THE PANCREAS – UNLOVED, BUT ESSENTIAL
The pancreas is an
essential organ responsible for both the digestion of food and blood
glucose regulation. It was first identified by Greek anatomist and
surgeon, Herophilus, around 2300 years ago. A few hundred years later,
Rufus of Ephesus, another Greek anatomist, gave the pancreas its name.
“Pancreas” originally meant sweetbread, a name that is still commonly
used in culinary circles for calf or lamb pancreas.
The
pancreas is located behind the stomach in the upper left part of the
abdomen. It is surrounded by other organs including the stomach, small
intestine (duodenum), liver, and spleen. It is spongy, about 15–25cm
(6–10in) long, 2.5cm (1in) thick, and is shaped a bit like a flattened
pear or a fish extended horizontally across the abdomen. The bulk (95%)
of the pancreas consists of tissues and cells that produce pancreatic
secretions for the digestion of carbohydrates, fats and proteins. The
remainder consists of little islands of cells called islets of
Langerhans. These look a bit like small bunches of grapes and produce
hormones that regulate blood glucose and help regulate pancreatic
digestive secretions.
Source: www.medicalook.com
Food digestion
Once food has been chewed in the mouth, then mulched and partially
digested in the stomach by acids, it is released into the first part of
the small intestine known as the duodenum. The pancreas then releases
its own digestive juices and enzymes into the partially digested food,
via a small duct connected to the duodenum. Pancreatic juices contain
enzymes that help breakdown carbohydrate, fat and protein. They are
activated once they reach the duodenum to prevent the protein-digesting
enzyme trypsin from breaking down the proteins in the pancreas itself,
or in its duct. Other enzymes produced by the pancreas and released into
the duodenum include amylase (to break down starches and maltodextrins
into sugars) and lipase (to break down fats into monoglycerols and fatty
acids). The pancreas also secretes sodium bicarbonate, which helps to
neutralise the stomach acids in the partially digested food.
Blood glucose hormones
Two of the most important pancreatic hormones are insulin produced by
beta cells and glucagon produced by alpha cells in the islets of
Langerhans which manufacture and release these hormones directly into
the bloodstream.
Insulin regulates the metabolism of
carbohydrates, fats and protein by promoting the absorption of glucose
from the blood into liver, fat and muscle cells. In these cells the
absorbed glucose is converted into either glycogen (a kind of starch
found in the liver and muscles) via a process known as glycogenesis or
fats (triglycerides) via lipogenesis. Circulating insulin also affects
the synthesis of proteins in a wide variety of cells and tissues. It is
therefore an anabolic hormone, promoting the conversion of small
molecules in the blood into large molecules inside the cells.
Glucagon
stimulates the liver to break down glycogen into glucose, which is then
released into the blood. It also activates gluconeogenesis, the
conversion of certain amino acids from proteins into glucose. Finally,
it facilitates the breakdown of stored fat (triglycerides) into fatty
acids for use as fuel by cells. It is therefore a catabolic hormone,
promoting the breakdown of large molecules in cells into smaller
molecules in the blood.
Pancreatic beta cells are
sensitive to blood glucose concentrations. When glucose levels are high,
they secrete insulin into the bloodstream and when glucose levels are
low, secretion of insulin is inhibited. On the other hand, alpha cells
secrete glucagon into the blood in the opposite manner to insulin: when
blood glucose levels are low, or in response to vigorous exercise,
secretion is increased, and when blood glucose levels are high,
secretion is decreased.
The secretion of insulin and
glucagon into the blood in response to changes in blood glucose
concentrations is the primary mechanism of blood glucose homeostasis. In
other words, the two hormones work in partnership with each other to
keep blood glucose levels balanced. Optimal maintenance of blood glucose
levels is critical to the functioning of key organs including the brain
and nervous system, liver, and kidneys.
If the beta
cells are destroyed by an autoimmune reaction, insulin can no longer be
synthesized or secreted into the blood in sufficient quantities. This
results in the development of type 1 diabetes. In type 2 diabetes, the
destruction of beta cells is less pronounced than in type 1 diabetes and
is not primarily due to an autoimmune process. The exact cause of type 2
diabetes is not fully understood but people have a reduced number of
islet beta cells, and of those that survive there is a reduced secretory
function, and there is also frequently (but not always) peripheral
tissue insulin resistance (the insulin that is produced does not work as
efficiently in the target cells as it should). Type 2 diabetes is also
characterized by high rates of glucagon secretion which are less
responsive to the concentration of glucose in the blood, but insulin is
still secreted into the blood in response to concomitantly increasing
blood glucose concentrations. As a result, insulin levels are typically
much higher than they are in people without type 2 diabetes.
Read more:
Alan Barclay, PhD is a consultant dietitian. He worked for Diabetes Australia (NSW) from 1998–2014 . He is author/co-author of more than 30 scientific publications, and author/co-author of The good Carbs Cookbook (Murdoch Books), Reversing Diabetes (Murdoch Books), The Low GI Diet: Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment, New York).
Contact: You can follow him on Twitter or check out his website.
