Day 3: Blood

Question 1

formed elements of blood

Answer 1

• platelets
• RBC
• WBC
  
  • granulocytes:
    
    • neutrophils
    • eosinophils
    • basophils
  • agranulocytes
    
    • lymphocytes
    • monocytes
    • others (stem cells, mast cell precursors, etc)

Question 2

serum

Answer 2

no clotting factors present

(clotted blood)

Question 3

plasma

Answer 3

• anticoagulant is present in the tube:
  
  • EDTA, heparin, sodium citrate
• mixture of fluids, proteins, and metabolites
• all proteins present, including fibrinogen
• unclotted blood remains at tube bottom

Question 4

neutrophil

Answer 4

• polymorphonuclear neutrophils (PMNs)
• most numerous of WBC & granulocytes (60-75% of nucleated cells)
• 3-5 lobes, 9-15 um in diameter
• form first line of defense against infection
• 3 different granules
  
  • tertiary granules
    
    • facilitate migration through tissue
• Phagocytosis: bacteria engulfed, internalized in phagosome, pH reduced
  
  • specific granules
    
    • kill bacteria with enzymes & reactive oxygen
  • azurophilic granules (all granulocytes)
    
    • lysosomal enzymes digest bacteria
• neutrophils secrete interleukin-1 (IL-1), a pyrogen (fever-causing)
  
  • dies, semidigested material and tissue fluid form pus
  • condensed chromatin may continue to trap bacteria extracellularly
• born in marrow, marginal pool stored in marrow (or bld vessels?) (mature or precursor band cells)
  
  • the peripheral blood neutrophil count measures only the circulating peripheral blood pool, not the marginal pool
• terminally differentiated cells, die by apoptosis after 1-4 days in connective tissue

Question 5

band cell

Answer 5

• immature neutrophil
• non-segmented U-shaped nucleus
• normally present in peripheral blood in small quantities, but over 2% (of circulating leukocytes) can indicate pathology
• released from the bone marrow in response to stress (infection)

Question 6

eosinophils

Answer 6

• 1-3% of WBC
• respond to parasitic infections, take part in hypersensitivity and allergic reactions
• 2 lobed nucleus, eosinophilic/acidophilic (pink) granules
  
  • specific granules are anti-inflammatory, anti-helminthic
• terminally differentiated; 2 week lifespan

Question 7

basophils

Answer 7

• least frequently encountered granulocyte in the blood (<1%)
• specific granules (basophilic) stain dark blue to black
  
  • contain histamine (inflammatory responses, capillary dilation + permeability), heparin (prevent coagulation), serotonin, and other mediators of hypersensitivity + allergic reactions
• have a bilobed nucleus
• basophil responsible for vascular disturbances (widespread vasodilation associated with hypersensitivity and anaphylaxis)
• considered to live + function primarily in blood stream, but have been recently discovered in connective tissue
  
  • primary function is in the blood

Question 8

lymphocytes

Answer 8

• 20-30% of WBCs, majority of agranulocytes
• predominantly small cells (6-10 um; larger ones 10-18 um)
  
  • in smaller cells, nucleus occupies most of cell
  • round to oval nucleus of homogenous heterochromatic condensed chromatin (dark/solid looking)
• primary mediators of immunity; only cells that circulate into and out of the peripheral blood, patrolling and scouting for antigenic stimlation
• 2 primary populations: memory and effector cells, natural killer cells are a 3rd class
  
  • effectors
    
    • B cells: humoral (antibody) immunity
      
      • response to extracellular pathogen
    • T cells (over 75% of circulating lymphocytes): cell-mediated immunity
      
      • response to virus (intracellular pathogen)
• lifespan of several months to years
• predominantly small cells (6-10 um; larger ones 10-18 um)
  
  • in smaller cells, nucleus occupies most of cell
  • homogenous condensed chromatin (dark/solid)

Question 9

monocytes

Answer 9

• largest of leukocytes (12-20 um)
• nucleus is eccentrically located + indented to varying degrees (sometimes kidney shaped, never lobed)
• nuclear chromatin is more dispersed than lymphocyte (nucleus not as small / darkly stained)
• cytoplasm tends to be gray rather than bright blue of lymphocytes; contains small vacuoles and irregular inclusions
• 3-8% of WBC
• born in marrow; released to circulation; “reserve pool” stored in spleen
• becomes macrophage when enters connective tissue

