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Question 1

What is the endocrine system, and how does it function?

Answer 1

The endocrine system uses hormones as signaling molecules to communicate throughout the body.
• Hormones are released into the bloodstream, allowing them to travel to specific target tissues.
• Target cells contain receptors complementary to the hormone molecules, enabling signal transmission.

Question 2

Define the terms endocrine system, hormones, and target cells.

Answer 2

• Endocrine system: A communication system that uses hormones for signaling.
• Hormones: Molecules (proteins or steroids) released by endocrine glands into the blood to act as messengers.
• Target cells: Cells with specific receptors on their plasma membrane that bind hormones to trigger a response.

Question 3

What are the two main types of hormones, and how do they differ?

Answer 3

1. Protein/peptide hormones & amino acid derivatives:
   • Examples: Adrenaline, insulin, glucagon.
   • Cannot pass through the cell membrane; bind to surface receptors and activate second messengers.
   
   2. Steroid hormones:
      • Examples: Oestrogen, testosterone.
      • Lipid-soluble, so they can pass through the cell membrane and directly affect DNA in the nucleus.

Question 4

What are endocrine glands, and how do they differ from exocrine glands?

Answer 4

• Endocrine glands: Ductless glands that secrete hormones directly into the blood (e.g., pituitary, thyroid, pancreas).
• Exocrine glands: Have ducts and release secretions (like enzymes) to specific locations (e.g., salivary glands).

Question 5

How do hormones target specific cells in the body?

Answer 5

• Hormones bind to specific receptors on target cells.
• The receptor shape is complementary to the hormone, ensuring specificity.
• Example: Adrenaline binds to receptors on heart or muscle cells to trigger a response.

Question 6

What are the two types of adrenergic receptors, and how do they function?

Answer 6

1. Alpha receptors:
   • Excitatory in smooth muscle and glands.
   • Cause relaxation in intestinal smooth muscles.
   
   2. Beta receptors:
      • Inhibitory except in the heart (where they are excitatory).
      • Beta blockers reduce the effect of adrenaline to manage heart conditions.

Question 7

Describe the roles of first and second messengers in hormone signaling.

Answer 7

• First messenger: Non-steroid hormones (e.g., adrenaline) bind to receptors on the cell membrane, triggering intracellular changes.
• Second messenger: Molecules like cyclic AMP (cAMP) are activated inside the cell to amplify and propagate the signal.

Question 8

Explain how non-steroid hormones activate their target cells.

Answer 8

1. Hormone binds to a receptor on the cell membrane, activating a G protein.
   
   2. G protein activates adenyl cyclase, which converts ATP to cAMP.
   3. cAMP acts as a second messenger to activate enzymes or initiate other cellular processes.