Chapter 3 - Connective Tissue
Connective tissue provides support, binds together, and protects tissues and organs of the body.
Connective Tissue Fibers
The three types of connective tissue fibers are:
- Collagen fibers - most abundant fibers contain type I collagen
- Tensile strength - resistance to stretching
- Elastic fibers - contain elastin
- Elasticity - can be stretched, yet still, return to its original length
- Reticular fibers - contain type III collagen
- Support - network of thin fibers
CONNECTIVE TISSUE CELLS
Connective tissue cells are usually divided into two types:
- Fixed cells (or resident cells) - resident population of cells that develop and remain within connective tissue. Fibroblasts, adipocytes (fat cells), macrophages, and mast cells are regarded as resident cells.
- Transient cells (or wandering cells) - leukocytes (white blood cells) that migrate from the bloodstream into connective tissue in response to a signal (e.g., inflammation or tissue damage).
Fixed cells are normal components of connective tissue.
Fibroblasts produce and maintain the extracellular matrix. They are the most common cell type in connective tissue.
Adipocytes (fat cells) are specialized for storage of fats. They also function as a cushion for organs and insulate the body.
Macrophages are phagocytic cells that engulf and digest microbes, cellular debris, and foreign substances. Monocytes develop in bone marrow, circulate in the bloodstream, and migrate into connective tissue, where they differentiate into macrophages.
Mast cells release molecules that dilate blood vessels and recruit more immune cells to a site of mast cell activation. Progenitor mast cells (agranular) develop in bone marrow, circulate in the bloodstream, and migrate into connective tissue, where they proliferate and differentiate into mature mast cells (granular).
Mast cells undergo rapid degranulation during an anaphylactic reaction.
Transient cells are leukocytes (white blood cells) that circulate in the bloodstream and migrate into connective tissue at sites of an immune response. These include neutrophils, eosinophils, basophils, lymphocytes, and monocytes.
Plasma cells are mature B lymphocytes that produce large quantities of antibodies. They are abundant wherever antigens may enter the body, such as the gastrointestinal tract and the respiratory system.
Eosinophils are involved in many inflammatory processes, including parasitic infections, allergic diseases, and asthma.
Lymphocytes develop the ability to recognize and respond to antigens. Their number increases dramatically at sites of inflammation.
Mast Cell / Plasma Cells / Eosinophils
Example of multiple types of immune cells in connective tissue.