Transcript Red Blood Cells

How does the micro and
nanostrure of blood influence
its rheology
Anna Kucaba-Piętal
(Rzeszów)
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Contents
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II.
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Blood as suspension
Plasma
Red Blood Cells
White Blood Cells
Platelets
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Rheological parameters of blood
Problems with theoretical modelling
Blood viscosity
Hematocrits’ effect on blood rheology
Blood viscoelasticity
Fahraeus–Lindquist Effect
Perspectives
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Blood
Blood is a liquid tissue.
Suspended in the plasma
are seven types of cells
and cell fragments
Microscopic view of blood
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Blood - functions
Blood performs two major functions:
1) transports through the body:
- oxygen and carbon dioxide
- food molecules (glucose, lipids, amino acids)
- ions (e.g., Na+, Ca2+, HCO3−)
- wastes (e.g., urea)
- hormones
- heat
2) defends the body against infections
and other foreign materials. All the
WBCs participate in these defenses.
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Blood - characteristics
• Adult ♂ contains 5-6L
• Adult ♀ contains 4-5L
• T is about 100.4 F
• 5 times as viscous as water
–pH ranges from 7.35 – 7.45 (slightly alkaline)
• Color ranges from scarlet (oxygenated blood) to
deep red (deoxygenated blood).
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Blood - components
Blood is made of four components:
Plasma (55%)
Platelets (0,17%)
White BC (0,1%)
Red BC (45%)
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Blood as suspension
Whole Blood
Plasma
Formed Elements
(46-63%)
(37-54%)
1. Water (92%)
1. Red Blood Cells (99.9%)
2. Plasma Proteins (7%)
2. Platelets
3. Other Solutes (1%)
3. White BC
(0,1%)
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Plasma
Plasma is the straw-colored liquid in
which the blood cells are suspended.
Composition of blood plasma:
Component
Water
Percent
~92
Proteins
Salts
Lipids
6–8
0.8
0.6
Glucose (blood sugar)
0.1
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Plasma - functions
Plasma transports materials needed by
cells and materials that must be removed
from cells:
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various ions (Na+, Ca2+, HCO3−, etc. )
glucose and traces of other sugars
amino acids
other organic acids
cholesterol and other lipids
hormones
urea and other wastes
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Plasma - components
Serum Proteins
Proteins make up 6–8% of the blood. They
are about equally divided between serum
albumin and a great variety of serum
globulins.
After blood is withdrawn from a vein and
allowed to clot, the clot slowly shrinks. As
it does so, a clear fluid called serum is
squeezed out. Thus:
Serum is blood plasma without fibrinogen
and other clotting factors.
The serum proteins can be separated by electrophoresis.
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Red Blood Cells (Erythrocytes)
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Red Blood Cells - characteristics
Most abundant blood cells
In ♂, 1µL of blood contains 4.5-6.3 million RBCs
In ♀, 1µL of blood contains 4.2-5.5 million RBCs
Contains the red pigment hemoglobin which
binds and transports O2 and CO2
Each RBC is a biconcave disc however while
moving it deforms itself adapting like a liquidfilled baloon to the shape of capilaries.
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Red Blood Cells
Red blood cells is a membrane
filled with a solution of hemoglobin
and various salts.
They manufacture hemoglobin until
it accounts for some 90% of the
dry weight of the cell.
The viscosity of the RBC interior
fluid is five to ten times greater
than of exterior fluid.
RBC in quiescent plasma tend to
form aggregates known as rouleax
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Hemoglobine
• Gas transporting
protein molecule that
makes up 95% of a
red cell
• Each chain contains a
single molecule of
heme, an ironcontaining pigment
• Each red cell has
about 270,000,000
iron-rich hemoglobin
molecules
Note the 2  chains
and 2 β chains. Notice
how each has an
associated heme
molecule with an iron
atom.
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Red Blood Cells - functions
•RBCs transport oxygen from the lungs to all of living
tissues of the body and carry away carbon dioxide.
•The RBC values can vary depending on such factors
as health and altitude.
