Blood Composition and Functions

• Blood makes up about 8% of the human body weight.
• Blood contains erythrocytes, leucocytes, thrombocytes, and plasma.
• The volume percentage of blood cells is about 45% in adults, known as hematocrit.
• Blood consists of cells, cell fragments, and aqueous solution (plasma).

Function

• Blood transports gases, nutrients, and end products of cell metabolism.
• Blood ensures substance exchange by providing tissues with gases and nutrients, and transporting end products to eliminating organs.
• Chemical messengers (hormones) are carried to their target organs.
• Acid-base homeostasis is regulated through gas diffusion in the lungs.
• Oxygen diffuses from alveoli to blood and binds to hemoglobin.
• Carbon dioxide diffuses from blood to alveoli to be breathed out.
• Blood transports oxygen from the lungs to the body's cells.
• Oxygen diffuses from plasma to tissues due to higher gas pressure.
• Carbon dioxide diffuses from cells to blood due to higher gas pressure in the tissue.
• Carbon dioxide forms carbonic acid, which dissociates into hydrogen ion and bicarbonate.
• Carbon dioxide is transported as carbonic acid (or hydrogen ion and bicarbonate).
• In the lungs, the chemical reaction reverses and carbon dioxide is exhaled.
• Blood regulates acid-base homeostasis through gas exchange.
• Water balance is maintained between capillaries, intracellular, and extracellular space.
• Body temperature is kept constant.

Coagulation

• Coagulation factors are dissolved in the blood.
• Bleeding stops through activation of coagulation factors, leading to thrombus formation.
• Fibrinogen/fibrin prevents pathological blood clots in blood vessels.
• Blood coagulation and fibrinolysis maintain a sensitive equilibrium.

Blood Cellular Components

Erythrocytes

• Erythrocytes transport oxygen from the lungs to the tissue.
• Oxygen binds to the heme group of hemoglobin.
• They are round and biconcave in shape, lacking a nucleus
• Diameter measures 8 to 10 µm.
• A healthy adult has about 5 million/µl erythrocytes.
• Blood group antigens are expressed on the surface membrane.

Leukocytes

• Leukocytes have a nucleus.
• Normal concentration ranges from 4,000 to 10,000 per µl.
• Types include neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
• Primary function of leukocytes is immune defense.

Lymphocytes

• Lymphocytes make up 25 to 40% of leukocytes.
• They facilitate the adaptive immune response and specific defense from pathogenic germs.
• B lymphocytes produce antibodies.
• T lymphocytes mediate antibody production and direct cellular immune response.

Monocytes

• Monocytes make up 4 to 8% of leukocytes.
• They are responsible for phagocytosis, removing foreign materials and bacteria.
• Monocytes can differentiate into fixed macrophages or free macrophages.

Platelets

• Platelets derive from megakaryocytes.
• They facilitate hemostasis during blood vessel damage for wound closure.
• Platelets adhere to the vascular wall and react with fibrin, forming a solid clot within 1 to 3 minutes.
• Physiological range for platelets is 150,000 – 400,000/µl.

Intro

• Blood is 45% cells and 55% blood plasma.
• Cells consist of erythrocytes, leukocytes, and platelets.
• Blood plasma mainly is composed of water, proteins, antibodies, and electrolytes.

Erythrocytes

• Erythrocytes make up 45% of the total volume of blood
• The percentage of red blood cells in the blood is the hematocrit.
• Erythrocytes lack nuclei and are biconcave.
• They measure 7.5 micrometers in diameter, 2.6 micrometers at the rim, and 0.75 micrometers in the center.
• Primary function is the transportation of oxygen to tissues and carbon dioxide away from the tissues.
• Cells are filled with hemoglobin.
• Hemoglobin reversibly binds oxygen and carbon dioxide for gaseous exchange.
• The absence of a nucleus and organelles allows more hemoglobin to be packed.
• Reticulocytes are precursors to red blood cells.
• Reticulocytes account for only 1-2% of cells in the blood.
• Structure allows them to be really flexible and easily deform or bend in order to pass through the narrow vessels of the capillary bed
• Glycoproteins and glycolipids, both of which are kinds of antigens, are present on the surface of red blood cells.
• Lifespan is 120 days.
• Old red blood cells lose their ability to deform, which is detected by the spleen and broken down.

Leukocytes

• Leukocytes have a lifespan ~ 120 days
• 5 types exist: neutrophils, eosinophils, basophils, lymphocytes and monocytes
• They are classified into granulocytes and agranulocytes based on the presence of granules.

Granulocytes

• Granulocytes contain granules in their cytoplasm

Neutrophils

• Neutrophils measure 12-15 micrometers in diameter.
• They make up 54-60% of circulating white blood cells.
• Nucleus is lobed, typically exhibiting 3-5 lobes; called polymorphonuclear leukocytes (PMNs).
• Nucleoloids are linked together by thin nuclear extensions
• Granules stain a light pink and secrete ECM-degrading enzymes.
• Enzymes give neutrophils with their functional phagocytic capability
• Neutrophils are the first responders to infection sites through chemotaxis.
• Key players in the inflammatory response
• They are phagocytes that engulf bacterial cells and other small particles
• Neutrophils release chemokines that attract other leukocytes.

Eosinophils

• Eosinophils make up 1-2% of leukocytes.
• Roughly the same size as neutrophils
• Bilobed nucleus
• Contain major basic proteins (MBPs), peroxidases and enzymes and other toxins that act to kill helminths and parasitic worms
• Found at sites where chronic inflammation occurs such as the lungs and in the connective tissue of the intestinal lining; modulate inflammatory response.
• Triggered into action by allergies; release chemicals such as cytokines, lipid mediators, and chemokines.
• They originate as band cells

Basophils

Blood constitutes about 8% of body weight, containing erythrocytes, leucocytes, thrombocytes, and plasma. It transports gases, nutrients, and metabolic end products, ensuring substance exchange. The blood also regulates acid-base homeostasis through gas diffusion in the lungs.