Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Endocrine System
Classification, Structure, and Functions of Endocrine Glands
Endocrine Portion of the Pancreas

The Endocrine portion of the Pancreas (pancreatic islets, islets of Langerhans) consists of Cell clusters richly supplied with Blood capillaries. The total number of islets ranges from 1 to 2 million, with each measuring 100—300 µm in diameter. The pancreatic islets are predominantly composed of so-called beta (β) Cells (60—80%), which secrete the hormone Insulin. They also contain alpha (α) cells (10—30%), which produce Glucagon. Additionally, the pancreas produces lipokain, which promotes fat oxidation in the Liver; vagotonin, which enhances vagal nerve activity and increases the tone of the parasympathetic Autonomic Nervous system; and centropenin, which stimulates the nerve Cells of the respiratory center and dilates the Bronchi.

The hormone insulin promotes the uptake of glucose from the blood into liver cells, Skeletal Muscle fibers, cardiac muscle cells, and smooth muscle. Under METABOLISM/18.html">The Influence of insulin, Glycogen is synthesized from glucose in these Organs. Insulin also facilitates The entry of glucose into fat cells, where it is converted into fats. Furthermore, insulin increases the permeability of cell membranes to Amino Acids, which is essential for Protein Synthesis.

Thus, thanks to insulin, glucose is utilized within cells as both an energy source and a building block for tissue.

Glucagon acts differently than insulin. It breaks down glycogen in the liver, increases blood sugar levels, and stimulates fat breakdown in adipose tissue.

The secretion of both insulin and glucagon is regulated by the autonomic nervous system. The Vagus nerve stimulates insulin production, whereas the sympathetic nervous system inhibits its secretion. Elevated blood sugar levels during Digestion lead to increased insulin secretion due to the activation of vagal nuclei. Conversely, a drop in blood sugar inhibits insulin release while increasing glucagon output. As a result, through the alternating or simultaneous release of these Hormones, blood glucose Homeostasis is maintained at a constant level of 80—120 mg%.

Deficiency in the internal secretory function of the pancreas leads to a severe condition known as Diabetes Mellitus. In this disorder, insulin deficiency causes a sharp spike in blood glucose levels, sometimes reaching 300—400 mg%. When blood sugar exceeds 150—180 mg, it spills over into the urine and is excreted from the body—a condition known as glucosuria. Sugar is eliminated alongside large amounts of Water, causing patients to excrete up to 4—5 liters of urine daily. This disrupts metabolic processes and drastically accelerates the Breakdown of Proteins and fats normally used for energy. Consequently, products of incomplete fat oxidation and intermediate Protein metabolism accumulate in the body. Affected individuals experience intense thirst, cardiovascular and respiratory dysfunction, and rapid fatigue.

Because their bodies lack or produce insufficient insulin, patients with diabetes mellitus must take exogenous insulin on a regular basis, with strict dosage control. An insulin overdose can cause a precipitous drop in blood sugar levels, potentially leading to hypoglycemic coma. In such cases, immediate intravenous administration of glucose is indicated.