The Police Officer-Neutrophil (some patrol in the blood, some guard at the vessel)

Neutrophil is an amazing cell inside our body. In fact every cell is. AT first I always thought neutrophil is an agent of inflammation. Talking about inflammation made me thought of neutrophil. BUT here I read something about neutrophil today and I felt that the way it works is amazing!

Adapted from Haematology ICT WH120 H849h pg6

The blood neutrophil is the end product of an orchestrated sequence of differentiation in the myeloid cells of the bone marrow. (revise haemopoiesis!).

The mature cell has a multi-lobed nucleus and four different type of granules in the cytoplasm. (Hmm...any application of this?) They have limited lifespan of 5-6 days. Approximately half the cells are included in a normal blood count (revise what is absolute count for WBC here!), the remainder being in the marginal pool.

so, what is the marginal pool mentioned here?

Neutrophils released from the marrow enter the blood where they distribute into two compartments of approximately equal size: the circulating and the marginal pools. Neutrophils in the former compartment are freely circulating, whereas those in the marginal compartment are temporarily adherent to endothelial cells, generally in the postcapillary venules. In normal adult humans, the total of these two compartments (termed the total blood neutrophil pool) contains about 0.6 × 10⁹ cells/kg body weight; with about one half of the cells (0.3 × 10⁹ cells/kg) in each (circulating and marginal) pool.

In the marrow, the proportion of band to segmented neutrophils is much higher than in the blood. On that basis, it is likely that a selective release of segmented neutrophils occurs from the marrow, whereas band neutrophils generally remain behind to mature.
from this website: http://www.expertconsultbook.com/expertconsult/ob/book.do?method=display&type=bookPage&decorator=none&eid=4-u1.0-B978-1-4160-3479-7..10143-0--s0025&isbn=978-1-4160-3479-7

From CLINICAL HAEMATOLOGY, BARNARD, pg3
After about 10 days of maturation and differentiation in the marrow,the mature neutrophil polymorph has a circulating lifespan of only a few hours.The marrow storage pool of neutrophils is approx. 12 times that present in the blood. Whilst a vernous blood sample can measure the circulating neutrophil pool, there is a further marginating neutrophil pool in close proximity to blood vessel wall. the normal fate is attraction to tissue sites by inflammatory mediators or excretion in body secretions. In response to the stimulus of infection or inflammation, large no. of neutrophils maybe relesed into the circulating pool from the marrow and marginating pool to give the neutrophil leucocytosis characteristics of such states. Less mature form with unsegmented nuclei maybe prematurely liberated from the marrow to produce a 'left shift' in the differential white cell count.

That's means when released into the blood, half is circulating and half is marginating due to adhesion molecules.

Notes to come: Hypersegmented neutrophil, neutropenia, acute inflammation