Blood: Components, Functions, Cells, Volume & Normal Ranges
Introduction
Blood is often called the fluid of life because it plays an essential role in maintaining homeostasis and supporting every system in the human body. Flowing through arteries, veins, and capillaries, blood delivers oxygen and nutrients to tissues, removes waste products, regulates body temperature, and defends the body against infections. Without blood, life would not be possible.
This article provides a comprehensive overview of blood, its components, functions, the types of blood cells, human blood volume, and normal cell ranges. It is useful for medical students, healthcare professionals, and anyone seeking to understand this vital fluid.
What is Blood?
Blood is a specialized connective tissue composed of cells (45%) and plasma (55%). It circulates through the cardiovascular system, driven by the pumping action of the heart.
• Color: Red, due to hemoglobin in red blood cells.
• pH: Slightly alkaline, around 7.35–7.45.
• Temperature: ~37°C (slightly warmer than body temperature in some areas).
• Viscosity: About 4–5 times thicker than water.
Components of Blood
Blood is made of two major components:
1. Plasma (55%)
Plasma is the liquid portion of blood that serves as a transport medium. It is about 90–92% water, with proteins, electrolytes, nutrients, hormones, and waste products dissolved in it.
• Plasma proteins: Albumin (maintains osmotic pressure), Globulins (immune defense), Fibrinogen (clotting).
• Electrolytes: Sodium, potassium, chloride, bicarbonate.
• Nutrients: Glucose, amino acids, fatty acids, vitamins.
• Waste products: Urea, creatinine, bilirubin.
• Hormones & enzymes: Regulate metabolism and body functions.
2. Formed Elements (45%)
These are the cellular components of blood, suspended in plasma. They include:
• Red Blood Cells (Erythrocytes) – transport oxygen and carbon dioxide.
• White Blood Cells (Leukocytes) – defend against infection.
• Platelets (Thrombocytes) – help in blood clotting.
Functions of Blood
Blood is indispensable for life due to its numerous physiological functions:
1. Transport:
•nOxygen from lungs to tissues.
• Carbon dioxide from tissues to lungs.
• Nutrients from digestive system to cells.
• Hormones from glands to target organs.
• Waste products to kidneys and liver.
2. Regulation:
• Maintains pH (acid-base balance).
• Regulates body temperature.
• Maintains fluid balance.
3. Protection:
• WBCs fight infections.
• Antibodies neutralize pathogens.
• Platelets and clotting factors prevent excessive bleeding.
4. Homeostasis:
• Ensures stable internal environment for cells.
Cells of Blood
1. Red Blood Cells (Erythrocytes)
• Structure: Biconcave disc, no nucleus.
• Lifespan: ~120 days.
• Main function: Carry oxygen (via hemoglobin) and carbon dioxide.
Normal ranges:
• Men: 4.7–6.1 million/µL
• Women: 4.2–5.4 million/µL
• Children: 4.1–5.5 million/µL
• Newborns: 4.8–7.1 million/µL
2. White Blood Cells (Leukocytes)
These are immune cells that protect the body from infections. Normal range: 4,000–11,000/µL. They are classified into:
a) Granulocytes
• Neutrophils (40–70%) – first responders, fight bacterial infection.
• Eosinophils (1–4%) – fight parasitic infections, involved in allergies.
• Basophils (0.5–1%) – release histamine in allergic reactions.
b) Agranulocytes
• Lymphocytes (20–40%) – T cells, B cells, NK cells; responsible for immunity.
• Monocytes (2–8%) – transform into macrophages, engulf pathogens and debris.
3. Platelets (Thrombocytes)
Small, irregular-shaped fragments of megakaryocytes.
• Lifespan: 7–10 days.
• Function: Initiate clot formation to stop bleeding.
• Normal range: 150,000–450,000/µL.
Blood Volume in Humans
The average adult has 4.5–6 liters of blood, depending on body size, gender, and health status.
• Men: ~5–6 liters
• Women: ~4–5 liters
• Children: ~80 mL per kg body weight
• Newborns: ~85–90 mL per kg body weight
Blood volume is regulated by kidneys, hormones (ADH, aldosterone), and fluid intake.
Normal Ranges of Blood Components
Component Normal Range
Hemoglobin (Men) 13.8–17.2 g/dL
Hemoglobin (Women) 12.1–15.1 g/dL
Hematocrit (Men) 40–52%
Hematocrit (Women) 36–47%
RBC count (Men) 4.7–6.1 million/µL
RBC count (Women) 4.2–5.4 million/µL
WBC count 4,000–11,000/µL
Platelets 150,000–450,000/µL
Neutrophils 40–70%
Lymphocytes 20–40%
Monocytes 2–8%
Eosinophils 1–4%
Basophils 0.5–1%
Disorders Related to Blood
Since blood is crucial for survival, abnormalities in its composition can lead to various diseases:
• Anemia – Low RBC or hemoglobin levels.
• Leukemia – Cancer of WBCs.
• Thrombocytopenia – Low platelet count, risk of bleeding.
• Polycythemia – Excess RBCs, risk of clotting.
• Hemophilia – Genetic disorder, impaired clotting.
• Septicemia – Infection in blood.
Importance of Maintaining Healthy Blood
To maintain optimal blood health:
• Eat a balanced diet rich in iron, vitamin B12, folic acid.
• Stay hydrated.
• Exercise regularly.
• Avoid smoking and alcohol.
• Go for routine blood tests.
Frequently Asked Questions (FAQs)
Q1. What are the main components of blood?
Blood has plasma, red blood cells, white blood cells, and platelets.
Q2. What is the normal blood volume in humans?
Adults have about 4.5–6 liters of blood.
Q3. Which blood cell lives the longest?
Red blood cells live about 120 days, while some lymphocytes can last years.
Q4. What is the normal WBC count?
4,000–11,000/µL of blood.
Q5. Why is hemoglobin important?
It binds oxygen and delivers it to tissues, making life possible.
Q6. What happens if platelet count is too low?
It increases the risk of excessive bleeding and delayed clotting.
Q7. How is blood tested in routine health checkups?
Through a Complete Blood Count (CBC) test.
Conclusion
Blood is a vital fluid that sustains human life by transporting oxygen, nutrients, hormones, and waste products. Its components—plasma, red blood cells, white blood cells, and platelets—work together to maintain balance, protect against disease, and ensure proper functioning of the body. Maintaining healthy blood levels is essential for overall well-being.
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Writer: Vandita Singh, Lucknow (GS India Nursing Group)