Circulatory System Class 10 ICSE — Selina Chapter 7

This page explains the circulatory system class 10 ICSE chapter from Selina Concise Biology. Chapter 7 covers blood, the heart, blood vessels, clotting, blood groups, and lymph. Each textbook section is explained in order, with formulas and worked patterns. Definitions and methods appear exactly as the book presents them. The chapter PDF is available for reference. For more on this subject, see the ICSE Class 10 Biology hub.

ICSE Class 10 Biology Selina Concise Chapter 7 The Circulatory System PDF

What is inside Chapter 7

22 pages · 15 sections · 67 exercise questions

• PROGRESS CHECK: 4 questions
• PROGRESS CHECK: 2 questions
• PROGRESS CHECK: 2 questions
• REVIEW QUESTIONS: 14 questions
• PROGRESS CHECK: 2 questions
• PROGRESS CHECK: 1 questions
• PROGRESS CHECK: 3 questions
• PROGRESS CHECK: 39 questions

7.1 NEED FOR TRANSPORT INSIDE THE BODY

Every organ needs circulating body fluids. The digestive system absorbs nutrients that must reach every cell. The respiratory system picks up oxygen in the lungs, and that oxygen must travel to all tissues. Carbon dioxide collected from the whole body must return to the lungs for removal.

Excess water, salts, and nitrogenous wastes like urea must reach the excretory system. Hormones from the endocrine system travel through blood to act where required. Two circulating fluids do all this work: blood and lymph. They do more than transport. Blood also protects against disease. Lymph drains tissue spaces and defends the body.

Without transport, no cell could get food or oxygen, and no waste could leave. This chapter explains how the system works, from the blood itself to the heart and vessels.

7.2 FLUIDS IN OUR BODY

Three principal fluids circulate in the body. Blood fills the heart and the blood vessels: arteries, veins, and capillaries. Tissue fluid occupies the spaces between cells in organs. Lymph flows within lymph vessels and lymphatic organs such as the spleen and tonsils.

The key distinction is closed versus open circulation. In humans, blood stays inside vessels the whole time. This is a closed vascular system. In insects, blood flows through open spaces without vessels. That is an open blood circulatory system. Their blood moves from the heart to body tissue spaces directly.

Some fluids do not circulate. Synovial fluid sits in skeletal joints. Vitreous humour fills the eye. These are non-circulating fluids, so they are not part of transport.

7.3 THE BLOOD

Blood is never stationary. It moves constantly from the heart to the arteries and back through the veins. Blood is a somewhat thick fluid. It is bright red when drawn from an artery and dark red from a vein. The blue colour in diagrams is only for contrast. Blood in veins is not blue; it is dark red.

An average adult carries 5 to 6 litres of blood. Blood tastes saltish and is slightly alkaline. Its pH ranges from 7.3 to 7.45. A pH of 7 is neutral, so blood sits on the alkaline side. This property matters for enzyme function and gas transport.

Common mistake: veins are drawn blue in diagrams, but the blood inside them is dark red. The blue is a drawing convention, not the real colour.

7.4 FUNCTIONS OF BLOOD

Blood has two broad roles: transport and protection. Its transport jobs include moving digested food, oxygen, carbon dioxide, excretory substances, hormones, and body heat. Digested food moves from the alimentary canal to the tissues. Oxygen moves from the lungs to the tissues. Carbon dioxide returns from the tissues to the lungs. Excretory material goes to the liver, kidney, or skin. Hormones spread from endocrine glands. Heat is distributed to keep body temperature uniform.

The oxygen reaction is reversible. Oxyhaemoglobin forms in the lungs and breaks down at the tissues:

\mathrm{Hb} + \mathrm{O}_{2} \rightleftharpoons \mathrm{Hb.O}_{2}

The carbon dioxide reaction works the same way, forming carbaminohaemoglobin:

\mathrm{Hb} + \mathrm{CO}_{2} \rightleftharpoons \mathrm{Hb.CO}_{2}

Protection functions follow. Blood clots at a cut to stop blood loss and block germs. White blood corpuscles engulf bacteria. Antibodies and antitoxins neutralise poisons or kill germs that enter the body.

