Pancreas Endo- and Exocrine Gland PDF

Pancreas endo-and exocrine gland Konstantinos Ekmektzoglou MD, PhD, FEBGH Assistant Professor School of Medicine European University Cyprus October 2024 Anatomical Position The pancreas is an oblong-shaped organ positioned at the level of the transpyloric plane (L1). With the exception of t...

Pancreas endo-and exocrine gland Konstantinos Ekmektzoglou MD, PhD, FEBGH Assistant Professor School of Medicine European University Cyprus October 2024 Anatomical Position The pancreas is an oblong-shaped organ positioned at the level of the transpyloric plane (L1). With the exception of the tail of the pancreas, it is a retroperitoneal organ, located deep within the upper abdomen in the epigastrium and left hypochondrium regions. Duct System The intercalated ducts unite with those draining adjacent lobules and drain into a network of intralobular collecting ducts, which in turn drain into the main pancreatic duct. The pancreatic duct runs the length of the pancreas and unites with the common bile duct, forming the hepatopancreatic ampulla of Vater. This structure then opens into the duodenum via the major duodenal papilla. Secretions into the duodenum are controlled by a muscular valve – the sphincter of Oddi. It surrounds the ampulla of Vater, acting as a valve. Anatomical Structure Head – the widest part of the pancreas. It lies within the C-shaped curve created by the duodenum and is connected to it by connective tissue. Uncinate process – a projection arising from the lower part of the head and extending medially to lie beneath the body of the pancreas. It lies posterior to the superior mesenteric vessels. Neck – located between the head and the body of the pancreas. It overlies the superior mesenteric vessels which form a groove in its posterior aspect. Body – centrally located, crossing the midline of the human body to lie behind the stomach and to the left of the superior mesenteric vessels. Tail – the left end of the pancreas that lies within close proximity to the hilum of the spleen. It is contained within the splenorenal ligament with the splenic vessels. This is the only part of the pancreas that is intraperitoneal.  Physiological Anatomy of the Pancreas The pancreas is composed of two major types of tissues (1) the acini, which secrete digestive juices into the duodenum (2) the islets of Langerhans, which secrete insulin and glucagon directly into the blood EXOCRINE pancreatic digestive enzymes secreted by pancreatic acini sodium bicarbonate secreted by small ductules and larger ducts leading from the acini ▼ flow through the pancreatic duct (in response to the presence of chyme in the upper portions of the small intestine) ENDOCRINE Insulin (beta cells) glucagon (alpha cells) somatostatin (delta cells) by the islets of Langerhans that occur in islet patches throughout the pancreas ▼ directly into the blood (not into the intestine) PANCREATIC DIGESTIVE ENZYMES ROLE to digest all the three major types of food Proteins Carbohydrates Fats ALSO contains large quantities of bicarbonate ions Neutralize the acidity of the chyme emptied from the stomach into the duodenum Trypsin Chymotrypsin Carboxypolypeptidase DO NOT FORGET When first synthesized in the pancreatic cells, the proteolytic digestive enzymes are in the inactive forms enzyme secreted by the intestinal mucosa when Trypsinogen enterokinase Trypsin chyme comes in contact with the mucosa Chymotrypsinogen Chymotrypsin Procarboxypolypeptidase Carboxypolypeptidase IS IT IMPORTANT? THIS CANNOT HAPPEN DUE TO TRYPSIN INHIBITOR TRYPSIN INHIBITOR prevents activation of trypsin both inside the secretory cells and in the acini and ducts of the pancreas  splits FAs from Phospho- lipids hydrolysis of cholesterol AAs esters disaccharides and trisaccharides FAs and peptides mono- glycerides Bicarbonate ions and water Secreted mainly by the epithelial cells of the ductules and ducts that lead from the acini cellular mechanism for secreting sodium bicarbonate solution CO2 and H2O combine in acinar cells to form H2CO3 H2CO3 dissociates into H+ and HCO3 – H + is transported into blood by Na+ - H+ exchanger at basolateral membrane of ductal cells HCO3 - is secreted into pancreatic juice by Cl- -HCO3 - exchanger at apical membrane of ductal cells Absorption of H+ causes acidification of pancreatic venous blood REGULATION OF PANCREATIC SECRETION Acetylcholine released from the parasympathetic vagus nerve endings and from other cholinergic nerves in the enteric nervous system Cholecystokinin Secretin secreted by the secreted by the duodenal and duodenal and upper jejunal jejunal mucosa mucosa when food when highly acidic enters the small food enters the intestine small intestine Acetylcholine and cholecystokinin stimulate the acinar cells of the pancreas, causing production of large quantities of pancreatic digestive enzymes but relatively small quantities of water and electrolytes to go with the enzymes Secretin stimulates secretion of large quantities of water solution of sodium bicarbonate by the pancreatic ductal epithelium REGULATION OF PANCREATIC SECRETION REGULATION OF PANCREATIC SECRETION REGULATION OF PANCREATIC SECRETION Secretin IS CRUCIAL FOR 2 REASONS released from the small intestine when the pH of