15.01 Coordination in Organisms
Key Concepts
- Complex Organisms (plants & animals)
- Composed of millions of cells with specialized functions.
- Communication between parts is vital for coordination of activities and responses to internal/external stimuli.
- Purpose of Communication
- Internal regulation (e.g., blood glucose control).
- Response to external stimuli (e.g., moving away from danger).
Animal Communication Systems
- Two main methods:
- Nervous System – uses electrical impulses.
- Endocrine System – uses hormones released into the bloodstream.
- Receptors and Effectors
- Receptors detect stimuli internally and externally.
- Effectors carry out responses.
Endocrine System Overview
- Endocrine Glands (ductless, secrete hormones directly into blood):
- Examples: Pituitary gland, pancreas, adrenal glands, testes, ovaries.
- Hormones are cell-signaling molecules that travel to target organs.
- Types of Hormones
- Water-soluble hormones (e.g., insulin, glucagon, ADH):
- Cannot pass through cell membranes; use cell surface receptors and second messengers.
- Steroid hormones (e.g., testosterone, oestrogen, progesterone):
- Lipid-soluble, can cross cell membranes; bind inside cells to initiate processes like transcription.
- Water-soluble hormones (e.g., insulin, glucagon, ADH):
Hormonal Communication
- Hormone Characteristics:
- Ideal for functions needing gradual coordination, e.g., homeostasis of blood glucose and water potential.
- Long-distance signaling – hormones produced in one part, affect distant target organs.
Study Questions
- Diagram Activity: Draw and label locations of pituitary gland, pancreas, adrenal glands, testes, and ovaries; annotate with endocrine roles.
- Hormone Function Explanation:
- Compare glucagon and ADH (similar signaling pathway but target different functions due to distinct receptor sites).
- Steroid Hormone Transport: Explain why steroid hormones cross membranes easily (lipid-solubility) vs. other hormones (water-solubility).
- Summary Table on Insulin, Glucagon, and ADH:
| Hormone | Role in Homeostasis | Mechanism of Action | Target Organs |
|---|---|---|---|
| Insulin | Lowers blood glucose levels | – Released by pancreas (β-cells in the islets of Langerhans) | Liver, muscle, and fat cells |
| – Promotes glucose uptake in cells by increasing glucose transporter proteins | |||
| – Stimulates glycogenesis (conversion of glucose to glycogen) in the liver | |||
| —– | —– | —– | —– |
| Glucagon | Raises blood glucose levels | – Released by pancreas (α-cells in the islets of Langerhans) | Liver |
| – Stimulates glycogenolysis (breakdown of glycogen to glucose) | |||
| – Promotes gluconeogenesis (formation of glucose from non-carbohydrate sources) | |||
| —– | —– | —– | —– |
| ADH | Regulates water balance and blood osmolarity | – Released by pituitary gland | Kidneys |
| (Antidiuretic | – Increases water reabsorption in kidney tubules by increasing aquaporin channels | ||
| hormone) | – Acts when blood osmolarity is high (e.g., dehydration) to conserve water |