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1. the major fuel-regulating hormone of the body, a double-chain protein formed from proinsulin in the beta cells of the islets of Langerhans in the pancreas. Insulin promotes the storage of glucose and the uptake of amino acids, increases protein and lipid synthesis, and inhibits lipolysis and gluconeogenesis. Secretion of insulin is a response of the beta cells to a stimulus; the primary stimulus is glucose, and others are amino acids and hormones such as secretin, pancreozymin, and gastrin. These chemicals play an important role in maintaining normal blood glucose levels by triggering insulin release after a meal. After insulin is released from the beta cells, it enters the blood stream and is transported to cells throughout the body. The cell membranes have insulin receptors to which the hormone becomes bonded or “fixed.” An interaction between the insulin and its receptors leads to biochemical processes that include (1) the transport of glucose, amino acids, and certain ions across the membrane and into the cell body; (2) the storage of glycogen in liver and muscle cells; (3) the synthesis of triglycerides and storage of fat; (4) the synthesis of protein, RNA, and DNA, and (5) inhibition of gluconeogenesis, degradation of glycogen and protein, and lipolysis. Although insulin increases the transport of glucose across the cell membrane of most cells, in the brain glucose enters the cells by simple diffusion through the blood--brain barrier.
2. a preparation of the hormone, first discovered in 1921, used in treatment of diabetes mellitus; it may be bovine or porcine in origin (prepared from the pancreas of the animals) or a recombinant human type, although insulin of bovine origin is no longer available in the United States. Recombinant human types may duplicate exactly the human insulin protein sequence, or may be analogues with small differences in sequence. Commercially prepared insulin is available in various types that differ in the speed with which they act and in the duration of their effectiveness. There are several different types of insulin, usually classified by their onset and duration of action. (See table.)

Patients with diabetes react differently in the rate at which they absorb and utilize exogenous insulin; therefore, the duration of action varies from person to person. Moreover, the site of injection, volume of injection, and the condition of the tissues into which the insulin is injected can alter its rate of absorption and peak action times, and exercising the limb which has been injected immediately after injection can increase the speed of absorption. Insulin is measured in units.
Problems of Insulin Therapy. The problem of either too much or too little insulin is always a potential hazard for the person on insulin therapy. The causes, symptoms, and treatment of hypoglycemic or insulin reaction and hyperglycemia are discussed under diabetes mellitus. Other problems of insulin therapy include insulin allergy, insulin resistance, insulin rebound due to the somogyi effect, and lipodystrophies or other localized tissue changes at injection sites.

