Endocrinology4

Endocrinology4 - THE PANCREAS AS AN ENDOCRINE ORGAN...

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THE PANCREAS AS AN ENDOCRINE ORGAN -located behind the stomach and has both endocrine and exocrine functions. 99 % of pancreas is exocrine and secretes the digestive enzymes . -However, scattered between the acini of the exocrine pancreas are small structures, the islets of Langerhans , which are endocrine structures - compact mass of cells with good vascularization. About 60 % of the cells of the islets of Langerhans are known as beta-cells and synthesize insulin . About 25 % of the cells of the islets are alpha-cells and synthesize glucagon . In addition to alpha- and beta- cells there are smaller numbers of other types of cells for example the delta cells, which synthesize somatostatin and others. -insulin and glucagon: small protein hormones and both control of glucose concentration in blood. -insulin is more important than glucagon and insulin deficiency or absence compromises significantly the well being of the individual and if not treated may lead to death.
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- Insulin controls blood glucose concentrations - only hormone that acts primarily to decrease blood glucose -glucose always present in the blood (the fasting level is about 80mg/100ml). However, very little free in tissues. Glucose does not diffuse very readily into most cells except in brain – must be transported. When it enters it is rapidly esterified with phosphate and (a) in the liver and muscle cells is converted to glycogen, (b) in the adipose tissue is converted to fat and stored for later use and (c) in many cells of the body is oxidized to produce energy . Insulin receptor: membrane receptor, stimulates insertion of glucose transport proteins stored in cytoplasm into plasma membrane – increases glucose uptake. ACTIONS OF INSULIN: Figure 4.8
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Insulin deficiency Results when the β -cells are destroyed, will lead to Diabetes Mellitus - most tissues cannot take up glucose efficiently, glucose accumulates in circulation -occurs even if no glucose in diet because of increased gluconeogenesis (e.g. breakdown of non-structural proteins to amino acids and synthesis of glucose). -Under these conditions free fatty acids (FFA), becomes the principal source of energy – increased lipolysis. -However, fat inefficiently used - incomplete oxidation of FFA and increased circulating acetoacetic acid and β -hydroxybutyric acid (metabolic acidosis) and acetone (ketosis - acetone smell in breath of untreated diabetics). -leads to decreased blood pH, diabetic coma and death unless appropriate treatment is provided. Figure 4.9
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OTHER SYMPTOMS OF DIABETES MELLITUS: -increase in blood glucose. -At >180mg% glucose spills over into urine, causing glycosurea . -leads to loss of water in urine, causing polyurea - dehydration and increased thirst ( polydipsia ). As mentioned above, untreated diabetes leads to ketosis, and metabolic acidosis. -administration of insulin is needed to restore individual back to normal.
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Endocrinology4 - THE PANCREAS AS AN ENDOCRINE ORGAN...

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