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AQA A-Level Biology > Organisms Respond to their Internal and External Environments: Homeostasis - Control of Blood Glucose Concentration, Insulin & Glucagon > Flashcards

Organisms Respond to their Internal and External Environments: Homeostasis - Control of Blood Glucose Concentration, Insulin & Glucagon Flashcards

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1
Q

What factors can increase blood glucose concentration?

A
  • Eating foods containing carbohydrates
  • Hydrolysis of glycogen (glycogenolysis)
  • Conversion of non-carbohydrates e.g glycerol, amino acids (gluconeogenesis)
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2
Q

What factors can decrease blood glucose concentration?

A
  • Exercising

- More glucose used in respiration to release energy

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3
Q

What hormones control blood glucose concentration?

A
  • Insulin

- Glucagon

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4
Q

What cells secrete insulin and glucagon?

A
  • Islets of Langerhans
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5
Q

Where are the islets of Langerhans located?

A
  • Pancreas
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6
Q

What type of cells do the islets of Langerhans contain?

A
  • Alpha (α) cells

- Beta (β) cells

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7
Q

Which cells in the islets of Langerhans secrete insulin?

A
  • β cells
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8
Q

Which cells in the islets of Langerhans secrete glucagon?

A
  • α cells
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9
Q

Where do α and β cells secrete hormones?

A
  • Secrete hormones into the blood
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10
Q

What are the three processes that the liver carries out to regulate blood glucose concentration?

A
  • Glycogenesis
  • Glycogenolysis
  • Gluconeogenesis
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11
Q

Define the term glycogenesis

A
  • The formation of glycogen from glucose in the liver
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12
Q

Define the term glycogenolysis

A
  • The hydrolysis of glycogen into glucose in the liver
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13
Q

Define the term gluconeogenesis

A
  • The production of glucose from non-carbohydrates e.g glycerol or amino acids
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14
Q

Does insulin lower or raise blood glucose concentration?

A
  • Insulin lowers blood glucose concentration
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15
Q

What are the main actions of insulin?

A
  • 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
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16
Q

What are the target cells of insulin?

A
  • Adipose cells
  • Skeletal muscle cells
  • Liver cells
17
Q

Explain how insulin is secreted when blood glucose concentration is too high

A
  • 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
18
Q

What are GLUT-2 molecules?

A
  • Found in plasma membrane of β cells
  • Carrier proteins for glucose
  • Move glucose into β cells by facilitated diffusion
19
Q

Explain what happens when insulin attaches to receptors on the surfaces of adipose and skeletal muscle cells

A
  • 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
20
Q

Explain what happens when insulin activates enzymes involved in glycogenesis

A
  • 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
21
Q

Does glucagon lower or raise blood glucose concentration?

A
  • Glucagon raises blood glucose concentration
22
Q

What are the main actions of glucagon?

A
  • 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
23
Q

What model does glucagon (and adrenaline) use in liver cells?

A
  • Second messenger model
24
Q

What is the second messenger model?

A
  • 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
25
Q

What are the target cells of glucagon?

A
  • Liver cells
26
Q

Explain how glucagon is secreted when blood glucose concentration is too low

A
  • Decrease in blood glucose concentration is detected by α cells in the islets of Langerhans in the pancreas
  • α cells secrete glucagon, which inhibits insulin secretion
27
Q

Explain what happens when glucagon attaches to receptors of target cells

A
  • Glucagon binds to receptors on liver cells
  • Activates enzyme adenylate cyclase
  • Adenylate cyclase converts ATP into cyclic AMP (cAMP), a second messenger
  • cAMP activates enzyme protein kinase A
  • Protein kinase A activates cascade involved in glycogenolysis
  • Also activates enzymes involved in gluconeogenesis
28
Q

What are the chemicals involved in the second messenger model of glucagon (and adrenaline) in liver cells?

A
  • Adenylate cyclase
  • cAMP
  • Protein kinase A
29
Q

What is adenylate cyclase?

A
  • Enzyme that converts ATP to cAMP
30
Q

What is cAMP?

A
  • Second messenger that activates protein kinase A
31
Q

What is protein kinase A?

A
  • Enzyme that activates cascade involved in glycogenolysis
32
Q

Explain the negative feedback mechanism for when there’s a rise in blood glucose concentration

A

• Detection

  • Rise in blood glucose concentration is detected by β cells in islets of Langerhans in the pancreas
  • Glucose moves into β cells by facilitated diffusion via GLUT-2
  • Vesicles of insulin fuse with membrane
  • β cells secrete insulin, which stops glucagon secretion

• In adipose and skeletal muscle cells

  • β cells bind to receptors
  • Vesicles of GLUT-2 fuse with membrane
  • More glucose absorbed into cells by facilitated diffusion

• In liver cells

  • Insulin binds to receptors
  • Insulin activates enzymes involved in glycogenesis
33
Q

Explain the negative feedback mechanism for when there’s a fall in blood glucose concentration

A

• Detection

  • Fall in blood glucose concentration is detected by α cells in islets of Langerhans in pancreas
  • α cells secrete glucagon, which stops insulin secretion

• In liver cells

  • Glucagon binds to receptors
  • Activates enzyme adenylate cyclase
  • Adenylate cyclase converts ATP into cyclic AMP (cAMP), second messenger
  • cAMP activates enzyme protein kinase A
  • Protein kinase A activates cascade involved in glycogenolysis
  • Also activates enzymes involved in gluconeogenesis
34
Q

What processes does insulin activate and inhibit?

A

• Activates
- Glycogenesis

• Inhibits
- Glucagon secretion

35
Q

What processes does glucagon activate and inhibit?

A

• Activates

  • Glycogenolysis
  • Gluconeogenesis

• Inhibits
- Insulin secretion

AQA A-Level Biology (117 decks)

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