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Introduction to Blood
Learning Objectives
The student should be able to :
1. Define what is hematology?
2. Know what blood is & its development.
3. Describe the composition of blood.
4. Ought to know the formed elements of blood.
5. What is plasma?
6. Must know the characteristics of different types of blood
cells.
7. Explain the cell morphology.
8. Must make out comparison of RBCs, WBCs and Platelets.
9. Must be familiar with functions of blood.
10. Make out what is inflammation and its types.
11. Explain clinical signs of inflammation.
12. Clarify the cellular events of inflammation.
13. Identify key characteristics of immune responses.
14. Compare innate and specific immunity.
15. Explain how immunity is acquired.
Lecture Outline
Introduction to Blood
What is hematology?
"Hematology" comes from the Greek words haima, meaning blood, and
logos, meaning study or science. So, hematology is the science of
blood.
Blood :
 Blood is a complex fluid tissue. It circulates in a closed system
of blood vessels and heart.

The normal adult total circulatory blood volume is about 8% of
the total body weight (5600 ml in 70 kg man).
The Blood Throughout Life :
 First blood cells develop with the earliest blood vessels.
 Mesenchyme cells cluster into blood islands.
 Late in the second month
 Liver and spleen take over blood formation.
 Bone marrow becomes major hematopoietic organ at month 7.
COMPOSITION OF BLOOD :
 Blood is the body’s only fluid tissue
 It is composed of liquid plasma and formed elements
 Formed elements include:
 Erythrocytes, or red blood cells (RBCs)
 Leukocytes, or white blood cells (WBCs)
 Platelets
 Hematocrit – the percentage of RBCs out of the total blood
volume
A centrifuge separates blood into two components.
Formed Elements:
 Erythrocytes, leukocytes, and platelets make up the formed
elements
 Only WBCs are complete cells
 RBCs have no nuclei or organelles, and platelets are just
cell fragments
 Most formed elements survive in the bloodstream for only a few
days
 Most blood cells do not divide but are renewed by cells in bone
marrow
Blood plasma :
 Blood plasma contains over 100 solutes, including:
 Proteins – albumin, globulins, clotting proteins, and
others
 Lactic acid, urea, creatinine
 Organic nutrients – glucose, carbohydrates, amino acids
 Electrolytes – sodium, potassium, calcium, chloride,
bicarbonate
 Respiratory gases – oxygen and carbon
Characteristics of different types of blood cells :
 RBCs: contain red haemoglobin which enables RBCs to carry
oxygen and some carbon dioxide.
 WBCs: lymphocytes & phagocytes, protect us from diseases.
 Platelets: broken cell fragments, help in blood clotting.
Erythrocytes :
 7-8 m diameter
 Biconcave disc shape
 Inc. surface area
 Inc. efficiency for diffusion of O2 & CO2
 Structure
 Plasma membrane
 Cytoplasm
 Hemoglobin
 Binds O2 & CO2
 No nucleus or organelles
 Immature version has nucleus and is called a reticulocyte.
 Flexible
 Elastic
 100-120 day life span
 Originate in bone marrow.
Platelet Count :
 Normal count is 140,000 to 440,000/mm3
 Life span of about 10 days
 Low platelet counts (thrombocytopenia) cause excessive bleeding
 Thrombycytopenia is common with the use of heparin, DIC,
bone marrow disease, liver failure and sepsis.
Cell Morhphology
The Neutrophils:
 Segmented neutrophil (40-70% of WBCs)
 Life span of about 10 days
 Moves from bone marrow to blood to tissues
 Mature more quickly under stressful conditions
 Primary defense for bacterial infections.
The Basophils :
 Mature basophil
 Least common of WBCs (< 2%)
 Nucleus does not always segment
 Increase in response to same conditions that cause eosinophils
to respond.
The Monocytes :
 Also not common in circulating blood
 Stay in blood for about 70 hours
 Become macrophages in tissue and live for several months or
longer
The Lymphocytes :
 May mature into B or T cells
 Main function is antigen recognition and immune response
 Life span quite varied (up to two years)
 Can pass back and forth between blood
Lymphocytes: B & T types :
 B cells are not only produced in the bone marrow but also
mature there.
 However, the precursors of T cells leave the bone marrow and
mature in the thymus (which accounts for their designation
Types of Lymphocytes :
 B lymphocytes (or B cells) are most effective against bacteria &
their toxins plus a few viruses
 T lymphocytes (or T cells) recognize & destroy body cells gone
awry, including virus-infected cells & cancer cells.
 T cells come in two types: helper cells and suppressor cells;
normally the helper cells predominate.
A comparison of RBCs, WBCs and Platelets
1. Site of
formation
Red blood
White blood
cells
cells
Platelets
formed in bone
marrow,
formed in bone
lifespan:
marrow or
4 months
thymus
2. Shape
phagocytes:
biconcave discs,
irregular, lobed
no nucleus,
nucleus &
red colour
granular
cytoplasm
3. Size
some large &
small in size
4. Number
5,000,000/mm3
5. Function
some small
7,000 /mm3
formed in blood
marrow
irregular shape,
no nucleus,
tiny pieces of
cell fragments,
no colour
tiny cell
fragments
250,000/mm3
phagocytes kill
contain
haemoglobin to
carry oxygen
from lungs to all
parts of body
pathogens &
digest dead
cells.lymphocytes
produce
antibodies for
killing
pathogens.
for blood
clotting
Inflammation:
Inflammation is the complex biological response of vascular tissues
to harmful stimuli, such as pathogens, damaged cells, or irritants.
It is a protective attempt by the organism to remove the injurious
stimuli as well as initiate the healing process for the tissue.
Characteristics of Inflammation :
 Vasodilation of the local blood vessels, with consequent
excess local blood flow.
 Increased capillary permeability with leakage of large
quantities of fluid into the interstitial spaces.
 Clotting of fluid in the interstitial spaces because of
excessive amounts of fibrinogen and other proteins leaking
from the capillaries.
 Migration of large numbers of granlocytes and monocytes
into the tissue.
 Swelling of the tissue cells.
Some tissue products that cause Inflammation are :

