Regulation of Blood Glucose Concentration

The concentration of glucose in the blood is regulated by a complex interplay of multiple pathways, modulated by a number of hormones. Glycogenesis is the conversion of glucose to glycogen. The reverse process, namely the break- 

Hormones That Regulate Blood Glucose Concentration 

Insuhn is a protein hormone produced by the (5-ceUs of the islets of Langerhans in the pancreas. Insulin was the first protein hormone to be sequenced, the first substance to be measured by radioimmunoassay (RIA), and the first compound produced by recombinant DNA technology for practical use. It is an anaboUc hormone that stimulates the uptake of glucose into fat and muscle, promotes the conversion of glucose to glycogen or fat for storage, inhibits glucose production by the liver, stimulates protein synthesis, and inhibits protein brealcdown. 

32 proinsuiin is the major proinsuiin conversion inter-mediate. Glucose regulates biosynthesis of both proinsuiin and PCI, but has no effect on PC2 and carboxypeptidase-H. At the cell membrane, insulin and C-peptide are released into the portal circulation in equimolar amounts. In addition, small amounts of proinsuiin and intermediate cleavage forms enter the circulation. 

Degradation. On the first pass through the portal circulation, approximately 50% of the insulin is extracted by the liver, where it is degraded. Because the amount extracted is. variable, plasma insulin concentrations may not accurately reflect the rate of insulin secretion. Additional insulin degradation occurs in the kidneys. Insulin is filtered through the glomeruh, reabsorbed, and degraded in the proximal tubule. The basal insulin secretory rate is about 1 U/hr, with total daily secretion of about 40 U. The half-life of insulin in the circulation is between 4 and 5 minutes. 

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In addition to the common pathways, glycolysis and the TCA cycle, the liver is involved with the pentose phosphate pathway regulation of blood glucose concentration via glycogen turnover and gluconeogenesis interconversion of monosaccharides lipid syntheses lipoprotein formation ketogenesis bile acid and bile salt formation phase I and phase II reactions for detoxification of waste compounds haem synthesis and degradation synthesis of non-essential amino acids and urea synthesis. 

B. Regulation of blood glucose concentration occurs initially through changes in its... 

The regulation of blood glucose concentration serves as a useful example of the control and integration of metabolism. The level of glucose in the portal circulation may vary widely as a... 

Diabetes mellitus — a failure of regulation of blood glucose concentration... 

Storage and utilization of tissue glycogen, maintenance of blood glucose concentration, and other aspects of carbohydrate metabolism are meticulously regulated by hormones, including insulin, glucagon, epinephrine, and the glucocorticoids. 

THE CONCENTRATION OF BLOOD GLUCOSE IS REGULATED WITHIN NARROW LIMITS... 

P cells of the pancreatic islets in combination with atoms of zinc, but when required to regulate blood glucose concentration, the prohormone is cleaved and functional insulin is released into the circulation along with the C-peptide. This example of post-translational processing is mediated by peptidases which are contained in the vesicles along with the proinsulin. The fusion of the secretory vesicles with the cell membrane and activation of the peptidase prior to exocytosis of the insulin are prompted by an influx of calcium ions into the P-cell in response to the appropriate stimulus. Similarly, catecholamines are synthesized and held within the cell by attachment to proteins called chromogranins. 

Figure 3.23 A sequence of processes explaining the role of glucokinase in the liver and fi-cells in regulation of the blood glucose concentration. The increase in the plasma insulin increases glucose uptake by muscle and decreases fatty acid mobilisation from adipose tissue which lowers the plasma fatty acid level which also increases glucose uptake (Chapter 12).

ROLE OF THE LIVER IN THE REGULATION OF THE BLOOD GLUCOSE CONCENTRATION... 

The role of glucagon and insulin in the regulation of glu-coneogenesis, along with other factors, is to maintain the blood glucose concentration in starvation. This is discussed in Chapter 12. 

As discussed in Chapter 5, the body regulates blood glucose concentration through the opposing actions of insulin versus glucagon and epinephrine. 

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