Introduction
The human pancreas, which is a lobulated gland that is located opposite the liver along the gastrointestinal tract, functions in two unique modes. In one mode, the organ fulfills an exocrine function, which involves secreting digestive juices and enzymes that aid in the digesting process in the stomach.1 These enzymes are secreted in an inactive form and they flow down through the duct of Wirsung.
The enzymes and digestive juices are activated by limited proteolysis once they enter the digestive tract at the head of the pancreas. In the second mode, the pancreas performs the endocrine function. This function is performed by the islets of Langerhans, which are clusters of specialized endocrine cells scattered throughout the pancreas.1 There are four cell types found in the pancreatic islets and they secrete a number of important hormones.
Physiology of the Endocrine Pancreas
The islet of Langerhans, which are tight aggregations of cells embedded in the surrounding exocrine tissue contain some distinct cell types. In each islet of Langerhans, there exist a number of alpha cells, beta cells, delta cells, and gamma cells.1 However, the two major types of cells are the alpha and beta cells.
Alpha Cells
This type of cells makes up 20% of the islets of Langerhans cells. Alpha cells secrete the glucagon hormone which plays a major role in regulating the blood sugar levels. The glucagon hormone is synthesized as a 29-amino-acid propeptide that serves to counteract the effects of insulin and increase the concentration of blood glucose.
It is desirable that sugar levels do not get too high since this will lead to diabetes.1 However, it is also desirable that the blood sugar level doesn’t fall too low since this will have a negative impact on the brain. Barron reveals that unlike other body organs, the brain lacks the ability to store sugar reserves within its self.1 As such, it relies on the sugar contained in the bloodstream and if this sugar level falls drastically the effects on the brain are immediate.
Glucagon production and secretion in the pancreas has to be regulated to ensure that it is not too much. This function is performed by chemoreceptors, which are present all over the body. These chemical receptors constantly monitor the blood sugar level. When they determine that the sugar level is too low, signals are sent to the alpha cells to release extra glucagon.1 This glucagon, produced in the pancreas, moves through the blood to the liver.
Here, it interacts with liver cells to convert glycogen into glucose through the glycogenolysis process. If necessary, the glucose can be obtained from the body’s amino acids and fat through gluconeogenesis. The glucagon release rate is also affected by the stimulation of the sympathetic nervous system.1 This system is stimulated when a person is preparing for stress or responding to fright. When this occurs, the level of glucagon released is higher than normal.
Glucagon secretion has to be inhibited to ensure normal blood sugar levels are maintained. The inhibition is performed by the amylin peptine that is obtained from the beta cells. Glucagon can be used to manage diabetes since it leads to the production of glucose. Diabetics who are experiencing an insulin reaction can have glucagon administered to them to increase the amount of glucose in their blood and therefore bring their blood sugar levels to normal.1 Glucagon acts in a mode that is opposite that of insulin since it promotes glucose increase while insulin reduces blood sugar levels.
Beta Cells
This cells are found in the islets of the mature human pancreas where they make up about 80% of the islet mass. These cells produce insulin, which is the most predominant and most studied pancreatic hormone. Insulin’s function is to regulate energy by lowering the blood sugar. Whenever the blood sugar level is higher than normal, the beta cells are stimulated to release insulin into the blood.1 When the blood sugar level is higher than normal, the beta cells are stimulated to secret insulin.
This action is critical to the health of the body since if the blood sugar level remains high for long, organs and cells will be damaged. The beta cells contain channels that monitor glucose levels and then the channels detect that the circulating glucose level is rising, insulin is secreted by the beta cells.
Insulin
Insulin is the hormone secreted by the beta cells in reaction to a rise in the levels of blood glucose. This small protein affects almost all cells in the body since it dictates how every single cell uses the glucose available in the bloodstream. Most of the blood glucose is used to sustain brain function while the rest is used to provide energy to the body cells.1 Before glucose can power the cells, it has to be converted into adenosine trihosphate (ATP) which is obtained from pyruvate. Pyruvate is created from glucose through the glycolysis process.1
Barron reiterates that insulin serves as the main regulator of blood sugar levels.1 It is the hormone that causes skeletal muscles to consume glucose from the bloodstream and through the glycolysis process turn it into pyruvate and then ATP. Inside the muscle tissue, the insulin functions to obtain amino acids from the blood and change them into proteins. Since glycogen is typically converted into glucose, insulin inhibits the production of the enzymes that process glycogen into glucose.1
By doing this, insulin ensures that the body’s energy storage system is well regulated since the glucose level is controlled. The liver function is affected by the dietary intake of an individual. If a person’s glycemic carbohydrates intake is too high, the amount of fat stored in the liver will be excessive. This will negatively impact liver function.
In all the cases, insulin binds to specific membrane-associated glycoprotein receptors thereby facilitating glucose transport from the blood into cells. Through the different actions, insulin causes soluble nutrients absorbed into the bloodstream to be converted into energy-rich products that are stored in the body cells.1
This causes a drop in the blood sugar level. Insulin is the natural opposite of glucagon and it has certain effects on the body cells. It increases the rate at which glucose diffuses into the cells. It increases the speed of conversion of glucose into glycogen. It accelerates amino acids synthesis into proteins.
Finally, it reduces the rate at which glycogen is broken down into glucose. All this actions have a net impact of lowering the glucose levels in the bloodstream. If the level of glucose in the blood is lower than normal, insulin secretion is turned off.1 Glucagon also causes insulin to be released since the two hormones act to balance each other out.
Delta Cells
These cells make up less than 1% of the islets of Langerhans cells. They secrete somatostatin, which is a 14-amino-acid polypeptide that has a wide anatomical distribution in neurons, pancreas, intestines, and other organs. It is a hypothalamic extract that inhibits the release of growth hormones and may regulate adjacent islet cell functions.