•Peruvians living at 18,000 feet may have as many as
8.3 x 106 RBCs per µl.
•People who are anemic have deficency in red cells.
•RBC precursors mature in the bone marrow closely
attached to a macrophage.
•The nucleus is squeezed out of the cell and is
ingested by the macrophage.
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Hematocrit
• Percentage of whole blood occupied by
packed red blood cells
• Average in a ♂ is 46 (range of 40-54)
Average in a ♀ is 42 (range of 37-47)
• Determined by centrifuging a blood
sample so that all formed elements
come out of suspension
• Low Hct values may indicate anemia
whereas high values may indicate
polycythemia
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Lifecycle of an RBC
• Are produced continously in our
bone marrow from stem cells
• They can never divide
• After ≈120d, the RBC cell
membrane ruptures, or the
damage is detected by
phagocytic cells in the liver and
spleen
macrophage phagocytizing
multiple RBCs
• Most of the iron in their
hemoglobin is reclaimed for
reuse
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RBC flow through capilaries
White Blood Cells
White blood cells are clear
round cells that are bigger than
red blood cells.
White blood cells produce
proteins called antibodies that
help our bodies fight infections
caused by bacteria, viruses, and
foreign proteins.
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White Blood Cells
• Leukocytes
(leuko=white, cyte=cell)
• All contain nuclei and organelles
• Help defend the body against invasion by pathogens, and
they remove toxins, wastes, and abnormal/damaged cells
• A typical µL of blood contains 6000-9000 WBCs (1% volume)
• Most of the WBCs in the body at a given moment are in the
connective tissue proper or in organs of the lymphatic system
• Remain viable only last 18-36 hours before they also are
removed
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Types of WBC
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Can be classified based on
the appearance of
granules when viewed
under the light
microscope.
1.
Granulocytes_protect
body from infection:
• Basophils
• Eosinophils
• Neutrophils
2.
Agranulocytes are a part
of immune system
• Lymphocytes
• Monocytes
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2
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Types of WBC
Neutrophil
60% neutrophils
30% lymphocytes
6% monocytes
3% eosinophils
1% basophils
Eosinophil
Monocyte
Basophil
Lymphocyte
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Platelets
Platelets aren't really cells at
all; they are just fragments of
cells.
When we are injured, platelets
gather at the site of the injury
and stick to the edges of the
wound.
They release chemicals that help
start the process of blood
clotting so that bleeding will
stop.
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Platelets
• Flattened disk-like cell fragments that are about 1µm by
4µm (1/3 size of RBC).
• Continuously being replaced. Each platelet circulates for 912 days before being removed by splenic phagocytes.
• On average there are
350,000 platelets/µL
of blood.
• Produced in the bone
marrow. Large cells
called megakaryocytes
release fragments
(platelets) into the
circulation.
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Platelets - functions
Act as a participant in the vascular clotting
system. Platelets are sometimes referred to as
thrombocytes (thrombus=clot)
When blood vessels are cut or damaged, the loss of
blood from the system must be stopped before shock
and possible death occur. This is accomplished by
solidification of the blood, a process called
coagulation or clotting.
A blood clot consists of
•a plug of platelets enmeshed in a
•network of insoluble fibrin molecules.
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Part Two
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Why is it important to predict rheological
parameters of blood?
• To use it in diagnostics of clinical disorders
• To maintain nonbiological fluids that has
rheological properties comparble to blood
• Due to formulation blood flow equations
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Rheological parameters
• The viscosity and elasticity determine the
pressure required to produce blood flow.
• The heart pumps energy into the blood with
each beat. Portions of this energy are either
dissipated or stored as the blood cells
rearrange, orient and deform.
• Viscosity is an assessment of the rate of
energy dissipation due to cell deformation and
sliding.
• Elasticity is an assessment of the elastic
storage of energy primarily in the kinetic
deformability of the red blood cells.
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Blood viscosity I
• The blood viscosity is a function of the protein
concentration of the haematocrit (Ht), of the pH of plasma,
and of the temperature (this dependence is negligible in
physiological condition).
