Connective Tissue 结 缔 组 织 Department of Histology and Embryology Medical college in Three Gorges University

What is connective tissue? As the name suggests, it connects the various tissues of the body and gives them support. 1) fill the interstices between the specialized elements 2)hold them together 3)support

Introduction General structure and function Two major constituents - cell & - extracellular matrix Classification of connective tissue:

cells 细胞 extracellular matrix 细胞外基质 Major constituents Fiber 纤维 Ground substance 基质

Connective tissue proper: Loose connective tissue Dense connective tissue Reticular tissue Adipose tissue:

Specialized connective tissue -bone -cartilage -blood

All the cells of connective(supporting) tissue are derived from mesenchymal cells. This cell is also named as undifferentiated mesenchymal cell. which are relatively unspecialized and are capable of differentiation into all the cell types found in mature supporting tissue.

Function: Connective tissue provides structural and metabolic support for other tissue and organs throughout the body.

Loose connective tissue

Two categories fixed cells (intrinsic) transient cells The cells of supporting /connective tissue

cells of CT Fixed cells Transient cells. Fibroblasts Adipose cells Mast cells Macrophages Undifferentiated mesenchymal cell Plasma cell Blood cell Macrophage

Fixed cells are a resident population of cells that have developed and remain in place within the connective tissue, where they perform their functions. The fixed cells are a stable and long-lived population that include:

Transient cells (free or wandering cells) originate mainly in the bone marrow and circulate in the blood stream. Upon receiving the proper stimulus or signal, these cells leave the blood stream and migrate into the connective tissue to perform their specific function.

1. Fibroblast 成纤维细胞 : Fibroblast, which synthesize the extracellular matrix of connective tissue are derived from undifferentiated mesenchymal cells. LM EM Function

Active fibroblast are readily demonstrated in healing wounds. The nuclei are large and rounded in shape with prominent nucleoli (large rounded vesicular nuclei). These are the cells with multiple processes, and basophilic cytoplasm.

In rest phase(inactive ), these are found along the bundles of collagen fibres and appear in section as spindle shaped cells and flattened nucleus with long tapering ends called fibrocytes (inactive fibroblast).

EM: RER Golgi

Function: Fibroblast can synthesize protein, such as collagen and elastic that form collagen, reticular and elastic fibers and ground substances.

The healing of injury or surgical incisions depends on the reparative capacity of connective tissue. The main cell type involved in repair is fibroblast. (during wound healing fibrocyte reveres to fibroblast, myofibroblast )

2.Macrophages: ( histiocytes) 巨噬细胞： They belong to the mononuclear phagocytic system analogous to the monocytes of blood and are distributed throughout all supporting tissues where they may show intense phagocytic activity.

fixed macrophages free macrophages They function in removing cellular debris and in protecting the body against foreign invaders. Secretion: cytokines, growth factor Antigen presenting cells

LM: Inactive macrophages are small and drape themselves it easily confused with fibroblast goal. In contrast, actively phagocytic macrophages are plump.They may be easily recognized by their large size content of engulfed material.

EM: In quiescent macrophages, lysosomes are abundant but their number is much reduced in actively phagocytic cells.

Function: 1.Actively phagocytic cells are involved in amoeboid movement and phagocytosis. 2. play an important role in immune mechanisms: antigen presenting cells.

In addition to their role as tissue scavengers, macrophages play an important role in immune mechanisms since they are often the first cells to make contact with antigens. Lymphocytes are then stimulated to undergo specific immune responses.

3. Mast cells 肥大细胞 : Mast cells are functionally analogous to basophils but there are structural differences.

LM: The cells are large round or ovoid in shape. The nucleus is round and small, relative to size of the cell, and is often observed by large number of intensely stained granules in the cytoplasm.

When stained with certain blue basic dyes such as toluidine blue the granules bind to the dye changing its colour to red. These components of a cell or tissue stain in a colour different from that of the dye used, the staining is said to be metachromatic 异染性.

Function: Mast cells degranulation results in the release of histamine and other vasoactive mediators which induce the immediate hypersensitivity response (characteristic of urticaria （荨麻疹）, allergic rhinitis and asthma) and anaphylactic shock.

The granules contain histamine, neutral proteases heparin and eosinophil cheotactic factor of anaphylaxis and slow-reacting substance of anaphylaxis. (SRS-A)

4.Plasma cell 浆细胞 : These differentiated cells,which are derived from B lymphocytes that have interacted with antigen,produce and secrete antibodies.

LM: Plasma cells are large, ovoid cells 20 micronmeter in diameter, with an eccentrically placed nucleus that have a relatively short life span of 2 to 3 weeks. The nucleus is spherical and typically offset or eccentrically positioned with basophilic cytoplasm. It is small, not much large than the nucleus of the lymphocyte.

