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Digestive Glands
The digestive glands are specialized structures that play a critical role in the human digestive system by producing and secreting enzymes, hormones, mucus, and other substances essential for breaking down food into absorbable nutrients. These glands ensure the efficient digestion of carbohydrates, proteins, and fats, as well as the absorption of nutrients and the elimination of waste.
1.0Salivary Glands
- Saliva is mainly produced by three pairs of salivary glands, the parotids (cheek), the sub maxillary/sub mandibular (lower jaw) and the sub linguals (below the tongue).
- These glands are situated just outside the buccal cavity, secrete salivary juice into the buccal cavity. In humans 3 pairs of salivary glands are present.
Composition of Saliva
- Water-99.5%
- Mucus, starch -digesting Ptyalin enzyme (Salivary amylase), lysozyme and thiocyanates and few ions like sodium, potassium, chloride, IgA antibody, urea and uric acid etc., are present.
- Ptyalin is secreted mainly by the parotid gland. Lysozyme and Thiocyanates mainly kill bacteria.
- Salivation is stimulated by cranial nerve VII & IX. The sympathetic nervous system decreases the secretion of saliva while the parasympathetic nervous system increases the secretion of saliva.
2.0Liver
- Weight 1.2 to 1.5 kg, in humans it is found in the right side of the , bile juice cavity, below the diaphragm.
- The liver is the largest gland of the body. It is made up of two lobes, the left and right lobe. The left lobe is smaller than the right lobe.
- The right and left liver lobes are separated from each other by the falciform ligament (Fibrous C.T.) which is made up of a fold of peritoneum.
- The right and left hepatic ducts arise from the right and left liver lobe. Both these ducts combine to form a Common Hepatic duct. The hepatic lobules are the structural and functional units of liver containing hepatic cells arranged in the form of cords.
- Each lobule is covered by a thin connective tissue sheath called the Glisson’s capsule.
- The bile secreted by the hepatic cells passes through the hepatic ducts and is stored and concentrated in a thin muscular sac called the gall bladder.
- The duct of gall bladder (cystic duct) along with the hepatic duct from the liver forms the common bile duct (ductus choledocus).
- The bile duct and the pancreatic duct open together into the duodenum as the common hepato-pancreatic duct which is guarded by a sphincter called the sphincter of Oddi. Gall bladder is situated below the right lobe of the liver.
Functions of Liver
- Most of the biochemical functions of the body are done by the liver.
Bile-Juice
- In the duodenum, bile juice is released.
- The Hepatocytes of the liver produce bile-juice and it is stored in the Gall-bladder. Bile juice does not contain any digestive enzymes.
- Therefore it is not a true digestive juice (Pseudodigestive juice).
Composition of Bile-juice
- Bile-juice is a greenish (Biliverdin) yellow (Bilirubin) coloured alkaline fluid.
- pH 8.0
- H2O 98%
- Constituents are bile salts, bile pigment, cholesterol, Phospholipid, Na+ , K+ etc.
Bile-salts are of two types
- (a) Inorganic-salts- Bile-juice contains NaCl, Na2CO3, NaHCO3 etc in it. Inorganic salts neutralize the acidity of the food and make the medium basic. It is necessary for making the medium basic, because the pancreatic-juice enzymes can act only in basic -medium.
- (b) Organic-salts- Organic salts like Na-glycocholate and Na-taurocolate are found in Bile juice. The main function of these salts is the emulsification of fats, because pancreatic Lipase can act only on emulsified fats.
Function of bile juice
- Neutralization of HCl. It neutralizes HCl of chyme (semifluid food found in the stomach).
- Emulsification. Sodium glycocholate and sodium taurocholate are bile salts which break the large fat droplets into the smaller ones.
- Absorption of fat and fat-soluble vitamins. Its salts help in the absorption of fat (fatty acids and glycerol) and fat-soluble vitamin (A, D, E and K).
- Excretion. Bile pigments (bilirubin and biliverdin) are excretory products.
- Prevention of decomposition. Bile is alkaline hence it prevents the decomposition of food preventing the growth of bacteria on it.
- Stimulation of peristalsis. Bile increases peristalsis of the intestine.
- Activation of Lipase. Bile contains no enzyme but activates the enzyme lipase. Bile-pigments, cholesterol and Lecithin are the excretory substances found in Bile-juice.
3.0Pancreas
- It is a soft, lobulated and elongated organ, situated between the limbs of C-shaped duodenum.
- It is made up of numerous acini. Acini is a group of secretory cells surrounding a cavity. Each acini is lined by pyramidal shaped cells. These acinar cells secrete the enzyme of pancreatic juice.
- Each acini opens into the pancreatic ductule. Many pancreatic ductules combine to form the main Pancreatic duct (duct of Wirsung). The main Pancreatic duct joins with the bile duct to form the hepatopancreatic ampulla which opens into duodenum.
- The accessory Pancreatic duct (duct of Santorini) opens into duodenum with a separate opening located above the opening of the major Pancreatic duct.
- Some groups of endocrine cells are also found in between groups of acini called islets of Langerhan's. These islets secrete insulin (-cell) & glucagon (-cell) hormone. So this gland is exocrine as well as endocrine (Heterocrine). Its 99% part is exocrine while 1% part is endocrine.
- In humans both bile duct and pancreatic duct combine to form a common duct called Hepato-Pancreatic duct. The terminal end of the common duct is swollen and is called Ampulla of Vater or hepato pancreatic ampulla. Ampulla of Vater opens into the duodenum and is controlled by the sphincter of Oddi while bile duct is controlled by sphincter of Boyden
Pancreatic Juice
- Pancreozymin stimulates the glandular cells of acini to secrete pancreatic juice.
- The pancreatic-juice is secreted by the exocrine cells of the pancreas.
- Pancreatic juice is highly odoriferous, colourless basic fluid which contains enzymes and salts.
Composition of Pancreatic Juice
- Water = 98%, pH = 7.5-8.3 (7.8), Salts = 2%
- Pancreatic juice contains only inorganic-salts.
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