The glands are formed from covering epithelia. Epithelial cells proliferate and penetrate connective tissue. They may or may not maintain contact with the surface. When contact is maintained, exocrine glands are formed. Without contact, endocrine glands are formed.The cells of endocrine glands can be arranged in cords or in follicles.
i. Components of Digestive glands:
a. The large salivary glands
b. The liver
c. The pancreas
d. The gallbladder.
These organs are located outside the digestive tract and have ducts open into the digestive tract.
a. The salivary glands:
The salivary glands are compound tubuloacinar glands. There are three pairs of large salivary glands. They are parotid, submandibular glands and sublingual glands.
b. The liver:
The liver is the largest solid organ in the body, weighing about 1.5 kg in the adult. Lies in the right upper quadrant of the abdomen and is completely protected by the thoracic rib cage. Completely surrounded by a peritoneal membrane, known as Glisson's capsule.
The major Functions of The liver:
1) Carbohydrate metabolism
B) Glycogen synthesis & metabolism
2) Fat metabolism
A) Fatty acid synthesis
B) Cholesterol synthesis & excretion
C) Lipoprotein synthesis
D) Ketogensis: Converting the fatty acid ketone bodies.
3) Protein metabolism
A) synthesis of plasma proteins
B) Urea synthesis
4) Hormone metabolism
Metabolism, conjugation & excretion of steroidal and poly peptide hormones.
5) Drugs & foreign compounds
Metabolism and excretion of drugs
6) Liver is a good part in storage of:
B) Vitamin A
C) Vitamin B12
7) Also liver plays a good part in metabolism and secretion of Bilirubin. There fore, any damage to the liver organ may affect any of the above functions.
The most common diseases affecting the liver are:
Hepatitis: Damage to the liver cells.
Cirrhosis: In this case an increase in the fibrous tissue formation result in shrinkage of the liver and a decrease in the hepatocellular function.
Tumours: Most frequently are secondary. Metastases from cancers of the large bowel stomach and the bronchus.
Obstruction of the bile flow: This due to pathological diseases or presence of stones.
Jaundice: It’s the yellowish discoloration of the tissue due to the deposition of Bilirubin.
Hyper Bilirubinaemia can be caused by:
‣ Increase production of Bilirubin
‣ Impaired metabolism
‣ Decreased excretion
‣ Combination of the above causes
c. The Pancreas:
The pancreas is a glandular organ in the digestive system and endocrine system of vertebrates. In humans, it is located in the abdominal cavity behind the stomach. It is an endocrine gland producing several important hormones, including insulin, glucagon, somatostatin, and pancreatic polypeptide which circulate in the blood. The pancreas is also a digestive organ, secreting pancreatic juice containing digestive enzymes that assist digestion and absorption of nutrients in the small intestine. These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme.
Pancreas has two parts
i) Duct part: In this pancreatic glands release pancreatic juice. Enzymes of pancreatic juice are tripsin, amylage, lypage, kymotripsin.
ii) Endocrine Part: It releases hormones.
Insulin: Insulin is secreted by the beta cells of the pancreas in response to high blood sugar, although a low level of insulin is always secreted by the pancreas. After a meal, the amount of insulin secreted into the blood increases as the blood glucose rises. Likewise, as blood glucose falls, insulin secretion by the pancreatic islet beta cells decreases.
In response to insulin, cells (muscle, red blood cells, and fat cells) take glucose in from the blood, which ultimately lowers the high blood glucose levels back to the normal range.
Glucagon: Glucagon is secreted by the alpha cells of the pancreas when blood glucose is low. Blood glucose is low between meals and during exercise. When blood glucose is high, no glucagon is secreted from the alpha cells. Glucagon has the greatest effect on the liver although it affects many different cells in the body. Glucagon's function is to cause the liver to release stored glucose from its cells into the blood. Glucagon also the production of glucose by the liver out of building blocks obtained from other nutrients found in the body.
d. The gallbladder: The gallbladder is an organ that is part of the human biliary system, which is involved with the production, storage and transportation of bile. Bile is a yellowish-brown fluid produced by the liver and used to break up and digest fatty foods in the small intestine.
The gallbladder is not absolutely necessary for human survival, as bile can reach the small intestine in other ways.
ii. Functions of digestive glands:
‣ Salivary gland: Produce saliva.
‣ Pancreas: Produce digestive enzymes and hormones.
‣ Liver: Produce bile and synthesize blood proteins.
‣ Gallbladder: Store and concentrate the bile.