Hyperglycemia: Definition and Causes
In biochemistry, hyperglycemia (or hyperglucosemia) refers to a pathological condition in which blood glucose rises above 5.5 mmol/L. It is important to note that this value is recorded specifically during the postabsorptive period (the state after nutrients from food have already been absorbed in the gastrointestinal tract).
The primary cause of hyperglycemia lies in impaired hormonal regulation. Pathological dysfunctions in the endocrine system prevent the body from adequately utilizing sugar, leaving it circulating in the bloodstream in excessive amounts.
Hypoglycemia: A Fatal Threat
Hypoglycemia (hypoglucosemia) is characterized by a drop in glucose levels below 3.3 mmol/L. Clinically, this condition poses a significantly greater danger to the patient's life than hyperglycemia.
The pathogenesis of this disorder is based on the phenomenon of neuroglycopenia. Since the brain is critically dependent on a continuous supply of sugar, glucose deficiency in the blood causes a sharp disruption in the energy supply of nerve cells.
If the sugar level is not restored, the cascade of pathological changes leads to severe consequences:
- Seizures occur;
- Loss of consciousness occurs (profound hypoglycemic coma develops);
- If left untreated, death ensues.
Classification of Hypoglycemic States
Depending on the persistence of the changes, hypoglycemia is divided into two main types:
- Transient hypoglycemia. Is strictly transient in nature. In completely healthy individuals, this condition occurs extremely rarely and is usually quickly compensated for by the body's internal reserves.
- Persistent (pathological) hypoglycemia. Requires medical intervention as it is associated with serious diseases or iatrogenic factors.
Causes of pathological persistent hypoglycemia include:
- Insulinoma. This is a specific tumor formed from pancreatic $\beta$-cells. Tumor cells uncontrollably secrete the hormone, causing chronic hyperinsulinism.
- Diabetes mellitus. In this case, a critical drop in glucose occurs against the background of an insulin overdose, when the patient receives a dose of the drug exceeding current metabolic demands.
Briefly: answers to topical questions
Which counterregulatory hormones increase blood glucose levels?
Counter-regulatory hormones mentioned in sources include:
- Glucagon;
- Epinephrine;
- Cortisol;
- Iodothyronines (thyroid hormones);
- Somatotropin (growth hormone, GH).
During fasting, glucagon, GH, cortisol, and adrenaline prevent blood sugar from dropping critically by initiating glycogenolysis and gluconeogenesis.
What is the mechanism of hyperglycemia development specifically in diabetes mellitus?
The elevation of glucose is caused by a decrease in the insulin-glucagon ratio, which leads to two main consequences.
- Decreased glucose uptake by tissues: the effects of counter-regulatory hormones are enhanced, and the number of GLUT-4 transporter proteins on the membranes of insulin-dependent cells (in adipose tissue and muscles) decreases. As a result, glucose is not stored as glycogen.
- Activation of gluconeogenesis: under the action of counter-regulatory hormones (primarily glucagon), the synthesis of glucose from amino acids, glycerol, and lactate is activated. Nitrogen-free residues of glycogenic amino acids are also included in gluconeogenesis, enhancing hyperglycemia.
To easily remember the causes of persistent hypoglycemia, keep in mind the "two sources of excess": internal (an endogenous tumor—insulinoma) and external (insulin overdose in diabetes mellitus). Both factors lead to an excess of the hormone and a drop in sugar.
Class and exam questions
Why is hypoglycemia considered more dangerous than hyperglycemia?
In hypoglycemia, neuroglycopenia—energetic starvation of the brain—develops rapidly. This leads to swift and irreversible consequences: seizures, hypoglycemic coma, and death, whereas hyperglycemia damages the body more slowly.
What are the diagnostic thresholds for these pathologies?
Hyperglycemia is defined as a glucose level above 5.5 mmol/L in the postabsorptive period, while hypoglycemia is diagnosed when the indicator drops below 3.3 mmol/L.
What is an insulinoma and how does it affect glycemia?
An insulinoma is a tumor of the pancreatic beta cells. It causes pathological hypoglycemia because it continuously and in large volumes produces insulin, which lowers blood sugar levels.
What else to study on this topic
- Mechanisms of Hormonal Regulation of Carbohydrate Metabolism
- Biochemical Features of the Postabsorptive Period
- Pathogenesis of Hypoglycemic Coma at the Cellular Level
- Metabolism and Functions of Pancreatic Beta Cells
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