Page 212 - Atlas of Histology with Functional Correlations

of time before migrating into the connective tissue. They are abundant in the

connective tissue of the respiratory tract and intestinal organs. The cytoplasm
of eosinophils is filled with large acidophilic granules that contain major
basic proteins, which are powerful hydrolytic enzymes and toxins. One of
the main functions of eosinophils is to defend the organism against
helminthic parasite (worms) infestation. During such parasitic infestations,

circulating eosinophils increase in number and combat the parasites by
destroying them with the toxic hydrolytic enzymes. Eosinophils are also
phagocytic cells. They phagocytize the parasites and the antigen–antibody

complexes that are formed in tissues after allergic responses. The eosinophils
also release enzyme histaminase that neutralizes or inactivates the
vasoactive histamine released by basophils and mast cells and other
mediators related to inflammatory allergic reactions.

Similar to eosinophils, basophils have also a short life span, and their

function is similar to that of mast cells. They enter the connective tissue and
increase in numbers in response to inflammatory conditions and allergic
reactions. Their granules contain histamine and heparin. Basophils have
surface receptors that bind to immunoglobulin E and, when activated by

allergen binding, release histamine and other chemicals that effect and
intensify inflammatory responses. These reactions cause severe allergic
responses, vascular changes that lead to increased fluid leakage from blood
vessels (tissue edema), and hypersensitivity and anaphylaxis.

All lymphocytes are produced in the bone marrow. Lymphocytes that

mature in the bone marrow are the B lymphocytes, and those that mature in
the thymus gland are the T lymphocytes. Other less abundant cells
differentiate into natural killer (NK) cells in the bone marrow.

Lymphocytes have a variable life span, from days to months, and show size
variability. The difference between small and large lymphocytes has a
functional significance. Small lymphocytes are the inactive cells, whereas
large lymphocytes represent the cells that were activated by specific antigens
and are considered as NK cells. Lymphocytes are essential for immunologic

defense of the organism. Some lymphocytes (B lymphocytes), when
stimulated by specific antigens, differentiate into plasma cells in the
connective tissue and produce antibodies to counteract or destroy the

invading organisms.

Monocytes can live in the blood for 2 to 3 days, after which they move
into the connective tissue, where they become active and powerful

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