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Human Physiology - Homeostasis

Grade 9IB

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

🔑Concepts

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Homeostasis is the maintenance of a constant internal environment (e.g., body temperature, blood glucose, and water levels) within narrow limits despite external changes.

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Negative Feedback: A regulatory mechanism where a change in a physiological variable triggers a response that counteracts the initial fluctuation to restore the set point.

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The components of a feedback loop include the Stimulus, Receptor (sensor), Control Center (usually the brain), Effector (muscles or glands), and the Response.

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Thermoregulation: The process of maintaining an internal core temperature of approximately 37∘C37^{\circ}C. Mechanisms include vasodilation, vasoconstriction, sweating, and shivering.

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Blood Glucose Regulation: Controlled by the pancreas. When blood glucose (C6H12O6C_6H_{12}O_6) is high, insulin is released to convert glucose to glycogen. When low, glucagon converts glycogen back to glucose.

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Osmoregulation: The control of water (H2OH_2O) and salt concentrations in the blood, primarily regulated by the kidneys and Antidiuretic Hormone (ADH).

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Positive Feedback: A less common mechanism where a change is amplified rather than reversed (e.g., the release of oxytocin during childbirth).

📐Formulae

C6H12O6+6O2→6CO2+6H2O+ATP (Energy)C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP (Energy)}

Rate of Response=ΔInternal VariableΔTime\text{Rate of Response} = \frac{\Delta \text{Internal Variable}}{\Delta \text{Time}}

n(C6H12O6)→Insulin(C6H10O5)n+nH2On(C_6H_{12}O_6) \xrightarrow{\text{Insulin}} (C_6H_{10}O_5)_n + nH_2O

Core Body Temperature≈37∘C±0.5∘C\text{Core Body Temperature} \approx 37^{\circ}C \pm 0.5^{\circ}C

💡Examples

Problem 1:

Explain the negative feedback loop that occurs when a person's body temperature rises above 37∘C37^{\circ}C during exercise.

Solution:

  1. Stimulus: Increased body temperature. 2. Receptor: Thermoreceptors in the skin and hypothalamus. 3. Control Center: Hypothalamus sends signals. 4. Effector: Sweat glands produce sweat and blood vessels undergo vasodilation. 5. Response: Heat loss through evaporation and radiation, returning temperature to ≈37∘C\approx 37^{\circ}C.

Explanation:

This is a negative feedback mechanism because the output (cooling) reduces the original stimulus (high heat).

Problem 2:

What is the chemical response when blood glucose concentration [C6H12O6][C_6H_{12}O_6] falls below the set point?

Solution:

The alpha cells of the pancreas detect the low level and secrete glucagon. Glucagon travels to the liver, where it catalyzes the breakdown of glycogen into glucose: (C6H10O5)n+nH2O→n(C6H12O6)(C_6H_{10}O_5)_n + nH_2O \rightarrow n(C_6H_{12}O_6).

Explanation:

Glucagon acts as the signaling molecule to increase the concentration of sugar in the blood to maintain metabolic needs.

Homeostasis - Revision Notes & Key Formulas | IB Grade 9 Science