Lipodystrophies are localized manifestations of disordered fat metabolism at the sites of insulin injection. Tissue hypertrophy can be seen as a mass of fibrous scar tissue and is sometimes called “insulin tumor.” atrophy of the tissues at the injection site appears as dimpling and pitting of the skin and underlying tissues. These problems are more common in adult females and in children. Atrophy of the tissues is relatively harmless, but hypertrophy can cause malabsorption of the insulin and a possible misdiagnosis of insulin resistance. Measures that can help prevent lipodystrophies include (1) systematic rotation of injection sites, (2) warming insulin to room temperature before injection, (3) pinching the skin when injecting the insulin so that it is deposited between fat and muscle tissue, and (4) use of human insulin.
insulin allergy a hypersensitivity reaction to insulin, usually a reaction to its protein components. More purified insulins have now been developed that are less likely to cause an allergic reaction and other complications. Human insulin, prepared by recombinant genetic engineering, eliminates many problems associated with repeated insulin injections, because of reduced antibody concentrations.
insulin pump a device consisting of a syringe filled with a predetermined amount of short-acting insulin, a plastic cannula and a needle, and a pump that periodically delivers the desired amount of insulin. The basal rate of insulin delivery usually is one pulse every 8 minutes, but the pump can deliver as many as 60 pulses at a time. Before each meal or snack the patient manually administers a bolus of insulin by adjusting the pump setting to the desired one-time dose. Some insulin pumps will automatically reset themselves to the basal rate of infusion after each bolus. Research is ongoing regarding implantable pumps that release insulin in response to the pump's glucose sensor. This method could potentially administer insulin in a manner resembling the normal absorption from the pancreas.
Insulin pumps are worn externally and connected to an indwelling subcutaneous needle, usually inserted in the abdomen. From Black and Matassarin-Jacobs, 2001.
insulin rebound extreme fluctuations in blood sugar levels owing to overreaction of the body's homeostatic feedback mechanisms for control of glucose metabolism. When exogenous insulin is given, the hypoglycemia triggers an outpouring of glucagon and epinephrine, both of which raise the blood sugar concentration markedly. Although the patient may actually have periods of hypoglycemia, urine and blood glucose tests will show hyperglycemia. Treatment is aimed at modifying the extremes by gradually lowering the insulin dosage so as to reduce stimulation of the feedback system of glucose regulation. The patient may need to take smaller doses of insulin or take it at more frequent intervals and at different times during the day
insulin resistance impairment of the normal biologic response to insulin, which may result from abnormalities in the B-cell products, binding of insulin to antagonists such as anti-insulin antibodies, defects in or reduced numbers of receptors, and defects in the insulin action cascade in the target cell. Diabetic persons with this problem require more than 100 units daily, and some may need as much as 500 or 1000 units daily. Besides diabetes, the condition has also been associated with diseases such as obesity, acromegaly, uremia, and certain rare, possibly genetic, autoimmune diseases.
insulin sensitivity test a test used to differentiate diabetes mellitus from pituitary and adrenal diabetes. A test dose of exogenous insulin will produce a rapid and marked decrease in blood glucose if the pancreas is not secreting sufficient quantities of insulin. A much less dramatic response is produced if hyperglycemia is due to excessive secretion of either pituitary or adrenocortical hormones rather than insufficient insulin production.

insulin, regular (insulin injection)

Humulin R, Humulin-R Regular U-500 (concentrate), Insulin-Toronto (CA)

insulin (lispro)

Humalog, Humalog Pen

insulin glulisine, recombinant

Apidra, Apidra SoloSTAR

insulin lispro protamine, human

Humalog Mix 50/50, Humalog Mix 75/25

isophane insulin suspension (NPH insulin)

Humulin N, Novolin N

isophane insulin suspension (NPH) and insulin injection (regular)

Humulin 70/30 (70% isophane insulin and 30% insulin injection), Humulin 70/30 PenFill, Novolin 70/30, Novolin 70/30 PenFill

Pharmacologic class: Pancreatic hormone

Therapeutic class: Hypoglycemic

Pregnancy risk category B


Promotes glucose transport, which stimulates carbohydrate metabolism in skeletal and cardiac muscle and adipose tissue. Also promotes phosphorylation of glucose in liver, where it is converted to glycogen. Directly affects fat and protein metabolism, stimulates protein synthesis, inhibits release of free fatty acids, and indirectly decreases phosphate and potassium.


Glulisine, recombinant: 100 units/ml in 10-ml vials, 100 units/ml in 3-ml cartridge system, 100 units/ml in 3-ml prefilled pen

Isophane suspension, injection (regular): 70 units NPH and 30 units regular insulin/ml (100 units/ml total), 50 units NPH and 50 units regular insulin/ml (100 units/ml total)

Isophane suspension (NPH insulin): 100 units/ml

Lispro: 100 units/ml in 10-ml vials and 1.5-ml cartridges

Regular insulin injection: 100 units/ml

Regular U-500 (concentrated), insulin human injection: 500 units/ml

Zinc suspension, extended (ultralente): 100 units/ml

Zinc suspension (lente insulin): 100 units/ml

Indications and dosages

Type 1 (insulin-dependent) diabetes mellitus; type 2 (non-insulin-dependent) diabetes mellitus unresponsive to diet and oral hypoglycemics

Adults and children: In newly diagnosed diabetes, total of 0.5 to 1 unit/kg/day subcutaneously as part of multidose regimen of short- and long-acting insulin. Dosage individualized based on patient's glucose level, adjusted to premeal and bedtime glucose levels. Reserve concentrated insulin (500 units/ml) for patients requiring more than 200 units/day.

