Blood

Dr. Amal M. Moustafa, , Department of Histology & Cytology


The Blood 


• Definition:- 

The Blood 

• It is the viscid fluid, present in the closed 

circulatory system. 

• Contents: 

1-blood cells: 

• They form about 45% of the blood volume. 

• The Blood cells are:- 

– a- Red cells (erythrocytes). 

– b- White cells (leukocytes). 

– c- Blood platelets (thrombocytes). 

2-Plasma: it forms 55% of the blood volume. 


The Blood Cells 


RED BLOOD CORPUSCLES (RBCS) 

Erythrocytes 

• A- Shape of RBCs:- 

• They are rounded, biconcave 

disc shape. 

• In slow blood stream and in blood 

film they adhere together forming 

“Rouleaux” due to high surface 

tension. 

• B- Size:- 

• Normal diameter: 

• 6-9 um 

• (average 7.5 um). 


C- Colour:- 

• Fresh, single RBC is greenish 

yellow due to minimal HB. 

• A drop of blood appears red as 

it contains large number of 

RBCs. 

• In stained sections, RBCs with 

normal HB appear acidophilic 

with pale centre 

(normochromic). 

• D- Number:- 

• In males: 5 - 5.5 million /mm3. 

• In females: 4.5 - 5 million 

/mm3.(due to loss of blood 

during menstruation and 

depression of bone marrow by 

female sex hormones). 


E- Structure of RBCs:- 

• They are non nucleated cells (now called corpuscles). 

• They have no organoids but filled with HB. 

• They are surrounded by cell membrane, which is plastic and has selective 

permeability. 

• They contain important enzymes e.g. carbonic anhydrase enzyme. 

• Adaptation of RBCs to its function:- 

• Its biconcave shape increases surface area for more gas 

exchange. 

• Absence of nuclei and cell organoids allows more space to HB 

for gas exchange. 

• Carbonic anhydrase enzyme plays an important role in 

transportation of CO2 from tissues to the lung. 

• Selective permeability of the cell membrane allows easy 

exchange of oxygen and CO2 but not HB. 

• Plastic cell membrane allows RBCs to be squeezed in narrow 

vessels, then regain its normal shape in wide vessels thus 

prevent their rupture. 


LEUCOCYTES (WBCS) 

• - :Definition 

• They are true nucleated cells having cell 

organoids, cell inclusions, but no hemoglobin. 

• :Colour 

• Single WBC is colourless (leucocyte) but when 

aggregated, they appear white (WBCs). 

• :Number. 4000-11000/mm 3 


Classification of leucocytes: 

-1-Granular leucocytes:- 2- Non-granular:- 

a- Neutrophils. a- Lymphocytes. 

b- Eosinophils. b- Monocytes. 

• c- Basophils. 


Neutrophils 

(leucocytes polymorphonuclear) 

• Percentage: 60-75% of total leucocytes. 

• Shape: spherical 

• Size: 10-12 um. 

• Nucleus:- 

• Single, dark stained and segmented (2-5 

segments connected by fine chromatin threads. 

• About 60% of female nuetrophils have Barr 

bodies attached to their nuclei. 

• Cytoplasm:- contains fine neutrophilic 

granules. 


E/M: 

• Few mitochondria and 

• endoplasmic reticulum. 

• Two types of granules are present:- 

• Specific granules: 

• Numerous & small in size. 

• Contain bacteriostatic and bactericidal substances. 

• Azurophilic granules: 

• Few in number & large in size. 

• Contain hydrolytic enzymes (lysosomes). 

• Life span: 1- 4 days. 


Function:- 

• Defense against microorganisms. 

• When microorganism invades the surrounding tissue, 

the neutrophils migrate from the capillaries and 

phagocytose it (so called microphages). 

• They also secrete proteolytic enzymes. 

• During infections, they stimulate the bone marrow to 

produce more leucocytes (neutrophilia). 

• They attract monocytes to the infected area. 

• Precipitate in pus formation. 

• They secrete trephone substances, that help in 

healing of wounds. 


Eosinophils 

• Percentage: 2- 5% of total leucocytes. 


• Size: 12-15 um. 

• Nucleus: Bilobed “horse shoe-shaped”. 

• Cytoplasm: contains acidophilic refractile 

granules. 

• E/M: 

• Few mitochondria, rER, and Golgi. 

• Coarse ellipsoid granules, with electron dense 

crystalloid core in the centre. 

• These granules contain histaminase and 

sulphatase enzyme. 

• Life span: 8-12 days. 


Function:- 

1-In allergic conditions, the mast 

cells attract eosinophils to the site 

of allergy to perform anti-allergic 

action through: 

2-They can phagocytose the 

antigen-antibody complex. 

