BLOOD

Formed Elements of Blood

• In adults about 5 liter of blood contributes 7-8 % to the body weight.

• The cellular element composed of erythrocytes (red blood cells), leucocytes (white blood cells), and platelets.

• Plasma is a viscous, translucent, and yellowish fluid composed of water (90%), proteins(7%), organic salts (1%), and organic compound (2%) such as amino acids, lipids, and vitamins.

Functions

• Erythrocytes and blood platelets perform their functions inside the blood vessels

• leukocytes reside temporarily in the blood and can leave the blood stream through the walls of capillaries and venules and enter either connective or lymphoid tissues.

Composition of plasma

• Plasma proteins composed of:-• - Albumins (bulk): bind and transport.• - Globulins: alpha, beta and gamma

globulins.• - Lipoproteins• - Blood coagulation proteins: prothrombin,

fibrinogen which gives rise to fibrin.

celluar Elements of Blood

• Erythrocytes (RBC)• Leukocytes (WBC)– Granulocytes– Agranulocytes

• Platelets (Thrombocytes)

ERYTHROCYTE

•4.5 -5 million /mm3•Mature cell has no nucleus, or organelles.•They contain hemoglobin, which fills almost the entire cytoplasm •Fetal erythrocytes (up to the 4th month of gestation) are larger than "adult" erythrocytes, and they are nucleated.•Erythrocytes are remarkably elastic and can withstand deformation.

•Function :Transports O2 and CO2.

RBC

• Readily deform and pass through capillaries.

• Lifespan is 120 days.

• Removed by spleen and liver.

• Reticulocytes are immature RBCs released from bone marrow; normally estimated ~ 1% of circulating RBCs.

TEM RBC

Reticulocyte with a few organelles.

RBC in capillary

White blood cells (WBC) or leucocytesLeukocytes can be subdivided into:

1.granular leukocytes (neutrophils, basophils andeosiniphils)

2. non-granular leukocytes (monocytes and lymphocytes).

•In healthy individuals the total number of circulating leukocyte is about 4000-10000/mm3. this number can increase in infection.

The frequencies of WBC· ~ 60% neutrophils (50% - 70%)· ~ 40% lymphocytes (20% - 40%)· ~ 5% monocytes (1% - 9%)· ~ 4% eosinophils (>0% - 5%)· ~ 0.5-1% basophils (>0% - 2%)

A larger than usual number of neutrophils (neutrophilia) would indicate e.g.an acute or chronic infection.

The number of basophils and eosinophils may increase (eosinophilia or basophilia) as a consequence of e.g. allergic disorders.

Granular Leukocytes

•Granular leukocytes are all approximately the same size (12-15 μm in diameter). •Their nuclei are lobulated and nucleoli cannot be seen.

•The number of nuclear lobes varies according to cell type. All granulocytes are motile.

•The term granulocyte refers to the presence of granulesin the cytoplasm of these cells.

•The granules correspond to secretory vesicles and lysosomes.

1. Neutrophil Characteristics

• 60-70% of leukocytes • diameter 10-12 µm • nucleus 2-8 lobes• The number of lobes increases with cell age• 'drumstick' on lobe in 3% of neutrophils in

females (Barr body)

NEUTROPHIL

Neutrophils, mature and almost!

Function

•Neutrophils play a central role in inflammatory processes.

• Neutrophils are the first wave of cells invading infection

•Receptors in their plasma membrane allow them to recognize foreign bodies, e.g. bacteria, and tissue debris, which begin to phagocytose and destroy.

Neutrophils

Mature and youngerCells (lobes)

Movement by pseudopodia. Engulfed bacterium.

Basophil Characteristics

• Less than 1% of leukocytes. • Diameter 14 µm. • Nucleus large and bilobed. • Cytoplasm filled with large dark-blue staining

granules (basophilic) which may obscure nucleus .

BasophilFunction: • immunological response to parasites. •Contain many mediators of inflammatory response. •Closely related to mast cells. Basophils and mast cells bind to IgE produced in response to allergens.

Basophil

Bilobed nucleusGranules (S) contain heparin, leukotrienes, histamine.Mitochondria, ribosomes, glycogen in cytoplasm.

EOSINOPHIL

Eosinophil Characteristics

• 1-5% of leukocytes. • Diameter 12-15 µm.• slightly larger than neutrophils• Nucleus usually bilobed. • Cytoplasm filled with numerous large

eosinophilic (acidophilic) granules which stain pale-pink.

Functions of Eosinophils

• Phagocytic for antigen-antibody complexes.• Defense against parasites.• Release granules against parasites which are

injured by enzymes. • respond to basophils and mast cells.

SEM Eosinophil

Specific granules (S) stainsreddish. S granules contain manyhydrolytic enzymes.Contains glycogen, somemitochondria, rER,sER.

Non-granular leukocytes1- Monocytes:

- Monocytes are large cells, 12-18 μm in diameter; represent 2-10 %white cell count.

-Monocytes are highly motile phagocytic cells; i.e. they can migrate into tissues; engulf and destroy tissue debris & foreign material.

-Their nucleus less dense than lymphocytes; deeply indented, C-shaped or kidney shaped.

Function

•Once monocytes enter the connective tissue they differentiate into macrophages that phagocytose microorganisms, tissue debris and the dead neutrophils.

2. Lymphocytes (B and T cells):Lymphocytes represent 20 to 40% of the differential white cell count.

There are two structural types:

Most small lymphocytes in the blood stream belong to either the group of B-lymphocytes (~5%) or the group of T-lymphocytes (~90%).

Cell shapeThe cell is rounded with densely stained nucleus, small amount of pale basophilic cytoplasm (seen in EM) more numerous on B lymphocytes than T lymphocytes.•the two groups can not easily be distinguished using routine light or electron microscopy..

Functions

Upon exposure to antigens B-lymphocytes differentiate into antibody producing plasma cells that produce antibodies which directed against foreign antigen.

- T-lymphocytes represent the "cellular arm" of the immune response (cytotoxic T cells) and may attack foreign cells, cancer cells and cells infected by e.g. a virus.

Blood platelets (thrombocytes):

-Blood platelets do not contain nucleus

-they are cytoplasmic fragments of very largethrombocyte (megakaryocytes) that are found in the bone marrow.

-Their number is 150,000 - 400,000/mm3.

-They are rounded or oval, biconvex discs, 1.5 to 3.5μm in diameter.

-Different types of vesicles contain either serotonin) or compounds important for blood coagulation

-Serotonin is a potent vasoconstrictor. The release of serotonin from thrombocytes, which adhere to the walls of a damaged vessels,is sufficient to close even small arteries.