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Human Body Systems - The Respiratory System

Grade 7IB

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

🔑Concepts

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The primary function of the respiratory system is gas exchange: the intake of oxygen (O2O_2) and the removal of carbon dioxide (CO2CO_2) from the body.

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Air follows a specific pathway: Nasal Cavity →\rightarrow Pharynx →\rightarrow Larynx →\rightarrow Trachea →\rightarrow Bronchi →\rightarrow Bronchioles →\rightarrow Alveoli.

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Alveoli are the site of gas exchange, adapted with a large surface area, moist surfaces, and walls that are only one cell thick to allow for rapid diffusion.

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Breathing (ventilation) is driven by pressure changes in the thoracic cavity. According to Boyle's Law (P∝1VP \propto \frac{1}{V}), increasing volume decreases pressure, causing air to flow in.

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During inhalation, the diaphragm contracts and moves downward, while intercostal muscles move the ribcage up and out.

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Cellular respiration is the chemical process in mitochondria that uses O2O_2 to break down glucose (C6H12O6C_6H_{12}O_6) to produce energy (ATP).

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Gas exchange occurs via diffusion, where molecules move from an area of high partial pressure (PO2P_{O_2} or PCO2P_{CO_2}) to an area of low partial pressure.

📐Formulae

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

P1V1=P2V2P_1V_1 = P_2V_2

Inhaled Air≈21% O2, 0.04% CO2\text{Inhaled Air} \approx 21\% \text{ } O_2, \text{ } 0.04\% \text{ } CO_2

Exhaled Air≈16% O2, 4% CO2\text{Exhaled Air} \approx 16\% \text{ } O_2, \text{ } 4\% \text{ } CO_2

💡Examples

Problem 1:

Explain why the concentration of CO2CO_2 is higher in the blood entering the lungs than in the air within the alveoli.

Solution:

The blood entering the lungs has returned from body tissues where cellular respiration (C6H12O6+6O2→6CO2+6H2OC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O) has occurred, producing CO2CO_2 as a waste product.

Explanation:

Because CO2CO_2 is produced in the cells, it diffuses into the blood. When this blood reaches the alveoli, the partial pressure of CO2CO_2 is higher in the blood than in the inhaled air, causing CO2CO_2 to diffuse into the alveoli to be exhaled.

Problem 2:

Calculate the difference in O2O_2 percentage between inhaled and exhaled air based on standard values.

Solution:

21%−16%=5%21\% - 16\% = 5\%

Explanation:

Inhaled air contains approximately 21%21\% oxygen. The body absorbs some of this oxygen for cellular respiration, resulting in exhaled air containing roughly 16%16\% oxygen. The 5%5\% difference represents the oxygen taken up by the blood.

Problem 3:

What happens to the pressure inside the chest cavity when the diaphragm relaxes and moves upwards?

Solution:

The volume of the thoracic cavity decreases, which causes the internal pressure to increase (P>PatmosphericP > P_{\text{atmospheric}}).

Explanation:

Based on the inverse relationship between volume and pressure, decreasing the volume forces the air molecules into a smaller space, increasing pressure and pushing air out of the lungs (exhalation).