the duodenal contents falls < 4.5- 5.0, and its release increases greatly as the pH < 3.0 copious secretion of pancreatic juice that contains abundant amounts of sodium bicarbonate the acid contents that are emptied into the duodenum from the stomach become neutralized peptic digestive activity by the gastric juices in the duodenum is immediately blocked (the mucosa of the small intestine cannot withstand the digestive action of acid gastric juice THEREFORE NO ULCERS) Bicarbonate ion secretion by the pancreas provides an appropriate pH for action of the pancreatic digestive enzymes, which function optimally in a slightly alkaline or neutral medium, at a pH of 7.0-8.0 Disorders of the… Hormones of the Pancreas Associated hormones Chemical class Effect Reduces blood glucose Insulin (beta cells) Protein levels Increases blood glucose Glucagon (alpha cells) Protein levels Inhibits insulin and Somatostatin (delta cells) Protein glucagon release Pancreatic polypeptide (PP Protein Role in appetite cells) REGULATION OF BLOOD GLUCOSE LEVELS BY INSULIN AND GLUCAGON Glucose is required for cellular respiration and is the preferred fuel for all body cells. The body derives glucose from the breakdown of the carbohydrate- containing foods and drinks we consume. Glucose not immediately taken up by cells for fuel can be stored by the liver and muscles as glycogen, or converted to triglycerides and stored in the adipose tissue. Hormones regulate both the storage and the utilization of glucose as required. Receptors located in the pancreas sense blood glucose levels, and subsequently the pancreatic cells secrete glucagon or insulin to maintain normal levels. GLUCAGON Receptors in the pancreas can sense the decline in blood glucose levels, such as during periods of fasting or during prolonged labor or exercise. In response, the alpha cells of the pancreas secrete the hormone glucagon, which has several effects: It stimulates the liver to convert its stores of glycogen back into glucose. This response is known as glycogenolysis. The glucose is then released into the circulation for use by body cells. It stimulates the liver to take up amino acids from the blood and convert them into glucose. This response is known as gluconeogenesis. It stimulates lipolysis, the breakdown of stored triglycerides into free fatty acids and glycerol. Some of the free glycerol released into the bloodstream travels to the liver, which converts it into glucose. This is also a form of gluconeogenesis. GLUCAGON Taken together, these actions increase blood glucose levels. The activity of glucagon is regulated through a negative feedback mechanism; rising blood glucose levels inhibit further glucagon production and secretion. Homeostatic Regulation of Blood Glucose Levels. Blood glucose concentration is tightly maintained between 70 mg/dL and 110 mg/dL. If blood glucose concentration rises above this range, insulin is released, which stimulates body cells to remove glucose from the blood. If blood glucose concentration drops below this range, glucagon is released, which stimulates body cells to release glucose into the blood. INSULIN The primary function of insulin is to facilitate the uptake of glucose into body cells. Red blood cells, as well as cells of the brain, liver, kidneys, and the lining of the small intestine, do not have insulin receptors on their cell membranes and do not require insulin for glucose uptake. Although all other body cells do require insulin if they are to take glucose from the bloodstream, skeletal muscle cells and adipose cells are the primary targets of insulin. The presence of food in the intestine triggers the release of gastrointestinal tract hormones such as glucose-dependent insulinotropic peptide (previously known as gastric inhibitory peptide). This is in turn the initial trigger for insulin production and secretion by the beta cells of the pancreas. Once nutrient absorption occurs, the resulting surge in blood glucose levels further stimulates insulin secretion. INSULIN Precisely how insulin facilitates glucose uptake is not entirely clear. However, insulin appears to activate a tyrosine kinase receptor, triggering the phosphorylation of many substrates within the cell. These multiple biochemical reactions converge to support the movement of intracellular vesicles containing facilitative glucose transporters to the cell membrane. In the absence of insulin, these transport proteins are normally recycled slowly between the cell membrane and cell interior. Insulin triggers the rapid movement of a pool of glucose transporter vesicles to the cell membrane, where they fuse and expose the glucose transporters to the extracellular fluid. The transporters then move glucose by facilitated diffusion into the cell interior. INSULIN 1.Insulin also reduces blood glucose levels by stimulating glycolysis, the metabolism of glucose for generation of ATP. 2.Moreover, it stimulates the liver to convert excess glucose into glycogen for storage, 3. it inhibits enzymes involved in glycogenolysis and gluconeogenesis. 4.insulin promotes triglyceride and protein synthesis. The secretion of insulin is regulated through a negative feedback mechanism. As blood glucose levels decrease, further insulin release is inhibited.