BLOOD

 

Blood is the vital fluid that circulates through the cardiovascular system, delivering nutrients, gases, hormones, and waste products to and from cells throughout the body. It is composed of cells suspended in a fluid matrix called plasma.

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Blood has two main components:

 

1. Plasma (about 55%)

 

Plasma is the liquid portion of blood (pale yellow), composing of:

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• Water (~90%)

• Proteins (albumin, globulins, fibrinogen)

• Electrolytes (Na⁺, K⁺, Ca²⁺, etc.)

• Hormones

• Glucose

• Waste products (urea, creatinine)

 

The functions of plasma include:

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• Transporting nutrients, hormones, and waste

• Maintaining blood pressure and volume

• Serving as a medium for chemical reactions

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2. Formed Elements (about 45%)

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These are the cellular components of blood:

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a) Red Blood Cells (RBCs or Erythrocytes)

• Most abundant (~4.5–6 million per μL of blood)

• Biconcave, disc-shaped cells without nuclei

• Contain hemoglobin, which binds oxygen and carbon dioxide

• Produced in bone marrow

 

Function: Transport oxygen from lungs to tissues and return carbon dioxide to the lungs for exhalation.

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b) White Blood Cells (WBCs or Leukocytes)

• 5,000–10,000 per μL of blood

• Nucleated cells involved in immune defense

 

Types include:

• Neutrophils (most common; fight bacteria)

• Lymphocytes (T cells, B cells — immune regulation and antibody production)

• Monocytes (become macrophages)

• Eosinophils (respond to allergens and parasites)

• Basophils (involved in allergic responses)

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Function: Defend the body against infections, cancer cells, and foreign substances.

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c) Platelets (Thrombocytes)

• Small, disc-shaped cell fragments (150,000–400,000 per μL)

• Not true cells; derived from megakaryocytes in bone marrow

 

Function: Essential for blood clotting (hemostasis) by forming plugs in vessel injuries and releasing clotting factors.

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Based on antigens on the surface of RBCs, the main blood group systems are:

 

ABO System

• A, B, AB, O types

• Determined by the presence or absence of A and B antigens

 

Rh Factor

• Positive (+) or Negative (−) depending on presence of Rh(D) antigen

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