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Coordination and Response - Homeostasis

Grade 12IGCSEBiology

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

🔑Concepts

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Homeostasis is the maintenance of a nearly constant internal environment within a living organism, despite changes in external conditions. Key variables include blood glucose concentration, body temperature, and water potential of body fluids.

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Negative Feedback is a control mechanism where a change in a physiological variable triggers a response that reverses the direction of that change, returning the system to its set point. It involves a stimulus, receptor, coordinator (e.g., the hypothalamus), and an effector.

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Blood Glucose Regulation: Controlled by the pancreas. β\beta-cells in the Islets of Langerhans secrete insulin when glucose levels are high, while α\alpha-cells secrete glucagon when levels are low.

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Thermoregulation: The hypothalamus monitors the temperature of the blood. In response to heat, the body employs vasodilation of arterioles and sweating. In response to cold, it uses vasoconstriction, shivering, and the contraction of erector muscles (piloerection).

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Osmoregulation: The control of water potential in the blood. The hormone ADHADH (Antidiuretic Hormone) is released by the posterior pituitary gland to increase the permeability of the collecting ducts in the kidneys to H2OH_2O.

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Glucoregulation Chemistry: Glucose is converted to the insoluble storage polysaccharide glycogen (C6H10O5)nC_6H_{10}O_5)_n via glycogenesis stimulated by insulin.

📐Formulae

Glucose→InsulinGlycogen\text{Glucose} \xrightarrow{\text{Insulin}} \text{Glycogen}

Glycogen→GlucagonGlucose\text{Glycogen} \xrightarrow{\text{Glucagon}} \text{Glucose}

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

Water Potential (Ψ)=Ψs+Ψp\text{Water Potential (}\Psi\text{)} = \Psi_s + \Psi_p

💡Examples

Problem 1:

Explain how the body responds to a decrease in core body temperature below 37∘C37^{\circ}C.

Solution:

  1. Receptors in the hypothalamus and skin detect the drop in temperature. 2. The hypothalamus sends nerve impulses to effectors. 3. Vasoconstriction occurs: arterioles near the skin surface constrict, reducing blood flow to capillaries and minimizing heat loss via radiation. 4. Shivering: Rapid muscle contractions generate metabolic heat through increased rates of cellular respiration (C6H12O6+6O2→6CO2+6H2OC_6H_{12}O_6 + 6O_2 \to 6CO_2 + 6H_2O).

Explanation:

This is a negative feedback loop where the response (heat generation and conservation) opposes the stimulus (cooling).

Problem 2:

A person consumes a meal high in carbohydrates, leading to a spike in blood glucose. Describe the hormonal response.

Solution:

The increase in blood glucose is detected by the β\beta-cells of the Islets of Langerhans in the pancreas. These cells secrete the hormone insulin into the blood. Insulin targets the liver and muscle cells, increasing their permeability to glucose and activating enzymes that convert glucose into glycogen for storage.

Explanation:

Insulin lowers the blood glucose concentration back to the set point of approximately 5.5 mmol/L5.5\text{ mmol/L} through glycogenesis.

Homeostasis - Revision Notes & Key Diagrams | IGCSE Grade 12 Biology