Non-granular leukocytes

Non-granular leukocytes

Monocytes

These cells can be slightly larger than granulocytes (~ 12-18 µm in diameter). Their cytoplasm stains usually somewhat stronger than that of granulocytes, but it does not contain any structures which would be visible in the light microscope using most traditional stains (a few very fine bluish gains may be visible in some monocytes). The "textbook" monocyte has a C-shaped nucleus. Monocytes contain granules (visible in the EM) which in appearance and content correspond to the primary granules of neutrophils, i.e. the granules correspond to lysosomes.

Functions

Once monocytes enter the connective tissue they differentiate into macrophages. At sites of infection macrophages are the dominant cell type after the death of the invading neutrophils. The phagocytose microorganisms, tissue debris and the dead neutrophils. Monocytes also give rise to osteoclasts, which are able to dissolve bone. Osteoclasts are of importance in bone remodelling.

 
Suitable Slides

Blood Smear, human - Leishman stain

Monocytes and lymphocytes definitely look much prettier in darker stained smears (B2) than in lighter ones (B1) - mainly because of a clearer distinction between cytoplasm and nucleus. The cell is very likely to be a lymphocyte if the nucleus is round and surrounded by a narrow rim of cytoplasm (B1 and left in B2). Large lymphocytes with a wider rim of cytoplasm do occur (right in B2), but not often. The C-shaped nucleus of a textbook monocyte may not be easy to find. The nuclei will vary from a peanut- to a "fat" S-shape in smears. Whatever the shape of the nucleus, it is usually not lobed and not round. The nucleus is bound, at least on its concave side, by a wide rim of non-granular cytoplasm. Note also the light area of monocyte cytoplasm, which is often visible close to the concave surface of the nucleus. A large Golgi apparatus is located in the area. The Golgi apparatus does not stain as well as the remainder of the cytoplasm and leaves a light "impression" - the phenomenon is also called a "negative image". Identify and draw lymphocytes and a monocyte.

Lymphocytes

These cells are very variable in size. The smallest lymphocytes may be smaller than erythrocytes (down to ~ 5 µm in diameter) while the largest may reach the size of large granulocytes (up to 15 µm in diameter). How much cytoplasm is discernible depends very much on the size of the lymphocyte. In small ones, which are the majority of lymphocytes in the blood, the nucleus may appear to fill the entire cell. Large lymphocytes have a wider rim of cytoplasm which surrounds the nucleus. Both the nucleus and the cytoplasm stain blue (and darker than in most other cell types in the blood). The typical lymphocyte only contains the usual complement of cellular organelles. The appearance of lymphocytes may change drastically when they are activated (see below).

Functions

Most lymphocytes in the blood stream belong to either the group of B-lymphocytes (~5%) or the group of T-lymphocytes (~90%). Unless they become activated, the two groups cannot easily be distinguished using routine light or electron microscopy.
Upon exposure to antigens by antigen-presenting cells (e.g. macrophages) and T-helper cells (one special group of T-lymphocytes) B-lymphocytes differentiate into antibody producing plasma cells. The amount of cytoplasm increases and RER fills a large portion of the cytoplama of plama cells. 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.

T-lymphocytes and B-lymphocytes form the vast majority of lymphocytes in the blood stream, but they do not add up to 100%, and they usually are small lymphocytes. The much less frequent medium-sized or large lymphocytes may represent e.g. natural killer (Nk-) cells which belong to the group of large granular lymphocytes, or haemopoietic stem cells of which a very few will be circulating in the blood stream.

Title: Non-granular leukocytes
by:om at 2013-02-15T03:21:00+07:00
Rating: 4.8 of 5 Reviews
Non-granular leukocytes