ABDOMEN(CAVITY,ORGANS.... Continued)

PANCREAS

The pancreas

 is a glandular organ in the digestive system and endocrine system of vertebrates. 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 containingdigestive 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.

The pancreas is an endocrine organ that lies in the abdomen, specifically the upper, left abdomen. It is found behind the stomach, with the head of the pancreas surrounded by the duodenum. The pancreas is typically 5.75-9.5 cm long.

Anatomically, the pancreas is divided into a head, which rests within the concavity of the duodenum, a body lying behind the base of the stomach, and a tail, which ends abutting the spleen. The neck of the pancreas lies between the body and head, and is in front of the superior mesenteric artery and vein. The head of the pancreas surrounds these two vessels, and a small uncinate process emerges from the lower part of the head, lying behind the superior mesenteric artery

Endocrine

The part of the pancreas with endocrine function is made up of approximately a million^[7] cell clusters called islets of Langerhans. Four main cell types exist in the islets. They are relatively difficult to distinguish using standard staining techniques, but they can be classified by their secretion: α alpha cells secrete glucagon(increase glucose in blood), β beta cells secrete insulin (decrease glucose in blood), Δ delta cells secrete somatostatin (regulates/stops α and β cells) and PP cells, or γ (gamma) cells, secrete pancreatic polypeptide.^[8]

The islets are a compact collection of endocrine cells arranged in clusters and cords and are crisscrossed by a dense network of capillaries. The capillaries of the islets are lined by layers of endocrine cells in direct contact with vessels, and most endocrine cells are in direct contact with blood vessels, either by cytoplasmicprocesses or by direct apposition. According to the volume The Body, by Alan E. Nourse,^[9] the islets are "busily manufacturing their hormone and generally disregarding the pancreatic cells all around them, as though they were located in some completely different part of the body." The islets of Langerhans play an imperative role in glucose metabolism and regulation of blood glucose concentration.

Exocrine

The pancreas as an exocrine gland helps out the digestive system. It secretes pancreatic fluid that contains digestive enzymes that pass to the small intestine. These enzymes help to further break down the carbohydrates, proteins and lipids (fats) in the chyme.

In humans, the secretory activity of the pancreas is regulated directly via the effect of hormones in the blood on the islets of Langerhans and indirectly through the effect of the autonomic nervous system on the blood flow.

The exocrine component of the pancreas, often called simply the exocrine pancreas, is the portion of the pancreas that performs exocrine functions. It has ducts that are arranged in clusters called acini (singular acinus). Pancreatic secretions are secreted into the lumen of the acinus, and then accumulate in intralobular 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 andduodenum, 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 andchymotrypsinogen. 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 form chymotrypsin

Beyond the Dish

Embryonic Stem Cell-Derived Beta Cells Cure 

Diabetic Mice

Stem cell scientists in Canada have collaborated with biotechnology industries to successfully reverse diabetes mellitus in mice by means of stem cell treatments. This is certainly a medical breakthrough that might lead to treatments in human patients.

The lead researcher, Timothy Kieffer, who is a professor at the University of British Columbia, and scientist from the New Jersey-based company BetaLogics showed that stem cell transplants can restore insulin production and reverse diabetes mellitus in mice.

Beta cells reside in an organ called the pancreas, which is behind the stomach. The pancreas has an “exocrine” function, which means that it secretes materials such as digestive enzymes and bicarbonate ions into a duct, and an endocrine function, which means that it secretes hormones directly into the bloodstream. The exocrine function of the pancreas is accomplished by clusters of cells known as “acinar cells.” Acinar cells cluster around a tiny branch of the pancreatic duct, and they secrete digestive enzymes and bicarbonate ions into the pancreatic duct, which are released into the upper portion of the small intestine (duodenum). These enzymes degrade fats, proteins, nucleic acids, and carbohydrates in the small intestine, which prepares the complex molecules in food for digestion. The endocrine functions are carried out by islands of cells dispersed throughout the pancreas that are away from the pancreatic duct, but clustered around blood vessels. These “pancreatic islets” as they are called secrete hormones that regulate the metabolism of food-derived molecules in our bodies.

There are five types of cells in pancreatic islets: alpha cells, beta cells, delta cells, epsilon cells and PP cells. Alpha cells secrete a hormone called glucagon, which mobilizes store sugar stores in the body and releases them into the bloodstream, this raising blood sugar levels. Beta cells secrete insulin, which stimulates the uptake and metabolism of bloodstream sugar, thus lowering blood sugar levels. Delta cells secrete somatostatin, which regulates growth hormone release by the anterior pituitary, but also affects the release of many hormones in the digestive system and inhibits the release of glucagon and insulin. The epsilon cells secrete a hormone called ghrelin, which is a potent appetite stimulant. The PP cells secrete PP or pancreatic peptide, which helps the pancreas to self-regulate its secretory activities, both exocrine and endocrine.

Once glucose levels rise in the blood, the beta cells release insulin, and when glucose levels in the blood decrease, insulin secretion decreases. This “feedback loop” is essential for proper regulation of blood glucose levels, and beta cells that are immature do not properly respond to rises in blood glucose levels. In this study, however, the research effort completely recreated the insulin/sugar feedback loop that enables insulin levels to automatically rise or fall according to the blood glucose levels.

Damage to the beta cells results in insufficient insulin production and poor regulation of the blood sugar levels. Damage to the beta cells results in type 1 diabetes mellitus, and without the secretion of sufficient quantities in insulin after a meal, the cells do not receive the signal to take up sugar, and are starved from energy. Meanwhile, extremely high sugar levels in the blood react with molecules in the organs of the body, which causes long-term damage to the nervous system, eyes, kidneys, and peripheral tissues. Consequently, type 1 diabetics are at increased risk for amputations, blindness, heart attack, stroke, nerve damage and kidney failure.

Regular injections of insulin are the most common treatment for type 1 diabetes mellitus, but experimental transplants of healthy pancreatic cells from human donors have shown to be effective. Unfortunately, such a treatment is severely limited by the availability of donors.

In this experiment, human embryonic stem cells were differentiated into beta cells and implanted into the diabetic mice. After the stem cell transplant, the diabetic mice were weaned off insulin. Three to four months later, the mice were able to maintain healthy blood sugar levels even after being fed large quantities of sugar. Transplanted cells removed from the mice after several months had all the markings of normal insulin-producing pancreatic cells.

These experiments, however, have one very large caveat. In the words of Kiefer: “We are very excited by these findings, but additional research is needed before this approach can be tested clinically in humans. The studies were performed in diabetic mice that lacked a properly functioning immune system that would otherwise have rejected the cells. We now need to identify a suitable way of protecting the cells from immune attack so that the transplant can ultimately be performed in the absence of any immunosuppression.”

Type 1 diabetes usually results from the immune system of the diabetic patient attacking their own beta cells. Replacing the beta cells mere gives the immune system something that it already recognizes to attack. Therefore, replacing the beta cells with new beta cells from any other source is potentially problematic.

There is a possibility that the beta cells could be implanted inside a porous encasement that is not accessible to the immune system, but can still secrete insulin into the bloodstream in response to increase blood sugar levels. Such a strategy would circumvent the immune system problems.

Hi My Name is  Omer Mujahid.  I am just adding this to check. will post about the pathological topics of each organs system later.