William A Beresford MA, D Phil ©
Professor of Anatomy
Anatomy Department, West Virginia University, Morgantown, USA
Chapter l7 BLOOD
Blood might be classed as a specialized connective tissue because its cells are
mesodermal in origin and are separated by plasma.
Plasma | Red blood corpuscles/Erythrocytes (RBCs)
formed, visible |
elements - -| White blood cells/Leucocytes (WBCs)
(46% by volume) |
A MICROSCOPIC TECHNIQUES FOR BLOOD
l A blood drop is smeared across a slide and
2 stained with a Romanowsky-type combined stain - a neutral combination of
acidic (eosin) and basic (azure) stains.
3 In the stained smear, a differential count by eye or automated
counter gives the proportions of the different varieties of leucocyte.
4 Absolute counts of blood, diluted by a known amount, in a counting
chamber give the numbers of the formed elements: RBCs - about 5.2 million
mm3 (man), 4-5 million (woman); WBCs - 5000-9000 mm3
(healthy adult); platelets 200000-400000 mm3.
5 EM study of WBCs and platelets in the buffy coat after its
centrifugal separation from the RBCs.
6 Light and EM examination of cells in the lumens of blood vessels in
sections of imbedded tissues.
7 Phase-microscopy and videorecording of leucocytes alive in
fresh blood on a warmed slide under a sealed coverslip.
8 Tagged monoclonal antibodies to recognise cell-surface glycoproteins
characteristic for particular subtypes of blood cell. This approach allows a
specific cell population to be sorted for culture and study using
automated flow cytometry.
B ERYTHROCYTES (gas transport)
- Biconcave discs; close to 7.5 µm diameter in a smear.
- Comprise a flexible membrane enclosing haemoglobin
(iron-porphyrin-protein) in a closely packed state which, with
membrane-spectrin-actin interactions, maintains the RBC's optimal shape for
gas exchanges involving the haemoglobin.
- Osmolarity of the plasma affects the shape of an RBC. Hypertonic
solutions in vitro cause crenation and shrinkage; hypotonic, swelling and
- Globin is acidophilic, and RBCs stain orange with eosin.
- Mature RBCs have no nucleus, Golgi body, ER, ribosomes or mitochondria.
- RBCs do have glycolytic enzymes and substrates, and methaemoglobin
reductase and carbonic anhydrase for their respiratory function:
- (a) Oxygen binds to ferrous iron of haemoglobin (RBC) for transport:
air --> lungs -- > blood --> tissues
- (b) Carbon dioxide leaves bicarbonate of the plasma and
carbaminohaemoglobin (RBC) for transport:
tissues --> blood --> lungs --> air
- Reticulocyte/polychromatophil erythrocyte. An immature RBC, when
stained supravitally with cresyl blue, has a blue condensed network of
clumped, residual ribonucleoprotein not yet used for protein (globin)
- Life in circulation is estimated by 51Cr labelling at around
l20 days, then the RBC is sequestered in the spleen, liver or bone
marrow to be phagocytosed by macrophages. The spleen is most responsible.
- The volume of RBCs as a percentage of centrifuged whole blood - the
haematocrit - is a quick, crude measure of the O2-carrying
C LEUCOCYTES (defence)
These are true cells, divided according to the granularity of their
cytoplasm into two groups - granular and agranular.
l Granular leucocytes
All kinds appear round in a smear with a diameter l0-l4 µm.
l Polymorphonuclear neutrophil (neutrophil/PMN/polymorph, for
- (a) Nucleus has coarse, clumped, deeply staining chromatin, usually
in two or more lobes or segments connected by thin chromatin strands.
Unlobated band nuclei are in immature cells; older nuclei have several lobes.
