Circulatory System ICSE Class 8: Heart, Blood Vessels, Double Circulation, Blood Groups and Lymph

What Circulatory System is about

Weightage: CISCE publishes no question paper, marking scheme or chapter weightage for Class VIII Biology: your school sets and marks the exam. Circulatory System sits in the Theme: Human Body - Endocrine, Circulatory and Nervous Systems theme of the CISCE Curriculum for Upper Primary Classes (VI-VIII).Source: CISCE Curriculum for Upper Primary Classes (VI-VIII), RDCD 2016

Key concepts

The heart: position, chambers and septum

The heart is a hollow, muscular organ about the size of your fist. It lies in the chest cavity between the two lungs, slightly to the left, protected by the ribcage. It is covered by a double membrane, the pericardium, with fluid between the layers that reduces friction as the heart beats.

Four chambers:

• Two upper chambers, the atria (singular: atrium): thin-walled, they receive blood from veins.
• Two lower chambers, the ventricles: thick-walled, they pump blood out into arteries.
• The left ventricle has the thickest wall, because it pumps blood to the whole body; the right ventricle pumps only to the nearby lungs.

The septum is a thick muscular wall that divides the heart into right and left halves. It prevents oxygenated and deoxygenated blood from mixing.

• Right side: deoxygenated blood (from the body, going to the lungs).
• Left side: oxygenated blood (from the lungs, going to the body).

The function of the heart is to pump blood continuously around the body; a resting adult heart beats about 72 times a minute.

Worked example

Why is the wall of the left ventricle thicker than that of the right ventricle?

Try it first, then show the solutionSolution

1. The left ventricle pumps blood into the aorta, to every part of the body, which needs great force.
2. The right ventricle pumps blood only to the lungs nearby, needing less force.

Answer: It must pump blood to the whole body, so it needs more muscle.

Valves and the pacemaker

Valves are flaps of tissue that let blood flow in one direction only and stop it flowing back.

Valve	Position	Flaps
Tricuspid	between the right atrium and right ventricle	three
Bicuspid (mitral)	between the left atrium and left ventricle	two
Semilunar valves	at the openings of the pulmonary trunk and the aorta from the ventricles	three half-moon pockets each

The flaps of the tricuspid and bicuspid valves are held by thin cords so they do not turn inside out when the ventricles contract. The 'lubb-dupp' sound of the heartbeat is the sound of valves closing: 'lubb' when the tricuspid and bicuspid valves close, 'dupp' when the semilunar valves close.

Pacemaker: a small patch of special muscle tissue in the wall of the right atrium, called the sinoatrial (SA) node. It produces the electrical signal that starts each heartbeat and sets its rhythm. If it fails, doctors can fit an artificial pacemaker, a small battery-run device placed under the skin that sends regular electrical signals to the heart.

Worked example

Name the valve between the left atrium and left ventricle, and state what would happen if it leaked.

Try it first, then show the solutionSolution

1. Bicuspid (mitral) valve.
2. When the left ventricle contracts, some blood would flow back into the left atrium, so less blood would go to the body.

Answer: Bicuspid; blood would flow back and the body would get less blood.

Main blood vessels of the heart

Arteries carry blood away from the heart; they have thick, elastic walls. Veins carry blood to the heart; they have thinner walls and valves. Capillaries are tiny, thin-walled vessels joining arteries to veins, where exchange with cells takes place.

Vessel	From → to	Blood
Aorta (largest artery)	left ventricle → whole body	oxygenated
Pulmonary trunk (dividing into pulmonary arteries)	right ventricle → lungs	deoxygenated (the only artery with deoxygenated blood)
Pulmonary veins	lungs → left atrium	oxygenated (the only veins with oxygenated blood)
Superior vena cava	head, neck, arms → right atrium	deoxygenated
Inferior vena cava	lower body → right atrium	deoxygenated
Coronary arteries	base of the aorta → heart muscle	oxygenated
Coronary veins	heart muscle → right atrium	deoxygenated

The heart muscle cannot use the blood passing through its chambers; it gets its own supply through the coronary arteries. If a coronary artery gets blocked (by fatty deposits or a clot), part of the heart muscle is starved of oxygen: a heart attack.

Worked example

Name the blood vessel that (i) brings oxygenated blood to the heart (ii) supplies the heart muscle itself.

Try it first, then show the solutionSolution

1. (i) Pulmonary veins bring oxygenated blood from the lungs to the left atrium.
2. (ii) Coronary arteries, which branch from the aorta.