Hitamine.

Bradykinin.

Serotonin.

Prostaglandins.

Reaction products of the complement system.

Reaction products of the blood – clotting system.

Lymphokines released by sensitized T cells.
WALLING – OFF EFFECT OF INFLAMMATION :
The tissue spaces and the lymphatics in the inflamed area are
blocked by fibrinogen clots so that fluid barely flows through the
spaces.
This process delays the spread of bacteria or toxic products.
MACROPHAGE AND NEUTROPHIL RESPONSE DURING
INFLAMMATION:
LINES OF DEFENSE:
 First line of Defense:
The tissue macrophages.
 Second line of defense:
Neutrophil invasion of the inflamed area.
 Third line of defense:
A second macrophage invasion of the inflamed area.
 Fourth line of defense.
Increased production of granulocytes and monocytes by
the bone marrow.
FEEDBACK CONTROL OF THE MACROPHAGES AND NEUTROPHIL
RESPONSES TO INFLAMMATION :
Five factors play dominant roles in the control of macrophage –
neutrophil response to inflammation :

Tumor Necrosis Factor (TNF )

Interlukin – 1 ( IL-1 )

Granulocyte – monocyte colony stimulating factor ( GM – CSF )

Granulocyte colony stimulating factor ( G – CSF )

Monocyte colony stimulating factor.
The feedback meachnism begins with tissue inflammation and then
proceeds to formations of defensive white blood cells and finally
removing the cause of inflammation.
Clinical Signs of Inflammation
Heat (calor) - fever, local warmth
Erythema (rubor) - redness in involved area
Swelling (tumor) - mainly edema fluid
Pain (dolor)
Loss or decrease of function. (functio laesa)
The hallmark of acute inflammation is increased vascular permeability
leading to edema.
Immunity:
Immune responses are generally subdivided into two categories:

Innate (or natural) and

Antigen specific (or "acquired").
Innate immune responses:
All of these are Antigen non-specific immune mechanisms.
They include,

