CIE iGCSE Co-ordinated Sciences-B13.3 Homeostasis- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-B13.3 Homeostasis- Study Notes
CIE iGCSE Co-ordinated Sciences-B13.3 Homeostasis – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Supplement
- Describe homeostasis as the maintenance of a constant internal environment
- Explain the concept of homeostatic control by negative feedback with reference to a set point
- Describe the control of blood glucose concentration by the liver and the roles of insulin and glucagon
- Identify in diagrams and images of the skin: hairs, hair erector muscles, sweat glands, receptors, sensory neurones, blood vessels and fatty tissue
- Describe the maintenance of a constant internal body temperature in mammals in terms of:
(a) insulation, sweating, shivering, the role of the brain
(b) vasodilation and vasoconstriction of arterioles supplying skin surface capillaries
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Homeostasis
📌 Definition
Homeostasis is the maintenance of a constant internal environment inside the body, even when external conditions change.
🌱 Key Idea
- Keeps body conditions (like temperature, water level, blood glucose) stable.
- Ensures that enzymes and cells work efficiently.
- Without homeostasis → cells may be damaged or reactions become too slow/too fast.
📊 Examples of Homeostasis
| Factor controlled | How it’s kept constant |
|---|---|
| Body temperature | Sweating, shivering, blood flow changes |
| Blood glucose | Insulin ↓, glucagon ↑ |
| Water balance | Kidneys adjust water reabsorption |
⚡ Quick Recap
Homeostasis = balance inside the body.
Keeps conditions steady for enzyme action + survival.
Examples: temperature, glucose, water levels.
Memory tip: “Homeo = same, stasis = state → staying the same inside.”
Negative Feedback in Homeostasis
📌 Definition
Negative feedback is the process by which a change in the internal environment is detected and the body makes adjustments to bring conditions back to the set point (the normal, stable level).
🌱 Key Idea
- The set point is the desired/normal level (e.g. body temperature = 37°C).
- If the body goes above or below this set point → negative feedback works to reverse the change.
- Ensures stability in the internal environment.
⚙️ How Negative Feedback Works
Stimulus → Receptor → Coordinator → Effector → Response → Balance restored
- Stimulus: Change away from set point (e.g. ↑ blood glucose).
- Receptor: Detects the change.
- Coordinator: Brain or hormone system sends signals.
- Effector: Muscles/glands respond to correct it.
- Response: Condition returns to set point.
📊 Example
| Condition | Change | Negative feedback response | Result |
|---|---|---|---|
| Blood glucose | ↑ after a meal | Pancreas secretes insulin → glucose stored as glycogen | Glucose returns to set point |
| Blood glucose | ↓ after exercise | Pancreas secretes glucagon → glycogen converted to glucose | Glucose returns to set point |
| Body temperature | ↑ | Sweating + vasodilation | Back to ~37°C |
| Body temperature | ↓ | Shivering + vasoconstriction | Back to ~37°C |
⚡ Quick Recap
Negative feedback = automatic correction system.
Works around a set point.
If condition rises → system brings it down.
If condition falls → system brings it up.
Memory tip: “Negative = neutralises the change.”
Control of Blood Glucose
📌 Introduction
Blood glucose concentration must be kept constant (homeostasis) to ensure a steady supply of glucose for respiration.
This control involves:
- Pancreas → secretes hormones (insulin & glucagon).
- Liver → stores or releases glucose depending on signals.
🌱 Role of Insulin (when blood glucose ↑ after a meal)
- Secreted by pancreas (β-cells).
- Stimulates liver and muscle cells to:
- Convert glucose → glycogen (storage form).
- Increase uptake of glucose by cells.
- Result: Blood glucose decreases → back to normal.
🌱 Role of Glucagon (when blood glucose ↓, e.g. after exercise)
- Secreted by pancreas (α-cells).
- Stimulates the liver to:
- Break down glycogen → glucose.
- Release glucose into the blood.
- Result: Blood glucose increases → back to normal.
🌱 Role of the Liver
- Acts as a glucose storehouse.
