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Study Notes On “BLOOD” For SSC & Railway Exams 2024

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Among the primary biological systems of the human body, the circulatory system is one of the most vital ones. The circulatory system consists of the heart, blood vessels, and blood. It is a network of pathways that transport the vital elements throughout our bodies. In this article, we take a look at the most important component of the human circulatory system i.e. Blood. Let’s start with some basic facts.

• Blood is a fluid connective tissue.
• The quantity of blood in the human body is 7% of the total weight.
• The pH value of blood is 7.4.
• There is an average of 5-6 liters of blood in the human body.
• Female contains half a liter of bloodless in comparison to male.
• It also fights infection and regulates temperature.

Blood cells are produced in BONE MARROW

Red cells, white cells, and platelets are made in the marrow of bones, especially the vertebrae, ribs, hips, skull, and sternum. These essential blood cells fight infection, carry oxygen, and help control bleeding thus protecting the body from foreign attacks.

Components Of Blood

Blood is a vital fluid that circulates throughout the human body, providing essential nutrients and oxygen to various organs and tissues. Blood consists of several components, including:

I. PLASMA- Plasma is a yellowish fluid that makes up about 55% of the blood’s total volume. It contains various proteins, such as albumin, immunoglobulins, and clotting factors, as well as other nutrients and waste products.

Function of Plasma-

1. Nutrients: Plasma transports nutrients such as glucose, amino acids, and fatty acids from the digestive system to the body’s cells where they are used for energy and growth.

2. Waste products: Plasma also carries waste products, such as carbon dioxide and urea, from the cells to the lungs and kidneys, respectively, where they are eliminated from the body.

3. Hormones: Hormones are chemical messengers that regulate various body functions. Plasma transports hormones from the glands where they are produced to the organs and tissues where they exert their effects.

4. Proteins: Plasma contains a variety of proteins, including albumin, fibrinogen, and immunoglobulins, which play important roles in maintaining the body’s fluid balance, blood clotting, and immune system function.

II. RED BLOOD CELLS- These are the most abundant cells in the blood and are responsible for carrying oxygen from the lungs to the body’s tissues. They also transport carbon dioxide from the tissues back to the lungs for removal.

Function of Red Blood Cells:

1. Oxygen transport: The main function of red blood cells is to transport oxygen from the lungs to the body’s tissues. Red blood cells contain a protein called hemoglobin, which binds to oxygen molecules in the lungs and carries them to the tissues.

2. Carbon dioxide transport: Red blood cells also transport carbon dioxide from the body’s tissues to the lungs, where it can be exhaled. Hemoglobin can also bind to carbon dioxide, allowing it to be carried away from the tissues.

3. Buffering: Red blood cells play a role in maintaining the body’s pH balance by acting as a buffer. They can absorb excess hydrogen ions and help prevent acidosis, which is a condition where the blood becomes too acidic.

4. Immune function: Red blood cells can play a role in the immune system by transporting antibodies and other immune cells to fight infections.

5. Nitric oxide transport: Red blood cells can also transport nitric oxide, a molecule that plays a role in regulating blood pressure and blood flow.

III. WHITE BLOOD CELLS -White blood cells, also known as leukocytes, are a vital component of the immune system, and they play a critical role in protecting the body against infections, diseases, and foreign invaders. Some of the functions of white blood cells include:

1. Fighting infections: White blood cells help to identify, target, and destroy bacteria, viruses, and other pathogens that enter the body. Different types of white blood cells work together to produce a coordinated immune response that eliminates the invading organisms.

2. Producing antibodies: Some white blood cells, such as B lymphocytes, produce antibodies that specifically target and neutralize particular pathogens. Antibodies help to prevent the spread of infections and can provide long-lasting immunity against future attacks.

3. Phagocytosis: Some white blood cells, such as macrophages and neutrophils, are able to engulf and digest bacteria and other foreign particles. This process, known as phagocytosis, helps to remove harmful substances from the body.

4. Regulating the immune response: White blood cells also play a role in regulating the immune response and preventing the body from attacking its own tissues. T cells and other immune cells help to distinguish between “self” and “non-self” cells and prevent autoimmune reactions.


Platelets, also known as thrombocytes, are tiny, colorless cell fragments that play a crucial role in blood clotting or hemostasis. Their main function is to help stop bleeding by forming clots to plug up small holes in blood vessels.

When there is an injury or damage to a blood vessel, platelets rush to the site and stick together to form a temporary plug or clot. They do this by releasing substances such as thromboxane A2 and adenosine diphosphate (ADP), which cause the platelets to become sticky and adhere to the damaged vessel wall and to each other.

Composition of blood

As seen above, blood consists of Plasma, RBC, WBC, and Platelets. Let’s look at some facts about these components.

1. Plasma constitutes about 54% of our blood. 92% of it is water.
2. White blood cells and platelets constitute about 1% of our blood.
3. Red blood cells constitute about 45% of our blood.

