HUMAN DIGESTIVE SYSTEM
Human digestive system consists of -
1.alimentary canal
2.digestive glands
ALIMENTARY CANAL starts with mouth (anterior) and ends or opens outside through anus (posterior).
MOUTH - It is a transverse slit bounded by two movable lips : upper and lower which are lined with mucous membrane on the inner side.It leads into vestibule.
VESTIBULE - It is a narrow space enclosed between lips and cheeks externally and gums and teeth internally.
BUCCAL CAVITY (oral cavity) - Large space lined with stratified squamous epithelium , bounded above by palate , below by throat and on sides by jaws.Its parts are as follows-
a.Palate - roof of the mouth in humans and other mammals.
i.The anterior part of the palate is supported by bones and is strong - Hard palate
ii.The posterior part of palate is smooth and fleshy - Soft palate
Function - They help in mastication of food (mixing of food with saliva).
b.Tongue - It is a large muscular and highly mobile organ which mainly lies in the oral cavity and partly in the pharynx. It contains sensory papillae which contain taste buds.
c.Teeth - They are present in the jaws and are -
i.Diphyodont : 2 sets of teeth appear during lifetime
-Milk teeth(deciduous teeth)
- Permanent teeth
ii.Thecodont : teeth are embedded in the sockets of bone on the jaws
iii.Heterodont : teeth are of different types
-Incisors : chisel shaped for cutting and biting
-Canines : pointed for tearing and piercing
-Premolar : broad and grooved for crushing and grinding
-Molar : broad and grooved for crushing and grinding ; molars are present in
permanent set only
Dental formula for-
Adults −
= 32 teeth in total
whereas temporary set has only 20 teeth
Structure of teeth-
PHARYNX - The pharynx is about 12 cm long and vertical canal beyond soft palate.It is of three types-
a.Nasopharynx : upper part of pharynx ; has internal nares on the roof and pair of openings of estuachian tube on sides leading to middle ear.
b.Oropharynx : middle part of pharynx into which oval cavity opens
c.Laryngopharynx : lower part of pharynx which leads into oesophagus(food pipe) behind and larynx infront. The opening to larynx is known as glottis which bears a leaf-like cartilegenous flap epiglottis.
OESOPHAGUS - Oesophagus is about 25 cm long narrow,muscular and straight tube lined by stratified squamous epithelium containing mucous glands ; acts as a passage of food into stomach by peristalsis : involuntary movement of gut by which food is pushed backward.
STOMACH - J- shaped muscular sac having greater curvature and lesser curvature on the lower and upper side . The stomach wall contains three muscle layers : outer longitudinal , middle circular and inner of oblique fibres.
It is divided into 4 main regions -
i.Cardiac part : left, broad and upper part into which oesophagus opens and this opening is known as cardiac aperture regulated by cardiac sphincter.
ii.Fundus (or Formix) : small , upper part projecting above the cardiac part; usually contains gas or air.
iii.Body : main middle region
iv.Pyloric part : narrow lower portion of stomach ; leads into duodenum and its opening is called pyloric aperture guarded by pyloric sphincter.
SMALL INTESTINE - longest part of alimentary canal(about 6 metre long).It consists of three parts:
i.Duodenum: It foolows stomach ; about 25 cm long ; shortest and widest part of small intestine ;
contains the opening of hepatopancreatic duct(union of bile duct and pancreatic duct).
ii.Jejunum : middle part of small intestine ; about 2.4 metres long ,walls are thick and highly vascular
iii. Ileum : lower part of small intestine ; about 3.6 metres long.
LARGE INTESTINE - It is about 1.5 metres long and is wider than small intestine.It consists of following parts:
i.Appendix : vestigial organ
ii.Caecum : just 6 cm wide ; at the junction of ileum and caecum ,there's presence of ileocolic valve
iii.Colon : contains three main regions - ascending , transverse and descending
iv.Rectum : about 15 to 20 cm long ; bears longitudinal folds and large blood vessels
ANUS -lies at the base of abdomen;opening of anal canal to outside ; guarded by internal sphincter of smooth muscle fibres and external sphincter of striated muscle fibres.
