Introduction to Blood
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
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.
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 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)
Hematocrit – the percentage of RBCs out of the total blood
A centrifuge separates blood into two components.
Erythrocytes, leukocytes, and platelets make up the formed
Only WBCs are complete cells
RBCs have no nuclei or organelles, and platelets are just
Most formed elements survive in the bloodstream for only a few
Most blood cells do not divide but are renewed by cells in bone
Blood plasma :
Blood plasma contains over 100 solutes, including:
Proteins – albumin, globulins, clotting proteins, and
Lactic acid, urea, creatinine
Organic nutrients – glucose, carbohydrates, amino acids
Electrolytes – sodium, potassium, calcium, chloride,
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.
7-8 m diameter
Biconcave disc shape
Inc. surface area
Inc. efficiency for diffusion of O2 & CO2
Binds O2 & CO2
No nucleus or organelles
Immature version has nucleus and is called a reticulocyte.
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.
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 :
Least common of WBCs (< 2%)
Nucleus does not always segment
Increase in response to same conditions that cause eosinophils
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
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
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
Red blood White blood
1. Site of formed in bone
formation marrow, formed in bone
formed in blood
lifespan: marrow or
4 months thymus
2. Shape irregular shape,
biconcave discs, irregular, lobed
tiny pieces of
no nucleus, nucleus &
red colour granular
3. Size some large &
small in size some small
7,000 /mm3 250,000/mm3
5. Function phagocytes kill
contain pathogens &
haemoglobin to digest dead
carry oxygen cells.lymphocytes
from lungs to all produce
parts of body antibodies for
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 :
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
This process delays the spread of bacteria or toxic products.
MACROPHAGE AND NEUTROPHIL RESPONSE DURING
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
Loss or decrease of function. (functio laesa)
The hallmark of acute inflammation is increased vascular permeability
leading to edema.
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.
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 non-
specific) 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
It accomplishes this by mechanisms that are,
Humoral (Antibody: 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
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
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
Generation of inflammatory response. More intense innate
immunity due to recruitment of more monocytes, polymorphs
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
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.
Passive immunity is intense and immediately effective ( several
days to months for development of a full immune response).
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 :
1. Oxygen - By RBCs in the form of oxyhaemoglobin
2. Carbon dioxide
- By plasma in the form of hydrogen carbonate ions
- Carries absorbed food substances such as glucose from the
small intestine to various parts of the body.
– 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.