Major Cell Types

Connective tissues contain a variety of cell types. Some of them are called fixed cells because they are usually present in stable numbers. These include fibroblasts and mast cells. Other cells, such as macrophages, are wandering cells. They temporarily appear in tissues, usually in response to an injury or infection.

The fibroblast (ficbro-blast) is the most common kind of fixed cell in connective tissues. It is a large, star-shaped cell. Fibroblasts produce fibers by secreting protein into the matrix of connective tissues (fig. 5.13).

White Blood Cell Blast Images

Figure 5.13

A scanning electron micrograph of a fibroblast (4,000x).

Macrophages (makxo-fajez) (histiocytes) originate as white blood cells (see chapter 14, page 556) and are almost as numerous as fibroblasts in some connective tissues. They are usually attached to fibers but can detach and actively move about. Macrophages are specialized to carry on phagocytosis. Because they function as scavenger cells that can clear foreign particles from tissues, macrophages are an important defense against infection (fig. 5.14). They also play a role in immunity (see chapter 16, page 662).

Mast cells are large and are widely distributed in connective tissues, where they are usually located near blood vessels (fig. 5.15). They release heparin, a compound that prevents blood clotting. Mast cells also release histamine, a substance that promotes some of the reactions associated with inflammation and allergies, such as asthma and hay fever (see chapter 16, page 672).

Cell being engulfed

Macrophage

Cell being engulfed

Macrophage

Macrophages are scavenger cells common in connective tissues. This scanning electron micrograph shows a number of macrophages engulfing a larger cell (3,330x).

Figure

Macrophages are scavenger cells common in connective tissues. This scanning electron micrograph shows a number of macrophages engulfing a larger cell (3,330x).

Cell membrane Nucleus

Cell membrane Nucleus

Cytoplasmic granule

Figure 5.15

A transmission electron micrograph of a mast cell (5,000x).

Figure 5.13

A scanning electron micrograph of a fibroblast (4,000x).

Cytoplasmic granule

Figure 5.15

A transmission electron micrograph of a mast cell (5,000x).

Release of histamine stimulates inflammation by dilating the small arterioles that feed capillaries, the tiniest blood vessels. The resulting swelling and redness is inhospitable to infectious bacteria and viruses, and also dilutes toxins. Inappropriate histamine release as part of an allergic response can be most uncomfortable. Allergy medications called antihistamines counter this misplaced inflammation.

Allergic To Everything

Allergic To Everything

The human body And Todays chemical infested world. Here is a news flash You are not allergic to pollen, pet dander, or whatever it is that makes your body revolt Rather, your body just can not handle that one thing, what ever it is, anymore, due to the massive barrage of toxic chemicals you and everyone else are ingesting every single day.

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