The Blood pdf - Dr. Suhair Majeed

Dr. Suhair Majeed

The Blood

Blood is a unique form of connective tissue that

consists of three major cell types: erythrocytes

(red blood cells), leukocytes (white blood cells), and

platelets (thrombocytes).

These cells, also called the formed elements of

blood, are suspended in a liquid medium called plasma.

Blood cells transport gases, nutrients, waste

products, hormones, antibodies, various chemicals, ions,
and other substances in the plasma to and from different
cells in the body.

Medical Histology

Laboratory Tests

Collect blood in a tube with an anticoagulant and

centrifuge:-

Two major layers form:-

1-Bottom solid cellular layer



Largest layer, red cells, bottom red layer



White cell, “buffy coat” small white/gray
layer



Top layer, invisible thin platelet layer

2-Top aqueous plasma layer

Blood composition

Cont.



Leukocytes (white blood cells, WBC)

1-Granulocytes (with specific granules)



Neutrophil (~60% of WBC)



Eosinophil (~4% of WBC)



Basophil (<1% of WBC)

2-Agranulocytes (without specific granules)



Lymphocyte (B-cell, T-cell) (~27% of WBC)



Monocyte (~8% of WBC)

Plasma

Typical sample of plasma is composed

of :-



90% water



8% protein



1% in organic salts



0.5% lipids



0.1% sugar

plasma



Straw colored, nonliving
part of blood.



90% Water



Helps to regulate body
temperature



Contains Electrolytes



Plasma transports blood
cells, products of
digestion and hormones
throughout the body.

Plasma proteins

There are three main groups of proteins in

plasma :

1-the blood coagulation proteins.

2- albumin.

3 -globulins.

The globulins can be divided in to :

*alpha globulins
*beta globulins
*gamma globulins
(mainly immunoglobulins).

Cont.

The plasma proteins are nearly all derived

from synthesis in the liver , with the exception of
the immunoglobulins which are synthesised by
plasma cells .

Major Blood Cell Types:

Microscopic examination of a stained blood

smear reveals the major blood cell types :

1- Erythrocytes :

or red blood cells are nonnucleated cells and are the

most numerous blood cells.

Erythrocytes remain in the blood and perform

their major functions within the blood vessels.

Cont.

2- leukocytes,

or white blood cells, are nucleated and subdivided into

granulocytes and agranulocytes, depending on the
presence or absence of granules in their cytoplasm

Granulocytes

are the neutrophils, eosinophils, and

basophils.

Agranulocytes

are the monocytes and lymphocytes.

Leukocytes perform their major functions outside of the
blood vessels. They migrate out of the blood vessels
through capillary walls and enter the connective tissue,
lymphatic tissue, and bonemarrow.

Cont.

The primary function of leukocytes is to defend the

body against bacterial invasion or the presence of foreign
material.

Consequently, most leukocytes are concentrated in the

connective tissue.

3- Platelets:

or thrombocytes are not blood cells. Instead, they are

the smallest, nonnucleated formed elements in the
blood and appear in the blood of all mammals.

Cont.

Platelets are produced when small, uneven portions

of the cytoplasm separate or fragment from the
peripheries of the megakaryocytes , are extruded into
the blood stream.

Like the erythrocytes, platelets perform their major

functions within the blood vessels. Their main function
is to continually monitor the vascular system and to
detect any damage to the endothelial lining of the
vessels.

If the endothelial lining breaks, the platelets adhere

to the damaged site and initiate a highly complex

chemical process that produces a blood clot.

1- erythrocytes :

Mature erythrocytes are specialized to transport

oxygen and carbon dioxide. This specialization is
attributable to the presence of the protein
hemoglobin in their cytoplasm.

Iron molecules in hemoglobin bind with oxygen

molecules.

As a result, most of the oxygen in the blood

is carried in the combined form of

oxyhemoglobin

which is responsible for the bright red color of
arterial blood.

Cont.

Carbon dioxide diffuses from the cells and tissues

into the blood vessels.

It is carried to the lungs partly dissolved in the

blood and partly in combination with hemoglobin
in the erythrocytes as

carbaminohemoglobin

, which

gives venous blood its bluish color.

Cont.

During differentiation and maturation in the bone

marrow, erythrocytes synthesize large amounts of
hemoglobin.

Before an erythrocyte is released into the systemic

circulation, the nucleus is extruded from the cytoplasm,
and the mature erythrocyte assumes a biconcave shape.
This shape provides more surface area for carrying
respiratory gases.

Thus, mature erythrocytes in the circulation are

nonnucleated biconcave disks that are surrounded

by a membrane and filled with hemoglobin and some

enzymes.

Cont.

The life span of erythrocytes is approximately

( 120) days, after which the worn-out cells are
removed from the blood and phagocytosed by
macrophages in the spleen, liver, and bone marrow.
Woman usually have ( 4-5 million )erythrocytes per
cubic millimeter of blood, men have (5-6 million).
If this number is considerably higher, polycythemia
may be the cause. If the number is considerably
less, the person has anemia.

CONT

Sickle cell anemia is an inherited condition which

results in some erythrocytes being malformed.
The gene for this condition causes the hemoglobin
to be incorrectly formed, which in turn causes some

erythrocytes to take on a crescent shape.

These cells are not able to carry adequate amounts
of oxygen to cells.

Blood smear - RBC

erythrocytes

RBC

RBCs, scanning electron microscopy

SICKLE CELL ANEMIA

2- platelets

The main function of platelets is to promote blood

clotting.

When the wall and the endothelium of the blood

vessel are damaged, platelets aggregate at the site and
adhere to the damaged wall.

