Digestive Glands Associated with Alimentary Canal of Human | Class 12 Biology Notes

Biology | Zoology
HSEB Notes on Digestive glands
Lesson :  Digestion
Class : 12

Glands associated with alimentary canal.

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 open near the upper 2nd molar. One pair of sublingual glands are small and situated beneath tongue. Ducts of Rivinus open into floor of oral cavity. One pair of submandibular(also submaxillary) glands are medium sized and situated at angle of lower jaw. Warton’s duct open near the lower central incisors.
  

Salivary glands secrete saliva into oral cavity. Saliva is slightly acidic pH 6.8. About 1 to 1.5 Liter of saliva is secreted daily. Saliva contains starch digesting enzyme salivary amylase also called ptyalin.

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. The right and left hepatic ducts join to form common hepatic duct. It joins the cystic duct which arises from GB. The cystic duct and other hepatic duct join to form bile duct. It runs down to join the pancreatic duct to form hepatopancreatic duct. It opens into duodenum. The liver lobes are made up of small lobules called hepatic lobules. Hepatic lobules are separated by Glission’s capsule. Liver cells are arranged radially and separated by hepatic sinusoids(wide capillaries). Attached to liver cells there are kupffer’s cells which are phagocytic in nature.

Functions of liver

• Liver is main organ of Bile production. Bile contains bile pigment and salts. Bile pigments are Bilirubin(yellow) and biliverdin(green) used in coloration of bile and faeces. Salts of Sodium and Potassium bicarbonate neutralize acids. Sodium glycocholate and taurocholate help in emulsification.
• Deamination - NH2 amino group is removed from aminoacid resulting in the production of ammonia. Ammonia is converted into urea.
• Glycogenesis - it is conversion of excess glucose into glycogen with the help of insulin. 
• Glycogenolysis - conversion of glycogen into glucose by liver cells with the help of glucagon.
• Lipogenesis - conversion of excess glucose and aminoacid into fats.
• Gluconeogenesis - formation of glucose or glycogen from non carbohydrate sources( aminoacid, fatty acid and glycerol). It also occurs in kidney and muscle.
• Detoxification – converts toxic substance into harmless substance eg harmful prussic acid is neutralized and rendered harmless.
• Haemopoises - formation of blood corpuscles, produces RBC in embryo.
• Destruction of RBC - old and worn out RBC broken down in liver.
• Synthesis of Blood protein - Prothrombin and fibrinogen are synthesized.
• Secretion of Heparin ( anticoagulant)
• Synthesis of vitamin A – synthesis of vitamin A from Beta carotene (carrot).
• Phagocytosis – Kupffer’s cell engulf microorganisms and dead cells.
• Production of heat - high metabolic activities, enough heat produced, maintain optimum body temperature, maintain homoestasis.
• Osmoregulation - produce angiotensinogen(protein) helping maintain body fluid.
• Storage – glycogen, fat, vitamins A D E K, comps of Fe Cu K etc.
• Lymph formation – important seat for lymph formation.

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.

Internal structure 

It has two parts, Exocrine part and Endocrine part. Exocrine part consists of rounded lobules(acini) which secrete alkaline pancreatic juice pH 8.4 about 500 to 800 ml of pancreatic juice secreted every day. The pancreatic juice contains 3 proenzyme, trypsinogen, chymotrypsinogen and procarboxypeptidase and some enzymes like pancreatic amylase, DNase, RNase, Lipase etc  Endocrine part consists of islet of Langerhans. About one million islets are found mostly in tail.

Types of cells

• Alpha cells - constitute about 25% , found at periphery, produce glucagon 
• Beta cells - constitute 60% , found at middle, produce insulin
• Delta cells- constitute 10% found at periphery, produce somatostatin(SS).

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