Background Information
Pancreas
The pancreas is an important part of the human body. Some individuals refer to the pancreas as an organ, but according to Kapit, Macey, and Meisami 8 the pancreas is actually a large gland that has both an exocrine and an endocrine function. Whether you consider the pancreas to be an organ or a gland, the importance of its functions in the human body is clear.
The structure of the pancreas, its anatomy and the arrangement of the gland within the human body, is strongly correlated to the pancreas' efficient and reliable function. This gland or organ is located in the abdominal cavity directly beneath the stomach 9. In fact, the pancreas is located deep in the abdomen – sort of hidden behind the liver.
The pancreas plays an important role in digestion, through its exocrine function. The construction of the portion of the pancreas responsible for digestion consists of several pancreatic ducts. The pancreatic duct then empties into the duodenum. As a part of the exocrine function of the pancreas, the duct cells secrete an alkaline solution, rich in sodium bicarbonate, to neutralize stomach acid. The pancreas also secretes enzymes that break down protein in food, digest carbohydrates, and digest triglycerides into fatty acids.
While the pancreas has two major functions, this unit will focus on the pancreas' endocrine function. Within the pancreas are located the islets of Langerhans. According to Corry and Shapiro 1 0, the overall volume of the pancreas includes one to two per cent islets of Langerhans with all of the islets of Langerhans working together as one endocrine organ. These islets are cellular aggregates that contain the endocrine cells of the pancreas 1 1, which produce three types of hormones: insulin, glucagon, and somatostatin. Four types of cells are located within islets, each secretes predominantly a specific hormone. Alpha (A) cells secrete the hormone glucagon, whereas the Beta (B) cells secrete insulin. Additionally, Delta (D) cells secrete somatostatin and the F cells (also now called the PP cells) secrete a polypeptide called the pancreatic polypeptide, which appears to function as an aid for regulation of the secretion of the other pancreatic hormones 1 2.
The table below summarizes the four types of cells found in the endocrine portion of the pancreas and their predominant hormone product:
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Insulin Cycle
The pancreas is necessary in the human body to maintain normal blood glucose levels 1 3. One method that it uses to maintain normal blood glucose levels is to produce a protein hormone called insulin, and actively release insulin into the blood 1 4. Since cells within the pancreas secrete insulin 1 5 they need help to move the insulin from the pancreas to other parts of the body. To aid in the distribution of insulin throughout the body, a rich blood supply surrounds the endocrine portion of the pancreas. In a normal pancreas, the pancreas senses large and small changes in glucose levels and responds to changes in glucose level by production of specific hormones 1 6 such as insulin. Insulin was discovered in 1922 1 7, and in the years since scientists have determined many important functions of insulin in the human body.
Glucose presence in the blood is the major physiological stimulator for insulin production and secretion by beta cells 1 8. In fact, glucose is the most important regulator of insulin gene expression in beta cells. Glucose affects gene transcription, mRNA translation, and secretion 1 9. Beta cells comprise about fifty to seventy per cent of the endocrine cells in the pancreas 2 0 because insulin secretion is a major function of the organ 2 1. The specialized beta cell is the only cell that can sense changes in blood glucose levels and respond by adjusting the insulin secretion rates 2 2. Islet cells are able to produce insulin and become activated when there is glucose in the blood and deactivated when there is less glucose in the blood. The amount of insulin secreted is dependent on the glucose concentration in the body 2 3.
One of the major functions of insulin is to stimulate storage of glucose in various human body cells 2 4. Glucose is a small molecule that is water soluble and therefore needs special passageways to cross the lipid-rich cell membranes. These passageways are called channels or glucose transporters. Channels are similar to pores except that they are only open for specific molecules and are sometimes gated. Glucose crosses the cell membrane using facilitated transport carriers. Facilitated transport channels have two gates, one on either side of the cell membrane. In facilitated transport, both channel gates are never open at the same time, instead each gate opens only when concentrations of glucose need to reach equilibrium. During the first stage of facilitated transport the carrier is open to the cell exterior. In the second step, glucose enters from the outside and binds to the channel binding site. Next, with glucose bound to the channel, the outer gate closes and the other side of the channel opens. If the concentration of glucose is lower on the other side of the gate, then glucose leaves the channel and enters the cell and the channel closes. The glucose molecule can also move from inside the cell to outside of the cell using the same mechanism. Once inside the cell, glucose is available for use or storage. In liver and muscle cells, glucose is stored by conversion to a different molecular form, called glycogen.
The Table below, adapted from Mark Saltzman 2 5, shows how insulin and glucose levels look inside of a human body that has received nutrients and a human body that has not received nutrients:
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Types of Diabetes
Diabetes is a common disease among adolescents and adults in the United States. In fact, there are about 25.8 million people in the world affected with this disease 2 6. In the United States, 8.3% of the population is inflicted with diabetes, this includes 215,000 people younger than 20 years old 2 7. In the field of science this disease is referred to as diabetes mellitus 2 8. Diabetes mellitus presents itself in two different ways – as Type I and Type II diabetes.
Although Type I diabetes presents itself most of the time in adolescents, it does not only affect young individuals. Type I diabetes mellitus accounts for five to ten per cent of all diagnosed cases of diabetes 2 9. Type I diabetes patients develop this disease after they have experienced an autoimmune destruction of their insulin cells 3 0. More specifically, the insulin-producing beta cells have been destroyed; therefore, the body loses its ability to sense glucose and produce insulin in response 3 1. Some individuals believe that there is a biochemical mechanism that is responsible for the onset of diabetic acidosis – the release of free fatty acids in the blood 3 2. Individuals with Type I diabetes often experience excess water in urine (osmotic dieresis), excess urine production (polyuria), excessive thirst (polydipsia), muscle wasting, muscle weakness, weight loss, production of keto acids in the liver, and sugar in urine (glycosuria) 3 3.
