Outside, the weather swings and meals come and go. Inside, your blood glucose and core temperature hardly move. Homeostasis keeps the internal environment steady, mostly by negative feedback around a set point. Insulin lowers blood glucose; the roles of glucagon and the liver, Type 1 diabetes and the control of body temperature by the skin and the brain are Extended content.
Homeostasis is the maintenance of a constant internal environment. Insulin decreases blood glucose concentration. Extended: homeostatic control works by negative feedback: when a condition moves away from its set point, the body responds in a way that brings it back. The pancreas secretes insulin or glucagon and the liver stores or releases glucose; the brain controls sweating, shivering and the arterioles of the skin to keep core temperature close to 37 °C.
Press Eat a sugary meal and watch the graph of blood glucose. The green band is the normal range, with a set point of about 5 mmol/dm3. Then press Exercise and watch which hormone the pancreas secretes.
Negative feedback does not mean the response is bad or stops something. It means the response acts in the opposite direction to the change, so the level returns towards the set point.
Extended. In the same tab, switch on Type 1 diabetes, eat a meal and watch the glucose stay high. Then press Inject insulin.
| Blood glucose too high | Blood glucose too low | |
|---|---|---|
| Detected by | the pancreas | the pancreas |
| Pancreas secretes | insulin | glucagon |
| Liver | converts glucose to glycogen and stores it | breaks glycogen down to glucose and releases it |
| Result | blood glucose falls to the set point | blood glucose rises to the set point |
Glycogen and glucagon sound alike. Glycogen is the storage carbohydrate in the liver; glucagon is the hormone that makes the liver break glycogen down.
Extended. Click each part of the skin to identify it, then drag the temperature of the surroundings from 0 °C to 45 °C. Below 15 °C and above 30 °C the brain switches on different responses.
| Too hot | Too cold | |
|---|---|---|
| Arterioles to skin capillaries | vasodilation: widen, more blood flows near the surface, more heat lost | vasoconstriction: narrow, less blood near the surface, less heat lost |
| Sweat glands | secrete sweat; evaporation of the water transfers heat away | stop secreting |
| Muscles | no shivering | shivering: rapid contractions release heat from respiration |
| Hairs (erector muscles) | lie flat | stand up, trapping a layer of insulating air |
In vasodilation the arterioles supplying the skin capillaries widen. Capillaries do not move up or down through the skin, and they cannot constrict: they have no muscle in their walls.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
In the blood glucose tab, which hormone does the pancreas secrete after the sugary meal?
Extended: in the sim, what does the liver do with glucose when insulin is secreted?
Extended: with Type 1 diabetes switched on, why does glucose stay high after a meal?
Extended: in the temperature tab, what happens to the arterioles supplying the skin capillaries at 40 °C?
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
Which is the best description of homeostasis?
Extended: blood glucose falls during a long run. Which response restores it?
Extended: how does shivering help to raise body temperature?
Extended: which statement explains why the response to a fall in body temperature is negative feedback?
This skill is now recorded on your profile. Keep the chain going.