What is Digestion:
The process by which complex food is converted into simplest food with the help of digestive enzymes(Hydrolytic enzymes) is called digestion.Hence process of digestion is a hydrolytic process.
Type of digestion
(1) Intracellular digestion:
When the process of digestion occurs within the cell in the food vacuole.Examples: Protozoa,porifera,Coelenterata and free living platyhelminthes.
When the process of digestion occurs outside the cell.Examples:Coelenterata and phylum platyhelminthes to phylum chordata.
Digestive system of human
Digestion in vertebrates occurs in the digestive tract or alimentary canal.The various parts involved in digestion can be broadly grouped in the two groups-
(i) Digestive tract or alimentary canal
Digestive tract or alimentary canal
On the basis of the embryonic origin,the alimentary canal of vertebrates can be divided into three parts-
Ectodermal.It includes buccal cavity/oral cavity, pharynx,oesophagus,stomach and small part of duodenum.
(2) Mid gut/Mesodaeum:
Endodermal.It includes small intestine and large intestine.
Ectodermal.It includes anal canal and anus.
Part of alimentary canal and its histology
The mouth is a transverse slit bounded by two movable lips or labia,upper lip and lower lip. Upper lip has small ridges on the sides,a tubercle in the middle and a vertical groove(philtrum) above.
It is a narrow space between lips and gums in front and gums and cheeks on the sides. Its lining contains mucous glands.In the vestibule,a small median fold of mucous membrane,the superior labial frenulum,connects the middle of the upper lip to the gum and usually a similar but smaller inferior labial frenulum connects the middle of the lower lip to the gum.
It includes anterior buccal cavity lined by stratified squamous epithelial cells and posterior pharyngeal cavity lined by columnar epithelial cells.It is distinguished into three region.Pharynx is a vertical canal beyond the soft palate.The food and air passages cross here.Pharynx may be divided into three parts ;Nasopharynx,Oropharynx and Laryngopharynx.
Main structures of Buccopharyngeal cavity are-
The roof of buccal cavity is called Palate.In crocodiles and mammals horizontal shelf like processes of premaxilla and maxilla and the palatine bones of upper jaw fuses and forms a secondary palate which separates the buccal cavity from nasal cavity.Palate is distinguished into three regions-
Anterior ,bony portion formed of maxilla and palatine bones in human and premaxilla, maxilla and palatine bone in rabbit.Hard palate have transverse ridges called palatine rugae. Such rugae or ridges are more developed in carnivorous mammals because their function is to firmly grip the food and prevent it from slipping out the cavity.
(ii) Soft palate:
Posterior soft part,made up of connective tissue and muscles.
Posterior most part of soft palate,which hangs in the region of pharynx.It closes the internal nostrils during degglutition.
Numerous mucous glands.Chiefly present in soft palate,secretes mucous for lubrication.