CIE iGCSE Biology-9.2 Heart- Study Notes- New Syllabus
CIE iGCSE Biology-9.2 Heart- Study Notes – New syllabus
CIE iGCSE Biology-9.2 Heart- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- Identify in diagrams and images the structures of the mammalian heart, limited to: muscular wall, septum, left and right ventricles, left and right atria, one-way valves and coronary arteries
- State that blood is pumped away from the heart in arteries and returns to the heart in veins
- State that the activity of the heart may be monitored by: ECG, pulse rate and listening to sounds of valves closing
- Investigate and describe the effect of physical activity on the heart rate
- Describe coronary heart disease in terms of the blockage of coronary arteries and state the possible risk factors including: diet, lack of exercise, stress, smoking, genetic predisposition, age and sex
- Discuss the roles of diet and exercise in reducing the risk of coronary heart disease
Supplement
- Identify in diagrams and images the atrioventricular and semilunar valves in the mammalian heart
- Explain the relative thickness of:
(a) the muscle walls of the left and right ventricles
(b) the muscle walls of the atria compared to those of the ventricles - Explain the importance of the septum in separating oxygenated and deoxygenated blood
- Describe the functioning of the heart in terms of the contraction of muscles of the atria and ventricles and the action of the valves
- Explain the effect of physical activity on the heart rate
Identifying Key Structures in the Mammalian Heart
Understanding the internal and external structures of the mammalian heart is key to learning how it functions efficiently to pump blood throughout the body. Below are the essential parts you should recognize and label in diagrams.
1. Muscular Wall (Myocardium)
The thick muscle layer of the heart, especially developed in the left ventricle to pump blood at high pressure throughout the body. It’s responsible for strong, rhythmic contractions.
2. Septum
The muscular wall dividing the left and right sides of the heart. It prevents mixing of oxygenated and deoxygenated blood, ensuring double circulation remains effective.
3. Right Atrium
This upper chamber receives deoxygenated blood from the body via the vena cava. It pushes blood into the right ventricle through the tricuspid valve.
4. Left Atrium
Receives oxygenated blood from the lungs via the pulmonary veins and passes it into the left ventricle through the bicuspid (mitral) valve.
5. Right Ventricle
Pumps deoxygenated blood to the lungs through the pulmonary artery. Its wall is thinner compared to the left ventricle.
6. Left Ventricle
Receives oxygen-rich blood and pumps it into the aorta to reach the entire body. It has the thickest wall to generate high pressure.
7. One-Way Valves
Atrioventricular (AV) valves:
- Tricuspid valve (right side)
- Bicuspid/Mitral valve (left side)
Semilunar valves:
- Located at the base of the aorta and pulmonary artery
These valves prevent backflow and ensure blood flows in one direction only.
8. Coronary Arteries
These are visible on the external surface of the heart and supply the heart muscle itself with oxygenated blood. If blocked, they can cause a heart attack.
📝 Summary Table
| Structure | Function |
|---|---|
| Muscular Wall | Contracts to pump blood, thickest in left ventricle |
| Septum | Separates left and right sides, prevents blood mixing |
| Right Atrium | Collects deoxygenated blood from the body |
| Left Atrium | Collects oxygenated blood from the lungs |
| Right Ventricle | Sends blood to lungs via pulmonary artery |
| Left Ventricle | Sends blood to the body via aorta |
| One-Way Valves | Ensure blood flows in one direction, prevent backflow |
| Coronary Arteries | Supply the heart muscle with oxygen-rich blood |
Direction of Blood Flow in Blood Vessels
Arteries – Carry Blood Away from the Heart
- Arteries have thick, muscular, and elastic walls.
- They carry blood under high pressure because it has just been pumped from the heart.
- Most arteries (except the pulmonary artery) carry oxygenated blood.
- Example: The aorta carries oxygen-rich blood from the left ventricle to the body.
Veins – Carry Blood Back to the Heart
- Veins have thinner walls and wider lumens than arteries.
- They carry blood under low pressure.
- Most veins (except the pulmonary vein) carry deoxygenated blood.
- Veins contain valves to prevent backflow and ensure one-way movement.
- Example: The vena cava brings deoxygenated blood from the body to the right atrium.
🧠 Simple Way to Remember
Arteries = Away from the heart
Veins = Visit the heart again (return to heart)
Monitoring the Activity of the Heart
The activity of the heart can be monitored using an ECG, by measuring pulse rate, and by listening to valve sounds caused by closure.
📊 1. ECG (Electrocardiogram)
- An ECG records the electrical activity of the heart.
- It shows how regularly the heart is beating and detects abnormal rhythms (e.g. arrhythmias).