Circulatory System

Circulation of Blood through the heart:

Systemic Vein ⇨ Sinus Venosus ⇨ Right Auricle ⇨ Right Ventricle ⇨ Pulmonary Artery ⇨ Lungs ⇨ Pulmonary Vein ⇨ Left Auricle ⇨ Left Ventricle ⇨ Truncus Arteriosus ⇨ Systemic Circulation

  • Open circulatory systems allow the blood to flow out of the vessels before returning to the heart via Ostia. (no veins involved)E.g. insects
  • Closed circulatory systems don’t allow the blood to leave the blood vessels E.g. human’s advantages include faster and controlled delivery of oxygen and nutrients which allow for longer periods of activity.

Important Points:

  • Aorta
    The largest artery in the body. It carries oxygen-rich blood away from the heart to vessels that reach the rest of the body.
  • Atria
    The chambers of the heart, to which the blood returns from the circulation.
  • Capillaries
    The smallest of the body’s blood vessels. Oxygen and glucose pass through capillary walls and enter the cells. Waste products such as carbon dioxide pass back from the cells into the blood through capillaries.
  • Cardiac Valves (Heart Valves)
    Any of the four heart valves that regulate the flow of blood through the chambers of the heart.
  • Heart Ventricles
    The lower right and left chambers of the heart.
  • Interventricular Septum
    The interventricular septum is the stout wall separating the lower chambers (the ventricles) of the heart from one another.
  • Myocardium
    The muscular substance of the heart; the middle of the three layers forming the outer wall of the human heart.
  • Oxygenated Blood -> Oxygen-rich blood.
  • Pulmonary Artery
    The pulmonary artery and its branches deliver blood rich in carbon dioxide (and lacking in oxygen) to the capillaries that surround the air sacs.
  • Pulmonary Circulation
    The circulation of the blood through the lungs.
  • Pulmonary Veins
    The veins return the oxygenated blood from the lungs to the left atrium of the heart.
  • Superior Vena Cava
    The large vein carries blood from the head, neck, arms, and chest to the heart.
  • Vena Cava
    A large vein that returns blood from the head, neck, and extremities to the heart.
  • The endothelium is the innermost layer of blood vessels that consists of just a single layer of cells.
  • Veins are blood vessels that carry blood to the heart in an even flow. They have thin walls with large lumens and valves.
    • The human circulatory system consists of two circuits systemic and pulmonary.
    • The coronary artery carries blood to the heart muscle from the aorta. (coronary vein)
    • The hepatic artery carries blood to the liver. (hepatic vein)
    • The renal arteries carry blood to the kidneys. (renal veins)
    • The mesenteric arteries carry blood to the small and large intestines.
    • The carotid arteries supply blood to the head. (jugular veins)
    • The subclavian arteries supply blood to the arms. (subclavian veins)
    • The iliac arteries carry blood to the legs. (iliac veins)


Blood-related diseases are one of the most asked topics in the General Awareness section of competitive exams. In the following points, we have tried to include the most important diseases that affect the blood and circulatory system as a whole.

  • Hematoma: A collection of blood inside the body tissues. Internal bleeding often causes a hematoma.
  • Leukemia: A form of blood cancer, in which white blood cells multiply abnormally and circulate through the blood. The excessively large numbers of white cells deposit in the body’s tissues, causing damage.
  • Multiple myeloma: A form of blood cancer of plasma cells similar to leukemia. Anemia, kidney failure, and high blood calcium levels are common in multiple myeloma.
  • Lymphoma: A form of blood cancer, in which white blood cells multiply abnormally inside lymph nodes and other tissues. The enlarging tissues, and disruption of blood’s functions, can eventually cause organ failure.
  • Anemia: An abnormally low number of red blood cells in the blood. Fatigue and breathlessness can result, although anemia often causes no noticeable symptoms.
  • Hemochromatosis: A disorder causing excessive levels of iron in the blood. The iron deposits in the liver, pancreas, and other organs, causing liver problems and diabetes.
  • Sickle cell disease: A genetic condition in which red blood cells periodically lose their proper shape (appearing like sickles, rather than discs). The deformed blood cells deposit in tissues, causing pain and organ damage.
  • Bacteremia: Bacterial infection of the blood. Blood infections are serious, and often require hospitalization and continuous antibiotic infusion into the veins.
  • Malaria: Infection of red blood cells by Plasmodium, a parasite transmitted by mosquitos. Malaria causes episodic fevers, chills, and potentially organ damage.
  • Thrombocytopenia: Abnormally low numbers of platelets in the blood. Severe thrombocytopenia may lead to bleeding.
  • Leukopenia: Abnormally low numbers of white blood cells in the blood. Leukopenia can result in difficulty fighting infections.
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What are components of blood?

Components of blood are:
1.White blood cells
2.Red blood cells (RBCs)

What is the primary function of Red Blood Cells?

The primary function of RBC is to carry oxygen from lungs to the rest of the body.

What is the primary function of white blood cells?

The primary function of white blood cells is to help the body fight infection and other diseases.

Where can I find detailed notes on 'Blood'?

Candidates can refer to this article to get detailed notes on 'Blood'.

What is the another name for white blood cells?

White Blood Cells are also called leukocyte .


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