Alimentary Canal in Human Beings | Biology Class 12

Zoology | Notes
Alimentary Canal in Human Beings
Class: 12

Alimentary canal in a continuous tube with varied diameter at different region and helps in digestion process. It runs from mouth to anus via pharynx, oesophagus, stomach and intestine. The initial steps in digestion takes place in a cavity called as oral cavity where teeth tongue and three pairs of salivary glands are present.

Oral Cavity 

Initial steps of digestion occur in oral cavity where teeth tongue and salivary glands are present. The floor of oral cavity bears a muscular organ called as tongue which helps in digestion process by thoroughly mixing ingested food with saliva. The ventral surface of tongue has a ridge called as Frenulum. The dorsal surface has taste buds which are sensitive to sweet, salt, sour and bitter.

Alimentary Canal in Human

The oral cavity has upper and lower jaws that bear teeth of different shape and size. The teeth help in crossing, grinding and smashing the ingested food and convert them into fine form. In humans four kinds of teeth are present. They are, incisor (I), Canine(C), premolar (PM), and molar (M). This condition of teeth is called Heterodont and is strongly attached to jaw bone. This condition of teeth is called Diphyodont and Thecodont respectively.

Structurally human tooth has three parts; root, neck and crown. The root remains attached to the jaw in the socket. The part of the tooth which remains embedded in the gum is called neck while the exposed part is called crown. The outer surface of a tooth except root remains covered with enamel which is hard and prevents dentine from injury. The dentine is composed of living cells called Odon oblasts which are innervated with nerves and capillaries and give sensitivity to tooth. Each tooth centrally bears a cavity called as pulp cavity where the nerves and capillaries are densely packed. The arrangement of teeth in upper and lower jaw in the order of I, C, PM and M is represented by a formula called dental formula which is 2, 1, 2, 3 / 2, 1, 2, 3 in humans. 

Internal Structure of Teeth

Pharynx

It is a wide opening at the back of mouth and is of cross road for both food and air. The pharynx bears opening of both trachea and Oesophagus. The opening of trachea remains closed during feeding with the help of epiglottis.

Oesophagus

It is along narrow muscular tube measuring about 25 cm in length and connects oral cavity with stomach. Oesophagus runs through neck and chest cavity along with trachea. The food passes through oesophagus by peristalsis movement.

Stomach

The Oesophagus after reaching in abdominal cavity swells and forms wide muscular part called as stomach. It is J-shaped and has outer smooth surface and inner rough surface that produces gastric juice, stomach has three parts, cardiac, fundus and pyloric. The upper part of stomach which is near to heart is called cardiac, the middle wider parts is fundus and lower narrower part is called pyloric which remains connected with duodenum of small intestine. The stomach receives food, shores food, mixes food with gastric juice and finally passes food small intestine.

Small Intestine

The anterior part of intestine which is coiled and longest is called small intestine that measure about 6.5 m in length. It has three parts; duodenum, jejunum and ileum. The anterior end of small intestine that joins with pyloric stomach is called duodenum which makes U-loop with stomach. The duodenum receives hepatopanorentic duct from liver and pancreas. The middle coiled part is called jejunum that measures 2.5 m in length and passes the food to ileum. The ileum is terminal part and measures about 3.5 m in length and internally bears in folding called as villi. The villi increase surface area for absorption.

Large Intestine:

It is wider and shorter part of intestine which measures about 1.5 m in length. It is concerned with absorption of water and removal of undigested materials as faces. Large intestine has three parts i.e. caecum, colon and rectum. The caecum contents small intestine to colon where water absorption takes place from undigested materials. The colon has four parts; Ascending colon, transverse colon, descending colon and sigmoid colon. The undigested materials become solid on traveling through colons and are temporarily stored in rectum till they are eliminated.

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