- (b) Cytoplasm is granular from many, small, weakly staining
(neutrophil) granules of two kinds:
.. (i) non-specific azurophil granules that are lysosomes with destructive enzymes; and
.. (ii) numerous specific non-lysosomal granules holding a selectin-type
glycoprotein for adhesion to endothelium and ECM, and lysozyme, and other
- (c) This motile cell is attracted out of vessels into the tissues, where
it attacks bacteria and phagocytoses them and immune complexes. The attack
on bacteria is two-pronged:
.. (i) with a respiratory burst that generates free radicals; also
myeloperoxidase catalyzes the production of hypochlorous acid; and
.. (ii) by proteins, e.g., defensins, and bactericidal permeability-inducing
protein (BPI), that damage bacterial cell walls.
- (d) PMNs make up 55-65 per cent of the total leucocytes.
- (a) Nucleus is darkly staining and bilobed.
- (b) Cytoplasm has many large, eosinophil granules 0.5-l µm
diameter, and some smaller core-less granules.
- (c) Specific granules are a form of lysosome, which in EM have a
crystalline core and a fine granular region. Defensive basic/cationic
proteins, e.g., major basic protein, give the acidophil reaction.
The enzymes differ somewhat from the neutrophil's, e.g., generating
antimicrobial O2 metabolites differently.
- (d) Motile, and enter inflamed tissues, especially at sites of
allergies and parasitic infestations. They attack helminths
using the basic proteins and oxygen derivatives, and also may dampen mast
cell-dependent reactions, e.g., by phagocytosing mast-cell granules.
- (e) They comprise 2-3 per cent of leucocytes (but rising for (d)).
- (f) In EM, the large granules, like a skunk, have a dark lengthwise
central stripe, which helps in identifying the eosinophil.
2 Agranular leucocytes
- (a) Nucleus is bilobed and sometimes twisted, but palely staining and
often obscured by
- (b) basophilic cytoplasmic granules, containing sulphated
proteoglycans, heparin and the vasodilator, histamine.
- (c) Basophils are reluctant to enter CTs, where there are mast cells
holding the same materials. Thus, the function of basophils is in
doubt, but they bind IgE and participate in various hypersensitivities.
- (d) They are rare; 0.5 per cent of the leucocytes.
- (a) Small spheroid cell about 5-8 µm in diameter.
- (b) Large, spheroid, darkly staining nucleus leaves only a
- (c) narrow rim of cytoplasm with a few small azurophil granules.
- (d) Motile to enter CT and epithelial tissue, but is not phagocytic.
- (e) Larger lymphocytes up to l2 µm diameter, with more abundant
cytoplasm, may be seen in small numbers. The large granular lymphocyte
is the natural killer cell.
- (f) Unlike granular leucocytes, small lymphocytes can be stimulated to enlarge
and divide by antigens, cytokines, and some plant lectins.
- (g) The complex role of lymphocytes in immune defences is outlined
in Chapter l9 and Fig. 10.
- (h) Lymphocytes circulate in blood and lymph systems and migrate to CT
and mucous membranes. Some lymphocytes have a lifespan of months or years.
- (i) They amount to 25-35 per cent of the leucocytes.
- (a) Large, spheroid cell about 12-20 µm in diameter.
- (b) Nucleus has fine chromatin not densely stained, and is an indented
- (c) Golgi body and centrioles lie by the nuclear indentation.
- (d) Cytoplasm is abundant, with a few granules that are precursors
of many larger lysosomes seen in EM when the cell is actively
- (e) Motile, to leave the vessels after only a day or so to become the
phagocytic macrophages/histiocytes of CT, or other derivatives.
- (f) Macrophages/MØs spend months in CTs cooperating with lymphocytes
in defensive responses (Chapter l9). Macrophages, by releasing cytokines
after activation, coordinate inflammatory and defensive reactions.
- (g) They comprise 3-l0 per cent of the leucocytes.
D PLATELETS (clotting and vessel-sealing)
l Rounded or ovoid parts of cells, 2-5 µm diameter.
