Connective Tissue - Anat

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Connective Tissue
Composed of :

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– Cells (fibroblast, mast cell, and etc.)
– Extra cellular matrix (ground substance and fibers)

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Connective Tissue
Its functions are:

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– Providing structural support
– Serving as a medium for exchange
– Aiding in defense and protection
– Storage of fat

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Connective Tissue
Is classified as:

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– Connective tissue proper
–Specialized connective tissue (bone, cartilage, blood).

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Connective Tissue
Arises from:

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-embryonic mesenchymal tissue

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Types of CT Proper (Loose CT)

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-Is composed of a loose  arrangement of fibers and dispersedcells embedded in a gel‐like ground substance and tissue fluid (lamina Properiain mucus membranes).
-It is the primary battle field between antigens, bacteria etc. and cells responsible for inflammation, allergic reactions and the immune response

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Types of CT Proper (Dense CT)

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-Contains a greater abundance of fibers and fewer cells than loose CT.
-Basedd on the orientation off collagen fibers, dense CT is classified intotwo groups:
1.Dense irregular CT;; collagen fibers distributed randomly and is found in the dermis and capsule of some organs.
2.Dense regular CT; collagen fibers are arranged into parallel cylinders. It is mainly found in tendons and ligaments.

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Fibroblasts

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-The most abundant cell type in the CT, that synthesizes almost all of the extra-cellular matrix
-They are usually elongated cells with cytoplasmic processes that contain a long euchromatin nucleus and abundant RER
-In active phase the cytoplasm is rather basophilic while in resting stage (fibrocyte) the cytoplasm is weakly acidophilic

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Collagen Fiber

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-Is the main ECM protein as well as major protein in body (30%-35%).
-It's flexible but strong and resistant to stretching
-Collagen is made from highly regular assembly of smaller subunits, tropocollagen molecules
-Each tropocollagen molecules is composed of 3 polypeptide chains (known as procollagens), in a triple helix.

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Collagen Synthesis

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-DNA is transcribed to mRNA in nucleus
-mRNA is translated to pre-procollagen at RER
-Pre-procollagen will be modified (to procollagen) in RER
-At ends of procollagen chains, some aa sequences (propeptides) are added to prevent spontaneous formation of collagen fibers in cell. Propeptides aren't part of the helix, so molecule resembles tightly wound rope with frayed ends.
-Procollagen will be secreted to ECM by trans golgi network
-Procollagen peptidases cleave the propeptides to form tropocollagen
-Newly formed tropocollagen molecules spontaneously self assemble to form fibrils

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Elastic CT

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-Is loaded with elastic fibers
-Elastic fibers are easily stretched, like an elastic band, so provide elasticity to ECM and thus to the structure that contain these fibers (skin, lung, bladder, arteries).
-The core of these fibers is composed of elastin
-The core is surrounded by a sheath of microfibrils

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Reticular CT

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-Type III collagen/reticular fiber is the major fiber component here
-Forms the architectural framework (stroma) of liver, adipose tissue, bone marrow, spleen, basement membrane, etc.

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Mast Cells

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-Arise from bone marrow stem cells
-Large cells with off-center usually spherical nucleus and lots of cytoplasmic granules (histamine, heparin, etc.) and processes (filopodia)
-Mast cells are found close to the arteries and in sites of inflammation and play a major role in allergic reactions as well

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Plasma Cells

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-Derived from B lymphocytes
-Produce and secret Ab's
-Large ovoid cells with eccentrically located nucleus, well developed RER, basophilic cytoplasm, and clock - face nucleus
-Close to the nucleus one may find a pale area which houses the golgi complex
-Lack of large secretory vesicles, is an indication of continuous secretion of antibodies by these cells.

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Macrophages

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-Derive from hematopoietic stem cells (monocytes)
-Remove cellular debris and protect against foreign invaders
-Produce cytokines and growth factors
-10-30 um in diameter with irregular cell surface (pseudopodia), basophilic cytoplasm, abundant lysosomes and RER plus a well developed Golgi, cytoskeleton and an indented eccentric nucleus

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Unolocular (White) Adipose Tissue

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-White (unilocular) adipose tissue is mainly found in subcutaneous layer, throughout the body and is richly vascularized
-Cell membranes possess receptors for insulin, growth hormone, norepinephrine and glucocorticoids, that regulate the uptake and release of f.a.'s and glycerol

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Multilocular (Brown) Adipose Tissue

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-Brown adipose tissue is found in the neck and inter-scapular region of infants and is highly vascularized
-The cells contain numerous mitochondria that are involved in rapid oxidation of f.a.'s (20x faster than white adipose tissue) to increase the body heat production rate (up to 3x)