Peripheral Endocrine Glands 1 PDF

The Peripheral Endocrine Glands 1 Goldsmith ⚫ Endocrine control of fuel metabolism ⚫ Endocrine control of calcium metabolism ⚫ Adrenal glands ⚫ Thyroid gland Peripheral endocrine glands ⚫ Endocrine pancreas: important in metabolizing nutrients ⚫...

The Peripheral Endocrine Glands 1 Goldsmith ⚫ Endocrine control of fuel metabolism ⚫ Endocrine control of calcium metabolism ⚫ Adrenal glands ⚫ Thyroid gland Peripheral endocrine glands ⚫ Endocrine pancreas: important in metabolizing nutrients ⚫ Parathyroid glands: important for Ca2+ metabolism ⚫ Adrenal glands: important for metabolizing nutrients, adapting to stress, maintaining salt balance ⚫ Thyroid: controls body’s basal metabolic rate 1  Objectives ⚫ After completion of this section, you will be able to: ⚫ describe the basics of nutrient metabolism ⚫ explain the central role of glucose in metabolism ⚫ explain the means by which nutrients are stored ⚫ define basic terms associated with nutrient metabolism ⚫ describe the pancreas’ role in nutrient metabolism ⚫ Describe the major cells of the endocrine pancreas and their secretions ⚫ Explain the effects of insulin and glucagon ⚫ Explain the synthesis of, control of production, and feedback for insulin and glucagon Fuel metabolism ⚫ Metabolism: all of the chemical reactions within the cells of the body ⚫ Fuel metabolism (AKA, intermediary metabolism): degradation, synthesis, and transformation of proteins, carbohydrates, and lipids ⚫ Digestion: macromolecules broken down into smaller absorbable subunits 2  Fuel metabolism (cont.) ⚫ Anabolism: synthesis of large organic molecules ⚫ Anabolic reactions require ATP ⚫ Catabolism: breakdown of large molecules ⚫ Reactions (hydrolysis and oxidation) make ATP ⚫ Smaller subunits produced by catabolism can be used for energy or cellular synthesis 3 Nutrient storage: glucose ⚫ Nutrients from meals must be stored and released between meals ⚫ Excess circulating glucose: stored as glycogen in the liver and skeletal muscles ⚫ Glycogen storage is limited ⚫ Once reach limit, rest is stored as triglycerides in adipose tissue Nutrient storage: glucose ⚫ The brain needs a constant supply of glucose ⚫ Cannot store glycogen ⚫ Thus, blood glucose concentration highly regulated ⚫ Fasting: many body cells burn fatty acids to spare glucose for the brain ⚫ To supply the brain, amino acids can be converted to glucose by gluconeogenesis 4  Nutrient storage: fat acids and amino acids ⚫ Excess circulating fatty acids: incorporated into triglycerides, mainly in adipose tissue ⚫ Excess amino acids: converted to glucose and fatty acids; ultimately stored as triglycerides in adipose tissue ⚫ Muscles are the main site of amino acid storage via structural proteins ⚫ Proteins are not first choice for E, though, as they serve essential functions Nutrient storage and use ⚫ Two functional metabolic states: ⚫ Absorptive (fed) state: occurs when ingested nutrients are being absorbed into the blood following a meal (~ 4 hours) ⚫ Metabolic fuels are stored during the absorptive state ⚫ Postabsorptive (fasting) state: Nutrients are not being absorbed at this time (between meals) ⚫ Metabolic fuels are mobilized during the postabsorptive state ⚫ Stored molecules are catabolized to maintain glucose concentration and for E production 5 6 Fuel metabolism regulation ⚫ Insulin and glucagon from pancreas regulate fuel metabolism ⚫ Pancreas: Endocrine cells in pancreas organized into the islets of Langerhans ⚫ b cells produce insulin ⚫ a cells produce glucagon ⚫ Somatostatin from pancreatic D cells can inhibit both ⚫ Epsilon cells: ghrelin ⚫ Gamma, or F cells: pancreatic polypeptide 7  Insulin: effects ⚫ Lowers blood glucose, fatty acid, and amino acid levels; promotes their storage ⚫ Facilitates glucose transport into most cells ⚫ Glucose transporters (GLUTs) act as plasma membrane carriers to accomplish this process: ONLY GLUT-4 is insulin responsive (skeletal muscle during rest and adipose cells) ⚫ Insulin and this transporter also assist the transport of fatty acids into tissues ⚫ Stimulates glycogenesis in skeletal muscle and liver cells ⚫ Inhibits glycogenolysis and gluconeogenesis ⚫ Catalyzes the production of fatty acids from glucose ⚫ Promotes entry of fatty acids from blood into adipose ⚫ Promotes the transport and incorporation of amino acids into cells for protein synthesis Insulin stimulation ⚫ Increase in blood glucose concentration (e.g., during absorptive state) increases insulin secretion* ⚫ This brings blood glucose down to a normal level ⚫ Decrease in glucose below normal inhibits insulin secretion ⚫ This shifts metabolism from the absorptive to the postabsorptive state ⚫ Elevated blood amino acids stimulate insulin secretion ⚫ Gastrointestinal hormones stimulate insulin secretion ⚫ Parasympathetic nervous system increases insulin secretion (sympathetic decreases) ⚫ Inadequate insulin action produces diabetes mellitus, resulting in hyperglycemia ⚫ Type I diabetes mellitus: due to insulin deficiency ⚫ Type II: due to reduced sensitivity of target cells to insulin 8 Insulin secretion 9  Glucagon ⚫ Opposes the actions of insulin ⚫ Promotes glycogenolysis and stimulates gluconeogenesis ⚫ Promotes fat breakdown ⚫ Promotes protein breakdown in the liver ⚫ Glucagon secretion increases during the postabsorptive state ⚫ Secretion increases when blood glucose concentration is too low Glucagon (cont.) ⚫ No known abnormalities due to glucagon deficiency ⚫ However, excess glucagon can aggravate the hyperglycemia of diabetes mellitus ⚫ Growth hormone, cortisol, epinephrine, and glucagon are insulin antagonists ⚫ That is, they increase blood glucose ⚫ Insulin and glucagon work as a team to control blood concentration of glucose and fatty acids 10 11