2 Consist of cytoplasm, organelles and inclusions, bounded by a cell membrane,
reflecting their formation as pseudopodia breaking away from extravascular
cells - megakaryocytes.
3 The dense central granulomere (organelle zone) has mitochondria,
dense bodies and alpha granules; the pale peripheral hyalomere
(sol/gel region) is cytoplasm deficient in organelles, except for contractile
filaments and a shape-giving ring of microtubules.
4 Platelets adhere to collagen, neutrophils and monocytes, and especially to
each other; this platelet aggregation/agglutination is used to seal
defects in blood-vessel walls.
5 Apart from several molecules for adhesion, the membrane supplies a
phospholipoprotein: one of many factors in the cascade causing blood
fibrinogen to form fibrin fibres in clotting. Platelets contract and cause a
compacting of the fibrin to which they adhere - clot retraction.
They also release from their granules several factors, e.g., serotonin
and cytokines, having vasoconstrictive and other actions.
E BLOOD IN BRIEF
Also available in colour as a series of
Liquid PLASMA + visible FORMED ELEMENTS - supplement, control, & extend
what goes on in the plasma
A GAS TRANSPORT - Erythrocytes/Red blood cells/RBCs |
B DEFENCE against the - Leucocytes/WBCs |___ Describe:
bad & the dead | appearances,
| roles, &
C DEFENCE for vessel integrity - Platelets | means
Description includes Measurements:
ABSOLUTE COUNT numbers/cubic mm RBCs - 6 X 106, Platelets - 2 X 105
WBCs - 6 X 103
DIFFERENTIAL COUNT individual % proportion of 5 kinds of leucocyte
HAEMATOCRIT Centrifuge tube
Plasma | |
Buffy | RBCs - 45% by volume
coat a measure of O2-carrying
ERYTHROCYTE <--- 7.5µm --->
Biconvave disc - high surface/volume ratio
Membrane with subplasmalemmal cytoskeleton: holds shape, but is
No organelles; no nucleus; haemoglobin binds O2
NEUTROPHIL/polymorphonuclear leucocyte/PMN [granular] 55% lobed nucleus
t phagocytosis of bacteria & debris m destructive acid hydrolases
a bacterial killing e generation of free radicals
s adhesion to & migration through a proteins, e.g., defensins
k venule & capillary walls* n adhesion molecules* to stick
s s to 'infected' endothelium
EOSINOPHIL [granular] 2%, bilobed nucleus, large granules
t m lysosomal enzymes } similar
a anti-parasites e oxygen-radical generation } to PMN's
s role in allergies a anti-parasite proteins, e.g. ECP
k n eosinophil cationic protein
s adhesion & migration* n cytokines
s adhesion molecules*
LYMPHOCYTE [agranular] 30% small cell, dense round nucleus
t attack foreign cells & microrganisms m immune responses
a attack foreign materials e cytokines
s instruct other cells - come, stay, a cell-surface contacts
k be quiet, be active, proliferate n
s proliferates itself s *
MONOCYTE [agranular] 8%, large cell, with indented nucleus
t general phagocytosis, e.g. of m becoming activated macrophage
a leftovers of damaged tissues e lysosomal enzymes
s coordination of defence and a cytokines
k repair n antigen presentation
s * a *
BASOPHIL [granular] ½% lobed, obscured nucleus
t back up mast cells' responses m histamine
a in inflammation e leukotrienes
s affects capillaries & speed & a prostaglandins
k intensity of immune responses m cytokines
s e.g. hypersensitivity s proteoglycans
PLATELETS small cast-off pieces of giant marrow cell - megakaryocyte
t stick together, and to endothelium m von Willebrand factor
a and vessel collagen e other clotting factors
s start blood clotting a 5-hydroxytryptamine
k control blood flow n thrombospondin
s s adhesion molecules
* adhesion to endothelium and the cell-specific means thereto
Note that some lymphocytes , e.g., NK cells, have azurophil lysosomal granules