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Blood Cells Simon Hunt Dunn School of Pathology OR Images from Wheater’s Functional Histology, 4 th edn

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blood cells

Blood Cells

Simon Hunt

Dunn School of Pathology


Images from Wheater’s Functional Histology, 4th edn

Some electron micrographs from the collection of the late Drs Poole and French, Dunn School

purposes of this presentation
Purposes of This Presentation
  • How structure relates to function in erythrocytes (red blood cells)
    • To the level of syllabus section 5.4.1
    • As living and dying ultra-specialised (“differentiated”) cells
  • Ditto for leukocytes (white blood cells)
    • To the level of syllabus section 5.4.2
    • A functional “Who’s Who?”
  • How we find out about the physiological properties of blood cells
    • Illustrated by some disease conditions

Blood Cells

erythrocytes greek red hollows


Erythrocytes – Greek: “Red Hollows”
  • Pink stain – eosin, not haem
    • Haemoglobin is a basic protein
    • Binds acid dyes (e.g. eosin)
  • Scanning e-m
    • Always black & white

Blood Cells

blood cells computer enhanced
Blood cells, computer-enhanced

© Dennis Kunkel Microscopy, Inc

Blood Cells

erythrocytes can form rouleau pl rouleaux
Erythrocytes can form Rouleau (pl. Rouleaux)
  • Like a stack of coins
    • Only when blood flow is slow

Blood Cells

rouleaux 2
Rouleaux 2
  • by fluorescence
    • Red shows DNA stain of leukocytes
    • Shows that rbc have no nuclei

Blood Cells

erythrocyte shape

(a):discocyte, (b) stomatocyte and (c) echinocyte

from Harriet Gershon

Erythrocyte shape
  • Anucleate (no nucleus)
    • also, no mitochondria
  • Shape depends on water content
    • Osmotic effects of solutes, especially ions
  • Shape maintained by cytoskeleton
    • Spectrin, ankyrin, & other membrane proteins

Blood Cells

advantages of being anucleate
Advantages of being anucleate
  • Better surface-volume ratio
    • About 25% greater than if an equivalent sphere
    • Improves gas exchange
  • Improves deformability
    • To fit through capillaries
      • diameter of true capillaries is only 5-10 mm, often less
  • Less work for heart as a pump
    • Pumps approximately 3 kg of erythrocytes per minute
    • 40% of total mass would be nucleus
    • Saves pumping 1 to 1.5 tons per day

Blood Cells

disadvantages of being anucleate
Disadvantages of being anucleate
  • No further protein synthesis or repair
    • Finite cell lifespan
      • 120 days on average
    • Requires vast new replacement cell production
      • Red blood cell production = “erythropoiesis”
  • Equally true for blood platelets
      • Platelet production = “thrombopoiesis”

Blood Cells

consequences of lacking mitochondria
Consequences of lacking mitochondria
  • Have to survive on anaerobic metabolism (glycolysis)
    • Energy needs not great, mainly ion pumps
    • Depends solely on blood glucose for energy supply
    • the glycolytic intermediate, 2,3-bisphosphoglycerate (2,3-BPG), is produced by an erythrocyte enzyme
      • BPG shifts dissociation curve to unload O2 from HbO2

Blood Cells

erythrocyte c ontents 1
ErythrocyteContents 1
  • Haemoglobin ~750 gm per adult body
    • Globin protein, alpha2beta2,~650 million molecules per cell
    • Haem prosthetic group
    • One Fe2+ per haem, ~2.2 gm per whole body
      • About 2/3 of all body iron
      • Must not oxidise to Fe3+ ( “methaemoglobin”)
        • cell needs reducing conditions
  • Functions in O2 and CO2 transport
    • Dr Dorrington’s lectures later this term

Blood Cells

erythrocyte c ontents 2
ErythrocyteContents 2
  • Glucose metabolising enzymes
    • Anaerobic glycolysis (Embden-Meyerhof Pathway)
    • Pentose Phosphate shunt
      • Uses G6PDH, Glucose-6-Phosphate Dehydrogenase, an X-linked enzyme
      • generates NADPH, slows build-up of oxidised proteins associated with erythrocyte ageing
      • thus maintains Glutathione, a Cysteine-containing tripeptide, in the reduced state