5. Adipose cells: (1)adipocytes, also are derived from undifferentiated mesenchymal cells. (2)Adipose cells are fully differentiated and do not undergo cell division. (3)They function in the synthesis and storage of triglycerides.

There are two types of fat cells, which constitute two types of adipose tissue. unilocular fat cell: with a single, large lipid droplet, formed white adipose tissue, (much more than brown fat) multilocular fat cells: with multiple droplets, form brown adipose tissue.

In the usual histological preparations, fat is dissolved during processing of the tissue and there remains only a thin layer of cytoplasm slightly thickened in one area to accommodate the nucleus.The fat cells can be stained with Sudan and Scharlach Red which impart these cells orange and red respectively.

This is a higher magnification of fat cell with a large droplets and cytoplasm pushed to the periphery membrane, nucleus is flattened against the membrane also.

What is about the brown fat cells? The nuclei of brown adipocytes are seen to be eccentrically located within the cell but, unlike those of white adipocytes, the nuclei are plump and surrounded by a significant quantity of strongly eosinophilic cytoplasm and are not pushed to the periphery.

6. Leucocytes in loose supporting tissue: The appearance of leucocytes within tissue sections differs greatly from the appearance seen in blood smears.

Leucocytes: lymphocytes monocytes Neutrophils Eosinophils Basophils

Extracellular matrix

extracellular matrix fiber Ground substance Elastic fiber Reticular fiber Collagen fiber

Ground substance derived its name from being an amorphous transparent material which has the properties of a semi-fluid gel. Tissue fluid is loosely associated with ground substance,thereby forming the medium for passage of molecules throughout supporting tissues and for the exchange of metabolites with the circulatory system. Ground Substance 基质

Ground substance is basically composed of glycosaminoglycans (mucopolysaccharide 粘多糖 ) in the form of hyaluronic acid （透明质酸） and proteoglycans （蛋白多糖）. These huge molecules are entangled and electrostatically linked to one another and water to form a flexible gel through which metabolites may diffuse. It consist of water, carbohydrates and proteins.

Collagen fiber 胶原纤维 Collagen is the main fiber type found in most supporting tissues and is the most abundant protein in the human body. Its most notable function is the provision of tensile strength. Fibers

Collagen fibers are seen in bundles.it is composed of a protein called Collagen, which is acidophilic due to its positively charged side groups; thus in standard H-E preparations. Collagen is eosinophilic (i.e. pink- stained).

Reticular fibers 网状纤维 : ( 1 )These fibers are finer ( 2 )They are uneven in thickness ( 3)They form a network(or reticulum) by branching they do not run in bundles (4)They cannot be stained in H-E but are able to absorb metallic silver by which they are stained black.

Elastic fibers 弹性纤维 : In areola tissue, elastic fibers are much fewer than those of collagen.they run singly ( not in bundles), branch and anastomose with other fibers and thinner than those of collagen ( µm). These are made up of a protein called elastin. When a fiber is broken, the ends retract or recoil. Elastic fibers do not stain with the usual stain for collagen.

Physical properties: As their name implies elastic fibers can be stretched (like a rubber band ) and return to their original length when tension is released.

Loose connective tissue 疏松结缔组织 : It is seen to be made up mainly of bundles of loosely arranged fibers that appear to enclose large spaces. Spaces are also called areolar. Such tissue is referred to as areolar tissue. The feature of connective tissue proper

Loose collagenous tissue supports the epithelial linings of the gastrointestinal, respiratory and urinary tracts, form the deeper layers of the skin and occurs as a loose interstitial packing in many other organs.

There are some space in the section, which are also called areola. Such tissue is referred to as areolar tissue.

Dense connective tissue:(fibrous tissue) In many situations the fiber bundles are much more obvious, and form a dense mass. This kind of tissue is referred to as dense connective tissue.

Dense regular connective tissue 致密结缔组织 : The bundles of collagen are arranged parallel to one another in a very orderly manner. This kind of tissue is called dense regular connective tissue. tendon of the muscles many ligament.

Dense irregular connective tissue: In other situations the collagen bundles do not show such a regular arrangement, but interlace in various directions forming dense irregular tissue.

Dense CT Capsule invest the organs

Reticular tissue 网状组织 : This is made up of reticular fibers. In many situations (e.g., lymph nodes, gland )these fibers form supporting networks for the cells. In some situations (bone marrow, spleen, lymph nodes) the reticular network is closely associated with reticular cells.

Adipose tissue 脂肪组织 White adipose tissue: 白色脂肪组织 It is distributed throughout the body particularly in the deep layers of the skin.(it is named as superficial fascia in anatomy)

Brown adipose tissue: 棕色脂肪组织 This type of adipose tissue is composed of multilocular fat cells. This tissue may appear tan to reddish brown because of its extensive vascularity and the cytochromes present in its abundant mitochondria.