A human digestive system which is also known as the alimentary canal is a muscular tube which extends from the mouth to the anus. The parts of the digestive system include – mouth, oral cavity, teeth, esophagus, pharynx, stomach, small intestine, large intestine, and anus.

(1) Mouth

Mouth is the opening through which intake of food occurs.

(2)Oral cavity

The oral cavity has three parts –palate, tongue, and teeth.

· Palate -It forms the roof of the oral cavity. Anterior part is called hard palate and the posterior part is called soft palate.

· Tongue -Tongue is a muscular and glandular structure attached to the base of the oral cavity. On the upper surface, it has a V - shaped furrow called sulcus terminalis. It divides the tongue into the anterior oral part and posterior pharyngeal part. Its upper surface also consists of tiny projections called lingual papillae.

· Lingual papillae are of three kinds in humans -

(i) Vallate or circumvallate papillae -have gustatory receptors to sense taste

(ii) Filiform papillae- smallest and contain touch receptors.

(iii) Fungi-form papillae- Rounded and mostly present at the tip of the tongue.

(3) Teeth

Humans are diphyodont i.e. they have two sets of teeth- milk or deciduous and permanent teeth.The structure of tooth consists of three parts- crown, neck, and root. The exposed part of the tooth is called the crown, the region where it is covered with gums is known as neck and root is embedded in the socket of the jaw bone.

(4) Pharynx

It forms the common passage for food and air.

(5) Esophagus

It is a muscular tube through which small bolus of food passes from the mouth to the stomach. It is sharply bent at the point at which it meets the stomach. This prevents the backward movement of food from the stomach into it. Food in the digestive tract moves by an involuntary movement of alternate contraction and relaxation of muscles called peristalsis.

(6) Stomach

It is a muscular bag which has three parts- cardiac part, fundus, and body.

· Cardiac part – It is so called because it is present close to the heart. The opening of the esophagus to the stomach is regulated by the cardiac sphincter.

· Fundus – It is dome-shaped and is usually filled with air.

· Body – This is the main part of the stomach. The opening of the stomach into the small intestine is regulated by the pyloric sphincter.

(7) Small Intestine

It is the longest part of the alimentary canal and comprises three parts- Duodenum, Jejunum, and Ileum.

· Duodenum – It is C- shaped and receives the hepatopancreatic duct formed by the union of bile and pancreatic duct.

· Jejunum –  Middle part of small intestine with thick walls and more vasculature.

· Ileum –  Lower part of the small intestine with thin walls and less vasculature.

(8) Large Intestine

The small intestine leads into the large intestine which has three parts- Caecum, Colon, and Rectum.

Caecum – It is a small sac-like structure at the point where the small intestine meets the large intestine.

Colon – It is divided into four regions-  transverse colon,  sigmoid colon ascending colon and descending colon.

Rectum – It opens into the anus.

(9) Anus

Anus is the terminal opening of the anal canal , it is the portion of the digestive tract through which fecal material is excreted

· Mouth

· Pharyns

· Esophagus

· Stomach

· Small intestine

· Large intestine

· Rectum

· Anus