Facts about Blood- Composition, Function & Types

Facts about Blood

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:40 PM IST

Blood is a vital fluid in the human body that transports oxygen, nutrients, hormones, and waste products. It is composed of plasma, red blood cells, white blood cells, and platelets. Blood accounts for about 7-8% of body weight and plays a crucial role in immunity and regulation of body temperature. In this article, blood, the composition of blood, functions of blood, and interesting facts about blood are discussed. Blood is a topic of the chapter Body Fluids and Circulation in Biology.

This Story also Contains

What Is Blood?
Composition of Blood
Blood Functions
Interesting Facts about Blood

Facts about Blood

What Is Blood?

Blood is one of the most important fluids in a human being's body. Blood transports oxygen and nutrition to the cells of the body and the removal of waste products from them. It further performs the function of maintaining homeostasis, protecting against diseases, and rendering service to the total organs of the body.

Knowing the composition of blood, functions, and related disorders is quite important in medical and biological studies. It helps diagnose and treat various health conditions, and hence the study is always ongoing for a healthcare professional.

Composition of Blood

Blood is composed of different constituents that play different functions.

These are as follows:

Plasma

Description: Liquid portion of blood
Functions: Transfers nutrients, hormones, waste products
Composition: 90% water, 10% proteins, electrolytes, nutrients

Red Blood Cells (Erythrocytes)

Structure: Biconcave discs without nuclei
Role: Transport of oxygen via haemoglobin
Lifecycle: Formed in the bone marrow; living for approximately 120 days.

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White Blood Cells (Leukocytes)

Types: Neutrophils, lymphocytes, monocytes, eosinophils, basophils
Role: Fight infections and other foreign invaders
Disorders: Leukemia, Lymphoma

Platelets (Thrombocytes)

Structure: Small pieces of cells
Function: Blood coagulation to avoid loss of blood from the body.

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Blood Functions

Blood performs many vital functions in the human body:

Transport

Oxygen and carbon dioxide between the lungs and tissues.
Nutrients from the digestive system to cells.
Hormones and enzymes all over the body.

Regulation

pH Balance for proper functioning of the body.
Temperature of body
Fluid balance

Protection

Immune protection through leucocytes
Blood clotting by thrombocytes.

Interesting Facts about Blood

Some interesting facts about blood are listed below-

Fact No. 1

The only liquid connective tissue that circulates throughout the body is blood. All essential elements, including proteins, glucose hormones, oxygen, minerals, electrolytes, and other waste products from metabolism, are also transported by it.

Fact No. 2

Approximately 7–8% of the body weight is made up of blood. The two primary components of blood are plasma and formed elements, or corpuscles, which include blood platelets, red blood cells, and white blood cells, or WBCs.

Fact No. 3

Transportation, defence against external invasion, and control of body temperature and pH are among the main roles of blood.

Fact No. 4

Humans have red blood, although the respiratory pigment, or haemoglobin, is primarily responsible for the varied blood hues of other species.

Fact No. 5

Red blood cells, also known as erythrocytes, white blood cells, also known as leukocytes, blood platelets, also known as thrombocytes, and plasma, which is made up of protein, ions, and water, make up the majority of blood.

Fact No. 6

White blood cells, or leukocytes, are vital to the human reproductive system because they support a robust immune system and help the ovary's blood artery network grow.

Fact No. 7

About 1.325 gallons of blood make up an adult, healthy human body. Millions of red blood cells, thousands of white blood cells, and lakhs of blood platelets are all present in a single drop of blood.

Fact No. 8

Blood group is inherited genetically from our parents, just like other body traits like the eye, skin colour, and hair texture. The ABO blood type system refers to the four primary blood groups of humans: O, A, B, and AB.

Fact No. 9

The hereditary antigenic materials on the surface of red blood cells serve as the primary basis for differentiating these blood groups.

Fact No. 10

Research indicates that the ABO blood type system influences a person's fertility, personality, stress levels, and other aspects of their life, as well as resulting in different nutritional needs.

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Coronary Circulation	Facts about Blood Group
Types of Blood Cells	Blood coagulation
ABO Blood Group	Circulatory System

Frequently Asked Questions (FAQs)

1. What are the main functions of blood in the human body?

Blood carries oxygen, nutrients, and waste products; it regulates pH and temperature; it protects from infections and bleeding.

2. How do blood types relate to transfusions?

The blood type should match perfectly to avoid some negative reactions during transfusions.

3. What are the possible symptoms and causes of anaemia?

The symptoms of anaemia include becoming tired and short of breath; the causes are low iron levels within the body and genetic problems.