Diabetic ketoacidosis

Adults and children: Loading dose of 0.15 units/kg (nonconcentrated regular insulin) I.V. bolus, followed by continuous infusion of 0.1 unit/kg/hour until glucose level drops. Then administer subcutaneously, adjusting dosage according to glucose level.


• Hypersensitivity to drug or its components

• Hypoglycemia


Use cautiously in:

• hepatic or renal impairment, hypothyroidism, hyperthyroidism

• elderly patients

• pregnant or breastfeeding patients

• children.


Be aware that insulin is a high-alert drug whether given subcutaneously or I.V.

Don't give insulin I.V. (except nonconcentrated regular insulin), because anaphylactic reaction may occur.

• When mixing two types of insulin, draw up regular insulin into syringe first.

• For I.V. infusion, mix regular insulin only with normal or half-normal saline solution, as prescribed, to yield a concentration of 1 unit/ml. Give every 50 units I.V. over at least 1 minute.

• Rotate subcutaneous injection sites to prevent lipodystrophy.

• Administer mixtures of regular and NPH or regular and lente insulins within 5 to 15 minutes of mixing.

Adverse reactions

Metabolic: hypokalemia, sodium retention, hypoglycemia, rebound hyperglycemia (Somogyi effect)

Skin: urticaria, rash, pruritus

Other: edema; lipodystrophy; lipohypertrophy; erythema, stinging, or warmth at injection site; allergic reactions including anaphylaxis


Drug-drug. Acetazolamide, albuterol, antiretrovirals, asparaginase, calcitonin, corticosteroids, cyclophosphamide, danazol, dextrothyroxine, diazoxide, diltiazem, diuretics, dobutamine, epinephrine, estrogens, hormonal contraceptives, isoniazid, morphine, niacin, phenothiazines, phenytoin, somatropin, terbutaline, thyroid hormones: decreased hypoglycemic effect

Anabolic steroids, angiotensin-converting enzyme inhibitors, calcium, chloroquine, clofibrate, clonidine, disopyramide, fluoxetine, guanethidine, mebendazole, MAO inhibitors, octreotide, oral hypoglycemics, phenylbutazone, propoxyphene, pyridoxine, salicylates, sulfinpyrazone, sulfonamides, tetracyclines: increased hypoglycemic effect

Beta-adrenergic blockers (nonselective): masking of some hypoglycemia symptoms, delayed recovery from hypoglycemia

Lithium carbonate: decreased or increased hypoglycemic effect

Pentamidine: increased hypoglycemic effect, possibly followed by hyperglycemia

Drug-diagnostic tests. Glucose, inorganic phosphate, magnesium, potassium: decreased levels

Liver and thyroid function tests: interference with test results

Urine vanillylmandelic acid: increased level

Drug-herbs. Basil, burdock, glucosamine, sage: altered glycemic control Chromium, coenzyme Q10, dandelion, eucalyptus, fenugreek, marshmallow: increased hypoglycemic effect

Garlic, ginseng: decreased blood glucose level

Drug-behaviors. Alcohol use: increased hypoglycemic effect

Marijuana use: increased blood glucose level

Smoking: increased blood glucose level, decreased response to insulin

Patient monitoring

• Monitor glucose level frequently to assess drug efficacy and appropriateness of dosage.

• Watch blood glucose level closely if patient is converting from one insulin type to another or is under unusual stress (as from surgery or trauma).

Monitor for signs and symptoms of hypoglycemia. Keep glucose source at hand in case hypoglycemia occurs.

Assess for signs and symptoms of hyperglycemia, such as polydipsia, polyphagia, polyuria, and diabetic ketoacidosis (as shown by blood and urinary ketones, metabolic acidosis, extremely elevated blood glucose level).

• Monitor for glycosuria.

• Closely evaluate kidney and liver function test results in patients with renal or hepatic impairment.

Patient teaching

• Teach patient how to administer insulin subcutaneously as appropriate.

• Advise patient to draw up regular insulin into syringe first when mixing two types of insulin. Caution him not to change order of mixing insulins.