Answer: (i) Pulmonary veins (ii) Coronary arteries

Double circulation

In humans, blood passes through the heart twice during one complete round of the body. This is double circulation.

1. Pulmonary circulation (heart ↔ lungs):
right atrium → right ventricle → pulmonary trunk → lungs (blood picks up oxygen, gives out carbon dioxide) → pulmonary veins → left atrium.

2. Systemic circulation (heart ↔ body):
left atrium → left ventricle → aorta → body organs (blood gives oxygen and food to cells, collects carbon dioxide and wastes) → venae cavae → right atrium.

Advantage: oxygenated and deoxygenated blood never mix, and blood is pumped at high pressure to the body after it has been oxygenated. This gives the body a rich, steady supply of oxygen, which warm-blooded animals that use a lot of energy need.

Worked example

Trace the path of a drop of blood from the right atrium back to the right atrium, naming the chambers, vessels and valves.

Try it first, then show the solutionSolution

1. Right atrium → (tricuspid) → right ventricle → (semilunar) → pulmonary trunk → lungs → pulmonary veins → left atrium.
2. Left atrium → (bicuspid) → left ventricle → (semilunar) → aorta → body → venae cavae → right atrium.

Answer: As traced above: two passes through the heart.

Blood: RBCs, WBCs and blood groups

Blood is made of a liquid, plasma, carrying red blood cells, white blood cells and platelets.

	Red blood cells (RBCs)	White blood cells (WBCs)
Shape	small, round, biconcave discs	larger, irregular
Nucleus	none in mature human RBCs	present
Contains	haemoglobin, a red, iron-containing pigment	no haemoglobin
Function	carry oxygen from lungs to tissues (and some carbon dioxide back)	fight infection: some engulf germs, some make antibodies
Number	very many	far fewer

Blood groups: in the ABO system, a person's blood belongs to one of four groups: A, B, AB or O, depending on markers on the RBCs. Giving the wrong group in a transfusion makes the RBCs clump together, which can be fatal, so blood is always tested and matched first.

Group	Can give to	Can receive from
A	A, AB	A, O
B	B, AB	B, O
AB	AB only	all groups (universal recipient)
O	all groups (universal donor)	O only

• O is the universal donor (its RBCs carry neither A nor B marker).
• AB is the universal recipient (its plasma has no antibodies against A or B).

Worked example

A patient of group B needs blood. Which groups can be given? Why can group A not be given?

Try it first, then show the solutionSolution

1. Group B can receive from B and O.
2. Group B plasma has antibodies against the A marker, so group A cells would clump.

Answer: B or O; A cells would clump.

Heart conditions and the lymphatic system

Palpitations: a feeling that the heart is beating very fast, strongly or irregularly. They can follow exercise, fear, anxiety, too much tea or coffee, or fever, and are usually harmless; frequent palpitations, or ones with chest pain, dizziness or breathlessness, need a doctor.

Cardiac arrest: the heart suddenly stops pumping blood effectively. The person collapses, has no pulse and stops breathing normally. Without help, the brain is damaged within minutes. Emergency help: call for medical help, start CPR (chest compressions) and use a defibrillator (a machine that gives an electric shock to restart a normal rhythm) if available.

Hypertension (high blood pressure): blood pressure stays higher than normal for a long time. Normal adult blood pressure is about 120/80 mm Hg. Causes and risks: too much salt, obesity, smoking, alcohol, stress, lack of exercise. It often has no symptoms but strains the heart and can cause heart attack, stroke and kidney damage. Prevention: less salt and oily food, regular exercise, no smoking, managing stress, regular check-ups.

Lymphatic system (a parallel circulatory system):

• Some plasma leaks out of capillaries and bathes the cells as tissue fluid.
• Extra tissue fluid enters thin lymph vessels; it is now called lymph, a pale yellowish fluid with many white blood cells (lymphocytes) but no RBCs.
• Lymph flows slowly through lymph nodes (glands in the neck, armpits and groin), which filter out germs, and is returned to the blood in large veins near the neck.

Functions of lymph: returns tissue fluid to the blood; fights infection (lymph nodes and lymphocytes); carries digested fats from the small intestine to the blood.

Worked example

Give two differences between blood and lymph.

