Human alimentary canal

Human alimentary canal

The alimentary canal of human consist of following parts:
Mouth :mouth is a small transverse aperture present below nose ,boardered by fleshy lips.it helps in holding food.
Vestibule : the mouth opens into a narrow ,vertical,slit like space called vestiule.it is bounded by lips and teeth.it is lined by mucous membrane.

Buccal cavity : the space situated between two jaws is called buccal cavity.it is lined by mucuous membrane.it contain following parts :

Palate:the roof of buccal cavity is made up of palate.it is the wall between buccal cavity and nasal cavity.anterior palate is called hard palate and posterior is called soft palate.the posterior part of soft palate hangs freely called uvula and it closes internal nares during swallowing process.

Tongue :
tongue is a freely movable muscular organ attached to the floor of the buccal cavity by the frenulum. The upper surface of the tongue has small projections called papillae, some of which bear taste buds. base of tongue is attached to hyoid bone.surface of tongue is lined by stratified squamous epithelium.

Teeth : in human teeth are present in both jaws.the teeth are thecodont i.e embeded in sockets of jaw bones, diphyodont i.e only two sets of teeth are formed in lifetime amd heterodont i.e variety of teeth are found.the first set of teeth is milk teeth which is replaced by permanent dentition in adult stage.

Structure of tooth:

The toooth is formed of epidermis and dermis both.a tooth cn be divided into three parts:

Crown: the crown consist of enamel and dentine.enamel is harsest non living substance in body and dentine is hardest living substance.dentine contain high network of canaliculies.dentine,internally contain pulp cavity which is lined by odontoblast cells.pulp cavity contain connective tissue,blood vessels and nerve endings.

Neck: neck lie below the gum and is supported by muscular gum.it separate crown and root.

Root:
root is covered by bony cement layer. blood vessels and nerves pass into teeth through the foramen at apex of root.root is embeded in the socket of jaw bones.root internally contain dentine and pulp cavity. number of root differs in types of teeth.

Tonsils: two oval lymphoid tissues are present in posterior side of buccal cavity called as palatine tonsils.they produce b-lymphocytes which kills the germs in food.tonsil often get inflammed causing tonsilities.

Pharynx: buccal cavity opens into short narrow chamber,pharynx. pharynx can be divided into naso,oral and laryngeal.pharynx is crossing of both food and air.the laryngopharynx opens into trachea through glottis ,situated jusst below the floor of pharynx.glottis is protected by cartilagenous flap of skin called epiglottis.larynxo pharynx opens into oesophagus through gullet. pharynx is internally lined by squamous epithelium.

Oesophagus:
pharynx opens into long,muscular and narrow elastic tube called oesophagus. it runs parallel to trachea.it contain two spinhter which prevent the regurgitation of food.cricopharyngeal spinchter is found between pharynx and oesophagus while cardiac spinhter is found between oesophagus and stomach.oesophagus enters abdominal cavity by piercing diaphragm.it helps in pristaltic movement of food.

Stomach:




The stomach is situated in the upper left portion of the abdominal cavity, has three major parts i.e a cardiac portion into which the oesophagus opens, a fundic region and a pyloric region which opens into duodenum.it is the thickest part of alimentary canal.the stomach connects with oesophagus and duodenum at cardiac and pyloric orfice respectively.cardiac and pyloric spinchter prevent the regurgitation of food.its inner wall is folded and folds disappears when stomach is full.

Small Intestine:
stomach leads into a long,much coiled,tubular organ,the small intestine. Small intestine is distinguishable into three regions, a ‘U’ shaped duodenum, a long coiled middle portion jejunum and a highly coiled ileum. The opening of the stomach into the duodenum is guarded by the pyloric sphincter.

Duodenum: it is smallest part of small intestine.it is u-shapes and it receives common hepato-pancreatic duct through spinchter of oddi.its inner wall contain brunner's gland.

Jejunum: 
it is the middle part of small intestine.it contain villi and help in absorption of food.

Ileum: it is distal part of small intestine.it opens into caecum.their opening is guarded by ileocaecal valve.it is provided with villi.its inner wall contain gland called crypts of lieberkuhn.active absorption takes place in ileum.

Large Intestine:
 Ileum opens into the large intestine. It consists of caecum, colon and rectum. 

Caecum: it isa blind sac which hosts some symbiotic micro-organisms.it consist of vestigeal vermiform appendix.in hervivores,appendix help in digestion of cellulose.

Colon: The caecum opens into the colon. The colon is divided into four parts i.e an ascending, a transverse and a descending colon ans a sigmoid colon. The sigmoid colon opens into the rectum which opens out through the anus. colon externally contain line of muscle cord called taeniae.

Rectum: it is the terminal part of alimentary canal.it opens out the body from anus passing through anal canal.anal canal contain enlarged vains called piles or haemorrhoids.