• Instruct patient to rotate subcutaneous injection sites and keep a record of sites used, to prevent fatty tissue breakdown.

Teach patient how to recognize and report signs and symptoms of hypoglycemia and hyperglycemia. Advise him to carry a glucose source at all times.

• Instruct patient to store insulin in refrigerator (not freezer).

• Teach patient how to monitor and record blood glucose level and, if indicated, urine glucose and ketone levels.

• Tell patient that dietary changes, activity, and stress can alter blood glucose level and insulin requirements.

• Instruct patient to wear medical identification stating that he is diabetic and takes insulin.

• Advise patient to have regular medical, vision, and dental exams.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, herbs, and behaviors mentioned above.


(in'sŭ-lin), [MIM*176730]
A polypeptide hormone, secreted by β cells in the islets of Langerhans, which promotes glucose use, protein synthesis, and the formation and storage of neutral lipids; available in various preparations including genetically engineered human insulin, which is currently favored. Insulin is used parenterally in the treatment of diabetes mellitus.
[L. insula, island, + -in]


/in·su·lin/ (in´sdbobr-lin)
1. a protein hormone formed from proinsulin in the beta cells of the pancreatic islets of Langerhans. The major fuel-regulating hormone, it is secreted into the blood in response to a rise in concentration of blood glucose or amino acids. Insulin promotes the storage of glucose and the uptake of amino acids, increases protein and lipid synthesis, and inhibits lipolysis and gluconeogenesis.
Enlarge picture
Insulin. The precursor proinsulin is cleaved internally at two sides (arrows) to yield insulin and C peptide.
2. a preparation of insulin, either of porcine or bovine origin or a recombinant form with sequence the same as or similar to that in humans, used in the treatment of diabetes mellitus; classified as rapid-acting, intermediate-acting, or long-acting on the basis of speed of onset and duration of activity.
3. regular insulin; a rapid-acting, unmodified form of insulin prepared from crystalline bovine or porcine insulin.

insulin aspart  a rapid-acting analogue of human insulin created by recombinant DNA technology.
buffered insulin human  insulin human buffered with phosphate; used particularly in continuous infusion pumps.
extended insulin zinc suspension  a long-acting insulin consisting of porcine or human insulin in the form of large zinc-insulin crystals.
insulin glargine  an analogue of human insulin produced by recombinant DNA technology, having a slow, steady release over 24 hours.
insulin human  a protein corresponding to insulin elaborated in the human pancreas, derived from pork insulin by enzymatic action or produced synthetically by recombinant DNA techniques; sometimes used specifically to denote a rapid-acting regular insulin preparation of this protein.
isophane insulin suspension  an intermediate-acting insulin consisting of porcine or human insulin reacted with zinc chloride and protamine sulfate.
Lente insulin  insulin zinc suspension.
insulin lispro  a rapid-acting analogue of human insulin synthesized by means of recombinant DNA technology.
NPH insulin  isophane i. suspension.
prompt insulin zinc suspension  a rapid-acting insulin consisting of porcine insulin with zinc chloride added to produce a suspension of amorphous insulin.
regular insulin  insulin (3).
Semilente insulin  prompt insulin zinc suspension.
Ultralente insulin  extended insulin zinc suspension.
insulin zinc suspension  an intermediate-acting insulin consisting of porcine or human insulin with a zinc salt added such that the solid phase of the suspension contains a 7:3 ratio of crystalline to amorphous insulin.


1. A polypeptide hormone that is secreted by the beta cells of the islets of Langerhans in the pancreas and functions in the regulation of carbohydrate and fat metabolism, especially the conversion of glucose to glycogen, which lowers the blood glucose level. It consists of two linked polypeptide chains called A and B.
2. Any of various pharmaceutical preparations containing this hormone or a close chemical analog, derived from the pancreas of certain animals or produced through genetic engineering and used in the medical treatment and management of type 1 and type 2 diabetes.


