Meghan Barboza, PhD
Online Course
Key Characteristics
 Highly specialized
CT– lacks usual ECM
 Involved in
 Gas exchange
 Transport of nutrients,
waste materials and
cells of defense
Withdraw
blood
Blood Composition
 Consists of formed elements:
- erythrocyte/red blood
cells
- leukocyte/white blood
cells
- clotting cells
(thrombocyte) or
portions (platelets)
 And plasma (blood’s liquid
ECM) ~55% of blood volume
 Aqueous, protein rich solution
Centrifuge
Plasma
(55% of whole blood)
Buffy coat: leukocytes
and platelets
(<1% of whole blood)
Erythrocytes
(45% of whole blood)
Formed
elements
Histological Evaluation: Blood Smear
 Views formed elements
 Drop of blood (pretreated w/
anticoagulant) spread onto
glass slide, air-dried (&
methanol-preserved)
 Single layer contrastingly
stained:
 Wright stain (eosin and
methylene blue)

Erythrocytes pink, other cells
blue/purple
 Wright & Giemsa stain
 Adds reddish color to some
cells such as mast
cells/leukocyte chromatin
Formed Elements
• 7 total
– Erythrocytes
– Platelets
– WBCs
•
•
•
•
•
Neutrophil
Lymphocyte
Monocyte
Eosinophil
Basophil
Formed Elements
Monocyte
Platelets
Small
lymphocyte
Neutrophil
Eosinophil
Small
lymphocyte
Neutrophil
Erythrocyte
Young (band)
neutrophil
Monocyte
Large
lymphocyte
Basophil
Neutrophil
Erythrocyte (RBC)
 Most common element
 Mammals
 disc-shaped
 bi-concave sides creating
pale centers in smears
 Anucleated, absence of
organelles
Erythrocyte (RBC)
 Occasional erythrocytes
react basophically
 reticulocytes; still have
some organelles (seen esp
during increased
hemopoeisis)
Species Variation
 Nonmammals:
 typically elliptical-shaped
(elliptocytes)
 Nucleated
 round to oval,
heterochromatic, centrally
placed
Erythrocyte (RBC)
 Principal function:
 transport hemoglobin
 carrying and exchanging
O2 and CO2
Pseudopod
Granules
Platelets or
Thrombocytes
• Circulate for 5-6 days
• 40% stored in spleen
Open
canalicular
system
Mitochondria
(a)
2 µm
Platelets
Bloodflow
Endothelium
Proplatelets
Sinusoid of
bone marrow
RBC
WBC
Megakaryocyte
(b)
a: ©NIBSC/Science Photo Library/Science Source
Thrombocyte
 Mammals
 Platelets: cell
portions/fragments
 Platelets usually seen in
clusters – each platelet
w/ stained center
(granulomere) and
lightened periphery
(hyalomere)
Platelets/Thrombocytes Function
• Hemostasis—the cessation of bleeding
– Stopping potentially fatal leaks
(hemorrhaging)
• Three hemostatic mechanisms
– Vascular spasm
– Platelet plug formation
– Blood clotting (coagulation)
• Platelets play an important role in all three
Mcgraw-Hill. A&P. Saladin Figure 18.21
Thrombocyte
 Nonmammals – entire
cells (nucleated)
 Cells smaller than
rbcs, often clustered
 Nuclei round to oval,
surrounded by rim of
clear, ‘foamy’
cytoplasm (often
difficult to see)
Check your Understanding
 When looking at tissue, not blood smears,
sometimes blood vessels will have an
eosinophilic solid stained region, what is this?
 What is the benefit of RBC’s having nuclei?
Cost?
 Why do you think almost half of platelets are
stored and not circulating?
Formed Elements: Leukocytes (WBC)
Cells of defense:
 Granulocytes
 Neutrophils
(60-70%)
 Eosinophils (2-4%)
 Basophils (1% or less)
Formed Elements: Leukocytes (WBC)
 Cells of defense:
 Granulocytes
 Neutrophils (60-70%)
 Eosinophils (2-4%)
 Basophils (1% or less)
 Non-granulocytes
Lymphocytes (25-30%)
 Monocytes (5-10%)