Individuals with Type II diabetes experience a lack of insulin responsiveness and/or their bodies do not produce enough insulin 3 4. This type of diabetes is seen more commonly in patients over the age of forty because of the disease's association with increased body fat and obesity 3 5. Insulin resistance seems to increase with an increase in patient age and weight 3 6. Weight gain and the aging process are part of the reason insulin fails to be secreted, thus leading to diabetes. As patients get older, their glucose tolerance and insulin secretion declines, while insulin resistance increases 3 7. Ninety percent of individuals diagnosed with Type II diabetes develop this disease due to a lifestyle disorder 3 8.
Avoidance of Disease
Although the side effects of diabetes are long term 3 9, the disease can be treated. Treatment for Type I diabetes patients includes a regular injection of insulin before eating, eating balanced meals, and exercise 4 0. Treatment for Type II diabetes patients is similar, but the treatment plan also includes reducing body fat and the possible use of oral hypoglycemic medications 4 1. Since a reduction in body fat often reduces a patient's dependence on diabetic medication, it is thought that a reduction in body fat may also prevent or put off the development of the disease 4 2. If necessary, Type II diabetes patients can inject insulin into their bodies to help maintain their blood glucose levels 4 3.
According to a publication written by the National Institutes of Health and the Centers for Disease Control and Prevention, both Type I and Type II patients can utilize specific meal plans to manage their diabetes. The food pyramid for a diabetic would include six or more serving of grains, beans, and starchy vegetables per day. Diabetics should also have three to five servings of vegetables and two to four servings of fruit each day. Milk, meat, and other protein sources should comprise about two to three servings per day. Food items that fall into the fat, sweets, or alcoholic categories should be avoided or consumed only on rare occasions.
Many individuals are interested in determining if they can prevent the spread of diabetes by examining different factors. The use of genetic markers has been thought to predict if an individual would develop diabetes. According to Kennedy, Idris, and Gazis 4 4, genetic markers are not able to predict if an individual will or will not be susceptible to diabetes. Another factor in determining the spread of diabetes concerns breast-feeding infants. Infants who are breast-fed may be less susceptible to developing diabetes due to increased tolerance of insulin and decreased risk of excessive weight gain 4 5.
Diabetes and Self-Esteem
For many young females, their image is important to the way they interact with their peers and in society. For some girls, diabetes is treated as a convention through which girls lose weight or control their current weight. In this manner, individuals can control their weight and have control over how they look or appear to others. If a girl's self-esteem is low and she is concerned about her weight, she may allow herself to lose weight drastically or misuse insulin to control or increase weight loss. According to Watkins 4 6 eating disorders are very common in young girls with diabetes. Girls with diabetes are tempted by their ability to lose weight while eating freely due to the production and administration of too little insulin 4 7. This temptation is especially hard to resist for girls who may be overweight.
Artificial Pancreas and Tissue Engineering
Artificial or synthetic organs are often used to replace human organs that have stopped working or been destroyed due to a disease. Cell and tissue cultures are important in the effort because they can provide for the synthesis of molecules such as insulin that are produced by beta cells. In the case of diabetes, the pancreas is not functioning properly and needs to be replaced or supplemented with cells that work. Tissue engineering provides the opportunity for the growth of a pancreas. Martin Press 4 8 explored the reasons surrounding the need for pancreatic transplantation. Diabetes has a high impact on communities and society; therefore, there is a lot of interest in exploring new treatment options 4 9.
One of the first ways invented to artificially control insulin secretion was with the use of insulin pump therapy. The pump consists of a soluble form of insulin in a syringe that is attached to the individual's body – usually in the abdominal area 5 0. A piece of tape usually keeps the pump in place, while the small pump is attached to a belt on the waist or a shoulder strap. Individuals who use an insulin pump are usually able to maintain an unaffected lifestyle – with the exception of extremely rigorous activities. However, patients using an insulin pump are still insulin dependent.
Pancreatic transplantation can also be used as a way to decrease the number of individuals suffering with diabetes. The first pancreas transplantation in a human was performed by Drs William D. Kelly and Richard C. Lillilei in 1966 at the University of Minnesota 5 1. In fact, the pancreas became the fourth kind of organ to be successfully transplanted 5 2. Whole organ transplant has been successful in some cases; however, cellular transplantation is also an option and an area of interest for scientists and medical professionals 5 3. Cellular transplantation has also been shown to work with islet cells: in this case, normal pancreatic cells are infused into the body so that they can sense changes in glucose levels and produce insulin 5 4.
To create a successful transplantation process for patients with diabetes, it is necessary to determine a viable way to transplant islet cells 5 5. Islet cells were first discovered in the 1860s by a medical student named Paul Langerhans 5 6. Currently there are about seventeen countries participating in human islet trials, nineteen of the centers conducting these trials are located in the United States 5 7. Pancreatic transplantation has evolved over a period of decades. In the late 1960s to the early 1970s it was common for the whole pancreas to be transplanted, whereas, in the late 1970s to early 1980s the pancreas was transplanted mostly in segments 5 8. The trend has now moved back to whole organ transplantation. Future research will focus on overcoming the current obstacles experienced in using an artificial pancreas in a human body 5 9.
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