Try it first, then show the solutionSolution

1. Blood contains red blood cells; lymph has none (it is pale yellow).
2. Blood is pumped by the heart through closed vessels; lymph flows slowly in lymph vessels through lymph nodes, without a pump.

Answer: Blood has RBCs and is pumped; lymph has no RBCs and flows slowly through lymph nodes.

Circulatory System in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Blood Cells, Blood Groups, Heart Conditions and the Lymphatic System
• Structure of the Heart, Valves, Pacemaker and Double Circulation

Circulatory System: key facts

Pulmonary circulation

$\text{right ventricle}\to \text{pulmonary trunk}\to \text{lungs}\to \text{pulmonary veins}\to \text{left atrium}$

Blood gets oxygenated.

Systemic circulation

$\text{left ventricle}\to \text{aorta}\to \text{body}\to \text{venae cavae}\to \text{right atrium}$

Oxygen delivered to cells.

Heart rate

$\text{beats per minute}=\text{beats counted}\times \frac{60}{\text{seconds counted}}$

Count the pulse for 15 s and multiply by 4.

Valves

$\text{right: tricuspid};\text{left: bicuspid};\text{exits: semilunar}$

One-way flow.

Blood groups

$O=\text{universal donor};AB=\text{universal recipient}$

Always match before a transfusion.

Circulatory System: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Circulatory System

The question patterns to expect, and the method that works for each.

Tricks to remember Circulatory System

Short memory aids. Say each one aloud once, then use it on a question the same day.

• LAB RAT

  Left Atrium: Bicuspid. Right Atrium: Tricuspid.

  Use it when: Positions of the tricuspid and bicuspid valves.

• A for Away

  Arteries carry blood Away from the heart; veins carry it in.

  Use it when: Arteries versus veins, including the pulmonary exceptions.

• Lungs Left

  Blood from the Lungs goes to the Left atrium.

  Use it when: Where the pulmonary veins enter.

• O gives, AB takes

  O is open-handed (gives to all); AB accepts both A and B (takes from all).

  Use it when: Universal donor and recipient.

• Lubb = Leaves shut, Dupp = Doors to arteries shut

  Lubb: tricuspid and bicuspid close. Dupp: semilunar valves close.

  Use it when: Heart sounds.

Circulatory System: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section B style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 6-mark question split into 2 + 2 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Circulatory System

The slips examiners see most often, and what to write instead.

• ✗Mistake: Swapping tricuspid and bicuspid

  The tricuspid is on the right; the bicuspid (mitral) is on the left.

  ✓Do this: Tri on the right.

  Usually costs: 1 mark, and diagram labels.

• ✗Mistake: Saying all arteries carry oxygenated blood

  The pulmonary trunk (pulmonary arteries) carries deoxygenated blood.

  ✓Do this: Arteries are defined by direction (away from heart), not by oxygen.

  Usually costs: 1 mark.

• ✗Mistake: Labelling the heart diagram as if facing it from behind

  Diagrams show the heart from the front, so the right side is on your left.

  Wrong working

  Left ventricle drawn on the left of the page

  Right working

  Left ventricle drawn on the right of the page

  ✓Do this: Imagine the person facing you.

  Usually costs: Several label marks.

• ✗Mistake: Calling AB the universal donor

  AB can receive from all; O can give to all.

  ✓Do this: O gives, AB takes.

  Usually costs: 1 mark.

• ✗Mistake: Writing that lymph contains red blood cells

  Lymph is pale because it has no RBCs; it is rich in lymphocytes.

  ✓Do this: Lymph = plasma-like fluid + WBCs.

  Usually costs: 1 mark.

Practice questions on Circulatory System

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   The valve between the right atrium and right ventricle is the:
   (a) bicuspid
   (b) tricuspid
   (c) semilunar
   (d) mitral

   Hint

   Tri on the right.

   Answer

   (b)

2. Q2 · 1 mark · Very short answerExam level

   Name the blood group known as the universal recipient.

   Hint

   Has both A and B markers.

   Answer

   AB.

3. Q3 · 2 marks · Short answerExam level

   Name the vessels that bring deoxygenated blood from the body to the heart, and the chamber they open into.

   Hint

   Superior and inferior.

   Answer

   Superior and inferior venae cavae; they open into the right atrium.

4. Q4 · 2 marks · Short answerExam level

   Give two functions of white blood cells.

   Hint

   Germs.

   Answer

   Some engulf and destroy germs; others make antibodies against germs (they fight infection).

