Blood sugar regulation is the process by which the levels of

blood sugar Glycaemia, also known as blood sugar level, blood sugar concentration, or blood glucose level is the measure of glucose concentrated in the blood of humans or other animals. Approximately 4 grams of glucose, a simple sugar, is present in the blo ...

, primarily

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...

, are maintained by the body within a narrow range. This tight regulation is referred to as glucose homeostasis. Insulin, which lowers blood sugar, and glucagon, which raises it, are the most well known of the hormones involved, but more recent discoveries of other glucoregulatory hormones have expanded the understanding of this process. The gland called

pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an en ...

secrete two hormones and they are primarily responsible to regulate glucose levels in blood.

Mechanisms

Blood sugar levels are regulated by negative feedback in order to keep the body in

balance Balance or balancing may refer to: Common meanings * Balance (ability) in biomechanics * Balance (accounting) * Balance or weighing scale * Balance as in equality or equilibrium Arts and entertainment Film * ''Balance'' (1983 film), a Bulgaria ...

. The levels of

in the blood are monitored by many tissues, but the cells in the

pancreatic islets The pancreatic islets or islets of Langerhans are the regions of the pancreas that contain its endocrine (hormone-producing) cells, discovered in 1869 by German pathological anatomist Paul Langerhans. The pancreatic islets constitute 1–2% o ...

are among the most well understood and important. Granule docking is an important glucose-dependent step in human insulin secretion that does not work properly in

type 2 diabetes Type 2 diabetes, formerly known as adult-onset diabetes, is a form of diabetes mellitus that is characterized by high blood sugar, insulin resistance, and relative lack of insulin. Common symptoms include increased thirst, frequent urinatio ...

Glucagon

If the blood glucose level falls to dangerously low levels (as during very heavy exercise or lack of food for extended periods), the

alpha cells Alpha cells (α cells) are endocrine cells that are found in the Islets of Langerhans in the pancreas. Alpha cells secrete the peptide hormone glucagon in order to increase glucose levels in the blood stream. Discovery Islets of Langerhans were ...

of the pancreas release glucagon, a

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...

which travels through the blood to the liver, where it binds to

glucagon receptor The glucagon receptor is a 62 kDa protein that is activated by glucagon and is a member of the class B G-protein coupled family of receptors, coupled to G alpha i, Gs and to a lesser extent G alpha q. Stimulation of the receptor results in the ...

s on the surface of liver cells and stimulates them to break down glycogen stored inside the cells into glucose (this process is called glycogenolysis). The cells release the glucose into the bloodstream, increasing blood sugar levels.

Hypoglycemia Hypoglycemia, also called low blood sugar, is a fall in blood sugar to levels below normal, typically below 70 mg/dL (3.9 mmol/L). Whipple's triad is used to properly identify hypoglycemic episodes. It is defined as blood glucose bel ...

, the state of having low blood sugar, is treated by restoring the blood glucose level to normal by the ingestion or administration of dextrose or

carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or m ...

foods. It is often self-diagnosed and self-medicated orally by the ingestion of balanced meals. In more severe circumstances, it is treated by injection or infusion of glucagon.

Insulin

When levels of blood sugar rise, whether as a result of glycogen conversion, or from digestion of a meal, a different hormone is released from

beta cells Beta cells (β-cells) are a type of cell found in pancreatic islets that synthesize and secrete insulin and amylin. Beta cells make up 50–70% of the cells in human islets. In patients with Type 1 diabetes, beta-cell mass and function are dim ...

found in the

islets of Langerhans The pancreatic islets or islets of Langerhans are the regions of the pancreas that contain its endocrine (hormone-producing) cells, discovered in 1869 by German pathological anatomist Paul Langerhans. The pancreatic islets constitute 1–2% of ...

in the pancreas. This hormone, insulin, causes the liver to convert more glucose into glycogen (this process is called

glycogenesis Glycogenesis is the process of glycogen synthesis, in which glucose molecules are added to chains of glycogen for storage. This process is activated during rest periods following the Cori cycle, in the liver, and also activated by insulin in re ...

), and to force about 2/3 of body cells (primarily muscle and fat tissue cells) to take up glucose from the blood through the

GLUT4 Glucose transporter type 4 (GLUT4), also known as solute carrier family 2, facilitated glucose transporter member 4, is a protein encoded, in humans, by the ''SLC2A4'' gene. GLUT4 is the insulin-regulated glucose transporter found primarily in a ...

transporter, thus decreasing blood sugar. When insulin binds to the receptors on the cell surface, vesicles containing the GLUT4 transporters come to the plasma membrane and fuse together by the process of endocytosis, thus enabling a facilitated diffusion of glucose into the cell. As soon as the glucose enters the cell, it is phosphorylated into

glucose-6-phosphate Glucose 6-phosphate (G6P, sometimes called the Robison ester) is a glucose sugar phosphorylated at the hydroxy group on carbon 6. This dianion is very common in cells as the majority of glucose entering a cell will become phosphorylated in this wa ...

in order to preserve the concentration gradient so glucose will continue to enter the cell.Ebey Soman, Scienceray
Regulation of Glucose by Insulin
, May 4, 2009. Retrieved November 1, 2009. Insulin also provides signals to several other body systems, and is the chief regulator of metabolic control in humans. There are also several other causes for an increase in blood sugar levels. Among them are the 'stress' hormones such as epinephrine (also known as adrenaline), several of the steroids, infections, trauma, and of course, the ingestion of food.

Diabetes mellitus Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

type 1 is caused by insufficient or non-existent production of insulin, while type 2 is primarily due to a decreased response to insulin in the tissues of the body ( insulin resistance). Both types of diabetes, if untreated, result in too much glucose remaining in the blood ( hyperglycemia) and many of the same complications. Also, too much insulin and/or exercise without enough corresponding food intake in diabetics can result in low blood sugar (

hypoglycemia Hypoglycemia, also called low blood sugar, is a fall in blood sugar to levels below normal, typically below 70 mg/dL (3.9 mmol/L). Whipple's triad is used to properly identify hypoglycemic episodes. It is defined as blood glucose bel ...

Hormones that influence blood glucose level

References

{{Endocrinology Diabetes Medical conditions related to obesity Nutrition Endocrinology