Etymology: L, insula, island
1 a naturally occurring polypeptide hormone secreted by the beta cells of the islets of Langerhans in the pancreas in response to increased levels of glucose in the blood as well as to the parasympathetic nervous system and other stimuli. The hormone acts to regulate the metabolism of glucose and the processes necessary for the intermediary metabolism of fats, carbohydrates, and proteins. Insulin lowers the blood glucose level and promotes transport of glucose into the muscle cells and other tissues. Inadequate secretion of insulin causes elevated blood glucose and triglyceride levels and ketonemia, as well as the characteristic signs of diabetes mellitus, including increased desire to eat, excessive thirst, increased urination, and eventually lethargy and weight loss. Uncorrected severe deficiency of insulin is incompatible with life. Normal findings of insulin assay in adults are levels of 5 to 24 mmU/mL.
2 a pharmacological preparation of the hormone administered in treating diabetes mellitus. The various preparations of insulin available for prescription vary in onset, intensity, and duration of action. Animal source insulins, pork and beef, have been discontinued in the U.S. market. Human insulin is derived by recombinant DNA technology and is termed quick acting, intermediate acting, or long acting. Most replacement insulin is given by subcutaneous injection in individualized dosage schedules and insulin pumps, but insulin also can be replaced intravenously. Adverse reactions include hypoglycemia and insulin shock that result from excess dosage and hyperglycemia and diabetic ketoacidosis from inadequate dosage. Fever, stress, infection, pregnancy, surgery, and hyperthyroidism may significantly increase insulin requirements; liver disease, hypothyroidism, vomiting, and renal disease may decrease them. Blood tests for glucose and ketones are performed to determine the need for adjustment of the dosage or of the schedule of administration. See also human insulin.


Physiology A disulfide-linked polypeptide hormone produced by the beta cells of the pancreatic islets, which controls serum glucose and anabolism of carbohydrates, fat, protein. See Biphasic insulin, PEPCK, Proinsulin, rDNA insulin.


A polypeptide hormone, secreted by beta cells in the islets of Langerhans, which promotes glucose use, protein synthesis, and the formation and storage of neutral lipids; available in a variety of preparations including genetically engineered human insulin, which is currently favored, insulin is used parenterally in the treatment of diabetes mellitus.
Compare: bioregulator
[L. insula, island, + -in]


(in'su-lin) [L. insula, island + -in]
Enlarge picture
A hormone secreted by the beta cells of the pancreas. As a drug, insulin is used principally to control diabetes mellitus. Insulin therapy is required in the management of type 1 diabetes mellitus because patients with this illness do not make enough insulin on their own to survive. The drug also is used in the care of patients with gestational diabetes to prevent fetal complications caused by maternal hyperglycemia (insulin itself does not cross the placenta or enter breast milk). In type 2 diabetes mellitus, its use typically is reserved for those patients who have failed to control their blood sugars with diet, exercise, and oral drugs. See: illustration; diabetes mellitus

Insulin preparations differ with respect to the speed with which they act and their duration and potency following subcutaneous injection. See: table

In the past, insulin for injection was obtained from beef or swine pancreas. These peptides differed from human insulin by a few amino acids, causing some immune reactions and drug resistance. Most insulin now in use is made by recombinant DNA technology and from an immunological perspective is equivalent to human insulin.


In health, the pancreas secretes insulin in response to elevations of blood glucose, such as occur after meals. It stimulates cells, esp. in muscular tissue, to take up sugar from the bloodstream. It also facilitates the storage of excess glucose as glycogen in the liver and prevents the breakdown of stored fats. In type 1 diabetes mellitus, failure of the beta cells to produce insulin results in hyperglycemia and ketoacidosis.


The insulin dosage should always be expressed in units. There is no average dose of insulin for diabetics; each patient must be assessed and treated individually Doses are titrated gradually to achieve near normal glucose levels, about 90–125 mg/dl.


The FDA requires that all preparations of insulin contain instructions to keep in a cold place and to avoid freezing.


