Homeostasis Introduction
Year 9 ๐ซ Physiology & Health Maintaining internal conditions: temperature, blood glucose.
๐ก๏ธ Homeostasis and Negative Feedback
Homeostasis is the maintenance of a stable internal environment despite changes in external conditions.
Negative Feedback Loop
Stimulus (change detected) โ Receptor โ Coordination centre โ Effector โ Corrective response โ Return to set point โ Response switched off- Variables controlled: core body temperature (37ยฐC), blood glucose concentration, water content (osmoregulation)
- Negative feedback is the main mechanism โ a change triggers a response that opposes the change
- Two sets of antagonistic effectors are usually involved (e.g. sweating + vasoconstriction)
๐ก๏ธ Blood Glucose Regulation
Blood glucose is maintained between 4โ6 mmol/L by two antagonistic hormones from the pancreas.
| Insulin | Glucagon | |
|---|---|---|
| Source | ฮฒ (beta) cells of islets of Langerhans | ฮฑ (alpha) cells of islets of Langerhans |
| Released when | Blood glucose HIGH (after eating) | Blood glucose LOW (fasting/exercise) |
| Effect on liver | Glucose โ glycogen (glycogenesis) โ cellular glucose uptake | Glycogen โ glucose (glycogenolysis) |
| Net effect | LOWERS blood glucose | RAISES blood glucose |
Diabetes: Type 1 โ autoimmune destruction of ฮฒ cells; no insulin made; requires insulin injections. Type 2 โ cells become resistant to insulin; managed with diet, exercise, medication.
๐ก๏ธ Thermoregulation
The hypothalamus acts as the body's thermostat, monitoring blood temperature and coordinating responses.
| Too HOT | Too COLD |
|---|---|
| Sweating (evaporation removes heat) | Shivering (muscle contractions generate heat) |
| Vasodilation (arterioles widen โ more blood near skin โ more heat lost) | Vasoconstriction (arterioles narrow โ less blood near skin โ less heat lost) |
| Hair lies flat (less insulating air layer) | Hair erects/goosebumps (more insulating air layer trapped) |
| Decreased metabolic rate | Increased metabolic rate |
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Interactive Demo โ Homeostasis Introduction
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