Blood and Circulatory System Notes for SSC Exams
Rahul Kumar
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The blood and circulatory system carry oxygen, food and waste in the body, and it is a high-scoring part of Biology in SSC General Science. Questions are asked on the blood groups, the parts of blood, the chambers of the heart and the diseases of blood. These blood and circulatory system notes for SSC explain every point in simple tables with practice questions.
Components of Blood
| Component | Share or number | Function |
|---|---|---|
| Plasma | About 55 per cent of blood; 90 per cent water | Carries food, hormones and waste |
| Red blood cells (RBC or erythrocytes) | About 4.5 to 5.5 million per cubic mm | Carry oxygen with haemoglobin; made in the red bone marrow; live about 120 days |
| White blood cells (WBC or leucocytes) | About 4,000 to 11,000 per cubic mm | Fight germs and give immunity |
| Platelets (thrombocytes) | About 1.5 to 4 lakh per cubic mm | Help in blood clotting |
- Haemoglobin is the red pigment in RBC, and it contains iron.
- An adult has about 5 litres of blood.
- The spleen is called the graveyard of RBC, because old RBC are destroyed there.
- Mammalian RBC have no nucleus.
Blood Groups
| Blood group | Antigen on RBC | Antibody in plasma | Can give blood to |
|---|---|---|---|
| A | A | Anti-B | A and AB |
| B | B | Anti-A | B and AB |
| AB | A and B | None | AB only |
| O | None | Anti-A and Anti-B | All groups |
- The ABO blood groups were discovered by Karl Landsteiner in 1901.
- Group O is the universal donor, and group AB is the universal recipient.
- The Rh factor was found in the Rhesus monkey; a person with the Rh antigen is Rh positive, and without it is Rh negative.
- O negative is the universal donor of all, and AB positive is the universal recipient of all.
The Human Heart
- The heart is a muscular organ of about the size of a fist, with four chambers: two upper atria and two lower ventricles.
- The atria receive blood, and the ventricles pump the blood out.
- The right side of the heart has deoxygenated blood, and the left side has oxygenated blood.
- The valves between the atria and ventricles are the tricuspid valve (right) and the bicuspid or mitral valve (left).
- The natural pacemaker of the heart is the SA node.
- A normal heart beats about 72 times a minute.
- William Harvey discovered the circulation of blood.
Blood Vessels
| Vessel | Carries blood | Facts |
|---|---|---|
| Arteries | Away from the heart | Thick walls; the aorta is the largest artery |
| Veins | Towards the heart | Thin walls with valves; the vena cava is the largest vein |
| Capillaries | Between arteries and veins | Very thin walls; exchange of gases and food |
- The pulmonary artery is the only artery that carries deoxygenated blood, and the pulmonary vein is the only vein that carries oxygenated blood.
- The path of blood from the heart to the lungs and back is the pulmonary circulation, and the path to the rest of the body is the systemic circulation.
Blood Pressure
- Normal blood pressure of an adult is about 120/80 mm of mercury (systolic/diastolic).
- It is measured with a sphygmomanometer.
- High blood pressure is called hypertension.
- The pulse rate is about 72 per minute.
Diseases of the Blood and Heart
| Disease | Cause or effect |
|---|---|
| Anaemia | Low haemoglobin, usually due to lack of iron |
| Leukaemia | Blood cancer with too many abnormal white blood cells |
| Haemophilia | Blood does not clot properly; a genetic disease |
| Thalassemia | Genetic disease in which the body makes less haemoglobin |
| Hypertension | High blood pressure |
| Heart attack | Blockage in the blood supply of the heart muscle |
Lymph
Lymph is a colourless fluid that flows in the lymph vessels. It carries white blood cells, fights infections and returns the extra fluid to the blood.
Quick Tips
- Learn the blood group table with the antigen, the antibody and the donor in one row.
- Remember that RBC carry oxygen, WBC fight germs and platelets help in clotting.
- Remember the exceptions: the pulmonary artery and pulmonary vein.
- Link diseases with the cause: anaemia with iron and haemophilia with clotting.
Quick Revision Points
- Plasma is about 55 per cent of blood.
- Group O is the universal donor and AB is the universal recipient.
- Karl Landsteiner discovered the ABO blood groups.
- The heart has four chambers.
- Normal blood pressure is 120/80 mm of mercury.
Practice Questions With Answers
- Which blood cells carry oxygen?
Answer: Red blood cells (RBC) - Which blood cells help in clotting?
Answer: Platelets - Who discovered the ABO blood groups?
Answer: Karl Landsteiner - Which blood group is the universal donor?
Answer: O - Which blood group is the universal recipient?
Answer: AB - How many chambers does the human heart have?
Answer: Four - Which instrument measures blood pressure?
Answer: Sphygmomanometer - What is the normal blood pressure of an adult?
Answer: 120/80 mm of mercury - Which is the largest artery of the body?
Answer: Aorta - Which disease is caused by a lack of haemoglobin?
Answer: Anaemia
How to Practise This Chapter
Learn the blood components and the blood group table first, and then the heart and vessels. Solve ten questions daily from the practice papers and the free SSC quizzes and check the previous year papers page. Read the next chapter, Acids, Bases and Salts, and see all topics on the General Science notes page. Also read Vitamins and Deficiency Diseases and the Human Digestive System.
Frequently Asked Questions
What are the components of blood?
Blood has plasma, red blood cells, white blood cells and platelets.
What is the function of red blood cells?
Red blood cells carry oxygen from the lungs to the body with the help of haemoglobin.
What is the function of platelets?
Platelets help in blood clotting and stop bleeding.
Who discovered the blood groups?
Karl Landsteiner discovered the ABO blood groups in 1901.
Which blood group is the universal donor?
Group O (especially O negative) is called the universal donor.
Which blood group is the universal recipient?
Group AB (especially AB positive) is called the universal recipient.
What is the Rh factor?
The Rh factor is an antigen on the red blood cells. A person who has it is Rh positive and who does not have it is Rh negative.
How many chambers are there in the heart?
The heart has four chambers: two atria and two ventricles.
What is the difference between an artery and a vein?
Arteries carry blood away from the heart and have thick walls, while veins carry blood towards the heart and have valves.
What is the normal blood pressure?
The normal blood pressure of an adult is about 120/80 mm of mercury.
What is haemophilia?
Haemophilia is a genetic disease in which the blood does not clot properly.
How many questions come from blood and circulation in SSC exams?
Usually one question comes from the blood and the heart in SSC General Science papers, but the number changes from year to year.
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Human Digestive System Notes for SSC Exams
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Acids, Bases and Salts Notes for SSC Exams
Rahul Kumar
SSC Exam Expert & Content Editor
Rahul is a senior SSC exam strategist with 8+ years of experience helping aspirants crack CGL, CHSL and MTS exams. He writes in-depth notification breakdowns, exam pattern guides and preparation strategies.