• Blood is considered as a Newtonian fluid for high values of
the gradient dv/dn (for the arterial flow) and
non-Newtonian for low values, because in these
circumstances the development of groups of 7-10
erythrocytes (rouleaux) is common; in this last case the
viscosity is no longer constant.
• Among the main factors from which the blood viscosity
depends, the haematocrit is quite effective. The
erythrocytes tend to reduce the speed gradient dv/dn. This
is the reason why the viscous term rises. Such increase is
reduced by the deformability of the erythrocytes (that
reduces the effect between the speeds of adjacent fluid
threads)
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Blood viscosity II
for Ht=45% the viscosity of blood is:
at 20ºC µ=3,45 cP
at 37ºC µ=2,72 cP
and that is it decreases with the temperature, even if in
the physiological field of variation of the temperature it
can be considered constant:
The viscosity of the plasma is µ=1,2 cP.
cP = 4 * 10-3 Pa * s
Plasma is a Newtonian fluid.
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Results
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Blood – viscosity
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Problems
• Blood is a concentrated
suspension of Red Blood
Cells; outside the range
of dilute suspension
• Particles change their shape in response to the
fluid forces
• The nature of RBC membrane and its deformation
stress/strain is much less established
• RBC tends to form agregates known as rouleaux
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Models
NEWTONIAN
FLUID
F
y
u(y)
NON-NEWTONIAN
FLUID
.
t = f(g)
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Blood – Casson model
.
g
mapp = t
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Results
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Hematocrit in blood circulation
Hmicro-microvessel hematocrit
Hsys- large blood vessels hematocrit
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Hematocrit’s effect on blood rheology
The influence of blood cell concentration
(hematocrit H)
on viscosity and viscoelasticity of blood
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Viscoelasticity
• The tendency of materials to respond to stress as if
they were a combination of elastic solids and
viscous fluids
• This property, possessed by all plastics to some
degree, dictates that while plastics have solid-like
characteristics such as elasticity, strength and form
stability
they also have liquid-like characteristics such as
flow depending on time, temperature, rate and
amount of loading
Blood Viscoelasticity I
• When the red cells are at
rest they tend to
aggregate
• In order for blood to flow
freely, the size of these
aggregates must be
reduced
• The forces that
disaggregate the cells
also produce elastic
deformation and
orientation of the cells,
causing elastic energy to
be stored in the cellular
microstructure of the
blood.
Parameters of human
blood measured
at a frequency near that
of the human pulse.
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Blood Viscoelasticity II
Modification of plasma such
as changes in osmotic
pressure, pH, concentration
of fibrinogen and other
plasma proteins, and
clinically introduced blood
volume expanders, can
have major effects on blood
viscoelasticity
The viscoelasticity for normal 0.46 H blood diluted to 0.31 H by
the addition of Dextran 40 (D), autogenous plasma (P), and
lactated Ringer's solution (L). Measurements were made at 2
40
Hz and 22 °C.
Blood Viscoelasticity III
• Variation in blood
viscoelasticity among
normals is very
small. So it can be
treated as a useful
clinical parameter.
• viscoelasticity of an
individual's blood
changes significantly
as the result of
disease or surgical
intervention
Cardiopulmonary bypass
surgery
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The Fahraeus Effect
In blood vessels with diameters less
than 500 mm both the hematocrit
and viscosity decrease with
diameter.
The hematocrit in the capillary is
greatly reduced because the red
cells speed up relative to the plasma
as they squeeze through the
capillary.
Since they must travel faster than
the plasma, there must be fewer of
them present to maintain the same
proportions of cells and plasma as
blood exits the capillary. This is the
so-called Fahraeus-Lindquist Effect.
µ
d
Viscosity (µ) of blood versus the
diameter (d) of the vessel (µm)
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Perspectives:
• Develop an understanding of how the
micro- and nano-structure of blood
influences its rheology
• Explore to use of rheological
parameters in diagnostics and
menagement of clinical disorders and
inoptimisation of blood processing
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