EM of cytoplasm of fibroblast that is actively producing collagen precursors. Since collagen is a protein, we are not surprised to see a prominent rough endoplasmic reticulum. RER cisterns are packed with granular synthetic product (1). Two mitochondria (2) are visible. On the upper left-hand surface of the fibroblast, notice that secreted tropocollagen is beginning to condense into fibrillar form.
Two large macrophages (one on either side of the picture) -- with engulfed particles of blue dye in their cytoplasm. Their nuclei are pink. Compare the irregular sizes of the blue phagocytized particles here with the more even-sized granules of the mast cells in the next two slides. Notice also that the particles in the macrophage are scattered randomly.
Mast cells in areolar c.t. -- their cytoplasm full of purple secretory granules , which often seem to be spilling out. The granules contain precursors of histamine and heparin. The nuclei are hidden by the granules.
Mast cells -- deep purple metachromatic stain for granules. Again, granules are spilling out as a result of the preservation techniques. Notice how round and seed-like the granules are and how tightly they are packed in the cell. The cell nuclei are light blue.
Three large, dark mast cells in a stretched preparation of areolar connective tissue. In H & E the secretory granules stain a deep red color. Most of the other nuclei in the field belong to fibroblasts.
EM of a rat mast cell, showing typically large, homogeneously dense granules in the cytoplasm.
On the left side of the micrograph, notice the presence of collagen fibrils in the extracellular
space. Their presence is diagnostic for connective tissue.
EM of a human mast cell, showing a different structure for the secretory granules. Instead of being homogenous, the granules contain lamellae, whorls, and so-called paracrystalline structures. They are often described as "hair curlers" or "hair rollers"! In this picture they don't seem very densely packed, but their function seems to be very similar to that of mast cells of other species.
Plasma cell -- with somewhat basophilic cytoplasm and an eccentric nucleus with dark blocks of chromatin in it. Note the pale cytoplasmic area to the left of the nucleus; this is the negative Golgi body. Note also the pink collagen fibers scattered irregularly throughout the pale ground substance of the whole field, which is typical of areolar connective tissue.
Another plasma cell with eccentric nucleus and smooth, basophilic cytoplasm. The large, elongate, pale nucleus to the right of center belongs to a fibroblast; its cytoplasm is not visible.
Plasma cell in EM -- showing nucleolus and "cart-wheel" chromatin configuration in the nucleus. The cytoplasm is packed with rough endoplasmic reticulum, indicating protein formation. Plasma cells produce antibodies (immunoglobulins).
Eosinophils (bright pink granules) -- in areolar connective tissue. Note the bilobed nucleus in the center cell. Pale oval nuclei in the upper left hand corner probably belong to fibroblasts. Small, dark, round nuclei, such as in the lower right quadrant, probably belong to lymphocytes. Macrophages are hard to identify unless their cytoplasm is filled with phagocytized particles.
Miscellaneous cells in areolar connective tissue. The central cluster with beady, dark nuclei are wandering neutrophils. Any small, round, dark nucleus with no visible surrounding cytoplasm is a lymphocyte. The large, pale, oval nuclei scattered around the field belong to fibroblasts. In the lower right corner are two fairly oval plasma cells with definite cytoplasm and dark, round, eccentric nuclei. Macrophages are probably in the area but are hard to identify without ingested particles to mark them; the most likely candidate here is a fairly large cell just left of the central cluster with definite cytoplasm and a small oval nucleus. The rounded space in upper right corner of the field is a blood vessel with endothelial cells lining it; inside the lumen is a neutrophil, showing a dark bilobed nucleus.
