lined by stratified epithelium with longitudinal folds. Wide, with three parts – 1. Cardiac part – recieves oesophagus, extended cardiac part – fundus. 2. Body of the stomach. 3. Pyloric part – joins intestine. • Two apertures – cardiac aperture with cardiac valve and pyloric aperture with pylorus. • Functions : storage of food, mechanical churning, churning of food, initiation of digestion. Slender, coiled tube, 1 – 1.2 m long. 3 parts : duodenum (recieves bile duct), jejunum and ileum. +ileo-caecal valve – regulates passage of food into caecum. Functions: completion of digestion and absorption of end products of digestion. Long tube, with 3 regions – caecum, colon and rectum. Caecum – a blind sac with distal, conical portion – vermiform appendix. Colon – with 3 regions – ascending, transverse and descending. Rectum – short tube – leads to exterior at the anus. Function: aids in formation and elimination of faeces, plays a role in absorption. At the end of abdomen, under the base of tail, guarded by anal sphincters. Salivary glands, gastric glands, liver, pancreas and intestinal glands. 3 pairs – submaxillary, sublingual and parotid. Salivary gland secretes alkaline juice – saliva (contains enzyme called salivary amylase or ptyalin). Numerous and microscopic, lie in the mucus membrane of stomach. Secrete gastric juice (acidic fluid) which is discharged in the lumen of stomach. Contains hydrochloric acid, pepsinogen (proenzyme), renin enzyme and mucus. Largest gland of body, fits in posterior concavity of the diaphragm. Has 4 lobes : left lateral lobe, medium lobe, right lateral lobe and caudate lobe. Liver secretes Bile, discharges by common bile duct into duodenum. Sphincter of oddi (a sphincter muscle) guards the duct opening into duodenum. A diffused dendritic gland held in mesentery between stomach and duodenum. Composed of minute acini, each acinus enclosed a lumen by a layer of large cells. Secretes pancratin or pancreatic juice (alkaline) through small ductules joined to form large ducts, drain into main pancreatic duct. Between acini are present compact cell masses – islands of langerhans, secrete insulin (hormone). Trypsinogen (proenzyme), chymotrysinogen (proenzyme) and several enzymes : amylase, lipase, nucleases, nucleotidases, etc acts on all types of food. Very numerous and microscopic, lie in the wall of small intestine, pour secretion, intestinal juice into the lumen. Juice is rich in mucus and many enzymes which act on all types of food.