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Human Physiology - The Circulatory and Respiratory Systems

Grade 9IB

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

🔑Concepts

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The Respiratory System facilitates gas exchange; oxygen (O2O_2) is absorbed into the blood while carbon dioxide (CO2CO_2) is removed from it.

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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 in the form of ATPATP.

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The Circulatory System is a double-loop system consisting of the pulmonary circuit (heart to lungs) and the systemic circuit (heart to body).

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The heart consists of four chambers: the right and left atria (upper) and the right and left ventricles (lower). Valves prevent the backflow of blood.

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Arteries carry blood away from the heart at high pressure and have thick muscular walls, while veins carry blood toward the heart at lower pressure and contain valves.

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Capillaries are the site of exchange between blood and tissues; their walls are only one cell thick to facilitate diffusion.

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Red blood cells contain a protein called hemoglobin (HbHb) which binds to oxygen molecules to form oxyhemoglobin (Hb(O2)4Hb(O_2)_4).

📐Formulae

Aerobic Respiration: C6H12O6+6O2→6CO2+6H2O+ATP\text{Aerobic Respiration: } C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}

Anaerobic Respiration (Humans): C6H12O6→2C3H6O3+Energy\text{Anaerobic Respiration (Humans): } C_6H_{12}O_6 \rightarrow 2C_3H_6O_3 + \text{Energy}

Cardiac Output=Stroke Volume×Heart Rate\text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate}

Diffusion Rate∝Surface Area×Concentration GradientDiffusion Distance\text{Diffusion Rate} \propto \frac{\text{Surface Area} \times \text{Concentration Gradient}}{\text{Diffusion Distance}}

💡Examples

Problem 1:

Calculate the Cardiac Output of an athlete whose heart rate is 60 beats/min60\text{ beats/min} and whose stroke volume is 110 mL/beat110\text{ mL/beat}. Express the answer in L/minL/min.

Solution:

Cardiac Output=60 beats/min×0.110 L/beat=6.6 L/min\text{Cardiac Output} = 60\text{ beats/min} \times 0.110\text{ L/beat} = 6.6\text{ L/min}

Explanation:

To find the total volume of blood pumped per minute, multiply the heart rate (frequency) by the stroke volume (volume per beat). Remember to convert 110 mL110\text{ mL} to 0.110 L0.110\text{ L} to provide the answer in the requested units.

Problem 2:

Explain the gas exchange occurring at the alveoli involving PO2P_{O_2} (partial pressure of oxygen).

Solution:

In the alveoli, PO2P_{O_2} is high (≈100 mmHg\approx 100\text{ mmHg}), while in the deoxygenated blood of the surrounding capillaries, PO2P_{O_2} is low (≈40 mmHg\approx 40\text{ mmHg}).

Explanation:

Due to the concentration gradient, O2O_2 diffuses from the high-pressure area (alveoli) to the low-pressure area (blood) across the thin respiratory membrane until equilibrium is reached.

Problem 3:

Identify the chemical change that occurs when CO2CO_2 dissolves in blood plasma.

Solution:

CO2+H2O⇌H2CO3⇌H++HCO3−CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-

Explanation:

Carbon dioxide reacts with water to form carbonic acid (H2CO3H_2CO_3), which dissociates into hydrogen ions (H+H^+) and bicarbonate ions (HCO3−HCO_3^-). This process helps transport CO2CO_2 but also lowers the pHpH of the blood if the concentration is too high.

The Circulatory and Respiratory Systems Revision - Grade 9 Science IB