Homeostasis

Homeostasis is the body's drive to keep internal conditions such as temperature, blood sugar, and pH steady. Negative feedback is the key: when something drifts, the response pushes the opposite way back toward normal. Rising glucose releases insulin and falling glucose releases glucagon, while the hypothalamus adjusts vessels, sweat, and shivering for temperature. Raise the blood-glucose slider and watch how insulin and glucagon respond.

What is Homeostasis?

🌡️ The Body Balances Itself

①You shiver when cold and sweat when hot — why?

②The body keeps internal environment (temperature, blood sugar, pH, osmotic pressure) stable

③This is "homeostasis" — negative feedback is the core principle

Visualizing Blood Glucose Regulation

Blood glucose (mg/dL)100 mg/dL

💡 Try it Yourself

①Glucose above 120 → insulin secretion (β-cells)

②Glucose below 80 → glucagon secretion (α-cells)

③Always returns to normal range (80~120)!

Principles of Homeostatic Regulation

Negative Feedback

Detect change → opposite response → return to baseline

Mechanism for body temperature, blood glucose, osmotic pressure, etc.

Blood Glucose Regulation

ChartInsulin vs Glucagon

Item	Insulin	Glucagon
Cell type	pancreas β-cells	pancreas α-cells
Trigger	high blood glucose	low blood glucose
Action	lowers glucose (glucose→glycogen)	raises glucose (glycogen→glucose)
Target organs	liver, muscle, fat	liver

Body Temperature Regulation

Temperature Regulation

ChartHeat Up vs Heat Down Responses

Item	When hot	When cold
Skin vessels	dilate (more heat loss)	constrict (less heat loss)
Sweat glands	sweat ↑	sweat ↓
Muscles	relaxed	shivering (heat generation)
Control center	hypothalamus	hypothalamus

Worked Examples

Example 1

After a meal, blood glucose rises to 140 mg/dL. Name the hormone secreted, its action, and the secreting cell.

When blood glucose is above the normal range (80–120), a hormone is secreted to lower it.

Insulin from pancreatic β-cells stores glucose as glycogen → blood glucose falls.

▸ Insulin (pancreatic β-cells) — lowers blood glucose

High glucose → insulin (β-cells) → glucose falls. Negative feedback returns it to the normal range (80–120).

Example 2

Going out into the cold, name two responses the body makes to maintain temperature, and identify the control center.

When body temperature drops, responses reduce heat loss and increase heat production.

Skin blood vessels constrict (less heat loss) + muscles shiver (more heat). The control center is the hypothalamus.

▸ Vasoconstriction · shivering / control center: hypothalamus

Temperature drop → (constriction + shivering) restores it. Both temperature and glucose are controlled by negative feedback.

Summary

Homeostasis Formula

stimulus → receptor → control center → effector → homeostasis maintained

Negative feedback keeps internal environment stable

CSAT-style

Which statement about human homeostatic regulation is INCORRECT?

①When blood glucose rises, insulin is secreted

②Insulin is secreted by pancreatic β-cells

③The temperature control center is the hypothalamus

④Most homeostasis is regulated by negative feedback

⑤When blood glucose falls, insulin is secreted to lower it further

▸ ⑤ When blood glucose falls, insulin is secreted to lower it further

When glucose is low, glucagon (α-cells) is secreted to raise it.

Insulin is secreted when glucose is high to lower it, so ⑤ has the direction reversed and is incorrect.

🎯 Exam Points

①Homeostasis = stable internal environment (temp, glucose, pH, osmotic pressure)

②Negative feedback: change → opposite response → restore

③Glucose↑ → insulin (β-cells) → glucose↓; glucose↓ → glucagon (α-cells) → glucose↑

④Temperature control center = hypothalamus

⑤Diabetes: insulin deficiency/dysfunction → glucose homeostasis breaks

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