4. What is a Complete Blood Count (CBC) blood test, and what are all the things it measures?

It is a blood test that measures RBC count, WBC count, haemoglobin, hematocrit, and platelets.

5. What is the current status of artificial blood?

Research focuses on developing artificial blood substitutes for emergencies and the treatment of various blood disorders.

6. What is the importance of iron in blood function?

Iron is crucial for blood function as it's a key component of hemoglobin. It allows hemoglobin to bind oxygen efficiently. Iron deficiency can lead to anemia, reducing the blood's oxygen-carrying capacity and causing fatigue and other symptoms.

7. How does blood viscosity affect circulation?

Blood viscosity, or thickness, affects how easily blood flows through vessels. Higher viscosity (thicker blood) increases resistance to flow and can strain the heart. Factors like hematocrit, plasma protein levels, and temperature influence blood viscosity.

8. What is erythropoiesis, and where does it occur?

Erythropoiesis is the process of red blood cell production. In adults, it primarily occurs in the bone marrow of large bones. The process is regulated by the hormone erythropoietin, which is produced mainly by the kidneys in response to low oxygen levels.

9. What is the function of transferrin in blood?

Transferrin is a plasma protein that binds and transports iron in the bloodstream. It helps regulate iron levels in the body and ensures that iron is delivered to tissues that need it, such as bone marrow for red blood cell production.

10. What is the role of platelets beyond blood clotting?

Besides their crucial role in hemostasis, platelets contribute to wound healing by releasing growth factors that promote tissue repair. They also play a role in inflammation and immune responses, interacting with white blood cells and releasing inflammatory mediators.

11. How does blood maintain body temperature?

Blood helps regulate body temperature through a process called thermoregulation. It absorbs heat from active organs and muscles, then distributes it throughout the body or releases it through the skin. Blood vessels can also dilate or constrict to control heat loss.

12. How do platelets contribute to blood clotting?

Platelets play a vital role in blood clotting (hemostasis). When a blood vessel is damaged, platelets adhere to the injury site, release chemicals to attract more platelets, and form a plug. This initiates a cascade of reactions leading to the formation of a fibrin clot.

13. How does blood transport oxygen throughout the body?

Oxygen is primarily transported by hemoglobin in red blood cells. Each hemoglobin molecule can bind up to four oxygen molecules. As blood passes through the lungs, oxygen attaches to hemoglobin. The oxygenated blood then travels to tissues, where oxygen is released for cellular use.

14. How does blood help maintain fluid balance in the body?

Blood helps maintain fluid balance through osmotic pressure and hydrostatic pressure. Plasma proteins, especially albumin, create oncotic pressure that keeps fluid within blood vessels. The kidneys also regulate blood volume by adjusting water and salt excretion.

15. What is the pH of blood, and why is it important?

The normal pH of blood ranges from 7.35 to 7.45, making it slightly alkaline. Maintaining this narrow pH range is crucial for proper enzyme function, oxygen transport, and overall cellular health. The body has several buffer systems to keep blood pH stable.

16. What is hematocrit, and what does it indicate?

Hematocrit is the percentage of blood volume occupied by red blood cells. It's typically around 45% for men and 40% for women. A low hematocrit may indicate anemia, while a high hematocrit could suggest dehydration or polycythemia.

17. What is the function of plasma proteins?

Plasma proteins serve various functions: maintaining oncotic pressure (albumin), transporting substances (lipoproteins), fighting infections (immunoglobulins), and aiding in blood clotting (fibrinogen). They also help buffer blood pH and contribute to blood viscosity.

18. How does blood volume affect blood pressure?

Blood volume directly influences blood pressure. An increase in blood volume typically leads to higher blood pressure as it increases the amount of fluid the heart must pump. Conversely, a decrease in blood volume can lead to lower blood pressure.

19. What is the role of albumin in blood?

Albumin is the most abundant protein in plasma. It helps maintain oncotic pressure, keeping fluid within blood vessels. Albumin also serves as a carrier for various substances, including hormones, fatty acids, and some drugs.

20. How does blood help in maintaining electrolyte balance?

Blood transports electrolytes throughout the body and helps maintain their balance. It carries excess electrolytes to the kidneys for excretion or reabsorption as needed. The composition of electrolytes in blood plasma is tightly regulated to ensure proper cellular function.

21. What are the ABO blood types, and why are they important?

The ABO blood types are A, B, AB, and O, determined by the presence or absence of A and B antigens on red blood cells. Knowing blood types is crucial for safe blood transfusions, as receiving incompatible blood can cause a severe immune reaction.