Those who use insulin should wear an easily seen bracelet or necklace stating that they have diabetes and use the drug. This helps to ensure that patients with hypoglycemic reactions will be diagnosed and treated promptly.

insulin analog

See: analog

insulin aspart

A rapidly acting insulin administered subcutaneously, with action similar to that of insulin lispro. Aspartic acid replaces proline at a crucial position in the insulin molecule.

biphasic insulin

An insulin preparation that includes two components, typically a rapidly acting insulin, e.g., regular insulin, and an insulin that has a longer duration of action, e.g., NPH insulin.

insulin glargine

A form of insulin that provides basal insulin coverage throughout the day, with little variation in drug levels. It is typically administered as a single injection (often at bedtime) and is usually part of a regimen that includes multiple injections of short-acting insulins or multiple doses of metformin at meal time. It is made by changing the glycine and arginine content of the insulin polypeptide.

human insulin

Insulin prepared by recombinant DNA technology utilizing strains of Escherichia coli. In its effect it is similar to insulins secreted by the human pancreas. Trade names are Humulin and Novolin. Synonym: Novolin 70/30 See: Humulin 50/50; Humulin 70/30; insulin for table

inhaled insulin

Insulin given by inspiration, with the use of an inhaler. It may be composed of liquid droplets or a dry powder. One inhaled insulin product was removed from use in 2008 because of its adverse effects on the lungs.

insulin injection site

See: site

insulin isophane suspension

Intermediate-acting insulin with onset in 1 2 to 1 hr and a duration of 18 to 28 hr.
See: insulin for table

insulin lipodystrophy

See: lipodystrophy

insulin lispro

A synthetic insulin with a very rapid onset and short duration of action. Diabetic patients typically use it immediately before meals to prevent postprandial hyperglycemia. Its absorption is more rapid than regular insulin. It is made by reversing the amino acids lysine and proline in the beta chain of the insulin polypeptide (hence its name lispro).

monocomponent insulin

Single-component insulin.

insulin protamine zinc suspension

Long-acting insulin with onset in 6 to 8 hr and a duration of 30 to 36 hr.
See: insulin for table

insulin pump

See: pump

insulin shock

Hypoglycemic shock.

single-component insulin

Highly purified insulin that contains less than 10 parts per million of proinsulin, which is capable of inducing formation of anti-insulin antibodies. Synonym: monocomponent insulin

synthetic insulin

Insulin made by the use of recombinant DNA technology.

insulin zinc extended suspension

Long-acting insulin with onset in 5 to 8 hr and duration of more than 36 hr.

insulin zinc prompt suspension

Fast-acting insulin with onset less than 1 hr and a duration of 12 to 16 hr.
* These times are estimates and may vary in individual patients. ** Contain NPH plus a rapid-acting insulin (Aspart, Lispro, or Regular); Novolog 70/30 contains 70% NPH, 30% Novolog
Type of InsulinGeneric (Trade Names)Onset (hr)Maximum (hr)Duration (hr)
Very rapid Aspart (NovoLog) 0.2–0.51–33–5
Very rapid Lispro (Humalog)0.2–0.50.5–2.53–5
Very rapid Glulisine (Apidra)0.2–0.51.6–2.83–4
Rapid Regular0.5–1.02.5–54–6
Intermediate-actingNPH (Humulin N, Novolin N)2–44–1210–18
Fixed-dose combination insulins **70/30, 50/50, etc. Variable, depending on mixture used
Very long- actingLantus (Glargine)2–4 none11–32
Very long- actingdetermir (Levemir)3–43–96–23 Dose dependent
U 500 regular very concentrated (5 X U100)0.5–1.02.5–5up to 24 hr