5. Q5 · 1 mark · Assertion-reasonHarder exam level

   Assertion (A): The left ventricle has a thicker wall than the right ventricle.
   Reason (R): The left ventricle receives blood from the lungs.
   (a) (A) is true and (R) is false.
   (b) (A) is false and (R) is true.
   (c) Both (A) and (R) are true, and (R) is the correct explanation for (A).
   (d) Both (A) and (R) are true, but (R) is not the correct explanation for (A).

   Hint

   Which chamber receives from the lungs?

   Answer

   (a): the left atrium receives blood from the lungs; the left ventricle is thick because it pumps to the whole body.

6. Q6 · 2 marks · Short answerHarder exam level

   If the heart pumps about 70 mL of blood with each beat and beats 72 times a minute, how much blood does it pump in a minute? Express in litres.

   Hint

   Multiply.

   Answer

   72 × 70 = 5040 mL = 5.04 litres per minute.

7. Q7 · 2 marks · Short answerHarder exam level

   Why does the heart muscle need its own coronary blood supply?

   Hint

   Thick walls.

   Answer

   The heart muscle works non-stop and needs a constant supply of oxygen and food; its thick walls cannot take these from the blood inside its chambers, so coronary arteries supply it directly.

8. Q8 · 3 marks · Short answerHarder exam level

   Distinguish between arteries and veins (three points).

   Hint

   Direction, walls, valves.

   Answer

   Arteries carry blood away from the heart, veins towards it; arteries have thick, elastic walls, veins thinner walls; veins have valves along their length, arteries do not (apart from the semilunar valves at their start).

9. Q9 · 2 marks · Short answerHarder exam level

   What are the 'lubb' and 'dupp' sounds of the heart caused by?

   Hint

   Valves closing.

   Answer

   Lubb: closing of the tricuspid and bicuspid valves when the ventricles contract. Dupp: closing of the semilunar valves at the bases of the aorta and pulmonary trunk.

10. Q10 · 3 marks · Short answerHarder exam level

    Give two ways in which hypertension can be prevented, and explain why it is called a 'silent' condition.

    Hint

    Lifestyle; no symptoms.

    Answer

    Prevention: eat less salt and fatty food; exercise regularly; avoid smoking; manage stress (any two). It is called silent because it usually has no symptoms until it damages the heart, brain or kidneys, so regular check-ups are needed.

11. Q11 · 2 marks · Short answerHarder exam level

    State two differences between RBCs and WBCs.

    Hint

    Nucleus, pigment, job.

    Answer

    RBCs have no nucleus (in mature human cells) and contain haemoglobin to carry oxygen; WBCs have a nucleus, no haemoglobin, and fight infection.

12. Q12 · 3 marks · Short answerHOTS / competency

    Suppose the septum between the ventricles had a hole. Predict the effect on the blood going to the body and on the person's energy levels.

    Hint

    Mixing.

    Answer

    Oxygenated blood of the left side would mix with deoxygenated blood of the right side, so the blood pumped into the aorta would carry less oxygen. Cells would get less oxygen for respiration, so the person would tire easily and may become breathless.

13. Q13 · 3 marks · Short answerHOTS / competency

    During an infection, the glands under a child's jaw become swollen and tender. Which system are these glands part of, and why do they swell?

    Hint

    Filters full of fighters.

    Answer

    They are lymph nodes of the lymphatic system. They filter germs from the lymph, and during an infection many white blood cells (lymphocytes) multiply there to fight the germs, so the nodes swell and become tender.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Which chamber has the thickest wall?Show answer

   Left ventricle.

2. 2.Function of the septum?Show answer

   Prevents mixing of oxygenated and deoxygenated blood.

3. 3.Where is the pacemaker?Show answer

   In the wall of the right atrium (SA node).

4. 4.Largest artery?Show answer

   Aorta.

5. 5.Vessels that supply the heart muscle?Show answer

   Coronary arteries.

6. 6.Universal donor?Show answer

   Group O.

7. 7.Normal adult blood pressure?Show answer

   About 120/80 mm Hg.

8. 8.Pigment in RBCs?Show answer

   Haemoglobin.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you draw and label the heart with 14 labels?
• ☐Can you name the valves and their positions?
• ☐Can you trace double circulation?
• ☐Can you name the vessel for any given job?
• ☐Can you fill the blood group table?
• ☐Can you define palpitations, cardiac arrest and hypertension?

Circulatory System: frequently asked questions