22. How do antigens on red blood cells determine blood type?

Antigens are proteins and carbohydrates on the surface of red blood cells. The presence or absence of A and B antigens determines the ABO blood type. Type A has A antigens, Type B has B antigens, Type AB has both, and Type O has neither.

23. What is the significance of blood groups in transfusions?

Blood group compatibility is crucial in transfusions to prevent potentially life-threatening immune reactions. Transfusing incompatible blood can cause the recipient's immune system to attack the donor red blood cells, leading to hemolysis and severe complications.

24. What is the function of white blood cells in the blood?

White blood cells (leukocytes) are crucial components of the immune system. They defend the body against infections and foreign invaders through various mechanisms, including phagocytosis, antibody production, and the release of inflammatory mediators.

25. What are the main components of blood?

Blood consists of four main components: plasma (the liquid part), red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). Plasma makes up about 55% of blood volume, while the cellular components make up the remaining 45%.

26. Why is blood red?

Blood appears red due to the presence of hemoglobin in red blood cells. Hemoglobin is an iron-containing protein that binds to oxygen, giving oxygenated blood a bright red color. Deoxygenated blood appears darker red.

27. What is the difference between serum and plasma?

Plasma is the liquid component of blood that contains clotting factors. Serum is plasma without clotting factors. To obtain serum, blood is allowed to clot, and the resulting liquid is separated. Plasma is obtained by adding anticoagulants to prevent clotting.

28. What is the role of plasma in blood?

Plasma, the liquid component of blood, serves multiple functions. It transports nutrients, hormones, and waste products; helps maintain blood pressure and pH; carries clotting factors for hemostasis; and contributes to the body's immune defense by containing antibodies.

29. How do white blood cells defend the body against pathogens?

White blood cells (leukocytes) protect the body through various mechanisms. Some directly engulf and destroy pathogens (phagocytosis), while others produce antibodies or release chemicals to neutralize threats. They also help coordinate the immune response.

30. How does blood help in waste removal from the body?

Blood collects waste products from cells, such as carbon dioxide and metabolic byproducts. It transports these wastes to excretory organs like the lungs (for CO2 removal) and kidneys (for filtering out other waste products), which then eliminate them from the body.

31. How do blood vessels work with blood to regulate blood pressure?

Blood vessels, particularly arteries and arterioles, can constrict or dilate to control blood flow and pressure. This vasomotor control, along with the heart's pumping action and blood volume, helps maintain appropriate blood pressure throughout the body.

32. How does blood contribute to the body's defense against infections?

Blood plays a key role in immune defense by carrying white blood cells and antibodies throughout the body. It also contains complement proteins that can directly attack pathogens and enhance the effectiveness of antibodies and phagocytes.

33. What is the function of fibrinogen in blood?

Fibrinogen is a plasma protein crucial for blood clotting. When activated by thrombin, it converts to fibrin, which forms a mesh-like structure that traps blood cells and platelets, creating a stable clot to stop bleeding.

34. How does blood help in hormone distribution?

Blood acts as a transport medium for hormones, carrying them from endocrine glands to target tissues throughout the body. This allows hormones to regulate various physiological processes, even in distant parts of the body.

35. What is the difference between arterial and venous blood?

Arterial blood is oxygen-rich and appears bright red, while venous blood is oxygen-poor and appears darker. Arterial blood flows away from the heart to tissues, while venous blood returns to the heart from tissues, carrying waste products.

36. How does blood oxygen content differ between arteries and veins?

Arterial blood typically has a higher oxygen content than venous blood. In healthy individuals, arterial blood is about 95-100% saturated with oxygen, while venous blood is about 70-75% saturated. This difference reflects oxygen usage by tissues.

37. How does blood contribute to the body's buffer systems?

Blood contains several buffer systems that help maintain pH balance. The most important is the bicarbonate buffer system, which can quickly neutralize small amounts of acid or base. Hemoglobin in red blood cells also acts as a buffer, particularly for CO2.

38. How does blood pH affect oxygen binding to hemoglobin?

Blood pH influences oxygen binding to hemoglobin through the Bohr effect. As pH decreases (becomes more acidic), hemoglobin's affinity for oxygen decreases, facilitating oxygen release to tissues. This effect helps deliver more oxygen to active, acidic tissues.