G6PDH deficiency is revealed by a serious haemolytic crisis when broad beans or the (now-obsolete) anti-malarial Pamaquine are ingested

Blood Cells

erythrocyte c ontents 3

[Na+] = 6 mM

[K+] = ~100 mM

ErythrocyteContents 3
  • Ions, especially K+
    • Maintained by membrane-associated ATP-dependent Na+-K+ ion exchanger

PLASMA concns:

[Na+] = 140 mM

[K+] = 3.5 - 5 mM

Blood Cells

membrane protein functions
Membrane protein functions
  • Cytoskeletal proteins maintain shape
    • spectrin, ankyrin, Band III
  • Channels, pores or pumps
    • Cations, anions, water, glucose
  • Glyoproteins & glycolipids: display extracellular carbohydrate
    • glycophorins maintain net negative charge
    • blood group substances
  • Regulatory proteins
    • complement-absorbing components
      • anti-inflammatory action

Blood Cells

osmotic effects
Osmotic effects



Blood Cells

hypotonic haemolysis

Hypotonic haemolysis
  • “Hypo-” means lower than normal
    • i.e. solute concentration outside is less than inside cell
      • allow for ions; count all osmotically active particles; use “Osmolarity”
    • water potential outside cell > intracellular
  • Cell membrane semi-permeable
    • Water permeates via “Aquaporin” proteins
    • >250 times cell volume crosses membrane per second

Blood Cells

osmotic fragility test


Diseased - fragile

Osmotic fragility test

Blood Cells

erythrocytes can deform

DHAG e-m#328

Erythrocytes can deform
  • To squeeze through arterioles or capillaries
  • Tend to keep to central axis of vessel
    • Plasma-rich at circumference
  • Blood is “visco-elastic”
    • Not easy to find good artificial substitutes

NB rbc are electron-dense – why?

Blood Cells

rheology the flow properties of blood suspensions
Rheology - the flow properties of blood suspensions
  • The Fåhraeus-Lindqvist effect(small-diameter phenomenon)
    • rbc concentration is lower near the vessel wall and higher in the centre
      • hence vessel haematocrit decreases in the smaller branches of the vasculature i.e. more fluid and fewer cells in capillaries
      • hence get misleading blood cell concentrations if capillaries are sampled

Blood Cells

anomalous viscosity of blood
Anomalous viscosity of blood
  • Viscosity of blood increases with decreased velocity
    • Blood flow is low in small vessels (1 mm/sec) –
      • viscosity can increase 10 times just because of slow velocity
      • due to adherence of RBCs to each other (form rouleaux) and to vessel walls
      • shear forces no longer enough to deform RBC, so they appear more rigid
  • Effect is even more noticeable
      • if membrane more rigid, e.g. Spectrin defect, or becomes crenated
      • in aged erythrocytes
      • if there are inclusions inside cells, e.g. sickled cells
      • if rbs are enlarged osmotically
  • In what circumstances might this matter clinically?

Blood Cells

hereditary spherocytosis 1

Spectrin defect

Ankyrin defect

Band III defect

Spectrin deficiency

Decreased rbc deformability, osmotic fragility

Splenic conditioning: further loss of membrane surface area

Rbc entrapment in splenic cords

Macrophage removal of severely abnormal rbc

Hereditary spherocytosis 1

Loss of membrane surface area  micro-spherocytosis

Blood Cells

summary erythrocytes
Summary - erythrocytes
  • Vast numbers, steady turnover
    • No nucleus, no mitochondria
    • Glucose essential as energy source
      • To maintain reducing conditions, and for ion pumps
    • Cells become “aged” as oxidation products build up
  • Lipid bilayer membrane, with attached & inserted glycoproteins
    • Cytoskeleton
      • Biconcave disc, but deformable
      • Flexibility important for proper plasma flow
    • Semi-permeable properties  lysis if not in isotonic medium
  • Will examine erythropoiesis in next lecture

Blood Cells

neutrophils 1
Neutrophils 1

Blood Cells

neutrophils 2
Neutrophils 2
  • The most abundant leukocyte in blood
  • Filled with granules
    • Lysosomes  fuse with ingested phagosome
    • Secrete toxic chemicals
  • Very active migration
    • Sensitive to chemotactic factors which attract them to infection site

