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Cambridge IGCSE Biology · 0610
Chapter 14: Coordination and response (Part 3)
Hormones
- Definition
- A chemical substance produced by a gland and carried by the blood, which alters the activity of specific target organs.
- Endocrine glands and secretions
-
- Adrenal glands: Secrete adrenaline.
- Pancreas: Secrete insulin (and glucagon).
- Testes: Secrete testosterone.
- Ovaries: Secrete oestrogen.
Exam Traps
- Avoid saying insulin is secreted by the liver — the pancreas secretes insulin.
Adrenaline and control systems
- ‘Fight or flight’
- Adrenaline is secreted during stress or excitement, leading to increased breathing rate, heart rate, and pupil diameter.
- Metabolic activity
- It also increases blood glucose concentration for respiration by converting glycogen to glucose in cells.
- Comparison
- Nervous control is quicker and short-lived (electrical), while hormonal control is slower and long-lasting (chemical).
Exam Traps
- Do not say adrenaline decreases heart rate — it increases heart rate and breathing rate.
- Avoid claiming hormonal control is faster than nervous control — hormones are slower and longer-lasting.
Homeostasis and blood glucose control
- Homeostasis
- The maintenance of a constant internal environment.
- Negative feedback
- Homeostatic control works with reference to a set point; if limits are exceeded, mechanisms correct the change.
- Glucose regulation
-
- High glucose: Detected by the pancreas; it secretes insulin. Insulin causes the liver to convert glucose to glycogen and move it into cells.
- Low glucose: Pancreas secretes glucagon. Glucagon causes the liver to convert glycogen to glucose.
- Type 1 diabetes
- Caused by an autoimmune response attacking insulin-producing cells; treated with insulin injections.
Exam Traps
- Do not say glucagon is released when glucose is high — insulin lowers high glucose; glucagon raises low glucose.
- Avoid confusing insulin (lowers glucose) with glucagon (raises glucose).
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