Republic Of Iraq
Al-Esraa University College
Medical Lab. Technology Dep.
Histology
Second year / lec : 6+7
Ass. Lec . Ihab Q. Ali
Blood is a specialized body fluid in animals that delivers
necessary substances such as nutrients and oxygen to the cells and
transports metabolic waste products away from those same cells.
Blood is a specialized connective tissue in which cells are
suspended in fluid ECM called plasma. Propelled mainly by
rhythmic contractions of the heart, about five liters of blood in an
average adult moves unidirectional within the closed circulatory
system
formed elements circulating in the plasma are erythrocytes (red
blood cells), leukocytes (white blood cells) and platelets
Blood - Functions
• Transports (Gases, Nutrients, Hormones)
• Regulates pH & Electrolyte Balance in
Interstitial Fluid
• Prevents Fluid Loss from Bleeding
• Defends against Pathogens & Toxins
• Aids in Body Temperature Regulation
Components - Plasma
• Liquid Component of Blood
• 92% Water
• 7% Proteins:
– Albumins (Most Abundant, Osmotic Pressure)
– Globulins (Antibodies, Transport Proteins,
Lipoproteins)
– Fibrinogen (Clotting)
• 1- 2% Inorganic Salts, Carbohydrates,
Lipids, Hormones, Gases, Wastes, etc.
Blood Cells
Leukocyte
Erythrocyte
Agranulocyte
Granulocyte
1-Monocyte
1-Neutrophile
2-Eosinophile
2-Lymphocyte
3-Basophile
Thrombocyte
Erythrocytes
Erythrocytes (red blood cells) are lack nuclei, and are packed with
the O2-carrying protein hemoglobin. Like most mammalian red
blood cells, human erythrocyte are flexible biconcave disks . They
are approximately 7.5µ m in diameter, 2.6µ m thick at the rim,
and only 0.75µ m thick in the center. This biconcave shape
provides a large surface-to-volume ratio and facilitates gas
exchange. The normal concentration of erythrocytes in blood is
approximately 3.9–5.5 million per microliter in women and 4.1–6
million per microliter in men.
Fate of Erythrocytes
 Unable to divide, grow, or synthesize proteins
 Wear out in 100 to 120 days
 Removed by phagocytes in the spleen or liver
 New RBCs made by stem cells in bone marrow
Erythrocyte Disorders
 Anemia (RBC or Hb Deficiency)
Hemorrhagic (Blood Loss)
Hemolytic (RBC Destruction)
Aplastic ( Bone Marrow Function)
Sickle Cell (Inherited Hb Mutation)
 Polycythemia (Abnormal  in RBCs)
 Viscosity & B.P. with  O2 Delivery
Cyanosis, Blood Clots
Leukocytes
•
Leukocytes (white blood cells) migrate to the tissues where they become
functional and perform various activities . According to the type of
cytoplasmic granules and the shape of their nuclei, leukocytes are divided
into two groups: polymorphonuclear granulocytes and mononuclear
agranulocytes. Both types are spherical while suspended in blood plasma,
but become amoeboid and motile after leaving the blood vessels and
invading the tissues.
• Chemotaxis – Chemicals released from sites of damage or inflammation
attract WBCs
• Phagocytosis – ingestion of bacteria, debris
Five Types Based on:
•
•
•
•
Size
Nuclear Shape
Cytoplasmic Granules
Affinity for Stain
Granulocytes
 Neutrophils (Polymorphonuclear Leukocytes)
•
•
Neutrophils constitute 60–70% of circulating leukocytes. They are 12–15 µ m in
diameter in blood smears, with nuclei having two to five lobes linked by thin
nuclear extensions . Neutrophils are inactive and spherical while circulating but
become actively amoeboid during (diapedesis)
The movement of white blood cells and
other cells out of small arterioles,venules, and capillaris as part of the
inflammatory response)
diapedesis
 Eosinophil
:
Eosinophils are far less numerous than neutrophils, constituting only 2–4% of leukocytes
in normal blood. Is about the same size as a neutrophil, but with a characteristic bilobed
nucleus . The main identifying characteristic is the abundance of large, red specific
granules that are stained by eosin.
