CIE iGCSE Biology-14.4 Homeostasis- Study Notes- New Syllabus
CIE iGCSE Biology-14.4 Homeostasis- Study Notes – New syllabus
CIE iGCSE Biology-14.4 Homeostasis- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- Describe homeostasis as the maintenance of a constant internal environment
- State that insulin decreases blood glucose concentration
Supplement
- 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
- Outline the treatment of Type 1 diabetes
- 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: insulation, sweating, shivering and the role of the brain
- Describe the maintenance of a constant internal body temperature in mammals in terms of vasodilation and vasoconstriction of arterioles supplying skin surface capillaries
Homeostasis – The Body’s Internal Balance
Definition of Homeostasis:
- Homeostasis is the maintenance of a constant internal environment within the body, even when external conditions change.
- This means the body keeps key conditions like temperature, water levels, and blood sugar within safe limits to keep cells functioning properly.
🧬 Why is Homeostasis Important?
- All cells need a stable environment to work efficiently.
- Enzymes (which control metabolism) only work well at specific conditions (e.g., right temperature and pH).
- Without homeostasis, cells can become damaged or die.
🔑 Key Conditions Controlled by Homeostasis:
| Controlled Variable | Why It’s Important | How It’s Controlled |
|---|---|---|
| Body Temperature | Enzymes work best at ~37°C | Thermoregulation (sweating, shivering) |
| Water Content | Cells need the right water balance | Controlled by kidneys and osmoregulation |
| Blood Glucose Level | Supplies energy for cells | Controlled by insulin and glucagon |
| Carbon Dioxide Level | Affects blood pH (too acidic = danger) | Controlled by lungs through breathing |
⚙️ How Does Homeostasis Work?
Controlled using a negative feedback system:
- Change detected by receptors (e.g., temperature sensors in skin or brain).
- Information sent to a coordination centre (like the brain or spinal cord).
- Response sent to effectors (e.g., muscles or glands).
- The effectors bring the condition back to normal.
🔄 Negative Feedback Explained:
When a change happens, the body responds in a way that reverses the change and brings conditions back to normal.
🟨 Homeostasis = Internal balance
✔ Temp ~37°C
✔ Glucose levels steady
✔ Water levels correct
✔ CO₂ removed
🛠 Controlled by:
Nervous system
Hormones
Kidneys, liver, lungs, brain
🧾Summary:
Homeostasis keeps internal conditions like temperature, water, and glucose steady so that enzymes and cells can function properly. It uses receptors, coordination centers, and effectors to correct any changes using negative feedback.
Homeostasis keeps internal conditions like temperature, water, and glucose steady so that enzymes and cells can function properly. It uses receptors, coordination centers, and effectors to correct any changes using negative feedback.
Role of Insulin in Blood Glucose Control
Key Statement:
Insulin is a hormone that decreases blood glucose concentration.
🔷 What is Insulin?
- A hormone produced by beta cells in the pancreas.
- Released into the bloodstream when blood glucose levels are high (e.g., after a meal).
🔁 How Insulin Works:
| Step | Action |
|---|---|
| 1 | Blood glucose rises after eating (especially carbs). |
| 2 | Pancreas detects the rise and releases insulin. |
| 3 | Insulin signals body cells (especially liver and muscle cells) to absorb glucose from the blood. |
| 4 | In the liver, excess glucose is converted into glycogen for storage. |
| 5 | Blood glucose level decreases to normal. |
🔍 Why is Insulin Important?
- Keeps glucose levels in a narrow, safe range.
- Prevents damage to tissues caused by too much glucose.
- Supports cellular respiration by ensuring cells get enough glucose.
📝Note:
🡇 Glucose ↑ → Insulin released
✔ Glucose ➝ Cells
✔ Glucose ➝ Glycogen
🡇 Blood sugar returns to normal
🡇 Glucose ↑ → Insulin released
✔ Glucose ➝ Cells
✔ Glucose ➝ Glycogen
🡇 Blood sugar returns to normal
📘 Summary:
Insulin lowers blood glucose by helping body cells absorb glucose and by promoting storage of excess glucose as glycogen in the liver and muscles.
Insulin lowers blood glucose by helping body cells absorb glucose and by promoting storage of excess glucose as glycogen in the liver and muscles.
Homeostatic Control by Negative Feedback
What is Negative Feedback?
Negative feedback is a control mechanism in homeostasis where a change in a condition triggers a response that reverses that change, bringing the condition back to normal (set point).
🔷 What is a Set Point?
The set point is the ideal or target level the body tries to maintain for any condition.
