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Blood: Type, Definition,Composition, Functions, Components

Blood: Type, Definition,Composition, Functions, Components

Edited By Irshad Anwar | Updated on Jul 02, 2025 05:30 PM IST

Blood is a vital fluid that circulates throughout the body, delivering oxygen and nutrients to cells and removing waste products. It plays a key role in maintaining bodily functions, including immune defence and regulation of temperature. In this article, blood, components of blood, types of blood cells, blood vessels, functions of blood, regulation, Blood Formation, and Importance of Blood are discussed. Blood is a topic of the chapter Body Fluids and Circulation in Biology

This Story also Contains
  1. What Is Blood?
  2. Composition of Blood
  3. Types of Blood Cells
  4. Blood Vessels
  5. Functions of Blood
  6. Regulation
  7. Blood Formation
  8. Importance of Blood
Blood: Type, Definition,Composition, Functions, Components
Blood: Type, Definition,Composition, Functions, Components

What Is Blood?

Blood is a fluid, very special, that courses in the arteries and veins throughout the body, carrying along every cell and tissue's requirements, from oxygen and nutrients to metabolic wastes. Its part in homeostasis assists in carrying on all functions in the body.

Composition of Blood

About 55% of the blood consists of plasma with different types of cells. They perform particular roles, and these roles help in running the human body.

Plasma makes up roughly 55% of the volume of blood. It is a fluid medium through which substances circulate. It comprises water, electrolytes, proteins, including albumin, globulins, and fibrinogen, hormones, and waste products.

Types of Blood Cells

The types of blood cells are listed below-

Red Blood Cells (Erythrocytes)

They are disc-shaped cells, nucleated, and have haemoglobin, which enables them to carry oxygen from the lungs to various tissues in the body. They also help transport carbon dioxide back to the lungs for exhalation.

White Blood Cells (Leukocytes)

WBCs represent one of the most important components of immunity and carry out host defence against various attacking infections. Major types of WBCs include neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Each subset performs different functions related to the immune response.

Platelets (Thrombocytes)

Platelets are described as small, irregular cell fragments playing a crucial role in hemostasis. When a blood vessel is injured, platelets are first to adhere to the damaged site. Various substances, known as clotting factors are released which activate other platelets. This whole activation mechanism results in platelet plugs, for sealing small breaks in the walls of the blood vessels, hence decreasing outliers of bleeding.

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Blood Vessels

Blood vessels are the channels or conduits, through which blood is distributed to all the parts of the body from the heart, and back to the heart.

Arteries

Arteries distribute blood from the heart to various regions in the body, and they are thick and muscular to withstand high pressure as blood is being pumped from the heart.

Veins

Veins return blood from different body organs back to the heart; they have thinner walls compared to arteries and have valves that prevent backflow of the blood, thus returning blood.

Capillaries

Capillaries are microscopic, thin-containing vessels in which gas exchange and nutrient exchange occur between blood and tissues; they connect arteries to veins and allow the exchange of oxygen, carbon dioxide, nutrients, and waste materials.

Functions of Blood

Blood performs several critical functions necessary to maintain health and homeostasis.

Transport

Oxygen and Carbon Dioxide: Red blood cells take up oxygen from the lungs to the tissues and in an exchange manner get out with carbon dioxide from the tissues and back to the lungs to be exhaled.

Nutrients And Waste Products

Nutrient absorptions by the digestive system are transported by the blood into the different cells of the body, while metabolic waste from cell activities is carried to places such as the kidneys for excretion.

Hormones

The blood distributes hormones that are secreted from endocrine glands to target organs/tissues, which regulate many of the body's physiological processes.

Regulation

Blood regulation is explained below-

Temperature:

By transport and re-distribution of heat generated from metabolically active tissues to the skin surface blood aids in the elimination of body heat.

pH Balance:

Blood behaves as a buffer regulating the hydrogen ion concentration, thus stabilizing pH to very narrow limits, optimal for the functioning of enzymes and other cellular actions.

