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Human Physiology - The blood system

Grade 12IBBiology

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

🔑Concepts

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William Harvey's discovery: Disproved the ancient theory of Galen; demonstrated that blood circulates unidirectionally through the body with the heart acting as a pump.

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Arteries: Transport blood at high pressure from the ventricles. They possess thick walls containing elastinelastin fibers and smooth muscle to maintain blood pressureblood\ pressure between pump cycles.

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Capillaries: The site of exchange between blood and interstitial fluid. Walls are one cell thick (tunica intimatunica\ intima) to minimize diffusion distance for O2O_2, CO2CO_2, and nutrients.

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Veins: Return blood to the atria at low pressure. They have thinner walls and a wider lumen than arteries, and contain valves to prevent the backflow of blood.

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Double Circulation: Humans have separate pulmonary (to lungs) and systemic (to body) circulations. This ensures oxygenated and deoxygenated blood do not mix and maintains high pressure for systemic delivery.

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Sinoatrial (SASA) Node: A group of specialized myogenic cells in the right atrium that acts as the primary pacemaker, initiating the electrical impulses for heart contraction.

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Control of Heart Rate: The heart rate is modulated by impulses from the medulla oblongata via the vagus nerve (parasympathetic) and sympathetic nerves, as well as by the hormone adrenaline (epinephrineepinephrine).

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Atherosclerosis: The buildup of plaques (lipidslipids and cholesterolcholesterol) in the lumen of arteries, which can lead to occlusion and Coronary Heart Disease (CHDCHD).

📐Formulae

Cardiac Output=Stroke Volume×Heart RateCardiac\ Output = Stroke\ Volume \times Heart\ Rate

Pulse Pressure=Systolic Pressure−Diastolic PressurePulse\ Pressure = Systolic\ Pressure - Diastolic\ Pressure

Mean Arterial Pressure (MAP)≈Diastolic BP+13(Systolic BP−Diastolic BP)\text{Mean Arterial Pressure (MAP)} \approx Diastolic\ BP + \frac{1}{3}(\text{Systolic BP} - \text{Diastolic BP})

💡Examples

Problem 1:

Calculate the cardiac output of an athlete at rest if their stroke volume is 80 mL80\ mL and their heart rate is 55 beats per minute55\ beats\ per\ minute. Provide the answer in L min−1L\ min^{-1}.

Solution:

80 mL×55 min−1=4400 mL min−1=4.4 L min−180\ mL \times 55\ min^{-1} = 4400\ mL\ min^{-1} = 4.4\ L\ min^{-1}

Explanation:

Cardiac output is defined as the total volume of blood pumped by the left ventricle per minute. It is calculated by multiplying the Stroke VolumeStroke\ Volume (volume per beat) by the Heart RateHeart\ Rate (beats per minute). To convert mLmL to LL, divide the result by 10001000.

Problem 2:

Explain the role of the SASA node and AVAV node during a single cardiac cycle.

Solution:

The SASA node fires an impulse causing atrial systole. After a delay of ≈0.1\approx 0.1 seconds at the Atrioventricular (AVAV) node, the signal travels down the Bundle of His to the Purkinje fibers, causing ventricular systole.

Explanation:

The delay at the AVAV node is crucial as it ensures that the atria have fully emptied their blood into the ventricles before the ventricles begin to contract.

The blood system - Revision Notes & Key Diagrams | IB Grade 12 Biology