Introduction:
Blood is a special type of fluid connective tissue that circulates through our entire body. It performs vital functions like transporting nutrients, gases, and hormones; regulating body temperature and pH; and protecting us from infections and blood loss.
Functions of Blood:
Blood performs three main functions — Transportation, Regulation, and Protection.
1. Transportation:
- Carries oxygen from the lungs to body cells and carbon dioxide back to the lungs.
- Transports nutrients from the digestive system to tissues.
- Delivers hormones from endocrine glands to target organs.
- Carries waste products to kidneys, lungs, and skin for elimination.
- Helps in heat distribution throughout the body.
2. Regulation:
- Maintains homeostasis (balance of body fluids).
- Regulates pH using chemical buffers.
- Controls body temperature through plasma’s heat absorption and release.
- Maintains water balance and osmotic pressure inside and outside cells.
- Hormones like aldosterone, ADH, and atrial natriuretic peptide help regulate blood volume.
3. Protection:
- Clotting mechanism prevents blood loss after injury.
- White blood cells (WBCs) fight infections through phagocytosis.
- Antibodies, interferons, and complement proteins defend against disease-causing organisms.
Physical Characteristics of Blood:
- Blood is denser and thicker than water and feels slightly sticky.
- Normal temperature: 38°C (100.4°F).
- pH: Slightly alkaline (7.35–7.45).
- Color:
- Bright red when oxygen-rich.
- Dark red when oxygen-poor.
- Makes up 8% of total body weight (~5–6 L in males, 4–5 L in females).
- Hormones like aldosterone and ADH maintain stable blood volume and osmotic balance.
Composition of Blood:
Blood has two main components:
- Plasma (liquid part)
- Formed elements (cells and cell fragments)
When centrifuged:
- Plasma (55%) forms the top layer.
- Buffy coat (WBCs & platelets) forms the middle thin layer.
- RBCs (45%) settle at the bottom.
1. Blood Plasma:
- Straw-colored liquid remaining after cells are removed.
- About 91.5% water and 8.5% solutes (mostly proteins).
- Plasma proteins (produced by the liver):
- Albumin (54%) – maintains osmotic pressure.
- Globulins (38%) – include antibodies (immunoglobulins) that defend against infection.
- Fibrinogen (7%) – helps in blood clotting.
- Other solutes: Electrolytes, nutrients, enzymes, hormones, gases, and wastes (urea, uric acid, bilirubin, etc.).
Antibodies (Immunoglobulins):
- Produced in response to antigens like bacteria and viruses.
- Each antibody binds specifically to its matching antigen and neutralizes it.
2. Formed Elements of Blood:
These include Red Blood Cells (RBCs), White Blood Cells (WBCs), and Platelets.
a) Red Blood Cells (RBCs / Erythrocytes):
- Transport oxygen from lungs to tissues and carbon dioxide back to lungs.
- Contain hemoglobin, the oxygen-carrying pigment.
- Make up about 45% of blood volume (hematocrit).
- Normal hematocrit:
- Females: 38–46%
- Males: 40–54% (higher due to testosterone stimulating RBC production).
Abnormal conditions:
- Anemia: Low RBC count → reduced oxygen-carrying capacity.
- Polycythemia: High RBC count → thicker blood, high BP, stroke risk.
b) White Blood Cells (WBCs / Leukocytes):
- Defend the body against infections and foreign materials.
- Types of WBCs:
- Neutrophils, Eosinophils, Basophils, Monocytes, Lymphocytes (B, T, and NK cells).
- Each type plays a special role in immunity and inflammation.
c) Platelets (Thrombocytes):
- Small cell fragments without a nucleus.
- Help stop bleeding by forming clots at the site of injury.
- Release chemicals that trigger clotting and tissue repair.
- Equivalent to thrombocytes in lower animals.
Detailed Notes:
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