- Doctors use ECG traces to monitor heart rate, rhythm, and the health of cardiac muscles.
💓 2. Pulse Rate
- A pulse is a pressure wave caused by the heart beating and blood pushing through arteries.
- You can feel it at points like the wrist or neck.
- It gives the heart rate in bpm (beats per minute) and reflects how fast the heart is working.
👂 3. Listening to Valve Sounds (Auscultation)
- A stethoscope is used to listen to the “lub-dub” sounds of the heart.
- These sounds are due to the closure of AV and semilunar valves.
- Murmurs (irregular sounds) may suggest problems like valve leakage or narrowing.
🧠 Summary
Monitoring heart activity helps in diagnosing conditions, tracking recovery, and ensuring the heart is functioning properly. Each method gives unique insights into heart health.
Investigating the Effect of Physical Activity on Heart Rate
Physical activity increases heart rate to supply muscles with more oxygen and glucose, and to remove carbon dioxide and heat more efficiently.
🔬 Investigation: How Exercise Affects Heart Rate
Aim: To investigate how physical activity affects a person’s heart rate.
Materials: Stopwatch, exercise equipment (e.g. skipping rope/stairs), timer, notebook or spreadsheet, optional: heart rate monitor.
Method:
- Measure resting heart rate by counting pulse for 1 minute while sitting.
- Perform activity (e.g. run on the spot or skip for 2–3 minutes).
- Immediately measure heart rate after exercise.
- Continue recording every minute until it returns to normal.
- Repeat to find an average and identify patterns.
📈 Expected Results
- Before exercise: Lower, steady resting heart rate.
- After exercise: Rapid increase in heart rate.
- Recovery: Gradual return to resting rate over a few minutes.
🧠 Biological Explanation
- Muscles need more oxygen and glucose for aerobic respiration.
- The heart beats faster to increase blood flow.
- Faster circulation removes carbon dioxide and heat from tissues.
- This response is controlled by the brain detecting CO₂ levels and adjusting heart rate via nerves.
🩺 Why It’s Important
Monitoring heart rate after exercise reveals fitness levels:
- A fitter person has a lower resting heart rate.
- They also recover more quickly after exercise.
This investigation highlights how the cardiovascular system adapts to the body’s needs during activity.
Coronary Heart Disease (CHD)
What is CHD?
Coronary Heart Disease is a condition where the coronary arteries become narrowed or blocked due to a buildup of fatty substances like cholesterol. This buildup forms plaques in a process called atherosclerosis.
As arteries narrow, less blood reaches the heart muscle. This can cause chest pain (angina) or a heart attack (myocardial infarction) if completely blocked.
💔 Why is CHD Dangerous?
- The heart needs a constant supply of oxygen-rich blood.
- If this supply is reduced, heart muscle cells may die.
- A heart attack may result in permanent heart damage or sudden death.
⚠️ Major Risk Factors for CHD
CHD is influenced by both lifestyle and genetic factors:
| Risk Factor | How It Contributes to CHD |
|---|---|
| High-fat diet | Raises cholesterol levels, encouraging plaque buildup in arteries. |
| Lack of exercise | Contributes to weight gain, high blood pressure, and poor circulation. |
| Stress | Raises blood pressure; may lead to smoking, overeating, or inactivity. |
| Smoking | Damages artery walls and reduces oxygen in the blood. |
| Genetic predisposition | Family history increases risk of developing CHD. |
| Age | Risk increases with age, especially after 45 for men, 55 for women. |
| Sex | Men are more at risk earlier; risk rises in women after menopause. |
CHD is a leading cause of death worldwide – but it is often preventable through healthy lifestyle choices.
🌿 Prevention and Management Tips
- Eat a balanced diet low in saturated fats and cholesterol.
- Exercise regularly (at least 30 minutes on most days).
- Avoid smoking and limit alcohol consumption.
- Manage stress through relaxation or hobbies.
- Get regular health check-ups to monitor blood pressure and cholesterol.
Diet and Exercise in Reducing CHD Risk
Coronary Heart Disease (CHD) occurs when the coronary arteries become narrowed or blocked by fatty deposits (plaques). This can lead to chest pain (angina) or even heart attacks. Fortunately, diet and exercise play a powerful role in lowering this risk.
1. Role of a Healthy Diet
A proper diet helps control cholesterol, blood pressure, and body weight all key factors in preventing CHD.
| Healthy Choice | How It Helps |
|---|---|
| Low in saturated fats | Reduces LDL (“bad”) cholesterol, lowering artery blockage risk. |
| High in fruits and vegetables | Provides antioxidants and fiber to protect heart tissue. |
| Whole grains and legumes | Stabilizes cholesterol and blood sugar levels. |
| Omega-3 fatty acids | Reduces inflammation and prevents blood clotting. |
| Low salt (sodium) | Helps lower blood pressure. |
| Limiting sugar | Reduces risk of obesity and diabetes. |
Note: Avoid fast food, sugary drinks, and fried items – they promote plaque buildup.