The major basic protein have cytotoxic effects on parasites such as helminthic worms and
protozoa. They are an important source of the factors mediating allergic reactions and
asthma.
In tissues, eosinophils are found in the connective tissues underlying epithelia of the
bronchi, gastrointestinal tract, uterus, and vagina, and surrounding any parasitic worms
present .
 Basophils :
Basophils are also about 12–15 µ m in diameter, but make
up less than 1% , therefore difficult to find in smears of
normal blood. The nucleus is divided into two or more
irregular lobes, but the large specific granules overlying the
nucleus usually obscure its shape.
AGranulocytes
 Lymphocytes :
Lymphocytes constitute a family of leukocytes with spherical
nuclei . They can be subdivided into functional groups according
to notably T lymphocytes, B lymphocytes, and natural killer
(NK) cells. Lymphocytes have diverse functional roles related to
immune defense against invading microorganisms, foreign or
abnormal antigens, and cancer cells. Most lymphocytes in the
blood are small with diameters of 6–8 µm; medium and large
lymphocytes range in size from 9 to 18 µm in diameter.
 Monocytes:
Monocytes are bone marrow–derived agranulocytes with diameters varying from 12
to 20µ m. The nucleus is large, and may be oval, kidney-shaped, or distinctly Ushaped. The chromatin is less condensed than in lymphocyt. The cytoplasm of the
monocyte is basophilic and contains very small azurophilic granules (lysosomes).. In
the electron microscope, nucleoli may be seen in the nucleus, and small mitochondria
are observed. Circulating monocytes are precursor cells of the mononuclear phagocyte
system . After crossing the walls of postcapillary venules, monocytes differentiate into
macrophages in connective tissues, microglia in the CNS, osteoclasts in bone, etc.
Platelets
Blood platelets (thrombocytes) are nonnucleated, disklike cell
fragments 2–4µ m in diameter. Platelets originate by
fragmentation at the ends of cytoplasmic processes extending
of cells called megakaryocytes in the bone marrow .
Platelets 1- promote blood clotting and 2- help repair minor
tears or leaks in the walls of blood vessels, preventing loss of
blood. Normal platelet counts range from 200,000 to 400,000
per microliter of blood. Platelets have a life span of about 10
days. In stained blood smears, platelets often appear in
clumps.
Pluripotent Hemopoietic Stem Cells
It is believed that all blood cells arise from a single type of
stem cell in the bone marrow called a pluripotent stem cell
because it can produce all blood cell type. The pluripotent
stem cells proliferate and form two major cell lineages: one
for lymphoid cells (lymphocytes) and another for myeloid
cells that develop in bone marrow. Myeloid cells include
granulocytes,monocytes, erythrocytes, and megakaryocytes.
Early in their development, lymphoid cells migrate from the
bone marrow to the thymus or to the lymph nodes, spleen,
and other lymphoid structures, where they proliferate and
differentiate .
Bone Marrow
Under normal conditions, the production of blood cells by the
bone marrow is adjusted to the body's needs, increasing its
activity several-fold in a very short time. Bone marrow and
adipocytes are found in the medullary canals of long bones and
in the cavities of cancellous bones. There are two types of bone
marrow based on their appearance at gross examination: bloodforming red bone marrow, whose color is produced by an
abundance of blood and hemopoietic cells, and yellow bone
marrow, which is filled with adipocytes and essentially excludes
hemopoietic cells. In the newborn, all bone marrow is red and
active in blood cell production, but as the child grows most of
the marrow changes gradually to the yellow variety. Under
certain conditions, such as severe bleeding or hypoxia, yellow
marrow reverts to red.