Fluid Balance:

Blood maintains the fluid balance in the body through the exchange of water and electrolytes between the blood and tissues.

Immune Response:

The white blood cells and antibodies contained in blood protect the body from infections; it identifies the pathogen and kills it.

Blood Clotting:

Platelets and clotting factors in blood form clots, which seal off the vessel, if injured, preventing a profuse loss of blood from the body.

Blood Formation

  • The process through which the blood's formed components are created is known as hemopoiesis (hematopoiesis). The epiphyses of flat bones (such as the ribs and cranial bones), long bones (such as the humerus and femur), vertebrae, and the pelvis are where hemopoiesis occurs. Hemocytoblasts, which are hemopoietic stem cells, divide in the red bone marrow to create several types of "blast" cells. Each of these cells develops into a distinct developed element.

  • The production of erythrocytes, or erythropoiesis, starts with the development of proerythroblasts from hemopoietic stem cells. Several phases of development occur for three to five days as ribosomes multiply and haemoglobin is produced.

  • Colony-stimulating factors (CSFs), which are hormones made by mature white blood cells, encourage leukopoiesis, the process of creating leukocytes. The division of the hemopoietic stem cells initiates the creation of each kind of white blood cell.

  • Megakaryoblasts, which are the precursors of thrombopoiesis, the production of platelets, are created from hematopoietic stem cells. Megakaryocytes, which are enormous cells with a massive, multilobed nucleus, are created when megakaryoblasts divide without cytokinesis. The plasma membrane then infolds into the cytoplasm, causing the megakaryocytes to split into pieces.

Importance of Blood

All of the body's components can continue to function by receiving oxygen and nutrition through the blood. The lungs, kidneys, and digestive system use the blood to transport carbon dioxide and other waste products for elimination from the body. Additionally, blood distributes hormones throughout the body and fights infections.

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Frequently Asked Questions (FAQs)

1. What are the main components of blood?

Blood is made up of plasma, red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

2. Compare and contrast the structure and the role of an artery with that of a vein.

Arteries take oxygenated blood away from the heart to the body at very high pressure, while veins return oxygen-depleted blood to the heart at very low pressure with the help of valves that do not let blood flow again in the same direction.

3. What are the functions of red blood cells in the body?

Red blood cells transfer oxygen from the lungs to tissues and carbon dioxide from tissues back to the lungs, which will eventually be exhaled out.

4. How does blood cool and warm the body?

Blood redistributes the transferred accumulative heat from active respiring tissue towards the skin surface and then transfers it out through radiation or sweat.

5. Why do you think blood coagulation is important?

Blood clotting, or hemostasis, becomes crucial so that after injury no one over-bleeds. Both platelets and clotting factors work together to form a clot to seal off the injured blood vessel.

