Organisms Respond to their Internal and External Environments: Homeostasis - Control of Blood Glucose Concentration, Insulin & Glucagon Flashcards
(35 cards)
What factors can increase blood glucose concentration?
- Eating foods containing carbohydrates
- Hydrolysis of glycogen (glycogenolysis)
- Conversion of non-carbohydrates e.g glycerol, amino acids (gluconeogenesis)
What factors can decrease blood glucose concentration?
- Exercising
- More glucose used in respiration to release energy
What hormones control blood glucose concentration?
- Insulin
- Glucagon
What cells secrete insulin and glucagon?
- Islets of Langerhans
Where are the islets of Langerhans located?
- Pancreas
What type of cells do the islets of Langerhans contain?
- Alpha (α) cells
- Beta (β) cells
Which cells in the islets of Langerhans secrete insulin?
- β cells
Which cells in the islets of Langerhans secrete glucagon?
- α cells
Where do α and β cells secrete hormones?
- Secrete hormones into the blood
What are the three processes that the liver carries out to regulate blood glucose concentration?
- Glycogenesis
- Glycogenolysis
- Gluconeogenesis
Define the term glycogenesis
- The formation of glycogen from glucose in the liver
Define the term glycogenolysis
- The hydrolysis of glycogen into glucose in the liver
Define the term gluconeogenesis
- The production of glucose from non-carbohydrates e.g glycerol or amino acids
Does insulin lower or raise blood glucose concentration?
- Insulin lowers blood glucose concentration
What are the main actions of insulin?
- Attaching to receptors on the surfaces of target cells
- Controlling the uptake of glucose by regulating the inclusion of channel proteins (GLUT-2) in the surface membranes of target cells
- Activating enzymes involved in glycogenesis
What are the target cells of insulin?
- Adipose cells
- Skeletal muscle cells
- Liver cells
Explain how insulin is secreted when blood glucose concentration is too high
- Rise in glucose concentration is detected by β cells found in the islets of Langerhans in the pancreas
- GLUT-2 molecules in plasma membrane of β cells, transport glucose into β cells by facilitated diffusion
- This stimulates vesicles of insulin to fuse with membrane and release insulin into blood, which inhibits secretion of glucagon
What are GLUT-2 molecules?
- Found in plasma membrane of β cells
- Carrier proteins for glucose
- Move glucose into β cells by facilitated diffusion
Explain what happens when insulin attaches to receptors on the surfaces of adipose and skeletal muscle cells
- Insulin in blood travels to adipose and skeletal muscle cells and binds to receptors
- GLUT-2 molecules in vesicles fuse with membrane
- Glucose moves into cells by facilitated diffusion
Explain what happens when insulin activates enzymes involved in glycogenesis
- Insulin binds to receptors on liver cells
- Activates enzymes in liver cells that carry out glycogenesis
- Maintains steep concentration gradient of glucose between blood and liver cells
Does glucagon lower or raise blood glucose concentration?
- Glucagon raises blood glucose concentration
What are the main actions of glucagon?
- Attaching to receptors on the surfaces of target cells (liver cells)
- Activating enzymes/chemicals (adenylate cyclase, cAMP, protein kinase A) involved in glycogenolysis
- Activating enzymes involved in gluconeogenesis
What model does glucagon (and adrenaline) use in liver cells?
- Second messenger model
What is the second messenger model?
- The binding of the hormone to cell receptors to activate an enzyme inside the cell membrane
- This produces a second messenger chemical
- The second messenger activates other enzymes to bring about a response
