Blood and its composition

1. Introduction :

Blood is a specialized body fluid that circulates through the blood vessels to supply oxygen and nutrients to the tissues and remove the waste products.

Blood cells produced in the bone marrow.

FUNCTIONS OF BLOOD:

  1. Oxygen, carbon dioxide, nutrients, hormones, and waste products transport

  2. Temperature regulation in the body, pH balancing, and fluid homeostasis.

3. Immunity to infection and stopping of blood loss via clotting mechanisms.

2. Blood Constituents:

Blood can be divided into two principal parts:

2.1. Plasma: The liquid component, around 55% of the blood.

2. Formed Elements: Comprise 45% of blood; these include erythrocytes, leukocytes and platelets.

2.1. Plasma:

It is the pale yellow liquid that makes up about ~55% of the blood.

Diagram : After centrifugation, Whole Blood ↑

Components:

2.1.1. Water (90-92%): Solvent carrying nutrients, hormones, and waste products.

2.1.2. Proteins (7-8%):

Albumin: Helps to maintain osmotic pressure and acts as carrier protein.

Globulins: Antibodies, and transport proteins.

Fibrinogen: Concerned in blood clotting.

2.1.3. Dissolved Substances (1-2%):

Electrolytes: Sodium, potassium, calcium, chloride, and bicarbonates.

Nutrients: Glucose, amino acids, fatty acids, and vitamins.

Hormones: Insulin, cortisol and other regulatory chemicals.

Metabolic Waste Products: Urea, creatinine, and carbon dioxide.

2.2. Formed Elements or cellular constituents :

The solid part of blood is comprised of three distinct types of cells which serve a different purpose,

A. Red Blood Cells (Erythrocytes) :

   – Structure:

  – Biconcave disc shape.

  – No nucleus and no organelles to create space for hemoglobin.

– Function:

– Transport oxygen from the lungs to tissues and carry carbon dioxide back to the lungs.

  – Hemoglobin is an iron-containing protein that binds to oxygen.

– Life Span: ~120 days.

– Normal Count:

  – Males: 4.7–6.1 million/µL.

  – Females: 4.2–5.4 million/µL.

B. White Blood Cells (Leukocytes)

– Role: Protect the body against infections, foreign invaders, and abnormal cells.

– **Types**:

  1. **Granulocytes** (contain granules):

– **Neutrophils**: Most common; first-line defenders against bacterial infections.

     – **Eosinophils**: Combat parasitic infections and are involved in allergies.

     – **Basophils**: Histamine release during allergic reactions.

 2. **Agranulocytes** (no granules):

     – **Lymphocytes**:

       – T cells: Organizers of immune responses.

– B cells: Produce antibodies.

  – Natural Killer (NK) cells: Destroy abnormal cells.

    – **Monocytes**: Become macrophages, engulfing pathogens and debris.

– **Lifespan**:

  – Neutrophils: Hours to days.

  – Lymphocytes and monocytes: Weeks to years.

– **Normal Count**: 4,000–11,000/µL.

###### **C. Platelets (Thrombocytes)**

– **Structure**: Small, disc-shaped fragments derived from megakaryocytes.

– **Function”:

– Facilitate hemostasis by the formation of a platelet plug and release of clotting factors.

– **Duration**: 7–10 days.

– **Normal Count**: 150,000–450,000/µL.

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### Functions of Blood

1. **Transportation**:

   – Oxygen from the lungs to tissues.

   – Carbon dioxide from tissues to the lungs.

   – Nutrients from the digestive tract to cells.

   – Hormones from endocrine glands to target organs.

– Waste products to the kidneys for excretion.

2. **Regulation**:

   Distributes heat to maintain body temperature.

   Helps in maintaining pH by its buffers, such as bicarbonate.

   Maintains osmotic balance and the fluid levels in tissues.

3. **Protection**:

   WBCs protect against infections and foreign bodies.

   Platelets and clotting proteins help prevent excessive bleeding.

– Antibodies and complement proteins neutralize pathogens.

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### **Blood Volume**

– **Average Blood Volume**:

  Adult male: ~5-6 liters.

  Adult female: ~4-5 liters.

– Blood volume accounts for ~7-8% of body weight.

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### **Hematopoiesis: Formation of Blood Cells**

– **Definition**: The process of blood cell production, which occurs in the bone marrow.

– **Stages**:

  1. **Erythropoiesis**: Formation of red blood cells, stimulated by erythropoietin (EPO) from the kidneys.

2. **Leukopoiesis**: Formation of white blood cells.

  3. **Thrombopoiesis**: Formation of platelets, regulated by thrombopoietin.

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### **Disorders Related to Blood**

1. **RBC Disorders**:

   – **Anemia**: Low RBC count or hemoglobin (e.g., iron-deficiency anemia, sickle cell anemia).

   – **Polycythemia**: Excess RBC production, leading to thickened blood.

2. **WBC Disorders**:

   – **Leukopenia**: Decreased WBC count, leading to immune suppression.

– **Leukocytosis**: An elevated WBC count is usually because of an infection.

   – **Leukemia**: Cancer of WBCs.

3. **Platelet Disorders**:

   – **Thrombocytopenia**: Low platelet count. It results in a propensity to bleed excessively.

   – **Thrombocytosis**: Elevated platelet count, raising the chance of thrombus formation.

4. **Plasma Disorders**:

   – **Hemophilia**: A genetic disorder that involves the clotting factors.

   – **Hypoproteinemia**: Low plasma protein causes edema.

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### **Conclusion

Blood is a fluid that undertakes the vital functions of transport, regulation, and protection. Knowledge about composition and function is essential in diagnosing various diseases and treating patients affected.