7.5 COMPOSITION OF BLOOD

Blood has two parts. Plasma is the fluid part, about 55–60 per cent of blood. Cellular elements make up 40–45 per cent.

Plasma is a light-yellow, alkaline liquid. It contains 90–92% water, 7–8% proteins, about 1% inorganic salts, and traces of other substances. Sodium chloride and sodium bicarbonate are the main salts. Glucose, amino acids, fibrinogen, hormones, and urea are also present. Removing fibrinogen from plasma leaves serum.

Cellular elements come in three categories: red blood cells (erythrocytes), white blood cells (leukocytes), and blood platelets (thrombocytes).

RBCs are biconcave discs about 7 microns across. Their small size and concavity give a large surface area for absorbing oxygen. Adult males have about 5 million RBCs per cubic mm; females about 4.5 million. Haemoglobin contains an iron part (haemin) and a protein (globin). It combines readily with oxygen.

Mature mammalian RBCs lack a nucleus, mitochondria, and endoplasmic reticulum. This makes them more efficient. More space holds more haemoglobin. Without mitochondria, RBCs do not consume oxygen themselves. Without ER, they stay flexible for narrow capillaries.

WBCs have a nucleus and no haemoglobin. They number 4000–8000 per cubic mm. They are amoeboid and squeeze through capillary walls by diapedesis. Five types exist: neutrophils (62%), eosinophils (2.3%), basophils (0.4%), lymphocytes (30%), and monocytes (5.3%). Neutrophils engulf bacteria. Lymphocytes produce antibodies. Basophils release histamine for inflammation.

Platelets are minute, non-nucleated, oval or round. Adults have 200,000 to 400,000 per cubic mm. They bud off from megakaryocytes in red bone marrow. At injury, they disintegrate to release thrombokinase, which starts clotting.

7.6 CLOTTING OF BLOOD (COAGULATION)

When a vessel is cut, blood escapes. A clot soon forms and stops the flow. Without clotting, a person would bleed to death. Coagulation happens in four steps.

• Step 1: Injured tissue cells and disintegrating platelets release thrombokinase (thromboplastin).
• Step 2: Thrombokinase acts as an enzyme. With calcium ions from plasma, it converts inactive prothrombin into active thrombin.
• Step 3: Thrombin, with calcium ions, converts soluble fibrinogen into insoluble fibrin. Fibrin forms sticky threads that make a network at the wound.
• Step 4: Blood cells get trapped in the fibrin network. The network shrinks and squeezes out clear liquid, the serum. The solid mass left behind is the clot, or thrombus.

In a test tube, blood clots the same way. Serum collects on top of the clot. Low platelet counts slow clotting and cause haemorrhage. This happens in dengue fever.

Common mistake: clotting does not depend on exposure to air. Blood can clot when it moves over a rough surface, like cholesterol deposits inside a vessel.

7.7 BLOOD TRANSFUSION AND BLOOD GROUPS (ABO and Rh systems)

Blood transfusion injects donor blood into a patient’s vein. The donor and recipient types must match. Karl Landsteiner discovered blood grouping. RBCs carry antigens on their surface. Plasma carries complementary antibodies.

• Group A: antigen A, anti-b antibody
• Group B: antigen B, anti-a antibody
• Group AB: both antigens, no antibody
• Group O: no antigen, both antibodies

O can donate to everyone, so O is the universal donor. AB can receive from everyone, so AB is the universal recipient. A receives from A and O. B receives from B and O. Mismatched transfusion causes a reaction and can be fatal.

The letter O actually means “zero” because these RBCs carry zero antigens.

The Rh factor was first found in the Rhesus monkey. An Rh-negative person receiving Rh-positive blood develops antibodies within about two weeks. A second transfusion then causes a reaction, sometimes fatal. In pregnancy, an Rh-negative mother carrying an Rh-positive child may become sensitised. The first child is usually normal, but a second positive child may suffer.

