Physiology
Endocrine
Which of the following factors increases glucagon secretion:
Answer:
Factors that increase glucagon secretion:- ↓ Blood glucose
- ↑ Amino acids
- Cholecystokinin
- Catecholamines
- Acetylcholine
- ↑ Blood glucose
- Insulin
- Somatostatin
- Fatty acids, ketoacids
Glucagon Physiology
Physiology / Endocrine / Pancreatic Function
Last Updated: 9th July 2020
Glucagon is produced by α cells, located peripherally within the islets of Langerhans, in the endocrine tissues of the pancreas.
Glucagon release patterns tend to be the mirror image of those of insulin. Low blood glucose initiates glucagon release directly and also drives nervous and hormonal release of catecholamines which activate beta-adrenoceptors on α cells to augment glucagon release.
Glucagon acts on guanosine triphosphate-binding protein (G-protein) coupled receptors that stimulate the production of intracellular cyclic adenosine monophosphate (cAMP). In liver cells, this results in the inhibition of glycogen synthesis and the activation of glycogen breakdown systems. Similar effects are obtained in muscle cells to increase circulating levels of glucose.
There are interactions between glucagon and insulin within the islets: insulin inhibits release of glucagon, but glucagon stimulates the release of insulin, an effect that ensures a basal level of insulin release regardless of glucose levels.
Comparison between Insulin and Glucagon
| Hormone | Insulin | Glucagon |
|---|---|---|
| Cell Type | Beta-cells | Alpha-cells |
| Factors that Increase Secretion |
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| Factors that Decrease Secretion |
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| Mechanism of Action | Acts on tyrosine kinase receptor to activate intracellular pathway that results in translocation of GLUT-4 transporter to plasma membrane | Acts on G-protein coupled receptor to stimulate production of cAMP |
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Major Actions |
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| Overall Effect on Blood Levels |
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
