Connective Tissue Structure = Cells + Extracellular Matrix
A connective tissue’s extracellular matrix is the material located between its widely spaced cells and is usually secreted by the connective tissue cells. Unlike epithelial tissue, connective tissue usually does not occur on body surfaces and are usually highly vascular (except cartilage and tendons). Like epithelial, CT is supplied with nerves (except cartilage). 1. Connective tissue cells arise from mesoderm germ layer and differentiate into various cell types:
a. Fibroblasts
Large flat cells with branching processes present in several CTs and are the most numerous. They migrate through the CT secreting fibres and components of the ground substance of the extracellular matrix.
b. Macrophages
Have irregular shapes with short branching and are capable of engulfing bacteria and cellular debris by phagocytosis. They develop from monocytes, a type of WBC (white blood cell).
c. Plasma cells
Develop from a WBC called a B Lymphocyte. Plasma cells secrete antibodies, proteins that attack or neutralize foreign substances in the body. Thus, plasma cells are an important part of the immune system.
d. Mast cells
Abundant alongside blood vessels that supply CT. They produce histamine, a chemical that dilates small blood vessels as part of the inflammatory response.
e . Adipocytes
Also called fat cells or adipose cells, these are the CT cells that store triglycerides (fats). They are found deep to the skin and around organs such as the heart and kidneys. WBC’s are not significant in CT but in response to certain conditions they migrate to CT (sites of infection, allergic responses, etc.) 2. The space between connective tissue cells is filled with a liquid medium called matrix . The matrix is maintained by continuous secretions from surrounding cells and has two main components: Ground Substance and fibres.
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