1. Definition:
Blood is a vital body fluid composed of plasma and cellular elements (red blood cells, white blood cells, and platelets), responsible for transporting oxygen, nutrients, waste, hormones, and playing a key role in immune defense and homeostasis.
2. Composition:
Cellular Components (45%)
- Erythrocytes (red blood cells):
Percentage: ~99% of cellular components
Actual number: 4.5 to 6 million cells per microliter (µL) of blood - Leukocytes (white blood cells):
Percentage: <1% of cellular components
Actual number: 4,000 to 11,000 cells per microliter (µL) of blood - Platelets:
Percentage: <1% of cellular components
Actual number: 150,000 to 450,000 platelets per microliter (µL) of blood
Plasma (55%)
- Water: ~90% of plasma
- Proteins: ~7-8% of plasma, including Albumin, Globulins and Fibrinogen proteins
- Other substances: ~2% of plasma , including: Electrolytes (e.g., sodium, potassium), nutrients (e.g., glucose, amino acids), gases (e.g., oxygen, carbon dioxide), waste products (e.g., urea, creatinine), Hormones
3. Functions
Blood performs several vital functions in the body:
- Transport of oxygen and carbon dioxide: Red blood cells carry oxygen from the lungs to the tissues and return carbon dioxide to the lungs for exhalation
- Nutrient and waste transport: Blood distributes essential nutrients such as glucose and amino acids while removing waste products such as urea for elimination by the kidneys
- Immune defense: White blood cells are key players in the immune system, identifying and attacking pathogens such as bacteria and viruses, and helping to repair tissue and regulate inflammation
- Blood clotting: Platelets and clotting factors prevent excessive bleeding by forming clots at sites of injury. Disorders such as hemophilia or thrombosis impair this critical function
- Maintaining homeostasis: Blood helps regulate body temperature, pH levels, and the distribution of fluids and electrolytes to maintain stable internal conditions
4. Medical Importance
- Complete Blood Count (CBC) (Small blood count): A basic blood test that measures the levels of red blood cells, white blood cells, hemoglobin, hematocrit, and platelets to assess overall health and detect conditions like anemia or infections
- Comprehensive Blood Count (Large blood count): An expanded blood test that includes the basic CBC parameters plus a detailed breakdown of white blood cell types (differential count) to provide more in-depth information about immune function and potential underlying infections or diseases
- Blood chemistry panel: Assesses levels of glucose, electrolytes, and waste products such as creatinine, providing insight into metabolic and kidney function
- Blood Typing and Crossmatching: Identifies blood type (A, B, AB, or O) and Rh factor, critical for safe blood transfusions and organ transplants
- Coagulation tests: Evaluate the blood’s ability to clot, helping to diagnose clotting disorders or monitor patients on anticoagulant therapy
5. Blood disorders
Several medical conditions directly affect the blood, including…
- Anemia: Caused by a low red blood cell count, or hemoglobin, which leads to fatigue and weakness.
- Leukemia: A type of cancer that affects white blood cells and is characterized by abnormal growth of these cells.
- Hemophilia: A genetic disorder that causes a deficiency of clotting factors, resulting in excessive bleeding.
- Thrombosis: The formation of blood clots in blood vessels, which can lead to heart attack or stroke. Blood thinners (anticoagulants) are often used for prevention and treatment.