7.8 BLOOD CIRCULATORY SYSTEM

The circulatory system has the heart, arteries, veins, and capillaries. The heart sits in the centre between the two lungs, above the diaphragm. It is not on the left side. The narrow end points left, and contraction is strongest there, which is why people feel it on the left. The heart is about the size of a closed fist, 12 cm long and 9 cm wide. A double-walled pericardium protects it. Pericardial fluid reduces friction during beats.

Four chambers exist: two upper atria and two lower ventricles. Atria have thinner walls because they only pump blood into the ventricles next door. Ventricles have thick muscular walls. The right ventricle pumps only to the lungs. The left ventricle pumps to the toes and brain against gravity, so its walls are thickest.

Vessels entering the heart: the anterior vena cava and posterior vena cava bring deoxygenated blood to the right atrium. Four pulmonary veins bring oxygenated blood to the left atrium. Vessels leaving the heart: the pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. The aorta carries oxygenated blood from the left ventricle to the body.

Coronary arteries arise from the base of the aorta. They supply the heart muscle itself. Blockage causes myocardial infarction, or heart attack. Angina pectoris is chest pain from poor blood supply to the heart muscle.

Four valves regulate one-way flow. The tricuspid valve sits between the right atrium and right ventricle. The bicuspid (mitral) valve sits on the left. Pulmonary semilunar valves guard the pulmonary artery opening. Aortic semilunar valves guard the aorta opening. Chordae tendinae hold the valve flaps in place.

Mnemonic: Tricuspid on Right, Bicuspid on Left. TRi = TRicuspid, Bi = BiCuspid.

7.9 CIRCULATION OF BLOOD IN THE HEART

The cardiac cycle starts with atrial contraction. The ventricles are relaxed and empty, so blood passes in easily. Next, ventricles contract and atria relax. Cuspid valves close to stop backflow. Chordae tendinae hold the flaps, like parachute cords. Blood must enter the pulmonary artery and aorta through the semilunar valves.

Each half beat lasts about 0.85 seconds: atrial systole 0.15 sec, ventricular systole 0.30 sec, all chambers relaxed 0.40 sec. The heart beats about 1,03,680 times a day.

The first sound, “LUBB”, comes from the atrioventricular valves closing sharply at the start of ventricular systole. The second sound, “DUP”, comes from the semilunar valves closing at the start of ventricular diastole.

Heart rate varies with body size. Smaller animals lose heat faster and need faster hearts. A whale beats 15 times a minute; a rat 250; a sparrow up to 900 during activity. Newborn infants beat about 140 times a minute.

The pacemaker is the sinu-atrial node (SAN) in the wall of the right atrium. It generates the impulse that starts each beat. The atrioventricular node (AVN) relays it. The Bundle of His and Purkinje fibres conduct it to the ventricles. A faulty pacemaker can be replaced with an artificial one.

7.10 THE BLOOD VESSELS

Blood vessels are branched tubes from the heart to all parts. Three kinds exist: arteries, capillaries, and veins. An artery carries blood away from the heart. It has thick muscular walls, a narrow lumen, and blood flows in spurts matching ventricular contractions. A vein carries blood toward the heart. It has thin muscular walls, a wider lumen, and blood flows uniformly. Pocket-shaped valves prevent backflow.

Arteries branch into arterioles, which are highly muscular. Arterioles break into capillaries. A capillary is a very narrow tube about 8 micrometres across. Its wall is a single layer of squamous epithelial cells (endothelium) with no muscle. If all capillaries were laid end to end, they would stretch 100,000 kilometres.

Capillary functions include outward diffusion of oxygen, inward diffusion of carbon dioxide, diffusion of glucose and amino acids, and passage of WBCs by amoeboid movement. Capillaries dilate (vasodilation) and contract (vasoconstriction). In hot sun the face turns pink from increased flow. In cold it turns bluish from reduced flow.