2. Role of Regular Exercise
Exercise keeps the heart and circulatory system strong, while helping manage weight and stress.
| Benefit | Explanation |
|---|---|
| Improves heart function | Heart pumps blood more effectively and efficiently. |
| Lowers blood pressure | Less stress on blood vessels and arteries. |
| Raises HDL (“good”) cholesterol | Helps clear LDL cholesterol from the bloodstream. |
| Maintains healthy weight | Reduces risk of obesity-linked heart disease. |
| Reduces stress | Exercise releases endorphins that boost mood and lower anxiety. |
Recommended: At least 30 minutes of moderate activity (e.g. walking, swimming, cycling) on most days.
Summary: A Powerful Combination
Diet + Exercise form the most effective and natural way to prevent and manage CHD. This combination supports heart health and improves overall quality of life.
Identifying Atrioventricular and Semilunar Valves in the Mammalian Heart
To ensure blood flows in only one direction, the heart contains specialized valves. These valves are easily identifiable in diagrams when you know where to look and what to label.
1. Atrioventricular (AV) Valves
Located between the atria and ventricles, these valves prevent blood from flowing backward into the atria during ventricular contraction.
| Valve | Position | Function |
|---|---|---|
| Tricuspid Valve | Between right atrium and right ventricle | Prevents backflow into the right atrium |
| Bicuspid (Mitral) Valve | Between left atrium and left ventricle | Prevents backflow into the left atrium |
Tip: AV valves are found between the upper and lower chambers and are connected by tendinous cords (chordae tendineae) to papillary muscles.
2. Semilunar Valves
Located at the exits of the heart’s ventricles, semilunar valves prevent blood from flowing back into the ventricles once it has been pumped out.
| Valve | Position | Function |
|---|---|---|
| Pulmonary Valve | At the entrance to the pulmonary artery (right ventricle) | Prevents backflow into the right ventricle |
| Aortic Valve | At the entrance to the aorta (left ventricle) | Prevents backflow into the left ventricle |
Tip: Semilunar valves are located at the base of arteries and appear like three half-moon shaped flaps.
✅ Quick Guide
| Valves | Found Between | Direction of Blood Flow |
|---|---|---|
| Tricuspid (AV) | Right atrium → Right ventricle | From atrium to ventricle |
| Bicuspid/Mitral (AV) | Left atrium → Left ventricle | From atrium to ventricle |
| Pulmonary (SL) | Right ventricle → Pulmonary artery | From heart to lungs |
| Aortic (SL) | Left ventricle → Aorta | From heart to body |
Relative Thickness of the Heart’s Muscle Walls
The human heart has four chambers: two atria at the top and two ventricles at the bottom. The thickness of each chamber’s muscle wall depends on the pressure it must generate during contraction.
(a) Left vs. Right Ventricle Wall Thickness
| Chamber | Muscle Wall | Reason |
|---|---|---|
| Left Ventricle | Thicker muscular wall | It pumps blood to the entire body, requiring high pressure and strong force. |
| Right Ventricle | Thinner muscular wall | It only pumps blood to the lungs, which are nearby and need lower pressure. |
👉 Key Point: The left ventricle has the thickest wall in the heart because it does the most work – pumping blood to the whole body.
(b) Atria vs. Ventricles Wall Thickness
| Part of the Heart | Muscle Wall | Reason |
|---|---|---|
| Atria | Thinner walls | They only push blood into the ventricles, so very little pressure is needed. |
| Ventricles | Thicker walls | They must pump blood out of the heart with more force. |
🔍 Why? Ventricles are more muscular than atria because they do the heavy pumping – to the lungs and body.
Summary
- Left ventricle: thickest wall – pumps to the whole body.
- Right ventricle: thinner – pumps to the nearby lungs.
- Atria: thinnest – just push blood into ventricles.
Importance of the Septum in the Heart
The septum is a thick muscular wall that separates the left and right sides of the heart. In mammals like humans, this separation is essential for proper blood circulation and oxygen delivery.
💡 Why Is This Separation Important?
- Right side: Receives deoxygenated blood from the body and pumps it to the lungs.
- Left side: Receives oxygenated blood from the lungs and sends it to the rest of the body.
- The septum: Prevents mixing between the two types of blood by acting as a barrier.
