32 Questions
What is the effect of adrenaline on insulin secretion?
It inhibits insulin secretion
What is the primary function of glucagon in the body?
To prevent hypoglycaemia after a protein meal
What is the result of insulin binding to its receptor on the pancreatic β cell?
K+ channel closes, leading to insulin secretion
What is the role of Ca+ in insulin secretion?
It stimulates insulin secretion by opening the Ca+ channel
What is the result of insulin promoting fuel storage after a meal?
All of the above
What is the structure of the insulin receptor?
A glycoprotein receptor with multiple subunits
What is the primary function of insulin in the body?
To decrease blood glucose levels
What is the primary function of glucagon in the body?
To increase blood glucose levels
What is the primary location of the pancreatic islets?
Pancreas
What type of modification occurs to enzymes in response to changes in metabolic patterns?
Covalent modification
What is the primary stimulus for insulin secretion?
A rise in amino acid concentration in the blood
What is the primary function of the δ cells in the pancreatic islets?
To secrete somatostatin
What is the percentage of the pancreatic mass that is composed of islets?
2%
What is the primary mechanism by which the body stores metabolic fuel?
Storing metabolic fuel
Which of the following tissues do not require insulin to use glucose?
Erythrocytes
What is the effect of high concentrations of insulin on its receptors?
Down-regulation
What is the primary function of glucagon during fasting?
Gluconeogenesis
What is the effect of adrenaline on muscle and liver?
Stimulates glycogenolysis
What is the primary function of cortisol?
Provides for long-term energy requirements
What happens to blood glucose and insulin levels after a high-carbohydrate meal?
Blood glucose increases and insulin increases
What is the role of the liver in the fed state?
Receives nutrients first from the hepatic portal vein
What is the effect of glucokinase on glucose metabolism in the liver?
Activates glycolysis
What is the function of the β subunit of the insulin receptor?
It activates tyrosine kinase
What is the role of PI3 kinase in the insulin signaling pathway?
It converts PI(4,5)P2 to PI(3,4,5)P3
What is the effect of insulin on glycogen synthesis in muscle and liver?
It activates glycogen synthase
What is the role of Akt/PKB in glucose transport?
It promotes glucose uptake by translocating GLUT4
What is the effect of insulin on lipolysis in adipocytes?
It inhibits lipolysis by activating Akt/PKB
What is the role of Ras in the insulin signaling pathway?
It activates MAPK
What is the effect of insulin on gene expression?
It promotes gene expression through Ras and MAPK
What is the role of SHC in the insulin signaling pathway?
It activates Ras
What is the effect of insulin on GLUT4 in muscle and adipose tissue?
It promotes the appearance of GLUT4
What is the role of PDK1 in the insulin signaling pathway?
It activates Akt/PKB
Study Notes
Hormonal Regulation of Metabolism
- The demand for fuel is constant, but the supply is intermittent, and the body adapts by storing metabolic fuel when available and mobilizing it in starvation, injury, and stress.
Changes in Metabolic Patterns
- Changes in metabolic patterns are achieved through:
- Variation in the amount of available fatty acid (FA) use in starvation
- Allosteric effects on enzymes (e.g., AMP and PFK in muscle)
- Covalent modification of enzymes (e.g., phosphorylation of glycogen phosphorylase and synthetase)
- Changes in enzyme synthesis (e.g., glucokinase and dietary CHO, HMG CoA reductase, and cholesterol synthesis)
Main Hormones Controlling Intermediary Metabolism
- Insulin and glucagon are the prime regulators of metabolism
- Insulin is the only hypoglycaemic hormone and promotes fuel storage after a meal, growth, glycogen synthesis, fatty acid synthesis, and amino acid uptake
- Glucagon is a hyperglycaemic hormone that mobilizes fuel, maintains blood glucose during fasting, and promotes glycogenolysis, gluconeogenesis, and fatty acid release
Pancreatic Islets
- The endocrine part of the pancreas (Islets of Langerhans) contains:
- β cells (60-70%) that secrete insulin
- α cells (30-40%) that secrete glucagon
- δ cells that secrete somatostatin
- Insulin secretion is stimulated by a rise in blood glucose, amino acid concentration, and gut hormones (e.g., secretin) and inhibited by adrenaline
Control of Insulin Secretion
- Regulation of insulin secretion involves:
- Binding of glucose, amino acids, and gut hormones to receptors on pancreatic β cells
- Closing of ATP-sensitive K+ channels, increasing Ca2+ influx, and insulin release
Processing of Pro-Insulin into Insulin and C Peptide
- Not specified in the provided text
Metabolic Effects of Insulin
- Insulin promotes:
- Fuel storage after a meal
- Growth and glycogen synthesis
- Fatty acid synthesis and storage from CHO
- Amino acid uptake and protein synthesis
Structure of the Insulin Receptor
- The insulin receptor consists of:
- α subunit (extracellular)
- β subunit (transmembrane and intracellular)
- Binding of insulin to the receptor activates the tyrosine kinase, leading to growth-promoting activity
Metabolic Effects of Glucagon
- Glucagon:
- Mobilizes fuel during fasting
- Maintains blood glucose during fasting
- Activates glycogenolysis, gluconeogenesis, and fatty acid release
- Stimulates uptake of amino acids by the liver for gluconeogenesis
Other Hormones Affecting Metabolism
- Adrenaline (adrenal medulla) mobilizes fuel during stress
- Cortisol (adrenal cortex) provides for long-term requirements, stimulating amino acid mobilization from muscle, gluconeogenesis, and fatty acid release from adipose tissue
This quiz explores how hormone concentration changes enable the body to store and mobilize metabolic fuel in response to availability, starvation, injury, and stress. It delves into the variations in metabolic patterns and the roles of enzymes in this process.
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