6. How do blood clotting disorders affect the body?
Blood clotting disorders can either increase or decrease the blood's ability to clot:
7. How does altitude affect blood composition and function?
At high altitudes, where oxygen levels are lower, the body adapts by:
8. How do anticoagulants work, and what are some common examples?
Anticoagulants prevent blood from clotting by interfering with different stages of the coagulation cascade. Common examples include:
9. How do blood types affect transfusion compatibility?
Blood type compatibility is crucial for safe transfusions. The general rules are:
10. What is the significance of blood groups beyond ABO and Rh systems?
While ABO and Rh are the most clinically significant blood group systems, there are over 30 other blood group systems, including:
11. How do blood cells develop from stem cells in the bone marrow?
Blood cell development, or hematopoiesis, occurs in the bone marrow from hematopoietic stem cells (HSCs). The process involves:
12. What are the main components of blood, and what percentage of blood volume does each occupy?
Blood consists of two main components: plasma and formed elements. Plasma makes up about 55% of blood volume and is the liquid portion. Formed elements, which include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes), make up the remaining 45%. Of this 45%, red blood cells account for about 44%, while white blood cells and platelets together make up about 1%.
13. How does plasma differ from serum?
Plasma is the liquid portion of blood that contains all blood proteins, including clotting factors. Serum is plasma from which clotting factors have been removed. To obtain serum, blood is allowed to clot, and the resulting liquid is separated. Plasma, on the other hand, is obtained by preventing blood from clotting (usually by adding an anticoagulant) and then separating the liquid portion from the cellular components.
14. What are the main functions of plasma proteins?
Plasma proteins serve several important functions:
15. What is the difference between innate and adaptive immunity in blood?
Innate immunity is the body's first line of defense, present from birth. It includes physical barriers (like skin), chemical barriers (like stomach acid), and certain white blood cells (like neutrophils and macrophages) that respond quickly but non-specifically to pathogens. Adaptive immunity, on the other hand, develops over time as the body is exposed to various pathogens. It involves specialized white blood cells called lymphocytes (B and T cells) that provide a specific, targeted response to pathogens and can remember them for future encounters, providing long-lasting protection.
16. What is the role of the spleen in blood function?
The spleen serves several important functions related to blood:
17. What are platelets, and how do they contribute to blood clotting?
Platelets, also called thrombocytes, are small, disc-shaped cell fragments that play a crucial role in blood clotting (hemostasis). When a blood vessel is damaged, platelets adhere to the injury site and release chemicals that attract more platelets. They then aggregate and form a plug to stop bleeding. Platelets also activate the coagulation cascade, which results in the formation of fibrin, strengthening the clot.
18. How does the ABO blood typing system work?
The ABO blood typing system is based on the presence or absence of certain antigens on red blood cells. There are four main blood types:
19. What is the Rh factor, and why is it important in blood typing?
The Rh factor is a protein found on the surface of red blood cells. People who have this protein are Rh-positive, while those who don't are Rh-negative. It's important in blood typing because Rh-negative individuals can develop antibodies against Rh-positive blood if exposed to it. This is particularly crucial during pregnancy, where an Rh-negative mother carrying an Rh-positive fetus may develop antibodies that could harm future pregnancies.
20. How does the body regulate the production of red blood cells?
The production of red blood cells, called erythropoiesis, is primarily regulated by the hormone erythropoietin (EPO). When oxygen levels in the body are low, the kidneys produce more EPO, which stimulates the bone marrow to increase red blood cell production. This process is also influenced by other factors such as iron availability, vitamin B12, and folate levels. The body maintains a balance between red blood cell production and destruction to keep a constant supply of oxygen-carrying cells.
21. What is hematocrit, and what does it indicate about blood composition?
Hematocrit is the percentage of blood volume occupied by red blood cells. It's typically measured as part of a complete blood count (CBC). A normal hematocrit range is about 40-54% for men and 36-48% for women. A high hematocrit may indicate dehydration or disorders that increase red blood cell production, while a low hematocrit could suggest anemia or blood loss. Hematocrit provides valuable information about the oxygen-carrying capacity of blood and overall blood health.
22. How does blood contribute to the body's buffer systems?
Blood contributes to the body's buffer systems in several ways:
23. What is the role of blood in the lymphatic system?
While blood and lymph are separate circulatory systems, they interact closely:
24. How does blood maintain homeostasis in the body?
Blood plays a crucial role in maintaining homeostasis by regulating various bodily functions. It helps maintain body temperature by distributing heat, regulates pH through buffer systems, transports hormones for communication between organs, delivers nutrients and oxygen to cells, and removes waste products. Blood also contains immune cells that defend against pathogens, maintaining the body's internal balance.