3-They secrete histaminase and 

sulphatase enzymes which 

destroy histamine and sulphate 

substances of allergy. 


Basophils 

• Percentage: ½ - ١ % of .total leucocytes 


• Size: -١٠- ١٢ .um 

• Nucleus: .Large and irregular 

• -:Cytoplasm 

• Filled with large basophilic granules. 

• These granules can be stained metachromatic . 

• They also stained with Giemsa stain. 

• E/M 

• They contain coarse electron dense granules. 

• These granules contain histamine and heparin. 

• Life span ١٥-١٠ : .days 

• -:Function 

• They produce heparin and histamine during allergy. 

• They have minimal phagocytic activity. 

• They release eosinophil chemotactic factor. 


Lymphocytes 

Non granular leucocytes 

Percentage: 25-30%. 

• Classification : 

• 

1-Small sized lymphocytes: 

4-7 um. 

2-Medium sized lymphocytes: 7-10 um. 

3-Large sized lymphocytes: 

10-15 um. 

• Lymphocytes found in the blood are mainly 

small and medium sized, while the lymphoid 

organs contain the three types. 


Large or medium-sized lymphocytes 

• Percentage: 5-10%. 

• Size: ١٠ - ١٢ um . 

• Nucleus: 

.indented 

Large, pale and 

• Cytoplasm: abundant, more 

.basophilic and non granular 

• E / M - : 

• The cytoplasm contains 

polyribosomes, numerous 

mitochondria, large Golgi and 

lysosomes. 


Small Lymphocytes 

• Percentage: 15-20%. 

• Shape: spherical. 

• Size: 6-8 um. 

• Nucleus:- 

• Central, round and dark stained. 

• Surrounded by a thin rim of cytoplasm. 

• Cytoplasm:- few in amount & pale 

basophilic. 

• E/M:- 

• They have few ribosomes, few 

mitochondria, a very small Golgi and few 

azurophilic granules. 

• Classification:- 

• B. lymphocytes. 

• T. lymphocytes . 


B- 

lymphocytes 

• :Development 

• U.M.C in the bone marrow colony forming cells … lymphoblast . B… .lymphocyte . B 

• Percentage: 30% .lymphcytes 

• Types: 

• B.lymphocytes of humoral immunity. 

• B.memory cells. 

• :Life span .3months 

• Function 

• 1- Humoral immunity: 

• When exposed to antigen, they are activated into medium sized lymphocytes. 

• Some of the active cells are differentiated into plasma cells which produce 

antibodies. 

• This is called primary immune response. 

2- Secondary response (B memory cells): 

• Some of the active cells are not changed into plasma cells but remain as memory 

cells. 

• When exposed to the same antigen again, they produce more rapid and more 

extensive humoral immune response. 


T. Lymphocytes 

• Development: 

• UMC in the bone marrow colony 

forming cells which migrate to the 

thymus gland where they develop into 

T.lymphocytes (thymus dependent). 

• :Percentage 

• ٧٠ % of small lymphocytes 

• :Life span .years 

• :Types 

• T. killer cells: produce cytotoxic 

substances. 

• T. memory cells 

• T. helper cells. 

• T. suppressor cells. 

• Lymphokines secreting cells. 


T. Lymphocytes 

Function: • 

• Cell mediated immunity:- 

• When exposed to cellular antigen, the T-lymphocytes are activated and 

come in contact with the antigen. 

• They secrete cytotoxic substance to destroy it. 

• Graft rejection cells in organ transplantation: 

• .(by cell mediated immunity) 

• T-memory cells: 

• Some of the activated T-cells remain in the body as memory cells, that 

can attack the same antigen after a long period of time. 

• T-helper cells:- 

• T-lymphocytes, can help the B-lymphocytes to be activated by the 

antigen. 

• .٥ Se cretion of lymphokines: 

• Interferon: antiviral. 

• Colony stimulating factor: stimulate bone marrow cells. 

• Macrophage factor: antibacterial. 

• ٦ . They act as macrophage attracting cells . 


Classification of lymphocytes 

Development: 

Percentage : 

Life span 

Function : 

Types : 

B. lymphocytes 

In bone marrow 

30% 

٣months 

Humoral immunity 

T. lymphocytes 

In the thymus 

٧٠ % 

years 

Cell mediated 

immunity 


Monocytes 

• Percentage : 3-8%. 

• Size : ١٥ um . 

• Nucleus : .large, pale and kidney shaped 

• ytoplasmC: .abundant and appears pale blue * 

• . 

• M/E -: 

• Many microvilli and pinocytotic vesicles near the cell surface. 

• Few cell organelles, small Golgi and azurophilic granules 

(lysosomes). 

