Discuss the structure of digestive organs of man with the help of labelled diagram.

Discuss the structure of digestive organs of man with the help of labelled diagram.

Ans: The digestive system consists of alimentary canal and digestive glands. Alimentary canal is complete and has well defined regions. It is concerned with ingestion, digestion, absorption and egestion of waste material.

Alimentary canal:

Fig: parts of alimentary canal of human.
It is a long coiled tube of about 8 to 10 meters long. It is of various diameters at various parts. It starts from mouth and ends in anus. It consists of following parts they are as;

Mouth:
It is a transverse slit like opening bounded by movable upper and lower lip. It opens into a small gap called vestibule. Vestibule is a space between lips and jaw. It opens not buccal cavity.

Buccal cavity:
It is known as oral cavity or mouth cavity also. It is bounded by upper and lower jaws. The upper jaw is fixed and lower jaw is only movable up and down and sidewise. The jaws are provided with teeth in a row. At the floor, there is tongue. The roof of buccal cavity is made by palate.

Pharynx:
It is wide opining at back of mouth cavity. It leads to two openings : gullet and glottis. There is a muscular flap called epiglottis which closes glottis when food is swallowed. There are 2 openings of internal nares above and two openings of Eustachian tubes at the sides. It is the only part common to digestive and respiratory system.

Oesophagus:
It is a long narrow muscular tube which connect mouth to stomach. It is about 25 cm long. It pierces diaphragm to open into stomach. It undergoes peristalsis to carry down food and water or fluid.

Stomach:
It is a large muscular elastic bag situated below diaphragm on left side. It has four parts
1.Cardiac: it is so called because it lies near heart. In between oesophagus and cardiac part of stomach there is cardiac sphincter.
2.Fundus: it extends superiorly from the cardiac part. It is usually filled with air.
3.Body: it is main part of stomach.
4.Pyloric part: it is distal part of stomach. it opens into duodenum. It opens and closes several times. At the time of opening, a small amount of partially digested food(chime) is passed into duodenum. Gastric gland secretes gastric juice.

Small intestine:
It is divisible into 3 parts.
1.Duodenum – it is c shaped and about 25 cm long. It receives bile juice and pancreatic juice through common bile duct.
2.Jejunum - it is about 2.5 meter in length. It is coiled part.
3.Ileum – it is about 3.5 meter long. It is highly coiled part. Both jejunum and ileum are suspended by mesenteries. The inner wall of ileum has number of folds called villi. It is mainly for digestion and absorption.
large intestine

It is about 1.5 meter long and divisible into following parts:

1.Caecum: It is pouch like structure about 6 cm long. There is ileocaecal valve preventing back flow. Attached to caecum is a slender vermiform appendix of about 10 cm long. It is vestigial in man but functional in herbivores. The inflammation of appendix is called appendicitis at the time of infection.

2.Colon: It is inverted U shaped and divisible into
• Ascending colon: It is the first part on right side. It moves upward from caecum.
• Transverse colon: It is horizontal part.
• Descending colon: It moves down at left side. It descends down
• Pelvic colon: It is s shaped or sigmoid. Undigested material can remain in colon for about 36 hours.
Colon is for absorption of water mainly.

3. Rectum: small muscular region, straight, about 15 cm long. It opens to the exterior through anus. Undigested material remains here for a short time. The anus is guarded by 2 sphincters Throughout the alimentary canal, mucous glands secrete mucus.

Digestive glands:
Associated with digestion, there are following digestive glands which secrete enzymes serving the chemical digestion of food.
1.Salivary glands:
There are three pairs of salivary glands. There is one pair of Parotid gland. It is the largest of the salivary glands. It is situated near the ears. Stenson’s duct of Parotid gland opens near the upper 2nd molar. One pair of sublingual glands is small and situated beneath tongue.
2.Liver:
It is the largest gland. It lies in the upper right side of abdominal cavity just below diaphragm. It is reddish brown and weighs about 1.4 to 1.5 Kg. It has two lobes right and left separated by falciform ligament. The right lobe is further divisible into right lobe proper, quadrate lobe and caudate lobe. Gall bladder is a pear shaped sac like structure. It stores bile juice.
3.Pancreas:
It is soft, lobulated, greenish pink gland. It weighs about 60 grams, 2.5 cm wide and 12 to 15 cm long. It located posterior to stomach. It comprises head, body and tail. Head lies in the curve of duodenum, body behind the stomach and tail reaches the spleen near left kidney. The main pancreatic duct is formed by smaller ducts within pancreas. The main pancreatic duct open into hepatopancreatic ampulla.

Absorption :
Absorption takes place in the ileum mainly. For this, the internal lining of ileum is provided with large no. of finger like projections called villi. The villi increase the absorptive surface. These are provided with blood vessels and lymph. Glucose, amino acid etc are absorbed into the blood vessel. Blood takes them to liver for storage of glucose. The fatty acids and glycerol come into the lymph which is taken into adipose tissue for storage.

Assimilation:
Glucose, fatty acids and glycerol are used for the liberation of energy in the body. Amino acids are used to produce protoplasm in the body for growth and repair of damaged tissue.

Egestion:
Undigested materials are passed into large intestine. Water is absorbed here. Then these are carried down. Lastly undigested materials are discharged out from anus. It is called egestion.