2. Utilization of blood glucose :
Certain tissues like brain, erythrocytes, renal medulla and bone marrow are exclusively dependent on glucose for their energy needs. When the body is at total rest, about two-thirds of the blood glucose is utilized by the brain. The remaining one-third by RBC and skeletal muscle. A regular supply of glucose, by whatever means it may be, is absolutely required to keep the brain functionally intact.
Different metabolic pathways (glycolysis, glycogenesis, HMP shunt etc.) are responsible for the utilization of blood glucose. The synthesis of fat from acetyl CoA and glycerol in lipid metabolism also takes place via glucose.
Kidney plays a special roje in the homeostasis of blood glucose. Glucose is continuously filtered by the glomeruli, reabsorbed and returned to the blood. If the level of glucose in blood is above 160-180 mg/dl, glucose is excreted in urine (glycosuria). This value (160-180 mg/dl) is referred to as renal threshold for glucose. The maximum ability of the renal tubules to reabsorb glucose per minute is known as tubular maximum for glucose (TmG). The value for TmG is 350 mg/minute.
The term hyperglycemia refers to an increase in the blood glucose above the normal level. An increased level of glucose is seen in diabetes mellitus; as also in increased endocrine activity, or pregnancy. Hypoglycemia represents a decreased blood glucose concentration. It is often associated with starvation, hyperinsulinism and decreased activity of endocrine glands. The concentration of blood glucose is dependent on the quantity of glucose that enters the circulation from various sources (dietary carbohydrates, glycogenolysis, gluconeogenesis etc.) and the amount that is utilized for different metabolic purposes (glycolysis, glycogenesis, fat synthesis etc.)
Hormones play a significant role in the regulation of blood glucose concentration. Primarily, insulin lowers blood glucose level (hypoglycemic) while the rest of the hormones oppose the actions of insulin (hyperglycemia).
When the blood glucose concentration falls to less than 45 mg/dl, the symptoms of hypoglycemia, appear. The manifestations include headache, anxiety, confusion, sweating, slurred speech, seizures and coma, and, if not corrected, death. All these symptoms are directly and indirectly related to the deprivation of glucose supply to the central nervous system (particularly the brain) due to a fall in blood glucose level.
The mammalian body has developed a well regulated system for an efficient maintenance of blood glucose concentration. Hypoglycemia, therefore, is not commonly observed. The following types of hypoglycemia are encountered by physicians - post-prandial hypoglycemia, fasting hypoglycemia, hypoglycemia due to alcohol intake, hypoglycemia due to insulin overdose and hypoglycemia in premature infants.