Example:
Normal human body temperature = 37°C
Normal blood glucose level ≈ 90 mg/dL
⚙️ How Negative Feedback Works:
| Component | Role |
|---|---|
| Stimulus | A change away from the set point (e.g., temperature rises). |
| Receptors | Detect the change (e.g., temperature receptors in the skin). |
| Control Centre | Usually the brain (e.g., hypothalamus), processes the information. |
| Effectors | Muscles or glands that carry out a response (e.g., sweat glands). |
| Response | Reverses the original change (e.g., cooling the body down). |
📘 Example 1: Body Temperature Control
| When temp ↑ above 37°C | When temp ↓ below 37°C |
|---|---|
| Detected by skin & brain | Detected by skin & brain |
| Sweat produced | Shivering begins |
| Blood vessels widen (vasodilation) | Blood vessels narrow (vasoconstriction) |
| Body cools down → back to 37°C | Body warms up → back to 37°C |
📘 Example 2: Blood Glucose Control
| Glucose level too high | Glucose level too low |
|---|---|
| Insulin is released | Glucagon is released |
| Glucose stored as glycogen | Glycogen broken into glucose |
| Blood glucose falls to normal | Blood glucose rises to normal |
📒Revision Tip:
Negative Feedback:
Works to cancel out the change
Keeps internal environment stable
Always tries to return to the set point
Negative Feedback:
Works to cancel out the change
Keeps internal environment stable
Always tries to return to the set point
📌 Key Summary:
Negative feedback maintains stability by keeping internal conditions close to a set point. It works by reversing the direction of change.
Negative feedback maintains stability by keeping internal conditions close to a set point. It works by reversing the direction of change.
Control of Blood Glucose Concentration
Why is Blood Glucose Control Important?
- The body needs a constant supply of glucose for cellular respiration.
- Too much glucose: can damage tissues (hyperglycaemia).
- Too little glucose: can cause fainting or even death (hypoglycaemia).
⚙️ Key Organs Involved:
| Organ | Function |
|---|---|
| Pancreas | Detects blood glucose levels and releases hormones. |
| Liver | Stores or releases glucose based on signals from the pancreas. |
🔁 The Two Hormones:
| Hormone | Secreted by | Role |
|---|---|---|
| Insulin | Pancreas (β-cells) | Lowers blood glucose |
| Glucagon | Pancreas (α-cells) | Raises blood glucose |
🔽 When Blood Glucose Is Too High (after eating):
- Pancreas detects high glucose.
- Releases insulin into the blood.
- Insulin stimulates:
- Liver and muscles to convert glucose into glycogen.
- Cells to take in glucose from the blood.
- Blood glucose levels fall back to normal.
🔼 When Blood Glucose Is Too Low (between meals/exercise):
- Pancreas detects low glucose.
- Releases glucagon into the blood.
- Glucagon stimulates:
- Liver to break down glycogen into glucose.
- Glucose is released into the blood.
- Blood glucose levels rise back to normal.
| Condition | Hormone Released | Effect on Liver | Outcome |
|---|---|---|---|
| High glucose | Insulin | Converts glucose → glycogen | Glucose level decreases |
| Low glucose | Glucagon | Converts glycogen → glucose | Glucose level increases |
📝 Note:
Insulin = In → stores glucose (as glycogen)
Glucagon = Gone → frees glucose (from glycogen)
Liver is the storehouse, pancreas is the sensor!
Insulin = In → stores glucose (as glycogen)
Glucagon = Gone → frees glucose (from glycogen)
Liver is the storehouse, pancreas is the sensor!
Treatment of Type 1 Diabetes
What is Type 1 Diabetes?
- A condition where the pancreas does not produce insulin.
- Without insulin, blood glucose levels become dangerously high.
- Usually diagnosed in childhood or adolescence.
- It is an autoimmune disease: the body’s immune system attacks the insulin-producing β-cells in the pancreas.
💉 Main Treatment: Insulin Therapy
| Method | Details |
|---|---|
| Insulin injections | Regular injections of insulin (before meals) help lower blood glucose. |
| Insulin pump | A device worn under the skin that delivers insulin continuously. Can be adjusted depending on meals and activity. |
Diet Management
- Controlled carbohydrate intake to avoid spikes in blood sugar.
- Balanced diet with complex carbs, fiber, and low sugar content.
Exercise
- Regular physical activity helps lower blood glucose naturally.
- Insulin dose may need adjusting before exercise to prevent hypoglycaemia.
Monitoring Blood Glucose
- Frequent blood sugar testing using a glucose meter.
- Continuous glucose monitors (CGMs) may be used for real-time tracking.
🔄 Summary of Treatment Strategies
| Strategy | Purpose |
|---|---|
| Insulin therapy | Replaces missing insulin |
| Diet control | Prevents blood glucose spikes |
| Exercise | Helps manage blood sugar naturally |
| Monitoring | Ensures blood glucose stays in safe range |
Type 1 Diabetes = No Insulin ➝ Needs daily injections.
