Insulin vs Glucagon

Insulin vs Glucagon

Insulin and glucagon have both similarities and differences.  Both are hormones secreted by the pancreas but they are made from different types of cells in the pancreas.  Both help manage the blood glucose levels in the body but they have opposite effects.  Both respond to blood glucose levels but they have opposite effects.

Each of us has insulin and glucagon in our systems because it is a strict requirement that the blood sugar level in the body is kept in a narrow therapeutic range.  You need both insulin and glucagon to respond to various levels of glucose in the bloodstream.  While insulin responds and is secreted by the pancreas upon having high glucose levels in the bloodstream, glucagon responds and is secreted by the pancreas upon having low glucose levels in the bloodstream.  This maintains homeostasis in the body and keeps the blood sugar stable at all times.

Function of Insulin

Insulin is a protein-based hormone that is secreted by the beta cells inside the pancreas whenever the pancreas senses that the blood sugar is too high.  Low levels of insulin are constantly being secreted into the bloodstream by the pancreas, even when blood glucose levels are normal.

Function of Insulin

After you eat a meal, the glucose from the food you eat is taken up by the gastrointestinal tract, increasing the level of glucose in the blood.  When this happens, the beta cells get activated and more insulin is secreted to help decrease the glucose levels, primarily by helping the glucose enter the cells to be used as cellular fuel.  When the glucose level in the blood decreases, insulin levels by the islet (beta) cells of the pancreas return to a baseline status.

In response to the elevated insulin level, the various cells of the body bind to insulin and the insulin facilitates the transfer of glucose from the blood to the inside of the cells.  The cells then use this glucose to make energy to power the cells.  The blood sugars are then decreased.

Insulin is a protein consisting of 51 amino acids.  It weighs 5808 Daltons, which is how the weight of such small molecules are measured.  It consists of 2 separate amino acid chains that are connected by a disulfide bond.   The INS gene codes for the synthesis of preproinsulin, which is considered a precursor molecule of insulin.  The preproinsulin is modified in the pancreatic beta cells, resulting in insulin being secreted.

The beta cells that make the insulin are located in tiny clusters within the pancreas, known as the Islets of Langerhans.  When a type 1 diabetic develops the disease, antibodies are made against the Islets of Langerhans cells so that no insulin can be produced.

Triggers for the release of insulin include high blood sugar, while epinephrine and other stress hormones block the insulin secretion.  The main purpose of insulin is to keep the blood glucose levels as much within the normal range as possible.

We need insulin as a part of the normal cellular lipid and carbohydrate metabolism.  This protein helps to regulate the lipid, protein, and glucose absorption by all the cells of the body.  It has been found to increase protein synthesis and DNA replication.

Insulin primarily acts to bring glucose to fatty tissue and muscle tissue but it also acts on the liver, where it aids in the making of glycogen out of pieces of glucose molecules.  Muscle cells also store glucose as glycogen under the influence of insulin.  Even so, it can be said that insulin acts on all the cells of the body because each cell is responsible for its own cellular metabolism.

Insulin also acts to antagonize and inhibit the alpha cells that primarily secrete glucagon.  When insulin levels are at their highest, glucagon production is shut off.  Insulin also blocks the use of fats to be used for cellular energy and blocks the excretion of sodium by the kidneys.

Function of Glucagon

In contrast to insulin, glucagon is secreted by the alpha cells of the pancreas.  Glucagon is secreted when the blood glucose levels are found to be too low.  This is usually when you are fasting, when you exercise, and between meals after insulin has reduced the blood sugar levels.  When the blood glucose levels are elevated, glucagon secretion by the alpha cells is shut down.

Glucagon

Glucagon mainly affects the liver by causing glycogen (the storage form of glucose in the liver) to break off pieces of glucose so that the blood glucose level increases. Glucagon also increases the production of glucose by liver cells out of proteins if there isn’t enough glycogen around to bring up the blood glucose levels.

Like insulin, glucagon is a protein-based hormone consisting of 29 amino acids in a chain weighing 2385 Daltons.  Glucagon has a precursor molecule called proglucagon.  In the alpha cells of the pancreas, proglucagon is modified into the glucagon that is ultimately secreted by the cells.  In the intestines, proglucagon is also broken down but it makes different proteins than are seen in the pancreas.

Things besides low blood sugar level that increase glucagon production are epinephrine (a stress hormone), arginine and alanine (both amino acids), acetylcholine (a neurotransmitter), and hormones, such as cholecystokinin.  Things that decrease glucagon secretion include human growth inhibiting hormones, urea, and insulin.

Glucagon increases glycogenolysis, which is the breaking down of glycogen into its component parts.  Glucagon allows for the creation of glucose from fatty acids but it doesn’t directly affect the breakdown of fat.

Glucagon can be used in therapeutic settings to relax the lower esophageal sphincter (LES) in cases where the individual has blockage or spasm of the LES.  It is used to treat severe hypoglycemia from insulin overdose and is also used to treat beta blocker overdoses.

Insulin and Glucagon Levels

A normal blood glucose level is between 70 mg/d: and 110 mg/dL.  When the blood glucose level drops to less than 70 mg/dL, a signal is given to the pancreas to release glucagon.  If the blood sugar level is above 180 mg/dL, glucagon level is shut down and the person is said to be hyperglycemic.  If the person has a blood glucose level on a random basis that is 200 mg/dL or more, the person is said to be diabetic and no glucagon is secreted by the pancreas.

Both insulin and glucagon are protein-based hormones regulating glucose and fat metabolism in the cells of the body.  While both originate from the pancreas, they are made from two different cell types and are structurally different proteins at oppose one another in the physiology of the body.

References:

  1. Insulin/Glucagon. http://biomed.brown.edu/Courses/BI108/BI108_2002_Groups/pancstems/stemcell/insulin_glucagon.htm. Accessed 5/28/16.
  2. Differnce between insulin and glucagon. http://www.differencebetween.com/difference-between-insulin-and-glucagon/. Accessed 5/28/16.
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