Phagocytosis and digestion of pathogen (ie. By neutrophil;
monocyte/macrophage, eosinophil )

Increased production or activation of Ag non-specific soluble
proteins such as acute phase reactants, complement cascade,
interferon, nitric oxide or lysozyme

Natural killer cells and T cells (cytotoxic, but Antigen nonspecific) make cytokines but exhibit very little variability in their
receptor for Antigen.
Specific
Immunity
(acquired
or
adaptive
immunity):
Ag specificity, self/non-self discrimination and memory are its
main hallmarks.
It accomplishes this by mechanisms that are,

Humoral
(Antibody:
cells/plasma cells
IgG,
IgA,
IgM,
IgE)
made
by
B

Cell mediated: Cytotoxic T cells, helper T cells.
The specific response exhibits a wide diversity of different effector
mechanisms aimed at destruction or localization of pathogens. All of
these share the characteristics of
(i)
recognizing each Antigen with great specificity and
(ii)
memory.
Generation of the cells responsible for the immune response involves a
process of self vs. non-self discrimination, where Antigens considered
"self"
are
not
attacked
(except
inappropriately,
such
as
in
autoimmunity). ANY molecule that is "non-self" triggers an immune
response, regardless of whether it is a pathogen or not.
Partnership
between
innate
and
acquired
immune
responses:
These are not two independent, redundant pathways to protection.
Rather,
they
form
an
integrated
defense
system.
Examples of integration include,
1. Antibodies bind to granulocytes to confer specificity on Antigen
non-specific cells in their killing (i.e. eosinophils).
2. Cytokine production generated during the innate response help
determine the type of specific response that develops (enhancing
Antibody production vs stimulating more cytotoxic cells)
3. Inflammation brings Antigen specific cells to the site, promoting
expansion of the Antigen-specific component of the response.
Immunity acquired by:

Exposure to Antigen/potential pathogens

Skin, Gut and other physical barriers to entry, mechanical
defenses (cough, etc)

Upon Antigen entry: Innate immune response (phagocytosis,
soluble proteins, NK cells depending on the Ag in question)
localizes Ag, attempts to lyse it and/or phagocytose it. This
leads to,

Generation of inflammatory response. More intense innate
immunity due to recruitment of more monocytes, polymorphs
and

Activation
of
specific
immunity:
Interactions
of
T
lymphocytes with "Ag presenting cells" and B lymphocytes,
leading to induction of specific immune responses.

These include, T cell activation (hence cytokine synthesis,
cytotoxicity) and Antibody formation by B cells/plasma cells.
Active vs. Passive immunity
Active immunity :

Results from natural (or vaccine induced) exposure to a
pathogen.

It is stronger, longer lasting, more diverse and usually results
in memory but it takes time to fully develop.
Passive immunity :

Refers to transfer of Antibody maternally (in utero, colostrum) or
for specific clinical purposes.
The advantages:
Passive immunity is intense and immediately effective ( several
days to months for development of a full immune response).
The disadvantages:
It is generally of short duration unless additional passive Antibody
is provided. Importantly, it does not activate the host's own
immune response, so no memory or lasting protection develops.
FUNCTIONS OF BLOOD :
A. Transport:
1. Oxygen
- By RBCs in the form of oxyhaemoglobin
2. Carbon dioxide
- By plasma in the form of hydrogen carbonate ions
3. Food
- Carries absorbed food substances such as glucose from the
small intestine to various parts of the body.
4. Urea
– produced in the liver, dissolves in plasma, is carried to the
kidney and excreted in the urine.
5. Hormones – Secreted by endocrine glands into blood for transport.
6. Antibodies – Carried by blood for body defence.
7. Heat –
- produced during respiration in muscles and liver and transported
to other parts of the body.
B. Blood clotting:
Prevent excessive bleeding by clot formation.
C. Regulation of body temperature
D. Defence against infection
 1. Phagocytes: engulf and kill pathogens
 2. Lymphocyte: produce antibodies to kill pathogens.