Biochemistry RNB:1903 - Energy Metabolism Quiz

Biochemistry and Nutrition (RNB:1903) - Regulation of Energy Metabolism

• Course title: Biochemistry and Nutrition (RNB:1903)
• Course topic: Regulation of Energy Metabolism
• Instructor: Sumathy Arumugam
• Date: October 27, 2028
• Topics covered:

Subtopics

• The brain and energy metabolism
• Glucagon and insulin (22/10/2021 - 27/10/2023)
• Creatine phosphate
• Creatinine
• Glycogen
• Gluconeogenesis
• Fructose
• Fatty acids
• The Krebs cycles
• Fermentative and aerobic metabolism

Glucagon and Insulin

• Why? Fasting can cause headaches due to lack of glucose. Glucose is needed for proper brain function.
• Insulin's role: Adipose cells take up glucose. Decreasing blood sugar level triggers the pancreas to release insulin.
• Glucagon's role: Eating causes increasing blood sugar. Pancreatic alpha cells release glucagon. The liver breaks down glycogen to glucose. Exercise decreases blood sugar, causing the release of glucagon.

Introduction

• Insulin and glucagon are hormones that regulate blood glucose levels.
• Glucose (from food) fuels the body by moving through the bloodstream.
• Insulin and glucagon work together to maintain blood sugar levels within a normal range.

Learning Outcomes

• Describe the biological actions of insulin and glucagon.
• List the major target organs for insulin.
• Identify the effect of insulin on the target organs.
• Describe the control of glucagon secretion.
• Identify the target organ for glucagon.

Description - Insulin

• Pancreatic endocrine cells, located in islets, contain four cell types.
• Beta cells (75%) secrete insulin.
• Alpha cells (20%) secrete glucagon.
• Delta cells (δ) secrete somatostatin (SRIF) inhibiting both insulin and glucagon secretion.
• Glucose stimulated insulin secretion (GSIS) is the process by which insulin is secreted.
• Insulin secretion occurs in a biphasic manner with an initial burst and a more gradual, sustained release. The initial burst lasts 5-15 minutes, then a second more gradual release follows, lasting 30 minutes.
• The half-life of insulin is approximately 5 minutes.
• Insulin is primarily degraded in the liver and kidneys.
• Insulin secretion is regulated by factors other than glucose, including plasma amino acids and glucagon-like peptide from the small intestine.

Insulin Secretion Mechanism

• Glucose enters the beta cells through GLUT 1/2, triggering ATP/ADP, thereby depolarizing the cell.
• Open Ca2+ channels allow Ca2+ influx, causing insulin release.
• Increased Ca2+ triggers two phases in insulin release. Immediately releasable pool or amplifying pathways in the second phase.

Insulin Deficiency Problems

• Problems arise from reduced glucose uptake into tissues (energy starvation) and increased glucose release from the liver (hyperglycemia).
• These factors lead to too little glucose in cells and too much glucose in the blood (hyperglycemia).

Positive and Negative Regulation of Insulin Secretion

• Insulin secretion is influenced by feed-forward mechanisms such as glucagon-like peptide (GLP-1) and parasympathetic nervous system activity,
• Negative feedback mechanisms such as sympathetic nervous system activity (SNS) and plasma epinephrine.

Effects of Insulin on Target Organs

• Liver: Promotes glycogen synthesis, inhibits glycogenolysis.
• Muscle: Promotes glucose uptake and protein synthesis.
• Adipose tissue: Encourages lipogenesis, inhibits lipolysis.

Description - Glucagon

• Glucagon is a peptide hormone secreted by pancreatic alpha cells when blood glucose levels are low (less than 4.4 mmol/L or 80 mg/dL).

• Glucagon circulates unbound and has a half-life of 6 minutes.

• The target tissue for glucagon is the liver. Glucagon binds to plasma membrane receptors, initiating a second messenger signaling cascade in the liver, increasing stored glycogen release in the liver.

• Glucagon acts synergistically with cortisol and epinephrine to increase blood glucose levels.

Summary

• The endocrine pancreas regulates fuel homeostasis in both fed and fasting states by producing insulin and glucagon.
• Insulin promotes storage of excess nutrients in the fed state, targeting liver, muscle, and adipose tissue.
• Glucagon promotes the movement of stored nutrients into the bloodstream in the fasting state, targeting the liver mainly.
• Glucose levels regulate insulin and glucagon secretion.