The salivary glands in mammals are exocrine glands (They pour their contents into the lumen of an internal organ), glands with ducts, that produce saliva. They also secrete amylase, an enzyme that breaks down starch into maltose.
All of the human salivary glands terminate in the mouth, where the saliva proceeds to aid in digestion. The saliva that salivary glands release is quickly inactivated in the stomach by the acid that is present there but the saliva also contains enzymes that are actually activated by the acid.
The submandibular glands are a pair of glands located beneath the lower jaws, superior to the digastric muscles. The secretion produced is a mixture of both serous fluid and mucus, and enters the oral cavity via Wharton’s ducts. Approximately 70% of saliva in the oral cavity is produced by the submandibular glands, even though they are much smaller than the parotid glands.You can usually feel this gland, as it is in the upper neck and feels like a rounded ball. It is located about two fingers above the Adam’s apple (on a man) and about two inches apart under the chin.
The sublingual glands are a pair of glands located beneath the tongue, anterior to the submandibular glands. The secretion produced is mainly mucus in nature, however it is categorized as a mixed gland. Unlike the other two major glands, the ductal system of the sublingual glands do not have striated ducts, and exit from 8-20 excretory ducts. Approximately 5% of saliva entering the oral cavity come from these glands.
Minor salivary glands
There are over 600 minor salivary glands located throughout the oral cavity within the submucosa of the oral mucosa. They are 1-2mm in diameter and unlike the other glands, they are not encapsulated by connective tissue only surrounded by it. The gland is usually a number of acini connected in a tiny lobule. A minor salivary gland may have a common excretory duct with another gland, or may have its own excretory duct. Their secretion is mainly mucous in nature (except for Von Ebner’s glands) and have many functions such as coating the oral cavity with saliva. Problems with dentures are usually associated with minor salivary glands.
Von Ebner’s glands
Von Ebner’s glands are glands found in circumvallate papillae of the tongue. They secrete a serous fluid that begin lipid hydrolysis. They facilitate the perception of taste.
The liver is located in the upper right-hand portion of the abdominal cavity, beneath the diaphragm, and on top of the stomach, right kidney, and intestines. Shaped like a cone, the liver is a dark reddish-brown organ that weighs about 3 pounds.
There are two distinct sources that supply blood to the liver, including the following:
- Oxygenated blood flows in from the hepatic artery
- Nutrient-rich blood flows in from the hepatic portal vein
The liver holds about one pint (13 percent) of the body’s blood supply at any given moment. The liver consists of two main lobes, both of which are made up of thousands of lobules. These lobules are connected to small ducts that connect with larger ducts to ultimately form the hepatic duct. The hepatic duct transports the bile produced by the liver cells to the gallbladder and duodenum (the first part of the small intestine).
The liver can lose three-quarters of its cells before it stops functioning. In addition, the liver is the only organ in the body that can regenerate itself.
Functions of the liver
The pancreas is a glandular organ in the digestive system and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, somatostatin, and pancreatic polypeptide, and a digestive organ, secreting pancreatic juice containing digestive enzymes that assist the absorption of nutrients and the digestion in the small intestine. These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme.
The pancreas lies in the epigastrium and left hypochondrium areas of the abdomen
It is composed of the following parts:
- The head lies within the concavity of the duodenum.
- The uncinate process emerges from the lower part of head, and lies deep to superior mesenteric vessels.
- The neck is the constricted part between the head and the body.
- The body lies behind the stomach.
- The tail is the left end of the pancreas. It lies in contact with the spleen and runs in the lienorenal ligament.
The exocrine pancreas has ducts that are arranged in clusters called acini (singular acinus). Pancreatic secretions are secreted into the lumen of the acinus, and then accumulate inintralobular ducts that drain to the main pancreatic duct, which drains directly into the duodenum.
Control of the exocrine function of the pancreas is via the hormones gastrin, cholecystokinin and secretin, which are hormones secreted by cells in the stomach and duodenum, in response to distension and/or food and which cause secretion of pancreatic juices.
There are two main classes of exocrine pancreatic secretions:
|Secretion||Cell producing it||Primary signal|
|bicarbonate ions||Centroacinar cells||Secretin|
|digestive enzymes||Basophilic cells||CCK|
Pancreatic secretions from ductal cells contain bicarbonate ions and are alkaline in order to neutralize the acidic chyme that the stomach churns out.
The pancreas is also the main source of enzymes for digesting fats (lipids) and proteins. (The enzymes that digest polysaccharides, by contrast, are primarily produced by the walls of the intestines.)
The cells are filled with secretory granules containing the precursor digestive enzymes. The major proteases which the pancreas secretes are trypsinogen and chymotrypsinogen. Secreted to a lesser degree are pancreatic lipase and pancreatic amylase. The pancreas also secretes phospholipase A2, lysophospholipase, and cholesterol esterase.
The precursor enzymes (termed zymogens or proenzymes) are inactive variants of the enzymes; thus autodegradation, which can lead to pancreatitis, is avoided. Once released in the intestine, the enzyme enteropeptidase (formerly, and incorrectly, called enterokinase) present in the intestinal mucosa activates trypsinogen by cleaving it to form trypsin. The free trypsin then cleaves the rest of the trypsinogen, as well as chymotrypsinogen to its active formchymotrypsin.