Peripheral Endocrine Glands Overview

Peripheral Endocrine Glands

• Endocrine control of fuel metabolism is a function of the glands
• Endocrine control of calcium metabolism is a function of the glands
• Adrenal glands function in nutrient metabolism, responding to stress, and maintaining salt balance
• Thyroid gland controls the body's basal metabolic rate

Peripheral Endocrine Glands: Specific Glands

• Pancreas (endocrine): crucial for nutrient metabolism
• Parathyroid glands: vital for calcium metabolism
• Adrenal glands: critical for nutrient metabolism, stress response, and salt balance regulation
• Thyroid: regulates the body's basal metabolic rate

Objectives

• Students will be able to describe nutrient metabolism basics
• Glucose's central role in metabolism will be explained
• Mechanisms of nutrient storage will be explained
• Basic nutrient metabolism terms will be defined
• The pancreas' role in nutrient metabolism will be described
• Major cells and secretions of the endocrine pancreas will be described
• Insulin and glucagon effects will be examined
• Synthesis, control, and feedback mechanisms of insulin and glucagon will be explored

Fuel Metabolism

• Metabolism encompasses all chemical reactions within body cells
• Fuel metabolism (intermediary metabolism): involves the breakdown, synthesis, and transformation of proteins, carbohydrates, and lipids
• Digestion breaks down macromolecules into smaller absorbable subunits

Fuel Metabolism (continued)

• Anabolism: synthesis of large organic molecules, requiring ATP
• Catabolism: breakdown of large molecules, producing ATP
• Reactions like hydrolysis and oxidation are involved in ATP production
• Smaller subunits from catabolism fuel energy and cellular synthesis

Nutrient Storage: Glucose

• Nutrients from meals are stored and released between meals
• Excess glucose is stored as glycogen (liver and skeletal muscles)
• Glycogen storage is limited
• Remaining glucose is stored as triglycerides in adipose tissue.

Nutrient Storage: Glucose (Brain)

• The brain needs a constant glucose supply
• It cannot store glycogen
• Blood glucose levels are strictly regulated
• During fasting, other body cells burn fatty acids, preserving glucose for the brain
• Amino acids can be converted to glucose by gluconeogenesis to supply the brain

Nutrient Storage: Fats and Amino Acids

• Excess circulating fatty acids are incorporated into triglycerides mainly in adipose tissue
• Excess amino acids are converted to glucose and fatty acids, ultimately stored as triglycerides (primarily in adipose tissue)
• Muscles store amino acids as structural proteins
• Proteins are not prioritized for energy unless other sources are insufficient

Nutrient Storage and Use

• Two major metabolic states: absorptive and postabsorptive
• Absorptive state (immediately after eating): Nutrients are absorbed into the bloodstream, and metabolic fuels are stored
• Postabsorptive state (between meals): stored fuels are metabolized to maintain glucose levels and provide energy.

Table: Comparison of Absorptive and Postabsorptive States

• Table details how carbohydrates, fats, and proteins are handled in each state.

Table: Stored Metabolic Fuel in the Body

• Table provides data on fuel types, storage forms, locations, amounts, and roles in the body.

Fuel Metabolism Regulation

• Pancreas (endocrine portion) regulates fuel metabolism using insulin and glucagon
• Pancreas is organized into islets of Langerhans, containing specialized cells.
• Beta cells produce insulin, alpha cells produce glucagon, and other islet cells produce somatostatin.

Insulin Effects

• Insulin lowers blood glucose, fatty acids, and amino acid levels, promoting storage
• Facilitates glucose transport into cells (especially GLUT-4 in muscle and fat)
• Stimulates glycogen synthesis in muscle and liver
• Inhibits glycogenolysis and gluconeogenesis
• Influences fatty acid and amino acid metabolism

Insulin Stimulation

• Elevated blood glucose increases insulin secretion
• Decrease in blood glucose inhibits secretion
• Other factors include blood amino acid levels

Insulin and Glucagon

• Glucagon opposes the effects of insulin and promotes glycogenolysis, gluconeogenesis, and fat breakdown
• Glucagon secretion is increased during the postabsorptive state or when blood glucose levels drop too low
• Glucagon and insulin work together to regulate blood glucose.