A peptide hormone produced in the beta cells of the Islets of Langerhans in the PANCREAS. Insulin facilitates and accelerates the movement of glucose and amino acids across cell membranes. It also controls the activity of certain enzymes within the cells concerned with carbohydrate, fat and protein metabolism. Insulin production is regulated by constant monitoring of the blood glucose levels by the beta cells. Deficiency of insulin causes DIABETES. Insulin preparations may be in the ‘soluble’ form for immediate action or in a ‘retard’ form for prolonged action or as mixtures of these. Most insulins for medical use are now produced by recombinant DNA methods (genetic engineering) and are identical to human insulin. Bovine and porcine insulins are still used. Brand names include: Neutral Insulin injections: Humalog, Actrapid, Velosulin, Humulin S, Hypurin Bovine Neutral, Hypurin Porcine Neutral, Insuman Rapid, NovoRapid and Pork Actrapid. Biphasic Insulin injections: Humalog Mix25 and Mix50, Mixtard, Humulin, Hypurin Porcine, Insuman Comb, NovoMix 30 and Pork Mixtard 30. Isophane Insulin injections: Insulatard, Humulin, Hypurin Bovine Isophane, Isuman Basal and Pork Insulatard. Insulin Zinc Suspension (Mixed): Monotard, Humulin Lente and Hypurin Bovine Lente. Insulin Zinc Suspension (Crystalline): Ultratard and Humulin Zn. Protamine Zinc Insulin injection: Hypurin Bovine PZI. Long-acting Insulin Analogue: Lantus. The prefix ‘Human’ was deleted from insulin products in mid-2003.


the hormone controlling the amount of blood sugar, which is secreted by the beta cells of the ISLETS OF LANGERHANS in the pancreas. Insulin has three targets: the liver, the muscles, and adipose tissue, where its action helps to reduce the blood sugar level in the following ways:
  1. it stimulates the absorption of more glucose from the blood into respiring cells, by altering cell-membrane permeability;
  2. it stimulates the conversion of glucose into GLYCOGEN in the liver and muscles, reducing the supply of free glucose;
  3. it promotes the conversion of glucose into fats in the liver and adipose cells (LIPOGENESIS);
  4. it inhibits GLUCONEOGENESIS;
  5. it promotes GLYCOLYSIS of glucose in all cells.

Underproduction of insulin causes diabetes mellitus , resulting in an increase in blood sugar (hyperglycaemia) and sugar appearing in the urine (see GLYCOSURIA). The condition can be fatal if untreated, treatment being by injection of insulin into the blood stream. The hormone cannot be taken orally as, being a protein, it would be digested. Insulin was discovered by BANTING and BEST in 1921. The control of blood sugar, where a change in its level automatically brings about the opposite effect, is a good example of a negative FEEDBACK MECHANISM.


A hormone secreted by the pancreas in response to high blood sugar levels that induces hypoglycemia. Insulin regulates the body's use of glucose and the levels of glucose in the blood by acting to open the cells so that they can intake glucose.

insulin (inˑ·s·lin),

n hormone produced by the pancreas that regulates blood glucose levels by stimulating the absorption of sugars into the cells.
Enlarge picture
Insulin injection sites.


(in'sŭ-lin) [MIM*176730]
Polypeptide hormone, secreted by β cells in islets of Langerhans, which promotes glucose use, protein synthesis, and formation and storage of neutral lipids; available in various preparations including genetically engineered human insulin, which is currently favored; used parenterally to treat diabetes mellitus.
[L. insula, island, + -in]


a double-chain peptide hormone formed from proinsulin in the beta cells of the pancreatic islets of Langerhans. Insulin promotes the storage of glucose and the uptake of amino acids, increases protein and lipid synthesis, and inhibits lipolysis and gluconeogenesis.
The secretion of endogenous insulin is a response of the beta cells to a stimulus. The primary stimulus is glucose; others are amino acids, particularly leucine, and the 'gut hormones', such as secretin, pancreozymin and gastrin. These chemicals play an important role in maintaining normal blood glucose levels by triggering the release of insulin after ingestion of a meal.
Commercially prepared insulin is available in various types, which differ in the speed with which they act and in the duration of their effectiveness. There are three main groups: rapid acting (regular or semilente), intermediate acting (isophane suspension or NPH, zinc suspension or lente), and long acting (protamine zinc suspension or PZI, or ultralente). Mixtures are also marketed.

