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Transport in Animals - Heart structure and function

Grade 12IGCSEBiology

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

🔑Concepts

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Double Circulatory System: Humans have a double circulation where blood passes through the heart twice for every complete circuit of the body. This includes the Pulmonary circuit (Heart→Lungs→HeartHeart \rightarrow Lungs \rightarrow Heart) and the Systemic circuit (Heart→Rest of Body→HeartHeart \rightarrow Rest\ of\ Body \rightarrow Heart).

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Heart Anatomy: The heart consists of four chambers. The Right Atrium and Ventricle handle deoxygenated blood (CO2CO_2 rich), while the Left Atrium and Ventricle handle oxygenated blood (O2O_2 rich). The muscular wall of the Left Ventricle is significantly thicker than the Right Ventricle because it must pump blood at higher pressure to the entire body.

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The Cardiac Cycle: Consists of three stages: 1. Atrial Systole (atria contract, pushing blood into ventricles), 2. Ventricular Systole (ventricles contract, pushing blood into the AortaAorta and Pulmonary ArteryPulmonary\ Artery), and 3. Diastole (heart muscle relaxes, chambers fill with blood).

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Valves: Atrioventricular (AV) valves (Tricuspid on the right, Bicuspid/Mitral on the left) prevent backflow into the atria during ventricular contraction. Semilunar valves (Aortic and Pulmonary) prevent backflow from the arteries into the ventricles during diastole.

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Coronary Heart Disease (CHD): The coronary arteries supply the cardiac muscle with O2O_2 and glucose. If these become blocked by fatty deposits (cholesterol), it leads to restricted blood flow and potential myocardial infarction (heart attack).

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Pacemaker: The Sinoatrial Node (SAN) in the wall of the right atrium sends electrical impulses to stimulate contraction, regulating the heart rate.

📐Formulae

Cardiac Output (CO)=Stroke Volume (SV)×Heart Rate (HR)Cardiac\ Output\ (CO) = Stroke\ Volume\ (SV) \times Heart\ Rate\ (HR)

Heart Rate (bpm)=60Length of one cardiac cycle in secondsHeart\ Rate\ (bpm) = \frac{60}{\text{Length of one cardiac cycle in seconds}}

Percentage Increase=New Rate−Original RateOriginal Rate×100Percentage\ Increase = \frac{\text{New Rate} - \text{Original Rate}}{\text{Original Rate}} \times 100

💡Examples

Problem 1:

During a cardiac cycle diagram analysis, it is observed that one complete cycle (from the start of atrial systole to the end of diastole) takes 0.80.8 seconds. If the stroke volume of the left ventricle is 75 cm375\ cm^3, calculate the Cardiac Output in dm3/mindm^3/min.

Solution:

  1. Calculate Heart Rate: HR=600.8=75 bpmHR = \frac{60}{0.8} = 75\ bpm.
  2. Apply formula: CO=75 cm3×75 bpm=5625 cm3/minCO = 75\ cm^3 \times 75\ bpm = 5625\ cm^3/min.
  3. Convert to dm3dm^3: CO=56251000=5.625 dm3/minCO = \frac{5625}{1000} = 5.625\ dm^3/min.

Explanation:

Cardiac output is defined as the volume of blood pumped by one ventricle per minute. We first find how many beats occur in a minute by dividing 60 seconds by the duration of one beat, then multiply by the volume per beat.

Problem 2:

Explain why the pressure in the Left Ventricle (PLVP_{LV}) reaches a maximum of 120 mmHg120\ mmHg while the Right Ventricle (PRVP_{RV}) only reaches 25 mmHg25\ mmHg.

Solution:

PLV>PRVP_{LV} > P_{RV} because the Left Ventricle has a much thicker muscular wall.

Explanation:

The Left Ventricle must generate sufficient pressure to overcome high resistance in the systemic circulation to pump blood to the extremities. The Right Ventricle only pumps blood to the lungs (pulmonary circuit), which is a shorter distance and requires lower pressure to prevent damage to the delicate capillary beds in the alveoli.

Heart structure and function - Revision Notes & Key Diagrams | IGCSE Grade 12 Biology