Human Blood Quiz

Blood - Histology

• Blood is a fluid connective tissue
• Functions include transporting oxygen (O2), carbon dioxide (CO2), nutrients, metabolites, hormones, and other regulatory substances
• Maintains homeostasis (buffering, thermoregulation, blood clotting)
• Transports humoral agents and immune system cells

Blood Collection for Clinical Testing

• Blood is commonly drawn from a vein in the arm directly into evacuated tubes
• Tubes typically hold 5 mL of blood, enough for many clinical chemistry tests
• Automated analyzers require small amounts (2-100 µL) per test
• Capillary blood collection is used when venous collection is difficult, e.g., in newborns using a heel stick
• Phlebotomy is the act of drawing blood, venipuncture specifically refers to drawing blood from a vein.

Fractionation of Blood Components

• Blood is fractionated into plasma and formed elements
• Plasma (55% of whole blood) is the least dense component
• Buffy coat: leukocytes and platelets (<1% of whole blood)
• Erythrocytes (45% of whole blood) are the most dense component
• Hematocrit (HCT) measures the volume of packed erythrocytes in %, a normal value is ~45%

Composition of Blood

• ~90% water
• ~8% protein
• ~1% inorganic salts, 0.5% lipids, 0.1% glucose, and other minor components

Blood Smear (May-Grünwald-Giemsa Staining)

• A blood smear allows for examination of blood cells
• Stained using May-Grünwald-Giemsa stain
• Blood Smear: preparation technique and overview photomicrographs are used

Counting Blood Cells

• Traditional method: Bürker chamber (haemocytometer)
• Modern method: Hematology Analyzer

Complete Blood Count (CBC)

• Quantitative blood count of formed elements.
• Erythrocytes (red blood cells, RBC): 4.5-5.5 T/L
• Thrombocytes (platelets, Thr): 0.15-0.3 T/L
• Leukocytes (white blood cells, WBC): 4-11 G/L

Erythrocyte (Red Blood Cell, RBC)

• Anucleate cells, typically missing cellular organelles
• Biconcave disc shape, maximizing cell surface area for gas exchange
• ~7.2 - 7.8 µm in diameter
• ~120-day lifespan
• Normal number: 4.5-5.5 T/L
• Contains hemoglobin, which carries oxygen throughout the body

Erythrocyte Membrane Structure

• Special cytoskeletal network and cell membrane provide flexible cell shapes allowing passage in small capillaries

Erythrocyte Function

• Transports oxygen and carbon dioxide

Blood Typing and Transfusion

• Erythrocyte membranes contain blood group antigens important in transfusions
• ABO blood grouping system is a common example for recognizing blood groups

Platelet (Thrombocyte)

• Diameter ~ 2-4 μm
• Cytoplasmic fragments of megakaryocytes
• Lifespan: 7-12 days
• Normal number in peripheral blood: 0.15-0.3 T/L
• Removal of aged forms: spleen, liver
• Granules contain bioactive substances like mitogen growth factor, etc.

Platelet Release Reaction

• Upon injury, platelets contact connective tissue (collagen) which triggers aggregation and release of granule content, initiating blood clotting

Thrombosis

• Blood clots (thrombus) forming in intact blood vessels, preventing proper blood flow
• Thrombi have two components: aggregated platelets and red blood cells forming a plug, and a mesh of cross-linked fibrin protein

### Leukocyte (White Blood Cell, WBC) Differential

• Percentage ration of different leukocyte types
• Neutrophil granulocytes (60-70%)
• Lymphocytes (20-40%)
• Monocytes (3-8%)
• Eosinophils granulocytes (2-4%)
• Basophils granulocytes (0.5%)

Leukocytes (WBC) Types

• Granulocytes:
  • Neutrophils
  • Eosinophils
  • Basophils
• Agranulocytes:
  • Lymphocytes (small and large)
  • Monocytes

Granulocytes (WBCs) Description

• Contains primary and secondary granules, with specific functions
• primary (azurophilic) granules are lysosomes (primarily digestive enzymes)
• secondary (specific) granules include different types of enzymes for specific granulocytes (enzymes for digestion and/or killing)

Leukocyte Extravasation

• White blood cells exit blood vessels into tissues, responding to signals of inflammation

Neutrophil Granulocyte Function

• Phagocytosis (engulfing of pathogens)
• Degranulation (releasing enzymes from granules)
• NETosis (releasing chromatin traps to capture pathogens)

Eosinophil Granulocyte

• Diameter: 12-14 µm
• Bi-lobed nucleus
• 8-12 day lifespan
• 2-4% in differential count
• Granules: contain lysosomal acid hydrolase, and specific crystalloid bodies - major basic protein, histaminase, collagenase, cathepsins
• Function in tissues: attacking parasitic infections

Basophil Granulocyte

• Diameter: 10-12 µm
• Less segmented nucleus, covered by basophilic granules
• 8-12 day lifespan
• ~0.5% in differential count
• Granules contain: lysosomal acid hydrolase, heparin, histamine, leukotrienes, interleukins.
• Function in tissues: dealing with allergic and inflammatory reactions

Monocyte

• Diameter: 15-20 µm
• Kidney-shaped nucleus
• Months-years lifespan
• ~3-8% in differential count
• Functions: Phagocytosis, professional antigen-presenting cell, cytokine production, differentiate to macrophages (MPS = Mononuclear Phagocytic System)

Small Lymphocyte

• Diameter: 5-7 µm
• Thin cytoplasm, containing azurophilic granules
• Years lifespan (longer for memory cells)
• 40-60% in differential count
• Two Major types: T-lymphocyte (thymus-dependent), B-lymphocyte (bursa-dependent)
• Functions: Cellular (T-cells) and humoral (B-cells) immunity

Large Granular Lymphocytes

• Diameter ~15 μm
• Numerous azurophilic, large granules
• ~5-10% of lymphocytes
• Functions: Natural Killer (NK) cells; recognizing and killing tumor and virus-infected cells. Innate immunity

Left Shift in Blood Count

• Indicates presence of immature leukocytes (e.g., myelocytes, metamyelocytes, band neutrophils) in the blood
• Suggests an inflammatory response or acute infection
• Increased release of immature neutrophils into the blood due to demand
• Driven by the variety of growth factors and cytokines - G-CSF, GM-CSF, IL-3, and IL-5

Literature

• Includes various books on Functional Histology and Concise Histology, along with scientific papers and internet resources