DIGESTIVE SYSTEM

➡ Digestive system of human beings consists of alimentary canal or gut and some accessory organs like teeth, salivary gland, gall bladder, pancreas and liver. 

➡ Alimentary canal

• It is a coiled, muscular, continuous tube running through the central body cavity extending from the mouth to the anus. It is about 30 feet long. 

(a) mouth  

(b) oral (buccal) cavity 

(c) pharynx

(d) oesophagus

(e) stomach

(f) small intestine

(g) large intestine

(h) rectum and anus

⁍ Mouth

• Daily secretion of saliva in the mouth is 1 to 1.5 litre. Saliva is acidic in nature. Saliva contains ptyalin enzyme which acts on cooked starch changing them into sugar maltose. 

• There are three pairs of salivary glands viz. parotids, submaxilliary(sub mandibular) and sublingual. 

⁍ Buccal (oral) cavity

• The mouth leads into oral cavity that has two lateral walls (cheeks), an anterior roof (hard palate), a posterior roof (soft palate) and a pair of jaw (upper maxilla and lower mandible). 

• The buccal cavity is composed of palate, tongue and teeth. 

⁍ Pharynx

• It is small sized (12-14 cm) conical part where food and air passages cross each other. 

• It is divided into three parts viz. nasopharynx, oropharynx and laryngopharynx. 

⁍ Oesophagus

• It is a long (22-25 cm) narrow, muscular and tubular structure. 

• It runs downward through the neck behind the trachea, passes through the diaphragm and opens in the stomach in the abdomen. 

• It conducts the food to stomach by peristalsis. 

⁍ Stomach

• The stomach is a large muscular C-shaped sac and located on left side in the upper postion of the abdominal cavity. 

• Stomach secrets gastric juices with ph 1 to 3.5.

• Food mixed with gastric juice in the stomach is called chyme. 

• Pepsin enzyme digests protein into peptides. 

• Rennin is found in calf gastric juice. It is the milk regulating proteinase. 

• HCL is also secreted in stomach. The acid HCL is important because pepsin can act only in an acidic medium. 

⁍ Small intestine 

• It is divided into three parts:

i)  Duodenum: it is the widest and shortest (25cm) part of the small intestine. 

ii) Jejunum: it is the middle and is about 8 

feet long. 

iii) Ileum: it is the longest (12 feet) part of the small intestine. 

• It is 20 feet long in humans. 

•  Duodenum forms the typical U-shaped loop containing the pancreas. 

• In man there is common opening of bile duct and pancreatic duct opening in duodenum. 

• The duodenum leads into jejunum. 

• Ileum is the last part of small intestine. 

• Internal lining of duodenum, jejunum, and ileum is raised into innumerable minute finger-like processes called villi. Intestinal villi are mainly concerned with absorption. 

• Maximum absorption takes place in ileum. 

• The food in the small intestine is called chyle. 

⁍ Large intestine

• It is 5 feet long and 2-5 inches in diameter. 

• It is called large because of its large diameter, although it ja shorter in length than small intestine. 

• Caecum is a small pouch like structure which ends into a tubular structure (13cm) long called vermiform appendix. 

• Colon is thicker than small intestine and thinner than caecum. 

• Colon is concerned with conservation of water, sodium or other minerals and formations of faeces. 

• The rectum is the last part of the alimentary canal and is about 7-8 inches long. 

• The terminal 1 inch of rectum is called and anal canal and it's exterior opening is called the anus. 

• Rectum secrets no enzymes. It stores digestive residue and absorbs water from residue. 

• It plays only a minor role in the absorption of nutrients.