The level of glucose streaming through the blood is highly regulated by various processes in the body.^2,3 This state and process of maintaining a steady biological equilibrium is known as the glucose homeostasis and involves vital metabolic processes that are referred to as glucose metabolism.

What Is Glucose? 

Glucose is a type of monosaccharide, the simplest form of carbohydrate.¹ It consists of 6 carbon, 12 hydrogen, and 6 oxygen molecules, with the chemical formula of C₆H₁₂O₆. Importantly, it is the universal source of energy. 

Carbohydrates and proteins consumed during meals ultimately break down into glucose in the body and travel through the bloodstream.² Glucose is taken up by various cells and is broken down by metabolic processes into adenosine triphosphate (ATP) which serves as the final form of energy that allows every function in the human body.

What Is the Role of Pancreas and Its Hormone in Glucose Metabolism?

Pancreas is an organ with both exocrine and endocrine functions that plays a crucial role in glucose homeostasis.⁴ It is known to be composed of five different endocrine cell types that produce different types of hormones. The hormones insulin and glucagon – major players in glucose homeostasis – are produced by the beta and alpha cells of the pancreas, respectively.

Insulin – Insulin is a hormone produced by the pancreatic beta cells.⁴ It is a peptide hormone, meaning it is made up of strings of amino acids. It is first produced as proinsulin and then becomes insulin that acts on the body when a part of the proinsulin (i.e., C-peptide) gets cut off. Although C-peptide has no biological action, it is often used to measure the level of insulin secretion. Insulin is secreted by the pancreas when blood glucose levels rise after a meal.² This signals the cells in the body to take up and use glucose and for excess glucose to be stored in the liver as glycogen molecules, ultimately lowering blood glucose levels. It primarily targets liver, muscle, and adipose (i.e., fat) tissues.

Glucagon – Glucagon is a hormone produced by the pancreatic alpha cells.⁴ It is first produced as a preproglucagon, which then ultimately becomes secreted as glucagon after several enzymatic processes. Glucagon is secreted by the pancreas when blood glucose levels fall.² One of its primary actions is on the liver, where it signals the stored glycogen molecules to be broken down and made into readily available glucose molecules through a process called glycogenolysis. It also promotes the body to synthesize new glucose molecules through a process called gluconeogenesis to provide the needed energy supply. This, in effect, raises blood glucose levels.

What Are the Different Processes of Glucose Metabolism?

There are four major biochemical processes of glucose metabolism that govern how the body uses, makes, and stores glucose. They are glycogenolysis, gluconeogenesis, glycolysis, and glycogenesis.

When the body is in a fasting state and experiences a drop in blood glucose levels, the body produces glucose molecules through processes called glycogenolysis and gluconeogenesis.²

Glycogenolysis – Glycogenolysis is the scientific term for breaking up (“lysis”) glycogen molecules. Glycogen is a polysaccharide, a form of carbohydrate, that functions as an energy reserve mostly in the liver and muscles tissues.⁴ When blood glucose levels drop during fasting state or when muscles need extra glucose needed for contractions, the body signals the need for glycogenolysis to break down glycogen into glucose. Hormones such as glucagon, catecholamines, and glucocorticoids trigger glycogenolysis.

Gluconeogenesis – Gluconeogenesis is the technical term that describes the “neogenesis” (“newly making”) of glucose. It is another vital process to maintaining blood glucose levels during fasting states and provides glucose to various organs, especially the brain, eyes, and kidneys that rely solely on glucose for energy supply during short-term fasting states.^5,6 Hormones such as glucagon, catecholamines, growth hormone, and cortisol promote gluconeogenesis. 

On the other hand, when the body is in a fed state and experiences a rise in blood glucose levels, the body uses or stores glucose molecules through processes called glycolysis and glycogenesis.²

Glycolysis – Glycolysis is a process that describes the breakdown (“lysis”) of glucose molecule for energy use. It is the primary means of providing energy in nearly all living organisms and occurs constantly in the body.⁷ Glycolysis is the reverse process of gluconeogenesis.

Glycogenesis – Glycogenesis describes the “genesis” (“making”) of glycogen molecules for

storage. When not all the glucose from energy intake can be used and an excess is available for future storage, glycogen is formed from glucose molecules through glycogenesis.⁸ Insulin and other liver derived factors promote glycogenesis.² 

Through opposing yet stabilizing biochemical reactions governed by various hormones, the body keeps glucose levels in a tight range, allowing physiological functions to run smoothly.

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