Connective tissue may be defined as that group of tissues predominantly composed of extracellular or intercellular material (matrix), secreted mainly by its cells, which are, therefore, usually widely spaced. The extracellular matrix consists of fibers and amorphous ground substance. So there are three elements of connective tissue (cells, fibers and ground substance). ALLAH Subhanahu develops connective tissue from embryonic mesoderm and, in the head region, largely from neural crest cells.
CLASSIFICATION • Primitive or undifferentiated connective tissue Mesenchymal tissue • Intermediate or maturing connective tissue Mucoid tissue • Adult or Mature connective tissue
Mature Connective Tissue is mainly of three types • Soft, • Hard and • Fluid-like
Soft Connective tissue is again of two types • Loose connective tissue • Dense connective tissue
Classification of Loose connective tissue • Ordinary • Areolar (Loose Areolar connective tissue) • Cellular (Cellular connective tissue) • Vascular (Vascular connective tissue) • Special • Adipose • Reticular • Lymphoid • Pigmented
Classification of Dense connective tissue • Irregular (Dense Irregular connective tissue) • Regular (Dense Regular connective tissue) • White fibrous tissue • Yellow elastic tissue
Hard (Skeletal connective tissue) • Cartilage Hyaline Non-Articular Articular Elastic Fibrous • Bone Compact Spongy or Cancellous
Fluid like (Haemopoietic connective tissue) Bone marrow or Myeloid tissue Blood
CLASSIFICATION OF CONNECTIVE TISSUE • Primitive or undifferentiated connective tissue Mesenchymal tissue • Intermediate or maturing connective tissue Mucoid tissue • Adult or Mature connective tissue • Mature Connective Tissue is mainly of three types Soft, Hard and Fluid-like • Soft Connective tissue is again of two types • Loose connective tissue • Dense connective tissue • Classification of Loose connective tissue • Ordinary Areolar (Loose Areolar connective tissue) • Cellular (Cellular connective tissue) • Vascular (Vascular connective tissue) • Special Adipose • Reticular • Lymphoid • Pigmented
Classification of Dense connective tissue • Irregular (Dense Irregular connective tissue) • Regular (Dense Regular connective tissue) • White fibrous tissue • Yellow elastic tissue • Hard (Skeletal connective tissue) • Cartilage Hyaline Non-Articular • Articular • Elastic • Fibrous • Bone Compact • Spongy or Canccllous • Fluid like (Haemopoietic connective tissue) • Bone marrow or Myeloid tissue • Blood
COMPONENTS OF CONNECTIVE TISSUE • There are three components of connective tissue: • Cells • Fibers • Ground substance
Cells • Mesenchymal cells • Fibroblasts Fibrocytes • Macrophages • Plasma cells • Mast cells • Fat cells • Reticular cells • Lymphocytes • Pigment cells
Fibers • Following types of fibers are found in different types of connective tissues. • Collagen fibers • Reticular fibers • Elastic fibers
Mesenchymal connective tissue • It is also called Mesenchymal connective tissue or simply mesenchyme. • In fact it is nothing but embryonic mesoderm, may be extraembryonic or intraembryonic mesoderm. • It is typical unspecialized connective tissue of early weeks of embryonic life. • It is composed of mesenchymal cells and matrix.
Mesenchymal cells have branching processes. They often appear to join those of neighboring cells, although they do not form a true syncytium. Ground substance is a coagulable fluid in the earliest stages but later contains fine reticular fibers. So matrix consists of ground substance and fine reticular fibers. The mesenchymal cells and reticular fibers are gradually replaced by mature types of cells (e.g. fibroblasts) and collagen fibers respectively as the mesenchyme develops and differentiates into the adult connective tissue.
Undifferentiated Mesenchymal cells: • They are small and stellate in shape, usually located along the walls of blood vessels, particularly capillaries, where they are referred to as perivascular or adventitial cells. • They can differentiate into the usual cell types found within loose connective tissue or into smooth muscle cells of blood vessels when required.
Mucoid tissue • It is also called mucoid or mucous connective tissue. • It is an intermediate type of connective tissue, found chiefly as a stage in the development of connective tissue from mesenchyme to the adult type. • It also exists as Wharton's jelly, which form the bulk of umbilical cord, where it does not differentiate further.
It consists of a copious matrix and large stellate cells called fibroblasts. • The matrix is largely made up of soft and jelly like ground substance and a fine meshwork of collagen fibers. • Usually few fibers occur in typical mucoid tissue, though at birth the umbilical cord shows a considerable development of perivascular collagen fibers.