25. What is the role of iron in blood function, and how is iron homeostasis maintained?
Iron is crucial for the formation of hemoglobin in red blood cells, which is essential for oxygen transport. Iron homeostasis is maintained through careful regulation of absorption, storage, and recycling. The hormone hepcidin, produced by the liver, plays a key role by controlling iron absorption in the intestines and release from storage sites. When iron levels are low, hepcidin production decreases, allowing more iron to be absorbed and released from stores. Conversely, when iron levels are high, hepcidin production increases, reducing iron absorption and release.
26. How do blood vessels contribute to blood pressure regulation?
Blood vessels, particularly arteries and arterioles, play a crucial role in blood pressure regulation through vasoconstriction and vasodilation. When blood vessels constrict, they increase resistance to blood flow, raising blood pressure. When they dilate, resistance decreases, lowering blood pressure. This process is controlled by the autonomic nervous system and various hormones. Additionally, the elastic nature of large arteries helps maintain steady blood flow and pressure throughout the cardiac cycle.
27. What is the role of blood in thermoregulation?
Blood plays a crucial role in thermoregulation by:
28. How does blood pH affect oxygen binding to hemoglobin?
Blood pH affects oxygen binding to hemoglobin through the Bohr effect. When blood pH decreases (becomes more acidic), hemoglobin's affinity for oxygen decreases, causing it to release oxygen more readily to tissues. Conversely, when blood pH increases (becomes more alkaline), hemoglobin binds oxygen more tightly. This effect is crucial for efficient oxygen delivery, especially to active tissues that produce more acid as a result of increased metabolism.
29. What is the significance of hemoglobin in red blood cells?
Hemoglobin is a protein in red blood cells that binds to oxygen and carbon dioxide. Its primary function is to transport oxygen from the lungs to body tissues and to help transport carbon dioxide back to the lungs for exhalation. Each hemoglobin molecule can carry up to four oxygen molecules, significantly increasing the oxygen-carrying capacity of blood compared to plasma alone.
30. What is the difference between hemoglobin and myoglobin?
Hemoglobin and myoglobin are both oxygen-binding proteins, but they have different structures and functions:
31. How does blood contribute to the body's endocrine system?
Blood plays a vital role in the endocrine system by:
32. How do red blood cells differ structurally from other cells in the body?
Red blood cells (erythrocytes) have a unique biconcave disc shape and lack a nucleus and most organelles when mature. This structure maximizes their surface area for efficient gas exchange and allows them to squeeze through narrow blood vessels. The absence of a nucleus and organelles provides more space for hemoglobin, the protein responsible for oxygen transport.
33. How do white blood cells differ from red blood cells in terms of function and lifespan?
White blood cells (leukocytes) are part of the immune system and defend the body against infections and foreign substances. Unlike red blood cells, they have nuclei and can move independently. White blood cells have a shorter lifespan, typically a few days to weeks, compared to red blood cells which live for about 120 days. White blood cells also exist in much smaller numbers than red blood cells in the bloodstream.
34. What are the five main types of white blood cells and their primary functions?
The five main types of white blood cells are:
35. What is the difference between arterial and venous blood?
Arterial and venous blood differ in several ways:
36. What is blood and why is it considered a connective tissue?
Blood is a fluid connective tissue that circulates throughout the body. It's considered a connective tissue because it originates from the same embryonic layer as other connective tissues and performs the function of connecting various parts of the body. Unlike other connective tissues, blood has a liquid extracellular matrix called plasma, which allows it to flow and transport substances throughout the body.

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Option 3: To control the level of sugar in the body

 

Option 4: To check the level of iodine in the body

Correct Answer: To control the level of sugar in the body

 


Solution : The correct option is - To control the level of sugar in the body.

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In the following passage, some words have been deleted. Read the passage carefully and select the most appropriate option to fill in each blank.
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Option 1: implemented

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Solution : The correct choice is the third option.

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Therefore, the complete sentence is: "Two people, whose blood and body fluid samples were tested positive for the infection, are undergoing treatment."

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Like, a dentist deals with the issues related to teeth and gums.
Similarly, a dermatologist deals with the issues related to the skin.

Hence, the fourth option is correct.

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Solution : Given:
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