🔍 Function of the Septum
| Feature of Septum | Why It Matters |
|---|---|
| Separates right and left chambers | Prevents mixing of oxygenated and deoxygenated blood. |
| Keeps blood flowing correctly | Ensures correct routing: deoxygenated blood → lungs; oxygenated blood → body. |
| Maintains efficient circulation | Supports high oxygen delivery for cellular respiration. |
🚨 What If There Was No Septum?
If the septum was missing or had a hole (septal defect), oxygenated and deoxygenated blood would mix. This could lead to:
- Reduced oxygen supply to tissues
- Fatigue and breathlessness
- Decreased energy production in cells
Summary
The septum is essential in the heart’s double circulation system. By separating oxygen-rich and oxygen-poor blood, it ensures efficient oxygen delivery to all parts of the body and keeps cellular respiration running smoothly.
Functioning of the Heart (How the Heart Beats and Pumps Blood)
The human heart is a muscular organ that works like a double pump. Its main job is to circulate blood throughout the body – delivering oxygen and nutrients, and removing waste.
🔄 Step-by-Step Heartbeat Cycle
The heartbeat cycle includes two key stages:
- Contraction – called systole
- Relaxation – called diastole
It involves the atria, ventricles, and heart valves.
🫀 1. Atrial Contraction (Atrial Systole)
- Blood enters the right and left atria from the body and lungs.
- The atria contract, pushing blood into the ventricles.
- The AV valves (tricuspid & bicuspid) open to allow flow into ventricles.
Purpose: To fill the ventricles with blood before they contract.
💪 2. Ventricular Contraction (Ventricular Systole)
- Ventricles contract forcefully after filling.
- AV valves close, producing the first “lub” sound.
- Blood is pushed out via:
- Pulmonary artery (to lungs)
- Aorta (to the body)
- Semilunar valves open to let blood out.
Purpose: To pump blood to the lungs and body.
🛌 3. Relaxation Phase (Diastole)
- Both atria and ventricles relax.
- Semilunar valves close, creating the second “dub” sound.
- Blood flows back into atria from:
- Vena cava (from body)
- Pulmonary veins (from lungs)
- AV valves reopen to allow next cycle to begin.
🔁 Role of the Valves
| Valve | Location | Function |
|---|---|---|
| Atrioventricular (AV) valves | Between atria and ventricles | Open to let blood into ventricles, close to prevent backflow into atria |
| Semilunar valves | At exits of ventricles | Open to let blood out, close to prevent backflow into ventricles |
💡 Summary of the Heart’s Pumping Action
| Phase | Action | Valves Open | Valves Closed |
|---|---|---|---|
| Atrial Systole | Atria contract | AV valves | Semilunar valves |
| Ventricular Systole | Ventricles contract | Semilunar valves | AV valves |
| Diastole | Heart relaxes | AV valves | Semilunar valves |
Effect of Physical Activity on Heart Rate
Heart rate is the number of heart beats per minute (bpm). It rises or falls depending on how much oxygen and energy your body needs at a given time.
💓 How Exercise Affects Heart Rate
When you engage in physical activity, your muscles need more oxygen and glucose to produce energy via respiration. To meet this demand, the heart and lungs respond with several coordinated changes:
- Increased heart rate – The heart beats faster to supply more oxygenated blood to the muscles.
- Increased stroke volume – Each heartbeat pumps out more blood.
- Redirected blood flow – More blood is sent to the working muscles, less to non-essential organs like the digestive system.
- Faster breathing – The breathing rate rises to increase oxygen intake and expel carbon dioxide.
🔬 Why Does This Happen?
During physical activity:
- Muscles carry out aerobic respiration, which uses oxygen and produces carbon dioxide as a waste product.
- Chemoreceptors in the body detect rising carbon dioxide levels in the blood.
- The brain responds by sending signals via the nervous system to increase heart rate and breathing.
This automatic regulation helps maintain stable internal conditions – a key part of homeostasis.
📉 What Happens After Exercise?
Once the activity stops:
- The demand for oxygen decreases
- Carbon dioxide levels fall
- The heart rate gradually returns to its resting rate
Note: Fitter individuals typically recover faster due to a more efficient cardiovascular system.
📌 Investigation Idea: Measuring Heart Rate
Students can perform a simple experiment to observe how heart rate changes during and after exercise:
- Measure pulse at rest (beats per minute)
- Do light exercise (e.g., 1 minute of jumping jacks)
- Measure pulse immediately after
- Measure pulse every minute during recovery
- Plot a line graph to show how heart rate rises and returns to normal
🧠 Summary Table
| Stage | Heart Rate | Oxygen Demand | CO₂ Levels |
|---|---|---|---|
| Before Exercise | Normal | Low | Low |
| During Exercise | High | High | High |
| After Exercise | Decreasing to Normal | Decreasing | Decreasing |