Human digestive system consists of -
1.alimentary canal
2.digestive glands
MOUTH - It is a transverse slit bounded by two movable lips : upper and lower which are lined with mucous membrane on the inner side.It leads into vestibule.
VESTIBULE - It is a narrow space enclosed between lips and cheeks externally and gums and teeth internally.
BUCCAL CAVITY (oral cavity) - Large space lined with stratified squamous epithelium , bounded above by palate , below by throat and on sides by jaws.Its parts are as follows-
a.Palate - roof of the mouth in humans and other mammals.
i.The anterior part of the palate is supported by bones and is strong - Hard palate
ii.The posterior part of palate is smooth and fleshy - Soft palate
Function - They help in mastication of food (mixing of food with saliva).
b.Tongue - It is a large muscular and highly mobile organ which mainly lies in the oral cavity and partly in the pharynx. It contains sensory papillae which contain taste buds.
c.Teeth - They are present in the jaws and are -
i.Diphyodont : 2 sets of teeth appear during lifetime
-Milk teeth(deciduous teeth)
- Permanent teeth
ii.Thecodont : teeth are embedded in the sockets of bone on the jaws
iii.Heterodont : teeth are of different types
-Incisors : chisel shaped for cutting and biting
-Canines : pointed for tearing and piercing
-Premolar : broad and grooved for crushing and grinding
-Molar : broad and grooved for crushing and grinding ; molars are present in
permanent set only
Dental formula for-
Adults −
= 32 teeth in totalwhereas temporary set has only 20 teeth
Structure of teeth-
PHARYNX - The pharynx is about 12 cm long and vertical canal beyond soft palate.It is of three types-
a.Nasopharynx : upper part of pharynx ; has internal nares on the roof and pair of openings of estuachian tube on sides leading to middle ear.
b.Oropharynx : middle part of pharynx into which oval cavity opens
c.Laryngopharynx : lower part of pharynx which leads into oesophagus(food pipe) behind and larynx infront. The opening to larynx is known as glottis which bears a leaf-like cartilegenous flap epiglottis.
OESOPHAGUS - Oesophagus is about 25 cm long narrow,muscular and straight tube lined by stratified squamous epithelium containing mucous glands ; acts as a passage of food into stomach by peristalsis : involuntary movement of gut by which food is pushed backward.
STOMACH - J- shaped muscular sac having greater curvature and lesser curvature on the lower and upper side . The stomach wall contains three muscle layers : outer longitudinal , middle circular and inner of oblique fibres.
It is divided into 4 main regions -
i.Cardiac part : left, broad and upper part into which oesophagus opens and this opening is known as cardiac aperture regulated by cardiac sphincter.
ii.Fundus (or Formix) : small , upper part projecting above the cardiac part; usually contains gas or air.
iii.Body : main middle region
iv.Pyloric part : narrow lower portion of stomach ; leads into duodenum and its opening is called pyloric aperture guarded by pyloric sphincter.
SMALL INTESTINE - longest part of alimentary canal(about 6 metre long).It consists of three parts:
i.Duodenum: It foolows stomach ; about 25 cm long ; shortest and widest part of small intestine ;
contains the opening of hepatopancreatic duct(union of bile duct and pancreatic duct).
ii.Jejunum : middle part of small intestine ; about 2.4 metres long ,walls are thick and highly vascular
iii. Ileum : lower part of small intestine ; about 3.6 metres long.
LARGE INTESTINE - It is about 1.5 metres long and is wider than small intestine.It consists of following parts:
i.Appendix : vestigial organ
ii.Caecum : just 6 cm wide ; at the junction of ileum and caecum ,there's presence of ileocolic valve
iii.Colon : contains three main regions - ascending , transverse and descending
iv.Rectum : about 15 to 20 cm long ; bears longitudinal folds and large blood vessels
ANUS -lies at the base of abdomen;opening of anal canal to outside ; guarded by internal sphincter of smooth muscle fibres and external sphincter of striated muscle fibres.
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