insulin deficiency
diabetes mellitus.
insulin-dextrose therapy
a combination used in emergencies to lower blood potassium levels in acute hypoadrenocorticism.
insulin:glucagon ratio
ratio of insulin to glucagon; thought to determine the predominance of the action of one hormone over the other.
insulin:glucose ratio
a comparison of simultaneously obtained blood levels of immunoreactive insulin and plasma glucose. An increased ratio suggests an insulin-secreting tumor of the pancreas. A modification is the amended insulin:glucose ratio, based on the calculation:
$$\vskip13.5pt{\rm {serum\ insulin (\rmmu U/ml)\times100} \over {\rm plasma \ glucose (mg/dl) - 30}$$
immunoreactive insulin
radioimmunoassay methods are used in determining blood levels of insulin. Increased levels are found with hypoglycemia caused by functional islet cell tumors.
insulin pump
a device consisting of a syringe filled with a predetermined amount of short-acting insulin, a plastic cannula and a needle, and a pump that periodically delivers the desired amount of insulin. Sometimes used in humans, but of limited application in animals.
insulin sensitivity test, insulin response test
used to differentiate diabetes mellitus from pituitary and adrenal diabetes. A test dose of exogenous insulin will produce a rapid and marked decrease in blood glucose if the pancreas is not secreting sufficient insulin. A much less dramatic response is produced if hyperglycemia is due to excessive secretion of either pituitary or adrenocortical hormones rather than insufficient insulin production.
insulin syringe
disposable syringe with a capacity of 1 ml or less and a fine gauge needle (27-29G) attached, and graduation markings corresponding to insulin units in standard preparations. Needles may also be treated to minimize pain on injection.

Patient discussion about insulin

Q. what does an insulin shot do? and what is it good for?

A. Insulin is a hormone (substance that controls the activity of the body) that enables muscles and fat to use the glucose (sugar) we get from the diet as a source of energy for activity or for storage as fat. Thus, it lowers the concentration of glucose in the blood. It's produced and secreted from the pancreas, a gland located in the back of the abdomen. When people don't have insulin, or if the body doesn't respond to insulin (essentially diabetes mellitus type 1 and 2, respectively), therapy with insulin helps the body maintain a normal level of glucose. Excessive concentration of glucose in the blood is termed "hyperglycemia" and is deleterious in the long term.

You may read more here:

Q. Why is insulin injected and not taken as a pill?

A. so if that's the case, why can't you use a patch (like a nicotine patch)? wouldn't that do the same trick?

Q. is there an alternative for the Insulin shots? something less painful but yet effective as the old way?

A. Here is a good site on alternative insulin delivery: Hope this helps.

More discussions about insulin
References in periodicals archive ?
Premixed insulin can be co-prescribed with metformin, DPP4 inhibitors and alpha glucosidase, inhibitors.
A total of 5 insulin glargine recipients and 15 human premix insulin recipients withdrew from the study after beginning treatment.
But, based on the University of Vermont results, it did allow this claim: "One small study suggests that chromium picolinate may reduce the risk of insulin resistance, and therefore possibly may reduce the risk of type 2 diabetes.
Avonmouth, UK), tocopherol-stripped corn oil from MP Biomedicals, LLC (Solon, OH, USA), and soluble insulin from Humulina Regular (Lilly, Madrid, Spain).
The researchers had members of another quarter of that group swallow a daily capsule of insulin.
The insulin concentration of the proinsulin standard in the Dako intact proinsulin reagent set (76.
An advantage of this method is that, like insulin produced naturally from the pancreas, the insulin from the pump goes directly to the liver to prevent excess sugar production there.
Our enthusiasm for the future of our Technosphere Insulin System is based upon its ease-of-use characteristics and its ability to mimic the first phase insulin release of healthy individuals that no other insulin product currently available or in development can claim,'' Chairman and Chief Executive Officer Alfred Mann said in a statement.
Earlier studies had shown that among full-term babies, significantly underweight newborns are more likely to develop insulin resistance at some time than normal-weight newborns are.
Hepatoselective insulin fits into the current regimen of self injection, but provides a more efficient and targeted treatment that minimizes damage to other organs while providing the liver with the correct level of insulin to function properly.
The rise in blood glucose G after a meal stimulates the pancreas to secrete insulin I.