16.3 - Hormones And The Regulation Of Blood Glucose Concentration

Question 1

What are the two principal coordinating systems in animals, and how do they function together?

Answer 1

1) Nervous System: Communicates rapidly through electrical signals, responding quickly to changes in the internal and external environment.
2) Hormonal System: Communicates more slowly via hormones (chemical messengers) that have longer-lasting effects.

• Both systems interact to maintain homeostasis and respond to external changes.
• Both use chemical messengers: Nervous system = Neurotransmitters (in chemical synapses), Hormonal system = Hormones.

Question 2

What are the key characteristics of hormones?

Answer 2

• Produced in glands that secrete them directly into the bloodstream (endocrine glands).
• Transported in blood plasma to target cells with specific receptors complementary to the hormone.
• Effective in low concentrations but have widespread and long-lasting effects

Question 3

What is the second messenger model, and how does adrenaline regulate blood glucose through this mechanism?

Answer 3

1) Adrenaline binds to a transmembrane protein receptor in the liver cell’s surface membrane.
2) Binding causes the receptor to change shape, activating adenyl cyclase on the inside of the membrane.
3) Activated adenyl cyclase converts ATP into cyclic AMP (cAMP).
4) cAMP acts as a second messenger, binding to and changing the shape of protein kinase enzymes, activating them.
5) Protein kinase catalyzes glycogen breakdown into glucose, which diffuses into the blood via channel proteins.

Question 4

What is the pancreas, and how is it structured for blood glucose regulation?

Answer 4

• The pancreas is a large, pale-coloured gland in the upper abdomen, behind the stomach.

Functions:
- Produces enzymes (protease, amylase, lipase) for digestion.
- Produces hormones (insulin and glucagon) for regulating blood glucose.

Contains islets of Langerhans, made up of two cell types:
- Alpha cells: Produce glucagon.
- Beta cells: Produce insulin

Question 5

What are the roles of the liver in blood glucose regulation?

Answer 5

• The liver, located below the diaphragm and made up of hepatocytes, regulates blood glucose through:

1) Glycogenesis: Conversion of glucose into glycogen when blood glucose is high.
The liver stores 75–100g of glycogen, sufficient for 12 hours of resting energy needs.
2) Glycogenolysis: Breakdown of glycogen into glucose when blood glucose is low.
3) Gluconeogenesis: Production of glucose from non-carbohydrate sources like glycerol and amino acids when glycogen is exhausted.

Question 6

Why is blood glucose regulation critical for mammals?

Answer 6

• Glucose is a respiratory substrate, providing energy for cells.
• If blood glucose is too low = Cells lack energy, and brain cells may die as they only respire glucose.
• If blood glucose is too high = Water potential of blood decreases, causing dehydration due to osmotic imbalance.

Question 7

What are the three sources of blood glucose, and how do fluctuations occur?

Answer 7

Sources:
- Diet: Glucose from hydrolysis of carbohydrates (starch, maltose, lactose, sucrose).
- Glycogenolysis: Breakdown of glycogen in liver/muscle cells.
- Gluconeogenesis: Glucose production from non-carbohydrate sources (e.g., amino acids).

Fluctuations:
- Glucose intake varies due to diet.
- Glucose usage depends on respiration rates, influenced by mental and physical activity

Question 8

How does insulin lower blood glucose concentration?

Answer 8

• Beta cells in islets of Langerhans detect high blood glucose and secrete insulin into the blood.
• Insulin binds to glycoprotein receptors on nearly all body cells (except red blood cells).
  Insulin’s effects:
  1) Alters glucose transport proteins, allowing more glucose into cells by facilitated diffusion.
  2) Increases the number of glucose transport channels by fusing vesicles with the cell membrane.
  3) Activates enzymes for glycogenesis (glucose → glycogen) and glucose-to-fat conversion.
  4) Increases respiratory rate, consuming more glucose.
• These actions reduce blood glucose concentration, and negative feedback reduces insulin secretion

Question 9

How does glucagon increase blood glucose concentration?

Answer 9

• Alpha cells in islets of Langerhans detect low blood glucose and secrete glucagon.
• Glucagon binds to specific receptors on liver cell membranes, triggering:
  1) Activation of enzymes for glycogenolysis (glycogen → glucose).
  2) Activation of enzymes for gluconeogenesis, converting amino acids and glycerol into glucose.
• Blood glucose rises, and negative feedback reduces glucagon secretion.

Question 10

What is adrenaline’s role in regulating blood glucose concentration?

Answer 10

• Produced by the adrenal glands, located above the kidneys, during stress or excitement.

Effects:
1) Attaches to protein receptors on target cell membranes.
2) Activates enzymes that catalyze glycogen breakdown into glucose.

Question 11

How do insulin and glucagon interact in regulating blood glucose?

Answer 11

1) Antagonistic hormones:
- Insulin lowers blood glucose.
- Glucagon raises blood glucose.

2) Negative feedback mechanism:
- High glucose → insulin secretion → glucose lowered.
- Low glucose → glucagon secretion → glucose raised.

3) Blood glucose fluctuates around a set point, ensuring sensitive regulation

Question 12

What are glycogenesis, glycogenolysis, and gluconeogenesis, and when do they occur?

Answer 12

1) Glycogenesis: Glucose → glycogen (occurs when blood glucose is high).
2) Glycogenolysis: Glycogen → glucose (occurs when blood glucose is low).
3) Gluconeogenesis: Non-carbohydrate sources → glucose (occurs when glycogen is depleted)