Question 10

erythrocytes

Answer 10

• circular, pale center reflecting its biconcave shape
  
  • eosinophilic
  • biconcave shape allows it to deform without stretching the cell membrane
• make up 99% of cells in a blood smear
• function to protect hemoglobin from denaturation and degradation
• functional for 120 days
  
  • after, they display oligosaccharides in membrane that targets them for destruction by macrophages in spleen (mostly) and liver)
• reticulocytes : 2% of circulating RBCs

Question 11

granuloctes

Answer 11

cells with a segmented nucleus that also contain cell-specific granules (membrane-bound inclusions) within their cytoplasm

Question 12

CBC components

Answer 12

• determination of hemoglobin
  
  • measured colorimetrically after a treatment with dilute HCl
• hematocrit (% RBC)
• WBC counter (#/uL)
• WBC differential count (% of each type)
• reticulocyte count
• estimated platelet count

Question 13

leukocytes

Answer 13

• all contain azurophilic (primary, nonspecific) granules, which are small lysosomes containing acid hydrolases
• granulocytes (neutrophils, basophils, eosinophils) have specific granules

Question 14

diapedesis

Answer 14

• leave blood vessels by passing between endothelial cells of postcapillary venules and capillaries
• Involves recognition molecules of the WBC surface interacting with ligands (E-selectin and P-selectin) on endothelial cells

1. First phase: leukocytes are loosely tethered to endothelial cells, slowing their rate of flow as they roll along the endothelial cell surface
2. Second phase: integrins on the blood cell surface tightly bind to adhesion molecules on endothelial cell luminal surface
3. Aided by chemokines at injury site, the leukocyte extends a pseudopod to + through the interendothelial junction and migrates into surrounding connective tissue

Question 15

platelets

(thrombocytes)

Answer 15

• cytoplasmic fragments of large megakaryocytes that reside in the bone marrow
• smallest cellular elements of the blood
• have a lifespan of about 10 days
• biconvex (non-nucleated cell fragment has 2 parts:
  
  • outer hyalomere (structural zone)
    
    • ​contains actin + myosin
    • two tubular systems: surface-opening and dense tubular system
    • surface is glycocalyx rich in glycosaminoglycans (integral in platelet adhension)
  • inner granulomere (organelle zone; has basic + acidic granules)
    
    • ​alpha granules (fibrinogen + coagulation factors)
    • delta granules (factors that promote the clotting cascade)
    • lambda granules (lysosomes)
  • membrane zone (open canalicular system)
    
    • mediates degranulation

Question 16

Factors that affect RBC shape

Question 17

red marrow

Answer 17

• hematopoietically active, predominant until age 4
  
  • adipocytes (yellow marrow) replace hematopoietic islands when hematopoietic activity declines
• in adults: red marrow is confined to ends of long bones + middle of some flat bones (ie, iliac crest)

Question 18

stroma

(supporting tissue of bone marrow)

Answer 18

• adipose tissue
• reticular cells
• connective tissue
• blood supply

Question 19

mesenchymal + hematopoietic-derived cells

in bone marrow stroma

Answer 19

• Mesenchymal-derived cells
  
  • osteoblasts
  • adipocytes
  • fibroblasts
  • endothelial cells
• Hematopoietic-derived cells
  
  • osteoclasts
  • macrophages (monocytes)

Question 20

cells are capable of differentiating into the entire family of cells that make up a given tissue, and also of self-renewal

Answer 20

stem cell

Question 21

cells that are restricted in their ability to generate lineages (give rise to cells that are committed to one cell line), but still capable of renewing themselves

Answer 21

progenitors

Question 22

a cell that can only divide into a further differentiated cell, and cannot renew itself

Answer 22

precursor cell

the first precursor cell in each lineage is a “blast”

• proerythroblasts: ultimately form erythrocytes
• myeloblasts: ultimately form granulocytes

Question 23

control of blood cell formation

Answer 23

mitosis and differentiation of specific lineages of hematopoietic cells are influenced by many substances, including:

• colony-stimulating factors (CSFs)
• interleukins
• erythropoietin (for RBCs)
• thrombopoietin (for platelets)

collectively, these classes of molecules are subsets of compounds termed cytokines.