The platelets are activated and form a plug to occlude

the site of damage. The platelets in the plug release
adhesive glycoproteins that increase the plug size,

Cont.

The plug is then reinforced by a polymer fibrin

formed from numerous plasma proteins.

Fibrin forms a mesh around the plug, trapping

other platelets and blood cells to form a blood clot.
After blood clot formation and cessation of
bleeding, the aggregated platelets contribute to clot
retraction, which is later removed through
enzymatic action.

Cont.

platelets are small basophilic fragments,

often appearing in clusters. Small, biconvex disks,

2-3 µm in diameter. Each cubic millimeter of blood
should contain 250,000 to 500,000 of these.

If the number is too high, spontaneous

clotting may occur. If the number is too low,
clotting may not occur when necessary.

platelets

3- leukocytes - granulocytes

a-Neutrophils

have a short life span. They circulate in blood

for about ( 10 hours ) and then enter the connective
tissue, where they survive for another( 2 or 3 days).

Neutrophils are active phagocytes. They are

attracted by chemotactic factors (chemicals)
released by damaged or dead cells, tissues, or
microorganisms, especially bacterial, which they
phagocytose (ingest) and quickly destroy with
their lysosomal enzymes.

Cont.

Nucleus long and multi-lobed (usually 2-4 lobes).

Cytoplasm has small, neutrally stained specific
granules. (fine violet or pink granules,they are
difficult to see with LM ,therefor,the cytoplasm

appear clear.). Normally, neutrophils account for
50-70% of all leukocytes.

If the count exceeds this amount, the cause is

usually due to an acute infection such as
appendicitis, smallpox or rheumatic fever. If the
count is considerably less, it may be due to a viral
infection such as influenza, hepatitis, or rubella.

neutrophil

Leukocytes (cont.)

B-Eosinophils

also have a short life span. They remain in blood

for up to( 10 hours) and then migrate into the
connective tissue, where they remain for up to
( 10 days).

Eosinophils are also phagocytic cells with a

particular affinity for antigen–antibody complexes
that are formed in the tissues in allergic conditions.

Cont.

Esonophils have Bilobed nucleus. The

cytoplasm has prominent pink/red specific granules
(stained with eosin dye). If the smear is not stained

properly, the granules may be brownish. These cells
account for less than ( 5% of the WBC's ).

Increases beyond this amount may be due to

parasitic diseases, bronchial asthma or hay fever.

Eosinopenia may occur when the body is severely

stressed.

Esonophil

Cont.

The cells also release chemicals that neutralize

histamine and other mediators related to
inflammatory allergic reactions.

Eosinophils also increase in number during

parasitic infection and defend the organism against
helminthic parasites by destroying them.

Cont.

c-Basophils

have a short life span and their function is

similar to that of mast cells. Their granules contain
histamine(cause vasodilation) and heparin
(anticoagulant ).

Exposure to allergens results in release of

histamine and other chemicals that mediate and
intensify inflammatory responses. These reactions
cause severe allergic reactions, vascular changes
that lead to increased fluid leakage from blood
vessels, and hypersensitivity responses and
anaphylaxis.

Cont.

In a Differential WBC Count we rarely see these

as they represent less than (1% of all leukocytes).

If the count showed an abnormally high number

of these cells, hemolytic anemia or chicken pox
may be the cause.

Basophil

Cont.

The nucleus is usually bilobed, but usually is

partially obscured by granules, which can lie over it.
The cytoplasm contains large, purple/black specific
granules (stained with the basic dye) that are larger

but not as numerous as those of eosinophils.

Basophil & esonophil

Leukocytes - agranulocytes

a-Lymphocytes

have a variable life span, from days to months,

and show size variability.

The difference between small and large

lymphocytes has a functional significance. Large
lymphocytes represent the cells that were activated
by specific antigens.

Lymphocytes are essential for immunologic

defense of the organism. Some lymphocytes (B
lymphocytes), when stimulated by specific
antigens, differentiate into plasma cells in the
connective tissue and produce antibodies to
destroy the invading organisms.

Cont.



The nucleus is surrounded by a thin rim of

lightly basophilic cytoplasm in the smaller types.
The cytoplasm is more abundant in the larger
lymphocytes. When the number of these cells
exceeds the normal amount, one would suspect
infectious mononucleosis or a chronic infection.
Patients with AIDS keep a careful watch on their
T-cell level, an indicator of the AIDS virus' activity.

Cont.

Two major subtypes of usually

morphologically indistinguishable lymphocytes can
be identified (by lifespan, function, surface
receptors, site of differentiation) –

T cells and B

cells

. A third type of lymphocyte is referred to as

natural killer (NK) cells

Cont.

1-B-lymphocytes

these cells play a central role in humoral or

antibody-mediated immunity. Some divide and
differentiate into plasma cells in tissue. Some are
memory cells. They are immunologically
characterized by immunoglobulin on their cell
membrane.

Cont.

Plasma cells

Derive from B-lymphocytes. They have an

eccentrically placed nucleus, contain abundant
amounts of RER whose cisternae can be filled
with antibody, and have a well-developed Golgi.
Plasma cells produce
antibodies(immunoglobulins

Plasma cells

Cont.

2- T-lymphocytes

Processed by the thymus and participate in

cell-mediated immunity (such as graft rejection).
Some T-cells (cytotoxic) can elaborate cytotoxic
agents. They can make lymphokines (including
interferon, macrophage migration inhibitor factor,
chemotactic factors for basophils). There are also
memory T-cells that survive for years or decades.