The name large intestine is due to large diameter(4-6cm).
(1) Structure :
Endodermal ,approximately 1.5-1.75 metre long.
They are following-
Spirally coiled 6cm long in human and 45cm long in rabbit.Its posterior end is present as a blind sac in abdominal cavity called vermiform appendix. Vermiform appendix is vestigeal but contains lymphatic tissue.Caecum in human is concerned with passage of food whereas in rabbit it is concerned with cellulose digestion and conduction of food.
Single endodermal approximately 1.3 m long in human distinguished into four limbs as ascending ,transverse, descending and pelvic or sigmoid limb. Colon posses two specialized structures as Taeniae coli(present in the middle of colon) and Haustra,(dilated sac-like or pockets like structures surrounding taeniae). Colon is concerned with absorption of water of undigested food ,5%, salts,vitamins etc. hence concerned with faeces formation.Colon bacteria also synthesized vit.B12 and K.
Single small dilated sac like in human whereas large beaded in rabbit.It is concerned with storage of faeces.Rectum has strong sphincter muscles in its wall.The sphincter keeps the canal as well as anus,closed when not used for defecation.
Absorption of water from undigested food.
Anal canal and anus:
Anal canal connects rectum with anus and it is about 3cm long .Anus is the terminal inferior opening of alimentary canal,which is guarded by an internal involutionary sphincter and an external volutionary sphincter.