Human Blood and Its Functions Quiz

Blood Composition and Functions

• Blood is the major circulating fluid in the human body
• Hematology is the study of blood
• Blood is a fluid connective tissue derived from mesoderm
• Blood is bright red, slightly alkaline (pH 7.4), salty, and heavier than water
• An adult has about 5 liters of blood, which constitutes about 8% of total body weight

Blood Constituents

• Blood is divided into two main components: cellular and non-cellular components
• Cellular components include red blood cells (RBCs), white blood cells (WBCs), and platelets
• Non-cellular components include plasma

Cellular Components

• Red Blood Cells (RBCs):
  • Circular, biconcave, and enucleated cells
  • Transport oxygen from the lungs to tissues using hemoglobin
  • In healthy men, about 5,200,000 RBCs per cubic millimeter of blood
  • In healthy women, about 4,700,000 RBCs per cubic millimeter of blood
• White Blood Cells (WBCs):
  • Mobile units of the body's protective system
  • Travel to areas of infection or inflammation
  • Types include granulocytes (e.g., neutrophils, eosinophils, basophils) and agranulocytes (e.g., monocytes, lymphocytes, plasma cells)
  • Granulocytes and monocytes are formed in the bone marrow
  • Lymphocytes, and plasma cells are produced in various lymphogenous tissues (e.g., lymph glands, spleen, thymus).
  • Granulocytes circulate in the blood for 4-8 hours and another 4-5 days in tissues, (shorter life span if infection).
  • Monocytes circulate in the blood 10-20 hours and swell to be macrophages in tissues, (longer life span).
  • Lymphocytes have a lifespan of weeks or months.
  • Platelets are replaced about once every 10 days.
  • Neutrophils and tissue macrophages attack and destroy invading bacteria, viruses, and other injurious agents.
  • Concentrations of WBCs in an adult: neutrophils (62%), eosinophils (2.3%), basophils (0.4%), monocytes (5.3%), and lymphocytes (30%)
• Platelets:
  • Small fragments of bone marrow cells
  • Involved in vasoconstriction, forming temporary platelet plugs to stop bleeding, secreting procoagulants to promote clotting, digesting and destroying bacteria, secreting chemicals to attract neutrophils and monocytes to the site of inflammation, and secreting growth factor to maintain blood vessel lining.

Non-Cellular Component (Plasma)

• Straw-colored, slightly alkaline, viscous fluid
• Primarily composed of water (90-92%)
• Contains proteins (albumin, globulin, fibrinogen, prothrombin), nutrients (glucose, amino acids, glycerols), nitrogenous wastes (urea, uric acid), gases (O2, CO2, nitrogen), and inorganic substances (bicarbonates, chlorides, phosphates, sulfates, Na, K, Ca, Mg ions).

Phagocytosis by Neutrophils and Macrophages

• Neutrophils and macrophages employ phagocytosis to ingest foreign particles.
• First, neutrophils attach to the particle; then they extend pseudopodia around it, and form a chamber to contain the phagocytized particle.
• Next, this chamber invaginates to form a free-floating phagocytic vesicle or phagosome.
• A single neutrophil engulfs 3-20 bacteria; neutrophils then inactivate and die.
• Macrophages are much more powerful phagocytes and can digest larger particles, even whole red blood cells.
• After digesting particles, macrophages extrude residual products and often survive and function for months.

Digestion of Phagocytized Particles

• Lysosomes and other cytoplasmic granules (in neutrophils or macrophages) release digestive enzymes and bactericidal agents.
• The digestive vesicle now becomes a digestive vesicle where digestion of the phagocytized particle beings immediately.
• Macrophages also contain Lipases that digest thick lipid membranes of bacteria such as tuberculosis bacillus.
• Neutrophils and macrophages have bactericidal agents that kill most bacteria even when their lysosomal enzymes don't digest them.

Role of Macrophages and Neutrophils in Inflammation

• Tissue injury release substances that cause secondary changes in tissue, increasing local blood flow and permeability of capillaries.
• Resulting fluid leakage causes interstitial swelling, tissue spaces are blocked by fibrinogen clots, delaying spread of bacteria and toxic products.
• The intensity is proportional to the degree of tissue injury.
• Macrophages, the first line of defense, begin phagocytosis within minutes after inflammation.
• Many sessile macrophages break free and become mobile in response to chemotaxis.
• Neutrophils arrive as a second line during the first hour.
• Large numbers of neutrophils invade the inflamed area as a result of tissue products that attract them. They cause chemotaxis.
• Within a few hrs, many neutrophils increase by about four to five-fold.
• Inflammatory products are transported to the bone marrow, where neutrophils are mobilized and move into the bloodstream.
• A second wave of macrophages arrive, monocytes from the blood enlarge to become macrophages.
• Macrophage buildup is slower than for neutrophils.

Pus Formation

• When neutrophils and macrophages engulf large numbers of bacteria and necrotic tissue, essentially all of the neutrophils and many macrophages die.
• The combination of dead neutrophils, dead macrophages, portions of necrotic tissue, and tissue fluid is called pus.
• If infection is suppressed, the cells in the pus autolyze (themselves digest) over several days and are absorbed, so tissue damage can reverse

Other Blood Cells

• Eosinophils: High numbers in parasitic infections; attach to parasites to release substances (e.g., enzymes, oxygen, proteins) that kill parasites
• Basophils: Circulating mast cells, release heparin (anti-coagulation), histamine, bradykinin, serotonin (inflammation) that support allergic reactions. IgE antibodies become attached to mast cells and basophils to release histamine, bradykinin, serotonin, and heparin.

Blood Platelets

• Platelets are small fragments of bone marrow cells involved in vasoconstriction, platelet plug formation, blood clotting, digesting bacteria, attracting neutrophils, and monocytes to the inflamed area.

Macrophage Systems

• Monocyte-Macrophage System/Reticuloendothelial System: A system of monocytes that enter tissues, become macrophages, remain attached for weeks/months fulfilling local protective functions.
• Other tissue macrophages, such as alveolar macrophages, Kupffer cells, and macrophages found in the spleen and bone marrow, also perform various phagocytic and protective roles (alveolar macrophages in the lung, Kupffer in the liver, spleen/bone marrow).
• In the lymph nodes, macrophages in the lymph sinuses trap and phagocytize foreign particles entering the node.
• Macrophages in the spleen/bone marrow, are entrapped by the reticular meshwork of the organs

Factors Involved in Feedback Control

• Factors including TNF, IL-1, granulocyte-monocyte colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), and monocyte colony-stimulating factor (M-CSF).

Test your knowledge on various aspects of human blood, including its composition, functions, and the types of cells involved in its processes. This quiz covers essential topics such as oxygen transport, temperature regulation, and immune responses. Perfect for biology students or anyone interested in human physiology!