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Coordination and Response - Homeostasis

Grade 11IGCSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Homeostasis is defined as the maintenance of a constant internal environment within restricted limits, ensuring that conditions such as body temperature and blood glucose concentration remain stable.

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Negative Feedback is the primary mechanism for homeostasis; it detects a change in the internal environment and triggers a response to reverse that change to return to the 'set point'.

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Blood Glucose Control: The pancreas acts as a detector. If blood C6H12O6C_6H_{12}O_6 is high, the β\beta-cells secrete Insulin. If low, α\alpha-cells secrete Glucagon.

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Glucoregulation in the Liver: Insulin stimulates the conversion of Glucose→GlycogenGlucose \rightarrow Glycogen. Glucagon stimulates Glycogen→GlucoseGlycogen \rightarrow Glucose.

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Thermoregulation (Cooling): Includes vasodilation (widening of arterioles), sweating (evaporation of H2OH_2O takes away latent heat), and flattening of hairs.

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Thermoregulation (Warming): Includes vasoconstriction (narrowing of arterioles), shivering (muscle contraction to release heat via respiration), and hair erection to trap a layer of air.

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The role of the Hypothalamus: It acts as the control center for body temperature, monitoring the temperature of the blood as it flows through the brain.

📐Formulae

Glucose→InsulinGlycogenGlucose \xrightarrow{Insulin} Glycogen

Glycogen→GlucagonGlucoseGlycogen \xrightarrow{Glucagon} Glucose

C6H12O6+6O2→6CO2+6H2O+Heat (Aerobic Respiration during shivering)C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + Heat \text{ (Aerobic Respiration during shivering)}

Set Point±ΔChange→Correction→Set Point\text{Set Point} \pm \Delta \text{Change} \rightarrow \text{Correction} \rightarrow \text{Set Point}

💡Examples

Problem 1:

Explain the role of the skin in maintaining a body temperature of approximately 37∘C37^\circ C when the external environment becomes too cold.

Solution:

When the temperature drops, the hypothalamus signals the skin to conserve and generate heat. Arterioles near the skin surface undergo vasoconstriction to reduce blood flow to capillaries. Shivering occurs, which is the rapid contraction of muscles where C6H12O6C_6H_{12}O_6 is broken down to release heat energy. Hairs are pulled upright by erector muscles to trap a layer of insulating air.

Explanation:

This is an example of negative feedback where the body reacts to a decrease in temperature by initiating processes that increase thermal energy production and decrease thermal energy loss.

Problem 2:

Compare the response of the body to high blood glucose levels versus low blood glucose levels.

Solution:

High blood glucose: Pancreas secretes Insulin →\rightarrow Liver converts GlucoseGlucose to GlycogenGlycogen. Low blood glucose: Pancreas secretes Glucagon →\rightarrow Liver breaks down GlycogenGlycogen into GlucoseGlucose.

Explanation:

Both processes ensure that the concentration of C6H12O6C_6H_{12}O_6 in the plasma remains at a constant level to provide enough substrate for cell respiration without causing osmotic damage to cells.

Homeostasis - Revision Notes & Key Diagrams | IGCSE Grade 11 Biology