Blood Cells

neutrophils functions as effector cells
Neutrophils: functions as effector cells
  • Synonyms
    • Polymorphonuclear leukocytes, = PMNs or “Polys”
  • Don’t stain strongly with either eosin or basic dyes
  • Raised numbers (“neutrophilia” during acute bacterial infections
    • Increased mobilisation from extensive reserves
    • Increased production from progenitors
  • Adhere to vessel walls and transmigrate to areas of infection in tissues (acute inflammation)
    • Engulf bacteria, kill rapidly with very toxic molecules (incl strong oxidisers comparable to bleach)
    • Collateral damage to host cells, plus dead bugs,  pus
  • Defects in adhesion molecules, or in killing mechanism,  serious pyogenic (pus-forming) infections

Blood Cells

  • Generally larger than neutrophils
  • Stain orange-pink with eosin
    • Contain abundant basic protein
  • Elevated levels in
    • tropical parasite infections
      • defence against single-celled and multicellular parasites
    • Chronic allergic conditions
      • May reduce hypersensitivity via histaminase

Blood Cells

eosinophil e m
Eosinophil e-m
  • Large ovoid granules, very electron dense
  • Actively phagocytic
  • Passively adsorb certain kinds of antibodies
    • helps them recognise targets
  • Can exocytose (spit out) toxic substances
    • Different chemicals from neutrophils

Blood Cells

  • Least common leukocyte
  • Stains with basic dyes
  • Precursor of mast cells in tissues
    • Mast cells release histamine etc in allergies

Blood Cells

  • ~5 – 10% of wbcs
  • Nucleus often kidney-shaped
  • No obvious granules
  • Precursor of macrophages in tissues
    • Macro = “big”; phage = “eat”

Blood Cells

  • Next most common after neutrophils
  • No obvious granules
    • Except for Natural Killer subset
  • Subsets
    • T, B

Blood Cells


Autoradiograph by J.L. Gowans

  • Vary in size
    • Small = very dormant, out of cycle, long-lived
      • After stimulation  memory cells
    • Large = rapidly dividing
      • Incorporate DNA synthesis precursors
      • “Lymphoblasts”
      • Intermediates before full maturation
        • To antibody-forming cells in tissues (very rare in blood)
        • To cytotoxic T lymphocytes
  • These are from lymph (hence no rbc)

Blood Cells

lymphocytes patrol continuously
Lymphocytes patrol continuously
  • To connect functionally all the dispersed lymphoid tissues
    • Blood  lymph  blood …….
  • Leave blood at special endothelium only on certain venules, within lymph nodes, tonsils & other lymphoid organs
  • Ensures rare clones with a given specificity have a good chance of encountering their specific stimulus

Blood Cells

lymphocytes emigrate via high endothelial venules
Lymphocytes emigrate via High Endothelial Venules
  • To seek antigens outside the blood stream, which have been filtered, processed and presented by cells in lymphoid tissues

Blood Cells

summary of leukocytes 1
Summary of leukocytes 1
  • Granulocytes include:
    • Neutrophils
      • Move promptly into tissues to deal with any noxious event harmful to the body: infection, tissue damage and so on
      • Engulf, kill and digest invaders  inflammation and perhaps pus
    • Eosinophils
      • Defence against some parasites, in collaboration with antibodies
      • May diminish some immediate-type hypersensitivity reactions
    • Basophils
      • Move into tissues to become mast cells

Blood Cells

summary of leukocytes 2
Summary of leukocytes 2
  • Monocytes
    • Precursors of tissue macrophages, slower to act than neutrophils
  • Lymphocytes
    • Each call has one specificity for antigen, therefore needs to continuously patrol to meet up with the right molecule
      • perpetual motion into and out of vasculature - “lymphocyte recirculation”

Blood Cells

reading and online materials
Reading and online materials
  • Wheater’s Functional Histology, 4th edn, chapter 3
    • Leicester, immune system cells only, not complete haematology
    • Florida, in-depth, with self-test Qs at:
    • (textbook account, excellent hyperlinked glossary)
    • (proper haematologist’s site)

Blood Cells