Granulocyte: Neutrophil
 Most common
granulocyte in animals
 Segmented nucleus
(as all granulocytes)
 White ‘specs’ –
unstained granules
 Cytoplasm
chromophobic in most
species
 Can be mildly
eosinophilic in some
species (ruminants)
http://eclinpath.com/hematology/
morphologic-features/whiteblood-cells/normalleukocytes/normal-neutrophils-2/
Granulocyte: Heterophil
 In rabbits, guinea pigs
and var. wildlife species,
Neutrophils can be
strongly eosinophilic,
referred to as
heterophils
Granulocyte: Neutrophil
Copyright © The McGraw-Hill Companies, Inc.
 Function:
Splinter
 Defends against
microbial attack, esp.
bacteria
 Chemotactically drawn
to invaded sites
 Releases enzyme-filled
granules into ECM &
ingests foreign material
From
damaged
tissue
1
Inflammatory
chemicals
Bacteria
From
mast
cells
5
Phagocytosis
From
blood
4
Chemotaxis
Increased
permeability
Mast cells
 http://www.youtube.com/watch?v=J
nlULOjUhSQ
3
Neutrophils
Diapedesis
2
Margination
Blood capillary
or venule
Granulocyte: Eosinophil
 Segmented nucleus
 granules can mask
segmentation
 Granules strongly
eosinophilic w/ variations
in color (more orange than
red in ruminants and pigs)
 Granules evenly sized
(except canine)
Granulocyte: Eosinophil
 Relative granule sizes
vary w/ species
dog
cat
horse
Feline picture from:
http://eclinpath.com/category/hemato
logy/page/3/
Granulocyte: Eosinophil
 Granules - two types:
initially azurophilic (bone
marrow) w/ more
becoming “specific” in cell
maturation,
Granulocyte: Eosinophil
 Like those of neutrophils
 Have true lysosomes but
lack many bactericidal
substances
 Possess cationic proteins
 Suitable to combat
parasites (helminths)
 Also uses chemotaxis
 Can phagocytize but mostly
release granules to kill
Granulocyte: Basophil
 Least common
 Segmented nucleus
 Granules are basophilic in most
species; can be lavender (feline)
Granulocyte: Basophil
 Granules can be densely
packed (equine)diffuse
(canine)
 Granules - two types:
azurophilic and specific
granules (predominant)
 Specific granules similar to
those of mast cells:
Equine
Eosinophil
Eosinophil
 contain heparin, histamine
etc…
 slow degranulation (not w/
mast cell force)
 Facilitate directing
inflammatory activities
Canine
Non-Granulocyte: Monocyte
 Non-segmented nucleus
 Typically deeply indented
 Or lobed (bi-lobed, trilobed)
Non-Granulocyte: Monocyte
 Typically slightly larger
than other WBCs
 Lacks distinctly stained
granules
 Instead lightly
basophilically stained
cytoplasm with clear
vacuoles (lysosomes)
Non-Granulocyte: Monocyte
 Circulates in blood
stream for up to several
days
 If recruited to blood
vessel classified as a
macrophage
http://www.nature.com/nri/journal/v3/n1/box/nri978_BX1.html
Non-Granulocyte: Monocyte
 Elicited
monocyte/phage
engulfs & breakdowns
cellular and
extracellular foreign
substances:







Bacteria
Fungi
Protozoans
Viruses
Transformed cells
Dying cells
Cell debris
www.vetmed.vt.edu
Non-Granulocyte: Lymphocyte
 Non-segmented round
nucleus
 Sometimes w/ small
indentation (seen
ultrastructurally)
 Active lymphocytes have
more cytoplasm
Non-Granulocyte: Lymphocyte
 Numerous short
pseudopodial processes:
 ameoboid movement
 cellular interaction
Cancer cell
Non-Granulocyte: Lymphocyte
 Two types, T and B
 Cannot differentiate without IHC
 Functionally
 Close association with
monocyte/macrophage (Mo/Ma)
Non-Granulocyte: Lymphocyte
 Size varies for each sp:
divided into small, large,
& sometimes medium
categories
Lymphocyte vs Thrombocyte
(nonmammalian)
 Lymphocytes identical to
mammals – difficult to
distinguish from
thrombocytes when small
Check Your Understanding
What do monocytes become if they
enter the tissue?
What are basophils similar to in
function?
What is the difference between granules
and lysosomes?
What does a large lymphocyte indicate?
Questions