Pankreas Fizyolojisi
Özet
Pankreas, l-1 ve l-2 hizasında yer alan, %85'i ekzokrin ve %2'si endokrin dokudan oluşan retroperitoneal bir bezdir. Ekzokrin pankreas; nöral ve hormonal sistemlerin kontrolü altında duodenuma günlük yaklaşık 1500-2000 ml bikarbonattan zengin ve inaktif sindirim enzimleri içeren sıvı salgılar. Asiner hücrelerde üretilen tripsinojen, kimotripsin ve elastaz gibi proteolitik enzimler, kendi kendini sindirmeyi önlemek için tripsin inhibitörüyle birlikte inaktif olarak depolanır ve duodenuma ulaştığında enterokinaz ile aktive edilir. Kanal hücrelerinden su ve bikarbonat salgılanması ise mide asidini nötralize etmek için sekretin ve CFTR protein kanalları aracılığıyla düzenlenir. Endokrin fonksiyon ise Langerhans adacıklarındaki beş farklı hücre tipi tarafından yürütülür. Alfa hücrelerinden salgılanan glukagon glikojenoliz ve glukoneogenezi artırırken, beta hücrelerinden salgılanan insülin glukoz homeostazını ve enerji depolanmasını sağlar. Delta hücreleri somatostatin, epsilon hücreleri ghrelin ve upsilon hücreleri ise pankreas polipeptidi salgılayarak bu hormonal döngüyü parakrin etkileşimlerle modüle eder. Pankreas fizyolojisindeki bozukluklar; beta hücre hasarıyla seyreden Tip 1 ve insülin direnciyle karakterize Tip 2 Diabetes Mellitus, CFTR mutasyonuna bağlı Kistik Fibroz, enzimlerin erken aktivasyonuyla tetiklenen Akut Pankreatit ile Kronik ve Otoimmun Pankreatit gibi ciddi klinik tablolara yol açar.
The pancreas is a retroperitoneal gland located at the L-1 and L-2 levels, consisting of 85% exocrine and 2% endocrine tissue. Under neural and hormonal control, the exocrine pancreas secretes approximately 1500-2000 ml of fluid daily into the duodenum, which is rich in bicarbonate and contains inactive digestive enzymes. Proteolytic enzymes like trypsinogen, chymotrypsin, and elastase produced in acinar cells are stored in inactive forms alongside trypsin inhibitors to prevent autodigestion, and are activated by enterokinase upon reaching the duodenum. Water and bicarbonate secretion from ductal cells is regulated via secretin and CFTR protein channels to neutralize gastric acid. Endocrine function is carried out by five distinct cell types within the islets of Langerhans. Glucagon secreted from alpha cells increases glycogenolysis and gluconeogenesis, while insulin from beta cells ensures glucose homeostasis and energy storage. Delta cells secrete somatostatin, epsilon cells secrete ghrelin, and upsilon cells secrete pancreatic polypeptide, modulating this hormonal cycle through paracrine interactions. Defects in pancreatic physiology lead to severe clinical conditions, including Type 1 Diabetes Mellitus with beta-cell destruction, Type 2 Diabetes Mellitus with insulin resistance, Cystic Fibrosis linked to CFTR mutations, Acute Pancreatitis triggered by premature enzyme activation, and Chronic and Autoimmune Pancreatitis.
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