39. What is the significance of the heme group in hemoglobin?

The heme group in hemoglobin contains iron, which is crucial for oxygen binding. Each hemoglobin molecule has four heme groups, allowing it to bind up to four oxygen molecules. The iron in heme gives blood its red color and is essential for oxygen transport.

40. How does blood contribute to maintaining the body's acid-base balance?

Blood contains buffer systems, including bicarbonate and phosphate buffers, that help maintain a stable pH. It also transports excess acids or bases to the lungs or kidneys for elimination, thus playing a vital role in acid-base homeostasis.

41. How does blood help in regulating body pH?

Blood helps regulate pH through its buffer systems, primarily the bicarbonate buffer. It also transports excess hydrogen ions to the lungs for exhalation as CO2 or to the kidneys for excretion. This helps maintain the body's pH within a narrow, optimal range.

42. What is the role of blood in thermoregulation?

Blood plays a crucial role in thermoregulation by distributing heat throughout the body. When body temperature rises, blood vessels near the skin dilate, allowing more blood flow and heat dissipation. In cold conditions, these vessels constrict to conserve heat.

43. What is the role of blood in nutrient distribution?

Blood transports nutrients absorbed from the digestive system to cells throughout the body. It carries glucose, amino acids, fatty acids, vitamins, and minerals, ensuring that all tissues receive the necessary nutrients for energy production and cellular functions.

44. How does blood contribute to the regulation of body temperature?

Blood helps regulate body temperature by distributing heat throughout the body. When core temperature rises, blood vessels in the skin dilate, allowing more blood flow near the surface for heat dissipation. In cold conditions, these vessels constrict to conserve heat.

45. What is the role of hemoglobin in carbon dioxide transport?

While hemoglobin primarily transports oxygen, it also plays a role in CO2 transport. About 20-25% of CO2 is carried by hemoglobin as carbaminohemoglobin. The rest is transported as bicarbonate ions in plasma or dissolved directly in blood.

46. How does blood contribute to the body's defense against toxins?

Blood helps defend against toxins by transporting them to the liver and kidneys for detoxification and excretion. It also carries proteins that can bind to and neutralize certain toxins, and white blood cells in blood can engulf and destroy some toxic substances.

47. What is the role of blood in maintaining osmotic balance?

Blood helps maintain osmotic balance through plasma proteins, particularly albumin. These proteins create oncotic pressure that keeps fluid within blood vessels, preventing excessive fluid loss into tissues. This is crucial for maintaining blood volume and pressure.

48. How does blood facilitate hormone communication in the body?

Blood serves as the primary medium for hormone transport. It carries hormones from endocrine glands to their target tissues throughout the body, allowing for long-distance communication and regulation of various physiological processes.

49. What is the significance of blood viscosity in circulation?

Blood viscosity affects how easily blood flows through vessels. Higher viscosity increases resistance to flow, potentially straining the heart and affecting tissue perfusion. Factors like hematocrit, plasma protein levels, and temperature influence blood viscosity.

50. How does blood contribute to the body's antioxidant defenses?

Blood contains various antioxidants that help protect against oxidative stress. These include enzymes like superoxide dismutase and glutathione peroxidase, as well as non-enzymatic antioxidants like vitamin C, vitamin E, and uric acid in plasma.

51. What is the role of blood in maintaining calcium homeostasis?

Blood transports calcium throughout the body and helps regulate its levels. It carries both free calcium ions and calcium bound to proteins. Blood calcium levels are tightly controlled through hormones like parathyroid hormone and calcitonin, which act on bones, kidneys, and intestines.

52. How does blood contribute to the body's stress response?

During stress, blood carries stress hormones like cortisol and adrenaline throughout the body. It also transports glucose and oxygen to meet the increased energy demands of tissues. The stress response can alter blood flow patterns, prioritizing vital organs.

53. What is the significance of blood in exercise physiology?

During exercise, blood plays crucial roles in delivering oxygen and nutrients to working muscles, removing waste products, and dissipating heat. Blood flow to active muscles increases, and the body may produce more red blood cells to enhance oxygen-carrying capacity with regular exercise.

54. How does blood contribute to the regulation of blood sugar levels?

Blood transports glucose throughout the body and to the cells that need it for energy. It also carries hormones like insulin and glucagon, which regulate blood sugar levels. The concentration of glucose in blood (blood sugar) is tightly controlled to maintain homeostasis.

55. What is the role of blood in the lymphatic system?

While blood and the lymphatic system are separate, they work closely together. Blood capillaries leak fluid into tissues, which is then collected by the lymphatic system and eventually returned to the blood. This process helps maintain fluid balance and aids in immune function.