Key differences between arteries and veins:

• Arteries: thick, elastic, muscular walls; narrow lumen; no valves; blood under pressure in spurts; usually deep.
• Veins: thin, non-elastic walls; wide lumen; valves present; blood flows continuously under little pressure; usually superficial.

Common mistake: veins do not carry only carbon dioxide. Veins carry oxygen too, just a little less than arteries. The exceptions are the pulmonary artery (deoxygenated) and the pulmonary vein (oxygenated).

7.11 THE TWO BLOOD CIRCULATIONS — PULMONARY AND SYSTEMIC

Blood passes through the heart twice in one full round. This is why human circulation is called double circulation. The short pulmonary (lung) circulation and the long systemic (general body) circulation together make one complete round.

Pulmonary circulation involves the lungs. It starts with the pulmonary artery from the right ventricle. The artery divides into two branches entering the lungs. Pulmonary veins collect oxygenated blood and return it to the left atrium.

Systemic circulation covers the whole body. It starts with the aorta from the left ventricle. The aorta arches back and sends arteries to all body parts and their tissues. Veins collect the blood and pour it back into the heart.

7.12 HEPATIC PORTAL SYSTEM

Veins from the stomach and intestines do not go straight to the posterior vena cava. They first enter the liver as the hepatic portal vein. There it breaks into capillaries, unlike a normal vein. A new hepatic vein forms from their reunion and joins the posterior vena cava.

By definition, a portal vein starts with capillaries and ends in capillaries. The liver acts as a store. Excess sugar is stored as glycogen. Poisons absorbed with food are detoxified in the liver.

Main vessels to know:

• Heart entering: anterior vena cava, posterior vena cava, four pulmonary veins
• Heart leaving: pulmonary artery, aorta
• Liver entering: hepatic artery, hepatic portal vein
• Liver leaving: hepatic vein
• Kidney entering: renal artery
• Kidney leaving: renal vein

Blood pressure has two limits. Systolic pressure is the upper limit when fresh blood pushes through during ventricular contraction. Diastolic pressure is the lower limit when the wave has passed. Normal adult pressure is 100–140 systolic and 60–80 diastolic. Above 140/90 is hypertension.

Worked pattern: take a reading of 145/95 mmHg. Systolic 145 exceeds 140. Diastolic 95 exceeds 90. So 145/95 is labelled hypertensive. A reading of 125/75 falls within both ranges, so it is normal.

7.14 TISSUE FLUID AND LYMPH

As blood flows through tissue capillaries, plasma and leucocytes leak out through the walls. This fluid bathes the cells and is called tissue fluid, or intercellular fluid. Cells absorb oxygen and required substances from it. They give back carbon dioxide and wastes into it.

Some tissue fluid is reabsorbed into blood vessels. Most enters minute lymph vessels, where it is called lymph. Lymph flows because surrounding muscles contract, another benefit of exercise. Lymph vessels drain into lymph nodes. Fresh channels arise and pour lymph into the major anterior veins near the right atrium.

Lymph composition:

• Cellular part: only leukocytes, mostly lymphocytes; no platelets
• Non-cellular part: 94% water, 6% solids (proteins, fats, carbohydrates, enzymes, antibodies)

Lymph functions: nutritive (supplies nutrition and oxygen where blood cannot reach), drainage (removes excess tissue fluid and returns proteins), absorption (absorbs fats from the intestine through lacteals), and defence (lymphocytes and monocytes fight infection; lymph nodes localise it).

7.15 THE SPLEEN

The spleen is a large lymphatic organ, about the size of a clenched fist. It is reddish brown and lies in the abdomen behind the stomach and above the left kidney.

Four functions:

• Blood reservoir: releases stored blood in emergencies like haemorrhage or carbon monoxide poisoning
• Produces lymphocytes
• Destroys worn-out red blood cells, sharing this function with the liver
• Produces RBCs in the embryo

7.16 EXAMINATION OF BLOOD CORPUSCLES UNDER A MICROSCOPE

The procedure makes a blood smear. Take two clean slides. Prick a sterilised fingertip and wipe off the first drop of blood. Squeeze the finger and place a drop near the right end of one slide. Hold the second slide at an angle, touch the drop, and let blood spread evenly. Push the second slide smoothly across the first. A fine layer of blood forms: the blood smear.