Gamma Cells
These cells make up less than 1% of islets and they secrete the pancreatic polypeptide (PP). PP is a 36-amino-acid polypeptide secreted in response to protein and less so to glucose from F cells. An important role played by these cells is to inhibit somatostatin production.
Diabetes Mellitus
Diabetes mellitus refers to a heterogeneous group of metabolic disorders characterized by high levels of blood sugar.1 Since the disease affects the blood, its effects are felt by the entire body system. Diabetes mellitus is a significant cause of death in the US with Barron noting that if falls between the fourth and sixth most fatal disease.1 The threat posed by this disease to human life is even higher if you consider other outcomes of diabetes mellitus such as heart disease and kidney failure.
Diabetes mellitus is also referred to as “sweet urine” since the disease causes the glucose levels in the blood to be high making urine literally sweet. The disease presents a number of distinctive characteristic symptoms. The patient discharges a large volume of urine, a condition known as polyuria. Another symptom is excessive thirst causing the patient to consume large amounts of water. Finally, the patient experiences polyphagia, which is the excessive consumption of food.
Barron explains that the diabetes mellitus patient is in actual fact starving since their cells are not getting adequate sugar.1 Excessive eating is an attempt to provide the cells with the needed sugar. In most cases, the symptoms are not severe or they may even be absent. This means that a person might be suffering from diabetes for a long time before the diagnosis is made. In the absence of effective treatment, a patient may fall into a coma or even die.
The majority of diabetes cases are under the Type 1 and Type 2 categories. There exists a third rate type of diabetes that is caused by mutant genes. The patient inherits these mutated genes from his/her parents.
Type 1 Diabetes
About 10-20% of all diabetes patients suffer from type 1 diabetes. Type 1 is also known as insulin-dependent diabetes and it is characterized by the autoimmune destruction of the beta cells that secrete insulin. This leads to complete insulin deficiency which leads to excess blood sugar. Abnormally high blood sugar levels cause multiple problems including chronic starvation, cataracts in the eyes, and excess fat in the blood.1 Type 1 patients may require insulin injections since their bodies are not providing these hormone.
Inherited forms of Diabetes Mellitus
While very rare, diabetes is sometimes caused by the inheritance of defective genes.1 These mutant genes cause diabetes by preventing insulin secretion, causing insulin receptor sites to malfunction, or preventing the production of glucokinase, which is the enzyme needed for glycolysis.1 Inherited diabetes can be observed during the childhood or adolescence years of the patient.
Type 2 Diabetes
Type 2, is non-insulin-dependent diabetes, is the most prevalent form of diabetes and it affects up to 90% of all diabetes patients. Traditionally, this type of diabetes was referred to as the “maturity-onset” diabetes since it primarily affected individuals over the age of 40 years. However, this situation has changed dramatically and today Type 2 diabetes is becoming prominent in children at an alarming rate. Barron documents that 20% of all new Type 2 diabetes cases are diagnosed in children.1
The dietary changes experienced by people in the developed world are the reason why Type 2 diabetes has become prevalent among children. Barron confirms that in most cases, this is a self-inflicted disease.1 This is to say that people cause the disease upon themselves by indulging in high glycemic diets and gaining excessive weight.
In spite of being the prevalent form of the disease, Type 2 is milder than Type 1 diabetes especially if it is detected during the early stages. Patients are able to control these type of diabetes much easier than those suffering from Type 1. In most patients, their bodies are able to produce normal levels of insulin.
The problem arises since the body is forced to secrete a lot of insulin to tackle the high glycemic foods being consumed by the individual.1 Over time, the cells of the body loss their sensitivity to the action of insulin since they have been exposed to too much of it. In clinical terms, the cells are said to have grown insulin resistant. Insulin resistance develops slowly over many years due to poor dietary practices and sedentary behavior by the patient.
While all cells in the body convert glucose into fuel for their survival, the vast majority of glucose conversion is done in skeletal muscles. These muscles are the major means though which extra glucose is removed from the bloodstream and changed into glycogen. The ability of skeletal muscles to perform this important task in Type 2 diabetics is greatly diminished. Research indicates that the conversion rate is only 20% of the normal level due to insulin resistance.1
Luckily, the insulin resistance can be reversed through vigorous exercise. By engaging in vigorous exercising, the level at which the skeletal muscles move glucose across the cellular membrane therefore converting it into glycogen is increased.
Type 2 diabetes has the same symptoms as Type 1, which is excessive hunger, discharging a lot of urine and excessive thirst. Treatment options include engaging in exercise, losing weight, and in extreme cases insulin injections. It is important to manage the disease as early as possible since its symptoms become worse over time. Permanent damage might be caused to the beta cells if a person does not take measures to manage the disease early on.1 This damage occurs since the beta cells are exhausted after years of secreting too much insulin to counter insulin resistance by the body.
Conclusion
Diabetes is emerging as one of the preventable leading causes of death in the US. This paper set out to discuss the pancreas and diabetes. It started by highlighting the different modes of functioning by this organ in order to highlight its relationship with diabetes. The paper has shown how the pancreas contains specialized cells that produce the hormone insulin.
The insulin is secreted into the bloodstream where it interact with the membranes on all the cells leading to a reduction in the blood glucose levels. Diabetes occurs when the glucose levels in the blood are abnormally high due to autoimmune destruction of the beta cells in Type 1 diabetes or insulin resistance in Type 2 diabetes.
Reference
Barron, J. The Endocrine System: The Pancreas & Diabetes. Jon Barron Organization. Web.