Presentation
notes on Neutrophils Structure, Size,
Operation’s Mechanism in Blood of a Human Body in word /. ppt/ .pdf Format
THE NEUTROPHILS
The neutrophils have a diameter of 10-12 and are multilobed (multi lobe
perhaps helps emigration of the neutrophils) WBCs containing amphophillic or
neutrally stained granules. the lobes of the nucleus may be 2, 3 up to 5 but
even more lobes may also be seen. Younger the cell, less will be the number of
the lobes. Thus in a given blood film one may count the number of the lobes of
the neutrophil.
Preponderance of younger cells (2 or 3 lobed), is called, 'shift to
the left' whereas the opposite is called 'shift to the right' (Arneth count).
Shift to the left may be due to infection (due to greater release of neutrophils
from the RBM, so that younger cells dominate the film);shift to the right is
seen in megaloblastic anemia (vit B12 folate deficiency). The neutrophil
develops from stem cell → as the cell
grows it begins to acquire granules.
There are two types of granules in the neutrophil (1) primary or lysosomal or azurophilic
granules, (2) secondary granules. The primary granules begin to appear from the
stage of 'promyelocyte' while the 2ndary granules appear at the stage of
'myelocyte'.Neutrophils attack the bacteria → they engulf the bacteria (phagocytosis) → digest them by the contents of lysosomal
(primary) granules. The secondary granules, however, are not lysosomal, ie,
they do not directly kill the bacteria; instead, they are concerned with development of
inflammation and other issues.
The primary (lysosomal) granules contain various chemicals, which kill
the bacteria, eg, (1) hydrolase (2) myeloperoxidase (MPO) (3) cationic
proteins, (4) lysozyme and so on. They also contains 'defensins' (which are
very broad spectrum antimicrobial' agents killing a wide variety of bacteria,
fungus and even some virus). These agents kill the microbes by various means,
eg, (i) producing oxidants (like , superoxide etc; substances like H202 destroy
the bacteria), (ii) by lowering the pH within the bacteria (thus killing the
bacterial enzymes) and so on.
Secondary granules, include (1) lactoferrin (2) vit B12 binding
protein (3) and various sorts of receptor molecules. Major function of
secondary granules is to modify inflammation.In acute bacterial infections,
sometimes, bigger, sturdier, cytoplasmic granules, called, toxic granules,
appear in the neutrophil. Toxic granules are immature azurophilic granules.
Pool, margination
and its importance
As stated above, (i)
90% of the neutrophils are in marrow pool, (ii) 3% in the blood pool and (iii)
7% in tissue pool. The story, from 'birth to grave' of a neutrophil ('kinetics'
of neutrophil) is as follows : from the stem cell, the neutrophil is born in
the RBM (and constitutes marrow pool). A neutrophil spends about 10 days in
marrow pool → then it enters
the blood pool where it sta for about 7 hrs → nextly, from the blood pool, neutrophil emigrates into
the tissues (to constitute the tissue pool) where it stays for about 1 to 4
days, then it (= neutrophil) dies. The dead neutrophil is removed by tissue
macrophage.
Note, from the tissue pool, neutrophils do not return back to the
blood.
Importance of
margination:-
As stated above, 50% of
neutrophil of the blood pool stick to the vascular endothelium a phenomenon
called 'margination'. (i) During inflammation, these marginated neutrophils by
the help of their pseudopods, via the gap in between the endothelium of the
capillary, move out of the capillary to reach the tissue - a phenomenon called
emigration or diapedesis. Now the emigrated neutrophil attacks the bacteria
lodged in the tissue. (ii) Even normally, as stated above (kinetics of
neutrophil), the neutrophils emigrate to the tissue. (iii) In the lung
capillaries the phenomenon of margination is extremely important.
Mechanisms :
(i) On the neutrophils and the vascular endothelial cells, there are
molecules, called, "selectins". The selectins of neutrophil have
affinity for selectins of endothelial cells → result is that the neutrophil comes closer to the
endothelial cells;
(2) in the capillaries, the velocity of the blood is slow, therefore
the neutrophils can settle down.
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