Let the smear dry. Stain it with Leishman stain. Cover the smear with a few drops, wait two minutes, then add equal distilled water. Wait two more minutes, pour off the mixture, and rinse in tap water. Examine under the microscope once dry.

Visible cells include erythrocytes, neutrophils, eosinophils, basophils, lymphocytes, monocytes, and platelets. Each has a distinct appearance after staining. Granular WBCs show coloured granules. Non-granular types show a single large nucleus.

What to practise from this chapter

The chapter contains self-test and review blocks. Each one checks specific skills.

• PROGRESS CHECK (4 questions) — after section 7.4: fluids, vein colour, pulmonary vessels, transported substances
• PROGRESS CHECK (2 questions) — after section 7.5: naming parts of blood
• PROGRESS CHECK (2 questions) — after section 7.7: true/false on clotting, naming blood group terms
• REVIEW QUESTIONS (14 questions) — after section 7.7: multiple choice, very short, short, long, and structured questions
• PROGRESS CHECK (2 questions) — after section 7.9: heart beat phases
• PROGRESS CHECK (1 question) — after section 7.10: fill in the blanks on vessels
• PROGRESS CHECK (3 questions) — after section 7.12: circulations and blood vessels
• PROGRESS CHECK (39 questions) — after section 7.16: full-chapter practice

Exam-style questions recur in patterns. Diagram questions test the heart and blood vessels. Fill-in-the-blank items test valves and vessel names. Differentiate questions compare arteries with veins. Application questions trace the hepatic portal system. The official CISCE website sets the syllabus scope for all of these. Related topics appear in the excretory system chapter and the photosynthesis chapter.

Frequently asked questions

Why does the left ventricle have thicker walls than the right ventricle?

The left ventricle pumps blood to the farthest parts of the body, including the toes and the brain. That long journey needs more pressure. The right ventricle only pumps to the nearby lungs. Its wall is thinner because the distance is short.

What is the difference between systolic and diastolic blood pressure?

Systolic pressure is the upper limit, recorded when fresh blood pushes through the artery during ventricular contraction. Diastolic pressure is the lower limit, recorded when the wave has passed. Normal adult values are 100–140 systolic and 60–80 diastolic.

Why is O blood called the universal donor?

Group O red cells carry no antigens, so they do not trigger an antibody reaction in any recipient. Group AB is the universal recipient because its plasma has no antibodies. In the Rh system, an Rh-negative recipient needs Rh-negative blood to avoid sensitisation.

What is the role of platelets in blood clotting?

Platelets disintegrate at the site of injury and release thrombokinase. This enzyme, with calcium ions, converts prothrombin into thrombin. Thrombin then turns fibrinogen into insoluble fibrin, which forms the clot network. Low platelet counts slow clotting and cause haemorrhage, as in dengue.

How does lymph differ from blood in composition and function?

Lymph contains only leukocytes, mostly lymphocytes, and no platelets or RBCs. Its non-cellular part is 94% water and 6% solids. Blood carries oxygen, nutrients, and wastes through vessels. Lymph drains excess tissue fluid, absorbs fats, and defends the body.

Reference: ICSE Class 10 Biology textbook material, chapter 7: The Circulatory System — CISCE-aligned.

More from this book

• Chapter 2: Structure of Chromosomes Cell Cycle and Cell Division
• Chapter 3: Genetics Some Basic Fundamentals
• Chapter 4: Absorption By Roots the Processes Involved
• Chapter 5: Transpiration
• Chapter 6: Photosynthesis
• Chapter 8: The Excretory System
• Chapter 9: The Nervous System
• Chapter 10: Endocrine Glands
• Chapter 11: The Reproductive System
• Chapter 12: Population
• Chapter 13: Aids to Health
• Chapter 14: Health Organisations
• Chapter 15: Pollution