- Stores glucose as glycogen when insulin is high.
- Releases glucose when glucagon is high.
- Helps maintain the set point for blood sugar.
📊 Summary Table
| Hormone | Secreted by | Trigger | Effect on liver | Result |
|---|---|---|---|---|
| Insulin | Pancreas (β-cells) | High glucose | Stores glucose as glycogen | ↓ Blood glucose |
| Glucagon | Pancreas (α-cells) | Low glucose | Breaks glycogen into glucose | ↑ Blood glucose |
⚡ Quick Recap
Insulin = IN → stores glucose inside cells.
Glucagon = glucose gone → brings it back.
Both act on the liver to keep blood sugar constant.
Memory tip: “Insulin puts sugar in, Glucagon gets sugar gone.”
The Skin – Structures to Identify
📌 Introduction
The skin is not just a covering – it’s an organ with roles in protection, temperature regulation, and sensation.
🌱 Key Structures to Identify
- Hairs
Thin keratin structures growing from hair follicles.
Function: Help in insulation and sensation. - Hair erector muscles (arrector pili)
Small muscles attached to hair follicles.
Contract in cold/fear → hairs stand up (“goosebumps”). - Sweat glands
Coiled tubular glands in the dermis.
Release sweat onto the skin surface → evaporative cooling. - Receptors
Specialised cells for detecting stimuli.
Types: touch, pressure, pain, and temperature receptors. - Sensory neurones
Carry impulses from skin receptors → CNS (brain/spinal cord). - Blood vessels
Found in the dermis.
Can dilate (vasodilation) or constrict (vasoconstriction) to control heat loss. - Fatty tissue (adipose tissue)
Found in the subcutaneous layer (under dermis).
Insulates, cushions, and stores energy.
📊 Summary Table
| Structure | Function |
|---|---|
| Hair | Insulation & sensation |
| Hair erector muscle | Goosebumps → traps air for insulation |
| Sweat gland | Produces sweat for cooling |
| Receptors | Detect touch, pressure, temp, pain |
| Sensory neurone | Transmits impulses to CNS |
| Blood vessels | Control heat loss/gain |
| Fatty tissue | Insulation, energy storage, cushioning |
⚡ Quick Recap
Hair + erector muscle = insulation
Sweat glands = cooling
Receptors + neurones = sensation
Blood vessels = heat regulation
Fatty tissue = insulation + energy
Temperature Regulation in Mammals (Homeostasis)
📌 Introduction
Mammals keep their core body temperature (~37 °C) constant so that enzymes work efficiently.
This is controlled by the hypothalamus in the brain using negative feedback.
(a) Mechanisms of Temperature Control
🧥 Insulation
- Hairs + hair erector muscles trap a layer of air (reduces heat loss).
- Fatty tissue (under skin) also acts as insulation.
💦 Sweating (when too hot)
- Sweat glands release sweat.
- Sweat evaporates → cools the body by removing heat.
❄️ Shivering (when too cold)
- Muscles contract rapidly.
- This generates heat from respiration.
🧠 Role of the Brain
- The hypothalamus detects blood temperature changes.
- Sends nerve signals to effectors (muscles, sweat glands, blood vessels) to correct it.
(b) Blood Flow Adjustments
🌞Vasodilation (too hot)
- Arterioles supplying skin surface capillaries widen.
- More blood flows near surface → more heat lost by radiation.
❄️Vasoconstriction (too cold)
- Arterioles narrow.
- Less blood reaches skin surface → less heat lost.
📊 Summary Table
| Condition | Response | Effect |
|---|---|---|
| Too hot | Sweating, vasodilation | ↑ Heat loss |
| Too cold | Shivering, vasoconstriction, insulation | ↓ Heat loss, ↑ Heat production |
| Control | Hypothalamus | Detects & coordinates |
⚡ Quick Recap
Hot → sweat, vasodilation.
Cold → shiver, vasoconstriction, insulation.
Brain (hypothalamus) = control centre.
Memory tip: “Hot = Dilate, Cold = Constrict.”