connective tissue. origin of connective tissue cells

CONNECTIVE TISSUE

Origin of connective tissue cells

LOOSE CONNECTIVE TISSUE

• Characterized by loosely arranged fibers and an abundance of cells

• The primary location is :• beneath those epithelia that cover the body

surfaces and line the internal surfaces of the body

• In association with the epithelium of glands• surrounds the small vessels

Loose connective tissue (scheme)

Light micrograph of loose C.T.

Connective tissue cells can be categorized as fixed and wandering

Fixed cell population Wandering cell population

- Fibroblasts - Lymphocytes- Myofibroblasts - Plasma cells- Macrophages - Neutrophils- Mast cells - Eosinophils- Adipose cells - Basophils- Reticular cells - Monocytes- Undifferentiated stem cells

E.M. of fibroblast portion with the adjusting collagen fibers

E.M. of a macrophage surrounded with collagen fibers

L.M. of macrophages in liver (von Kupffer cells)

Specific names of different location macrophages (macrophage

system)• Monocytes (blood)• Macrophages-histiocytes (connective tissue)• Dust cells (lung alveoli)• Kupffer cells (liver)• Langerhans cells (skin)• Hofbauer cells (placenta)• Osteoclasts (bone)• Microglia (brain)• Dendritic cells (lymphoid organs)• Microfold (M) cells (intestine)

E.M. of a mast cell

Physiologically active substances secreted by mast cells

E.M. of adipocytes on different stages of maturation

Plasma cell schematic representation

NON-CELLULAR COMPONENTS OF CONNECTIVE TISSUE

Fibers• Collagen fibers – forms the most abundant fibers of

connective tissue • Reticular fibers – provide a supporting framework for

the cellular constituents of lymphoid organs mostly• Elastic fibers – provide tissues with the ability to

respond to stretch and distension

Ground substance – consists largely of highly hydrated proteoglycans, of hyaluronic acid, and GAG (chodroitin-sulphate, heparan-sulphate, dermatan-sulphate, keratan-sulphate)

CLASSIFICATION OF CONNECTIVE TISSUES

DENSE CONNECTIVE TISSUE

• DENSE IRREGULAR CONNECTIVE TISSUE is characterized by an abundance of fibers and few cells. It forms the reticular or deep layer of the dermis

• DENSE REGULAR CONNECTIVE TISSUE is characterized by ordered and densely packed arrays of fibers and cells. It is the main functional component of tendons, ligaments, aponevroses

L.M. of a tendon, cross section