14.1.8Coordination and Response
Homeostasis and Insulin — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions
5 min read 5 parts Lesson 7 of 7 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Homeostasis and Negative Feedback
Body cells work best when conditions around them stay close to a set point.
Homeostasis
- Homeostasis This is the maintenance of a constant internal environment, such as temperature, water content and blood glucose concentration.
Set point
- Set point The ideal value of a variable around which the body keeps it, for example the normal range of blood glucose.
Negative feedback
- Negative feedback When a factor moves away from its set point, the response brings it back, so the change is reversed.
Continuous cycle
- Continuous cycle The control system keeps cycling between raising and lowering the level, which keeps it within a narrow range.
Why needed
- Why needed Enzyme-controlled reactions in cells need steady conditions to work well, and cells need a steady supply of glucose for respiration.
Section 2 of 5Controlling Blood Glucose
The pancreas monitors blood glucose and secretes two hormones with opposite effects.
1
After a meal, digestion releases glucose into the blood and the blood glucose concentration rises above the set point.
2
The pancreas secretes insulin into the blood, which travels to the liver and muscles.
3
Insulin causes liver and muscle cells to take up glucose and convert it to glycogen for storage, so blood glucose falls.
4
Between meals, respiration uses glucose, and the blood glucose concentration falls below the set point.
5
The pancreas secretes glucagon, which causes the liver to break down glycogen into glucose, and this is released into the blood.
6
Blood glucose rises back to the set point, and the cycle repeats in a negative feedback loop.
| Hormone | Made in | Stimulus | Effect on blood glucose |
|---|---|---|---|
| Insulin | Pancreas | High blood glucose | Decreases it by glycogen formation |
| Glucagon | Pancreas | Low blood glucose | Increases it by glycogen breakdown |
Section 3 of 5Type 1 Diabetes
Type 1 Diabetes
Cause
- Cause The insulin-secreting cells of the pancreas do not make enough insulin, so blood glucose is not controlled and is often too high.
Symptoms
- Symptoms Common signs include extreme thirst, tiredness and weakness, blurred vision and glucose in the urine.
Treatment
- Treatment Injections of insulin, together with careful control of diet and carbohydrate intake, keep blood glucose within the normal range.
Why glucose is lost
- Why glucose is lost Kidneys can reabsorb only a limited amount of glucose, so very high blood levels lead to glucose passing out in urine.
Section 4 of 5Avoiding Confusion
Avoiding Confusion
Glucagon
- Glucagon This is the hormone that raises blood glucose by acting on the liver.
Glycogen
- Glycogen This is the polysaccharide in which glucose is stored in liver and muscle cells.
Glucose
- Glucose This is the small soluble sugar carried in the blood and used in respiration.
Section 5 of 5Exam Checklist & Tips
14.1.8 – Key Points for the Exam
- Homeostasis Maintenance of a constant internal environment.
- Negative feedback A response that reverses a change and returns a factor to its set point.
- Insulin A hormone from the pancreas that lowers blood glucose.
- Glucagon A hormone from the pancreas that raises blood glucose.
- Glycogen A storage polysaccharide made of many glucose units.
Common Mistakes
- Mixing up glucagon (a hormone) and glycogen (a storage carbohydrate).
- Saying insulin is made in the liver, when it is made in the pancreas.
- Describing negative feedback as making the change bigger, when it reverses the change.
- Writing that insulin injections cure type 1 diabetes, when they treat it by replacing the missing hormone.
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