• Life Span 3 Days 

• Function -: 

• Monocytes can penetrate through capillaries and venules to 

reach the C.T. where they can be transformed into 

macrophages. 


PLATELETS (THROMBOCYTES) 


PLATELETS (THROMBOCYTES) 

• : Definition 

• They are fragments of cytoplasm covered with 

membrane but have no nucleus (not true cells). 

• Origin : .in the red bone marrow megakaryocytes 

• Size : 2 - 4 .m 

• Shape : .oval or rounded discs 

• Number: ١٥٠٫٠٠٠ - ٤٠٠٫٠٠٠ / mm3. 

• L / M : 

• Appear as oval or rounded non nucleated discs. 

• Their outer part appears transparent and pale blue 

(called hyalomere). 

• Their central part contains dark stained granules 

(called granulomere). 


E/M: 

1-Cell membrane:- 

Irregular and covered with 

a thick cell coat. 

2- Hyalomere:- contains 

Tubules & vesicles invaginated 

from the cell membrane. 

Actin-like mirofilaments and 

microtubules to maintain the 

ovoid shape of the platelet. 

3- Granulomere: (chromomere): Contains:- 

Alpha granules: contain fibrinogen. 

Beta granules: mitochondria . 

Delta granules: contains serotonin, ATP, ADP and calcium. 

Lambda granules: lysosomes. 

Glycogen granules. 


Life span: 

١٠-٥ 

days . 

• Function -: 

• Stop bleeding (haemostasis) through : 

1-Secretion of serotonin vasconstriction 

.decrease blood loss 

2-The platelets adhere to the inner wall of the 

injured blood vessels forming platelet 

aggregation or white thrombus. 

3-Then, they secrete thromboblastin change 

into thrombin prothrombin change 

attract RBCs fibrinogen into fibrin network 

which )coagulation(to form red thrombus 

.close blood vessels and stop bleeding 


Number 

RBCs 

Neutrophils 

Anaemia or 

:(oligocythemia) 

Neutropenia: 

Polycythaemia 

Neutrophilia: 

Eosinophils 

Basophils 

Lymphocytes 

Eosinopenia: 

Eosinophilia: 

Basophilia: 

Lymphocytosis: 

Monocytes 

Platelet 

Thrompocytopenia 

Monocytosis: 


• 1- Anaemia or oligocythemia 

• Decease in number is 

caused by:- 

• A ،Deficiency of iron - 

B.vit12 .proteins، copper ، 

• - b Defect in bone marrow 

aplastic .anaemia 

• - c Haemorrhage 

haemorrhagic anaemia . 

• - d haemolytic 

.anaemia 

Haemolysis 

• Causes of haemolysis 

are -: 

• Incompatible blood 

transfusion. 

• Acids and alkalies. 

• Bacterial toxins and viruses. 

• Snake venom. 

• Hypotonic solutions and fat 

solvents. 

• 2- Polycythaemia 

Haemoconcentration): 

• The actual number of RBCs does 

not increase but the volume of 

plasma is reduced. 

• Occurs in cases of dehydration 

due to vomiting, diarrhea or 

polyuria. 

• -b Compensatory 

polycythaemia : 

• There is actual increase in 

production of RBCs from bone 

marrow. 

• Occurs as compensatory to 

hypoxia as in:- 

• The foetus due to intrauterine 

anoxia. 

• High attitude in low O2. 

• Severe muscular exercise 

.٢need for O 

• Congenital heart diseases mixed 

.blood 

• Chronic lung conditions impaired 

.oxygenation of blood 


• Neutropenia: 

• It is a decrease of 

neutrophils below 

60%. 

• It occurs in: 

• , Influenza, measles 

starvation, severe 

poisoning, chronic 

Typhoid .eg infections 

.TB & 

Neutrophilia: 

• It is an increase 

of neutrophils 

above 75%. 

• It occurs in: 

–Pyogenic 

infections: e.g. 

tonsilitis, 

appendicitis 

–Myocardial 

infarction. 

• 


• Eosinophilia: 

Allergic diseases. 

Parasitic : infections e.g. 

bilharziasis. 

• 

E osinopenia : 

It occurs after:- 

Prolonged steroid 

therapy. 

• Basophilia 

Allergic diseases. 

Parasitic diseases. 

Liver cirrhosis. 

• Lymphocytosis: 

• Whooping cough. 

• TB. 

• Syphilis. 

• Glandular fever 

• Monocytosis: 

• Malaria. 

• Typhus. 

• TB. 

• Syphilis. 

• Glandular fever. 



Blood 

Practical Cession 


PLATELETS 

RBCs 


Neutrophils.

Blood

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