Connective Tissue

Connective Tissue• The major component of connective tissue is the

extracellular matrix• Extracellular matrix in turn comprises of protein

fibres and ground substance• The wide variety of connective tissue types is

because of the variations in the composition and amount of 3 components (cells, fibres, and ground substance).This is the reason for the remarkable structural, functional diversities of connective tissue

• The connective tissue originates from Mesenchymal cells which in turn is originated from the mesoderm

• Three main components of connective tissue are

1. Cells2. Fibres3. Ground substance

Cells of the Connective Tissue

• Some important cell types present in Connective Tissue are

• Fibroblasts• Macrophages• Leukocytes• Adipose cells

Fibroblasts

• Fibroblasts systhesizes collagen, elastin, glycosaminoglycans and proteoglycans.

• Involved in production of growth factors• In the case where the spaces left after injury to

tissues whose cells do not divide (eg:cardiac muscle) are filled with connective tissue.This property is atributed to the presence of fibroblasts

• Most common cells in the connective tissue

Macrophages

• They constitute the mononuclear phagocyte system. • Monocytes and macrophages are phagocytes, acting in

both non-specific defense (innate immunity) as well as to help initiate specific defense mechanisms (adaptive immunity)

• In certain regions macrophages have special names • Kupffer cells in liver,• microglial cells in CNS• Langerhans cells in Skin• Osteoclasts in bone tissue

Leucocytes

• White blood cells are the wandering cells of the connective tissue which migrate from the blood vessels by a process called diapedisis.

• They function in defense against various foreign substances including micro-organsims

• Various types of leucocytes are plasma cell, neutrophil, eosinophil, basophil, lymphocye, monocytes.

Adipose cell

• Adipose cell is a specialized connective tissue cell that have become specialized for storage of energy and production of heat.

• Functions as a largest repositor of energy and thermal insulator.

• In certain places it fills up the spaces between organs where they keep the particular organs in place.

• Adipose tissue is nothing but a special type of connective tissue in which adipose cells predominate

Collagen fibers

• inelastic and give tensile strength• secreted by fibroblasts

• Reticular fibers:• flexible network (spongy texture) to the

organs that are subjected to changes in volume

• form extensive network forming the stroma of glands especially endocrine glands and liver, smooth muscle, endoneurium and stroma of hematopoietic organ

• Elastic fibers: formed by elastin• stretch easily in response to stretch

Classification of connective tissue

Connective tissue proper

depending on the density of the fibres and cells and arranged classified into various type

Loose areolar tissue : more abundant of the two types

- delicate, not resistant to stress, well vascualrised

- fills the spaces between muscles, form sheath for blood vessels in the dermis of the skin, in serous lining of the cavities

Dense connective tissue

Densely packed in places that require mechanical support

Contain more fibres (mainly collagen fibres) and few cells

Less flexible

Found in tendon, capsule of glands, ligament, dermis of skin, deep and superficial fascia, connective tissue septa between muscles

difference between loose and dense connective tissue

Dense irregular connective tissue

-collagen fibres in bundles without definite orientations

-- found in dermis of skin

Dense regular connective tissue:

- white fibrous tissue (collagen fibres)

- yellow elastic tissue (elastic fibres )

fibres arranged in definite pattern with nuclei of fibroblasts oriented parallel to fibres

Tendon – an example of dense regular white fibrous tissue

-since stress is exerted in one and same direction, fibre bundles are arranged linearly

vertebral column ligaments are example for elastic tissue (Yellow elastic tissue)

-arrangement may be in the form of fibres or in sheets (in the tunica media of large blood vessel)

Mucous tissue - embryonic tissue:

-loose tissue; contain pluripotent cells; has abundant ground substance and little fibres; high content of hyaluronic acid

e.g Wharton’s jelly in umbilical cord

Adipose tissue:

Aggregation of fat cells (adipocytes) in lobules

- store energy in the form of triglycerides (low density with high caloric value)