Study Notes on 'Blood' for SSC and Railway Exams

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• Blood is a liquid connective tissue.
• The amount of blood in the human body is 7% of the total weight.
• The pH value of blood is 7.4.
• The human body contains on average 5-6 liters of blood.
• Females have half a liter less blood as compared to males.
• It also fights infection and controls temperature.

Blood cells are formed in the bone marrow.

Red cells, white cells and platelets are made in the marrow of bones, especially in the vertebrae, ribs, hips, skull and sternum. These essential blood cells fight infection, transport oxygen, and help control bleeding.

The different components of blood are as follows.

Blood is a vital fluid that circulates throughout the human body. Provides essential nutrients and oxygen to various organs and tissues. Blood has many components. Which include:

(K) plasma– Plasma is a yellow fluid, which makes up about 55% of the total volume of blood. It contains various proteins. Such as albumin, immunoglobulins and clotting factors as well as other nutrients and waste products also play an important role.

Function of Plasma-

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

2. Waste Products: The plasma also carries away waste products such as carbon dioxide and urea. From the cells to the lungs and kidneys where they are eliminated from the body.

3. Hormone: Hormones are chemical messengers that regulate various body functions. Plasma transports hormones from glands. Where they are produced for organs and tissues. Where they increase their influence.

4. Protein: 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.

(b) 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 tissues 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 oxygen molecules in the lungs and carries them to the tissues.

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

3. Buffering: Red blood cells play an important role in maintaining the pH balance of the body 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. Helpful in strengthening the immune system: Red blood cells play a vital role in the functioning of 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. This is a molecule that helps regulate blood pressure and blood flow.

(G) white blood cell- Blood cells, also known as leukocytes, appear to be an important component of the immune system and play a vital role in defending the body against infections, diseases, and foreign viruses. Some functions of white blood cells include:

1. Immunity to diseases- White blood cells help recognize, 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. This is where everything together kills the bacteria.

2. Production of antibodies: Some white blood cells, such as B lymphocytes, produce antibodies that specifically target and neutralize particular pathogens. Antibodies help stop the spread of infection and can provide long-lasting immunity against future diseases.

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

4. Regulating 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 distinguish between “self” and “non-self” cells and prevent autoimmune reactions.

(d) platelets

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

When there is an injury or damage to a blood vessel, platelets travel 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 platelets to become sticky.

Composition of blood

As seen above, blood contains 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

  • An open circulatory system allows blood to exit the vessels before returning to the heart through the ostia. (No veins involved)
  • Closed circulatory systems do not allow blood to leave the blood vessels. It involves the rapid and controlled delivery of oxygen and nutrients that allows long-term activity.

Important points related to blood:

The largest artery of the body. It carries oxygenated blood away from the heart to the vessels that reach the rest of the body.
The chambers of the heart into which blood returns after circulation.
The smallest blood vessels in the body. Oxygen and glucose pass through the capillary walls and enter the cells. Waste products such as carbon dioxide move out of the cells through the blood through capillaries.
➧Cardiac Valves (Heart Valves)
One of four heart valves that control the circulation of blood through the chambers of the heart.
Deoxygenated blood –> Blood less saturated with oxygen.
➧heart ventricle
lower right and left chambers of the heart
➧interventricular septum
The interventricular septum is a rigid wall separating the lower chambers (ventricles) of the heart from each other.
A pair of thoracic organs that supply oxygen to the body and remove carbon dioxide from the body.
➧ Middle layer i.e. Myocardium
cardiac muscle; The middle of the three layers that form 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 deficient in oxygen) to the capillaries that surround the air sacs.➧pulmonary circulation
Circulation of blood through the lungs.
Pulmonary vein
Veins carry oxygenated blood from the lungs to the left atrium of the heart.
➧Superior Vena Cava
The large vein that carries blood from the head, neck, arms, and chest to the heart.
➧Vena Cava
The large vein that returns blood from the head, neck, and limbs to the heart.
➧endothelium Blood vessels have an innermost layer that consists of only a single layer of cells.
Vein They are the blood vessels that carry blood in a uniform flow to the heart. They have large lumens and thin walls with valves.
• The human circulatory system consists of two circuits, systemic and pulmonary.
• The coronary arteries carry blood from the aorta to the heart muscle. (coronary vein)
• The hepatic artery carries blood to the liver. (hepatic vein)
• The renal arteries carry blood to the kidneys. (renal vein)
• The mesenteric arteries carry blood to the small and large intestines.
• The carotid arteries supply blood to the head.
• The subclavian artery supplies blood to the arms.
• The pelvic arteries carry blood to the legs.
• A portal system is a network of capillaries in one organ or tissue that is connected through veins or veins to another network of capillaries in another organ or tissue.
• The pulse is the alternating contraction and relaxation of an artery as blood passes through it.
• Blood pressure is the force that blood exerts on the walls of blood vessels.
• Sphygmomanometer is used to measure blood pressure (normally 120/80 mmHg).
• Atherosclerosis is the hardening of artery walls due to fatty deposits.
• Smoking increases heart rate and blood pressure. A diet high in saturated fat increases blood pressure and atherosclerosis. Exercise helps lower blood pressure.


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 cover the most important diseases that affect the blood and circulatory system as a whole.

Hematoma: There is a collection of blood inside the body tissues. Internal bleeding is often the cause of hematoma.

Leukemia: A form of blood cancer in which white blood cells grow abnormally and spread in the blood. Excessive amounts of white cells accumulate in body tissues, causing damage.

Multiple Myeloma: Are a form of blood cancer of plasma cells similar to leukemia. Anemia, kidney failure and blood in multiple myeloma
It is common to have high calcium levels.

Lymphoma: A form of blood cancer in which white blood cells grow abnormally inside lymph nodes and other tissues. The enlarged tissue, and disruption of blood function, can eventually cause an organ to prolapse.

Anemia: There is an abnormal lack of red blood cells in the blood. Its
Fatigue and shortness of breath may result, although anemia often has no noticeable symptoms.

Hemochromatosis: It is a disorder caused by excessive levels of iron in the blood. Iron gets deposited in the liver, pancreas and other organs, leading to liver problems and diabetes.

sickle cell disease: It is a genetic disease in which red blood cells lose their proper shape from time to time. Deformed blood cells accumulate in the tissues, causing pain and organ damage.

Bacteremia: Bacterial infection of blood. Blood infections are serious, and often require hospitalization and continuous antibiotic infusion into veins.

Malaria: Infection of red blood cells by Plasmodium, a parasite spread by mosquitoes.

Thrombocytopenia: There is an abnormal lack of platelets in the blood. Severe thrombocytopenia may lead to bleeding.

Leukopenia: There is an abnormal lack of white blood cells in the blood. Leukopenia can cause difficulty fighting infections.

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