Exocrine Pancreas - Dra. Guzman - 2024.pdf

EXOCRINE PANCREAS Dra. Yisel Mi Guzmán Leguel [email protected] EXOCRINE PANCREAS Learning Objectives Describe the general characteristics of the pancreas as an exocrine gland Review the special histological features of the pancreatic acinar cells and how do they produce and secrete dige...

EXOCRINE PANCREAS Dra. Yisel Mi Guzmán Leguel [email protected] EXOCRINE PANCREAS Learning Objectives Describe the general characteristics of the pancreas as an exocrine gland Review the special histological features of the pancreatic acinar cells and how do they produce and secrete digestion proteins Describe the regulation of the pancreatic secretion Describe duct cells and how the change in electrolytes happen Anatomy of the pancreas It is a retroperitoneal organ, located deep within the upper abdomen in the epigastrium and left hypochondrium regions. Function Its main function is to aid in the digestion of food - Neutralizes the acidic gastric contents that enter the small intestine - Completes the intraluminal digestion of ingested carbohydrates, protein, and fat. Morphology Intercalated ducts merge to form intralobular ducts, which in turn merge to form interlobular ducts, and then the main pancreatic duct. Each secretory unit is composed of an acinus and a small intercalated duct. The acinus represents a cluster of 15 to 100 acinar cells that synthesize and secrete proteins into the lumen of the epithelial structure. The fundamental secretory unit is composed of an acinus and an intercalated duct. Acinar cells are polarized epithelial cells that are specialized for the production and export of large quantities of protein. Pancreas Salivary Glands The secretory granules of pancreatic acinar cells contain the mixture of zymogens and enzymes required for digestion The secretory granules of salivary acinar cells contain either αamylase or mucins Uniform Focal nodules of condensation within the granules Synthesis of secretory proteins ✓ The cellular uptake of aa and their incorporation into the rough endoplasmic reticulum (ER). ✓ Golgi complex, secretory proteins are segregated away from lysosomal enzymes. ✓ Exit the Golgi complex in condensing vacuoles or immature secretory granules. ✓ Maturation: condensation of the proteins within the vacuole and pinching off membrane vesicles. The most characteristic feature of the acinar cell is the abundance of electron-dense secretory granules at the apical pole of the cell. Stimulation of cell-surface receptors by either hormones or neurotransmitters Exocytosis Process by which secretory granules release their contents 1. Movement of the granules to the apical membrane 2. Fusion of these granules with the membrane vacuolar -type H 3. Release of their contents into the acinar lumen HCl ATP H+ H+ ClCl- H+ Cl- Cl- After fusion, the granule contents enter the acinar lumen and move down the ducts into the gastrointestinal tract. Duct cells Pancreas are epithelial cells specialized for fluid and electrolyte transport Salivary Glands The epithelial cells of the most proximal (intercalated) duct are squamous or low cuboidal, have an abundance of mitochondria Progressing distally, the cells become more cuboidal columnar and contain more cytoplasmic vesicles and granules. Secretin Gastrointestinal hormone that stimulates HCO3 secretion by the pancreatic duct The duct cells have secretin receptors Ach= Acetylcholine CCK= Cholecystokinin GRP= Gastrin-releasing peptide Activation of the secretin receptor on the duct cell stimulates adenylyl cyclase, which raises (cAMP) cAMP analogs stimulate ductal HCO3 secretion. The secretin response has been attributed to its effect on (cAMP) and activation of PKA. Secretin acts by stimulating the apical CFTR Cl − channel and the basolateral Na/HCO 3 cotransporter without affecting the Na-H exchanger. Ach activates Ca dependent protein kinases (PKC) Neutralizes the acidic gastric contents that enter the small intestine CCK Is a physiological mediator of pancreatic protein secretion Is secreted by the I cells of the duodenum in response to small peptides, amino acids, and fatty acids in the duodenal lumen Direct pathway Indirect pathway CCK stimulates enzyme secretion through a CCK 1 receptor on the acinar cell CCK stimulates enzyme secretion by activating the parasympathetic) nervous system. ACINAR CELL It acts on the acinar cells to increase enzyme secretion (amylase, lipases, proteases). CKK also potentiates the effect of secretin of stimulation of HCO3 − secretion. Inactive proenzymes Enterokinase Active enzymes DIGESTIVE ENZYMES SECRETED AS INACTIVE PROENZYMES Pancreatic Juice Is a protein-rich, alkaline secretion The secretory proteins responsible for digestion can be classified according to their substrates: • Proteases hydrolyze proteins • Amylases digest carbohydrates • Lipases and phospholipases break down lipids • Nucleases digest nucleic acids. PANCREATIC FLOW RATE Low flow rates: the pancreas secretes an isotonic fluid that is composed mainly of Na+ and Cl – High flow rates, the pancreas secretes an isotonic fluid that is composed mainly of Na+ and HCO3 -. Fasting state The pancreas has a basal rate of secretion even when food is not being eaten or digested. During this interdigestive (fasting) period, pancreatic secretions vary cyclically. I) Pancreatic secretion is minimal when intestinal motility is in its quiescent phase. II) Biliary and gastric secretions are also minimal at this time. III) Duodenal motility increase so does the pancreatic secretion. Enzyme secretion is maximal when intestinal motility is also maximal IV) Followed by a declining period Summary Question A 20-year-old female patient of European descent goes to your consulting room for regular check up. She has been diagnosed since she was 2 years old with cystic fibrosis. She asks you when she will be cured. However, you know that the disease is a progressive pancreatic and pulmonary insufficiency resulting from the complications of organ obstruction by thickened secretions. And that it is due to mutations in the CF gene that alter the function of CFTR. In which pancreatic cells can we find this regulator? a. Apical membrane of pancreatic duct cells b. Beta Cells c. Delta Cells d. Alpha Cells e. Apical membrane of the acinar cells Duct cells Bibliography • Boron, Walter F., MD, PhD, Medical Physiology, Third Edition. 2017 Elsevier. Chapter 43, 879-898