Treatment = Insulin + Balanced Diet + Exercise + Monitoring.
No cure, but manageable with proper care.
Treatment = Insulin + Balanced Diet + Exercise + Monitoring.
No cure, but manageable with proper care.
Identification of Skin Structures in Diagrams
1. Hairs
- Thin strands extending from the skin surface.
- Grow from follicles located in the dermis.
- Visible above the skin (epidermis).
2. Hair Erector Muscles (Arrector Pili)
- Small, slanted muscles attached to hair follicles.
- Contract during cold or emotional stimuli ➝ hair stands up (“goosebumps”).
3. Sweat Glands
- Coiled, tubular glands in the dermis.
- Connected to pores on the surface.
- Produce sweat to cool the body.
4. Receptors (Sensory Receptors)
- Tiny nerve endings or bulb-like structures.
- Found near the base of hair follicles or in the dermis.
- Detect touch, pressure, pain, temperature.
5. Sensory Neurons
- Thin nerve fibers linked to receptors.
- Carry electrical impulses from skin to brain.
- Often seen as lines running from receptors toward the spinal cord.
6. Blood Vessels
- Arteries and veins seen as red and blue tubes.
- Found in the dermis and subcutaneous (fat) layer.
- Help in thermoregulation and nourishing skin tissues.
7. Fatty Tissue (Adipose Tissue)
- Yellowish lobular layer at the bottom of the diagram.
- Acts as insulation and energy storage.
- Located in the subcutaneous layer (beneath the dermis).
Thermoregulation in Mammals
Definition:
Thermoregulation is the process by which mammals maintain a constant internal body temperature (around 37°C in humans), despite changes in the external environment.
🧠 Key Mechanism: The Role of the Brain
- The hypothalamus in the brain acts as the temperature control center.
- It detects changes in blood temperature or receives signals from temperature receptors in the skin.
- Then it sends nerve impulses to different parts of the body to adjust temperature.
❄️ When Body Temperature Falls (Too Cold)
| Response | Description |
|---|---|
| Insulation | Fat under the skin (adipose tissue) reduces heat loss. |
| Shivering | Muscles contract rapidly to produce heat by increasing respiration. |
| Vasoconstriction | Blood vessels near the skin narrow, reducing blood flow and minimizing heat loss. |
| Hair stands up | Traps air for insulation (limited effect in humans). |
🌡️ When Body Temperature Rises (Too Hot)
| Response | Description |
|---|---|
| Sweating | Sweat glands produce sweat which evaporates, cooling the skin. |
| Vasodilation | Blood vessels near the skin widen, increasing heat loss. |
| Reduced muscle activity | Less movement means less heat is generated. |
📌 Summary:
The brain regulates body temperature by detecting changes and triggering behavioral and physiological responses like sweating, shivering, or altering blood flow, helping maintain a stable internal condition (homeostasis).
The brain regulates body temperature by detecting changes and triggering behavioral and physiological responses like sweating, shivering, or altering blood flow, helping maintain a stable internal condition (homeostasis).
Why is it important to maintain body temperature?
Enzymes work best at around 37°C.
Extreme temperatures can cause enzymes to become denatured or inactive, affecting vital chemical reactions in the body.
Temperature Regulation via Blood Vessels
What are Vasodilation and Vasoconstriction?
| Term | Definition |
|---|---|
| Vasodilation | The widening of arterioles (small arteries) supplying blood to the skin surface capillaries. |
| Vasoconstriction | The narrowing of these arterioles, reducing blood flow to the skin surface. |
🔥 When the Body is Too Hot: Vasodilation
- Arterioles widen (vasodilation).
- More warm blood flows to capillaries near the skin surface.
- Heat is lost by radiation from the skin to the environment.
- Helps cool down the body.
Think: “Dilation = Disperse heat”
❄️ When the Body is Too Cold: Vasoconstriction
- Arterioles narrow (vasoconstriction).
- Less blood reaches the skin surface capillaries.
- Reduces heat loss from the skin to the surroundings.
- Helps the body retain heat.
Think: “Constrict = Conserve heat”
🧠 Controlled by the Hypothalamus
- The hypothalamus in the brain detects changes in core body temperature.
- It sends nerve signals to the arterioles to adjust their diameter, maintaining homeostasis.
🔁 Summary:
Vasodilation and vasoconstriction are essential mechanisms that help mammals regulate body temperature by controlling the amount of blood flow to the skin surface, thereby managing heat loss or retention.
Vasodilation and vasoconstriction are essential mechanisms that help mammals regulate body temperature by controlling the amount of blood flow to the skin surface, thereby managing heat loss or retention.
📝 Note:
Vasodilation = Lose heat ☀️
Vasoconstriction = Keep heat ❄️
Vasodilation = Lose heat ☀️
Vasoconstriction = Keep heat ❄️