ENDOCRINEPART2

• What is the approximate length of the pancreas?


  15 cm
• What is the approximate weight of the pancreas?


  85–100 g
• Where is the pancreas located in relation to the stomach?


  It lies posterior to the stomach
• What are the two main functions of the pancreas?


  Exocrine and endocrine functions
• What are the roles of the pancreas as an exocrine gland?


  • Produces pancreatic juices
  • Contains acini that produce the juices
  • Has a duct system to carry juices to the small intestine
• What are the roles of the pancreas as an endocrine gland?


  • Consists of Islets of Langerhans
  • Secretes hormones into the circulatory system
  • Includes alpha, beta, delta, and F/PP cells
• What hormone is produced by the beta cells of the pancreas?


  Insulin
• What hormone is produced by the alpha cells of the pancreas?


  Glucagon
• What is the chemical class of insulin?


  Protein
• What effect does insulin have on blood glucose levels?


  It reduces blood glucose levels
• What is the effect of glucagon on blood glucose levels?


  It increases blood glucose levels
• What is the role of somatostatin in the pancreas?


  It inhibits insulin and glucagon release
• What is the role of pancreatic polypeptide?


  It plays a role in appetite regulation
• What is the structure of insulin?


  It is a 51 amino acid peptide
• What is the half-life of insulin?


  5 minutes
• How is insulin transported in the circulation?


  It is dissolved in plasma
• When is insulin normally released?


  When glucose levels are high
• What is the relationship between insulin and glucagon?


  They have a reciprocal relationship
• What is the only hormone that decreases glucose levels?


  Insulin
• Where is insulin stored in the body?


  In the liver, skeletal muscle, and adipose tissue
• What metabolic processes does insulin promote?


  • Glycolysis
  • Lipogenesis
  • Glycogenesis
  • Decrease glycogenolysis
• What is proinsulin converted into?


  Insulin and C-peptide
• What is the process of insulin synthesis?


  1. Occurs in rough endoplasmic reticulum of β-cells
  2. Initially produced as Preproinsulin
  3. Cleaved to Proinsulin in the ER
  4. Further cleaved in Golgi to yield Insulin and C-peptide
  5. Packaged in secretory vesicles for release
• What is the most important regulator of insulin secretion?


  Elevated blood glucose level
• What is the threshold plasma glucose level for insulin secretion?


  Approximately 100 mg/dl
• How is insulin secreted in response to blood glucose levels?


  In a biphasic manner
• What happens during the initial burst of insulin secretion?


  It lasts 5-15 minutes from preformed insulin granules
• What are the stimulatory agents for insulin secretion?


  • Hyperglycemia
  • Increased amino acids and fatty acids
  • Gastrointestinal hormones (e.g., gastric-inhibitory peptide, gastrin, secretin)
  • Acetylcholine
• What are the inhibitory agents for insulin secretion?


  • Somatostatin
  • Norepinephrine
  • Epinephrine
• What is the mechanism of insulin secretion in response to glucose?


  1. Glucose binds to GLUT-2 transporter in β cells
  2. Enters cell via facilitated diffusion
  3. Metabolized to generate ATP and NADH
  4. Rise in ATP closes K+ channels, depolarizing β cell
  5. Opens voltage-gated Ca2+ channels, Ca2+ influx stimulates insulin release
  6. Ca2+ influx activates calmodulin and CamK, increasing insulin synthesis
• What are the actions of insulin in the liver?


  • Stimulates glucose oxidation
  • Promotes glucose storage as glycogen
  • Inhibits glycogenolysis
  • Inhibits gluconeogenesis
  • Inhibits ketone formation
• What are the actions of insulin in muscle tissue?


  • Increases uptake of amino acids
  • Increases protein synthesis
  • Decreases protein degradation
  • Promotes glycogen synthesis
• What are the actions of insulin in adipose tissue?


  • Stimulates glucose transport into adipocytes
  • Promotes conversion of glucose into triglycerides and fatty acids
  • Increases fat deposition
  • Decreases fat degradation
• What effect does insulin have on glucagon secretion?


  It decreases glucagon secretion
• What are miscellaneous actions of insulin?


  • Increases Na+-K+ ATPase activity
  • Increases cholesterol biosynthesis
  • Enhances wound healing and microvascular integrity
  • Supports neural integrity and growth factors
• What is the structure of glucagon?


  A 29-amino-acid polypeptide hormone
• What is the primary role of glucagon?


  To increase glucose levels
• When is glucagon released?


  During stress and fasting states
• What is the major target of glucagon?


  The liver
• What are the actions of glucagon in the liver?


  • Promotes gluconeogenesis
  • Increases glycogenolysis
  • Increases ketogenesis