Glucagon and Insulin

Somatostatin, a 14-amino-acid peptide (Figure 37-2), is found in the hypothalamus, other parts of the central nervous system, the pancreas, and other sites in the gastrointestinal tract. It inhibits the release of GH, glucagon, insulin, and gastrin. 

Interrelationship of glucagon, insulin and glucose. The insulino-genlc effect of glucagon. 

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. 

Acetyl-CoA carboxylase is also regulated by hormones such as glucagon, epinephrine, and insulin via... 

In adipose tissue, the effect of the decrease in insulin and increase in glucagon results in inhibition of lipo-genesis, inactivation of lipoprotein lipase, and activation of hormone-sensitive lipase (Chapter 25). This leads to release of increased amounts of glycerol (a substrate for gluconeogenesis in the liver) and free fatty acids, which are used by skeletal muscle and liver as their preferred metabolic fuels, so sparing glucose. 

Insulin and glucagon are produced in the pancreas by cells known as islets of Langerhans. P-Cells make up 70% to 90% of the islets and produce insulin, whereas P-cells produce glucagon. The main function of insulin is to decrease blood glucose levels, whereas glucagon, along with other counterregulatory... 

Discuss functions and factors regulating release of the following hormones thyroid hormones, calcitonin, parathyroid hormone, catecholamines, aldosterone, cortisol, adrenal androgens, insulin, and glucagon... 

When the actions of one hormone oppose the effects of another, the result is antagonism. For example, insulin decreases blood glucose and promotes the formation of fat. Glucagon, on the other hand, increases blood glucose and promotes the degradation of fat. Therefore, the effects of insulin and glucagon are antagonistic. 

Factors that stimulate glucagon secretion include a decrease in blood glucose an increase in blood amino acids sympathetic nervous stimulation stress and exercise. Factors that inhibit glucagon secretion include insulin and an increase in blood glucose. Table 10.2 summarizes the major functions of the hormones discussed in this chapter. 

The answer is a. (Hardman, p 1510.) Although the mechanism of action of metformin and other biguanicies is unclear, biguanides virtually never cause hypoglycemia They operate independently of pancreatic p cells but are not useful in insulin-dependent diabetes mellitus (IDDM). Some possible mechanisms of action are direct stimulation of glycolysis in peripheral tissues, increased sensitivity to insulin, and reduction of glucagon levels. 

The answer is b. (Hardman, p 1507. Katzung, pp 723-724J Three proposed mechanisms for sulfonylurea action are (1) the release of insulin from pancreatic cells, (2) reduction of serum glucagon levels, and (.3) increased binding of insulin to tissue receptors. On binding to a specific receptor that is associated with a K channel in cell membranes, sulfo-nylureas inhibit K efflux, which causes influx of Ca followed by release of preformed insulin. 

True endocrine hormones, however, remain a fairly well defined group. Virtually all of the hormones used therapeutically (discussed below) fit into this grouping. Examples include insulin, glucagon, GH and the gonadotrophins. 

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