2.7.10Inquiry Process
The Mammalian Heart — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 82 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Structure and Blood Flow
The septum keeps oxygenated and deoxygenated blood apart.
1
Deoxygenated blood from the body enters the right atrium through the vena cava.
2
It passes through the tricuspid valve into the right ventricle, which pumps it through the pulmonary valve into the pulmonary artery towards the lungs.
3
Oxygenated blood returns through the pulmonary veins into the left atrium.
4
It passes through the bicuspid valve into the left ventricle, which has a much thicker muscular wall.
5
The left ventricle pumps blood through the aortic valve into the aorta for distribution around the body.
Part 2 of 4Controlling the Heartbeat
Myogenic contraction
- Myogenic contraction Cardiac muscle contracts on its own without nerve stimulation;
- the heart is therefore described as myogenic.
Sinoatrial node
- Sinoatrial node A cluster of cells in the right atrium wall acts as the pacemaker, sending waves of excitation across both atria.
Atrioventricular node
- Atrioventricular node The wave reaches this node, which delays it briefly so that the atria finish emptying before the ventricles contract.
Conducting fibres
- Conducting fibres The signal then passes down the septum and through Purkyne fibres, so the ventricles contract from the apex upwards.
| Chamber | Wall thickness | Pumps blood to |
|---|---|---|
| Right ventricle | Thinner | Lungs |
| Left ventricle | Thickest | Whole body |
Part 3 of 4Modifying Heart Rate
Modifying Heart Rate
Cardiovascular centre
- Cardiovascular centre The medulla oblongata adjusts heart rate in response to carbon dioxide and pH detected by chemoreceptors.
Sympathetic nerve
- Sympathetic nerve Impulses from this nerve speed up the pacemaker and raise heart rate during exercise or stress.
Vagus nerve
- Vagus nerve Impulses along the vagus nerve slow the pacemaker and lower heart rate during rest.
Adrenaline
- Adrenaline This hormone from the adrenal glands increases the rate and force of contraction.
Part 4 of 4Exam Checklist & Tips
2.7.10 – Key Points for the Exam
- Myogenic Initiating its own contraction without a nerve impulse, as cardiac muscle does.
- Sinoatrial node The natural pacemaker of the heart located in the right atrium.
- Atrioventricular valve A valve between atrium and ventricle that prevents backflow into the atrium.
- Septum The muscular wall separating the left and right sides of the heart.
- Purkyne fibres Specialised fibres that spread the signal rapidly through the ventricle walls.
Common Mistakes
- Saying the heart is neurogenic because it is controlled by the brain; nerves only adjust the rate.
- Labelling the left side of the diagram as the viewer's left, when it is the patient's left.
- Forgetting that the pulmonary artery carries deoxygenated blood.
- Stating that the atria and ventricles contract together.
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