`star` Layers of Alimentary Canal
`star` Villi
`star` Digestive Glands


● The `color{violet}("wall of alimentary canal")` from `color{violet}("oesophagus")` to `color{violet}("rectum possesses")` four layers namely `color{violet}("serosa, muscularis, sub-mucosa")` and `color{violet}("mucosa.")`

`star` `color{green}("Serosa:")`

● `color{violet}("Serosa")` is the outermost layer and is made up of a thin `color{violet}("mesothelium")` (epithelium of visceral organs) with some connective tissues.

`star` `color{green}("Muscularis:")`

● `color{violet}("Muscularis")` is formed by `color{violet}("smooth muscles")` usually arranged into an `color{violet}("inner circular")` and an `color{violet}("outer longitudinal layer.")`

● An `color{violet}("oblique muscle layer")` may be present in some regions.

`star` `color{green}("Submucosa:")`

● The `color{violet}("submucosal layer")` is formed of loose connective `color{violet}("tissues")` containing `color{violet}("nerves, blood")` and `color{violet}("lymph vessels.")`

● In `color{violet}("duodenum, glands")` are also present in `color{violet}("sub-mucosa.")`

`star` `color{green}("Mucosa:")`

● The innermost layer lining the `color{violet}("lumen")` of the alimentary canal is the `color{violet}("mucosa.")`

● `color{violet}("Mucosal epithelium")` has `color{brown}("goblet cells")` which `color{violet}("secrete mucus")` that help in lubrication.

● `color{violet}("Mucosa")` also forms glands in the stomach (`color{brown}("gastric glands")`) and crypts in between the bases of `color{violet}("villi")` in the intestine (`color{brown}("crypts of Lieberkuhn")`).

● All the four layers show modifications in different parts of the `color{violet}("alimentary canal")`.


● The `color{violet}("Mucosal layer")` forms irregular folds (`color{brown}("rugae")`) in the stomach and small finger-like foldings called `color{brown}("villi")` in the `color{violet}("small intestine.")`

● The `color{violet}("cells lining the villi")` produce numerous `color{violet}("microscopic")` projections called `color{brown}("microvilli")` giving a brush border appearance.

● These modifications increase the surface `color{violet}("area enormously.")`

● `color{violet}("Villi")` are supplied with a network of capillaries and a large `color{violet}("lymph vessel")` called the `color{violet}("lacteal.")`


● The `color{violet}("digestive glands")` associated with the `color{violet}("alimentary canal")` include the salivary glands, the liver and the pancreas.

`star` `color{green}("Salivary Glands:")`

● `color{violet}("Saliva")` is mainly produced by three pairs of `color{violet}("salivary glands,")` the `color{violet}("parotids")` (cheek), the sub-maxillary/sub-mandibular (lower jaw) and the sublinguals (below the tongue).

● These glands situated just outside the `color{violet}("buccal cavity")` secrete salivary juice into the `color{violet}("buccal cavity.")`

`star` `color{green}("Liver:")`

● `color{brown}("Liver")` is the `color{violet}("largest gland")` of the body weighing about 1.2 to 1.5 kg in an adult human.

● It is situated in the `color{violet}("abdominal cavity")`, just below the `color{violet}("diaphragm")` and has two lobes.

● The `color{brown}("hepatic lobules")` are the structural and functional units of liver containing `color{violet}("hepatic cells")` arranged in the form of `color{violet}("cords.")`

● Each lobule is covered by a thin connective `color{violet}("tissue sheath")` called the `color{brown}("Glisson’s capsule.")`

● The bile secreted by the `color{violet}("hepatic cells")` passes through the `color{violet}("hepatic ducts")` and is stored and concentrated in a `color{violet}("thin muscular sac")` called the `color{brown}("gall bladder.")`

● The duct of `color{violet}("gall bladder")` (`color{brown}("cystic duct")`) along with the `color{brown}("hepatic duct")` from the liver forms the `color{brown}("common bile duct")`.

● The bile duct and the `color{violet}("pancreatic duct")` open together into the `color{violet}("duodenum")` as the common `color{brown}("hepato-pancreatic duct")` which is guarded by a sphincter called the `color{brown}("sphincter of Oddi.")`

`star` `color{green}("Pancreas:")`

● The `color{violet}("pancreas")` is a `color{brown}("compound")` (both `color{brown}("exocrine and endocrine")` ) elongated organ situated between the limbs of the `color{violet}("‘U’")` shaped duodenum.

● The exocrine portion secretes an `color{violet}("alkaline pancreatic juice")` containing enzymes and the endocrine portion secretes `color{violet}("hormones, insulin and glucagon.")`