Fibroblasts have oval nuclei and branching processes often appear to fuse with those of neighboring cells. A few macrophages and wandering lymphocytes are occasionally found. SITES: In addition to umbilical cord, after birth, mucoid tissue is still to be seen in the pulp of a developing tooth. In the adult the vitreous body of the eye and the nucleus pulposus of the intervertebral disc are persistent forms of mucoid tissue in which the fibers and cells ore very few in number,
Umbilical CordThe two arteries and one vein (upper left) of the umbilical cord are surrounded by a large amount of connective tissue. • The proportion of "ground substance" is higher in this tissue, and it is sometimes called "Wharton's jelly".
Umbilical CordA closer look shows the preponderance of ground substance (largely glycoproteins and proteoglycans) and relatively few cells.
Loose connective tissues • It is formed by direct differentiation of mesenchyme. • It is loosely arranged and fibroelastic. • It binds other tissues, organs and their components together. • Owing to its flexibility, it allows a considerable degree of mobility between different structures and organs.
It contains fibroblasts, macrophages, reticular cells, plasma cells, mast cells, and lymphocytes. • Neutrophils and eosinophils are also seen. • Collagen fibers are most prominent. • Elastic fibers form a continuous branching network. • Reticular fibers are present in the loose connective tissue that borders upon other structures.
Loose connective tissue derives its name from the fact that its fibers are loosely arranged. The cells and fibers are embedded in fluid like ground substance. • SITES: Loose connective tissue is widely distributed in the body. In fact it occupies any unoccupied space in the body.
Loose connective tissue is of two types: • Ordinary loose connective tissue • Special loose connective tissue
Ordinary loose connective tissue: • There are three varieties of ordinary loose connective tissue.
Areolar connective tissue: • The name areolar is descriptive of the general appearance produced by small spaces, which contain only an amorphous ground substance, which is usually not seen because it is washed off in routine preparations. Here the most common cells are fibroblasts and macrophages. Fat cells (adipocytes) are seen in small groups, particularly around blood vessels.Reticular cells, plasma cells and mast, cells are also seen.Lymphocytes are scattered throughout the areolar tissue.
SITES: • It forms all the superficial fascia and part of the deep fascia e.g. cribriform fasia. • It also forms Submucosa and mucosa (lamina propria) of digestive, respiratory and urogenital tracts. • It also covers these tracts. • Here it is in the forms of fibrosa or subserous connective tissue. • Fat free subcutaneous connective tissue as in eyelids, penis, scrotum and labia is also areolar connective tissue.
It is found between and around muscles, nerves and blood vessels, particularly endomysium and endoneurium. Similarly it is also found around and in the tendons, aponeurosis and ligaments. It is present underneath the endothelium as subendothelial connective tissue and forms the adventitia of the blood vessels.
It covers certain organs such as pancreas, kidneys etc. • It divides the organs and glands into lobes and lobules and even present within the lobules. • Here it is called Interlobar, interlobular and intralobular connective tissue.
Cellular connective tissue: • When the cellular component increases the loose areolar connective tissue becomes cellular connective tissue. • SITES: • Cortex of the ovary
Vascular connective tissue: • When the blood vessels increase in a loose areolar connective tissue, the tissue is given the name vascular connective tissue. • SITES: • Medulla of the Ovary • In fact in a loose connective tissue according to the requirements ALLAH subhanahu Taala increases the cellular element or vascular element, human beings name it cellular connective tissue or vascular connective tissue accordingly.
Fibroblasts • These are one of the two most numerous cells of areolar connective tissue, the other being macrophages or Histiocytes. Fibroblasts, as their name suggests, are considered to be responsible for the formation of the fibers and also are thought to elaborate most, if not all, of the amorphous component of the matrix (principally glycosaminoglycans ).
They are large, flat, branching cells, which appear fusiform, or spindle shaped in profile. • The branching processes are slender. In most histological preparations, the outlines of the cells are indistinct. • The nucleus is deeply stained with basic dyes. • It is oval or elongated with one or two nucleoli and finely granular chromatin.
In young fibroblasts, which are actively engaged in protein synthesis the high concentration of granular endoplasmic reticulum. Mitochondria appear as slender rods and are most numerous near the nucleus. Golgi apparatus is also present close to the nucleus. Microtubules are also present and seem to be required for translocation of secretary vesicles.
Fibrocytes • The old and relatively inactive fibroblasts are given the name fibrocytes. • Here the cytoplasm is sparse and only weakly basophilic, the endoplasmic reticulum is scanty. • The nucleus is flattened and heterochromatic (close-faced).
Macrophages • ALLAH Subhanahu Taala has placed important agents of defense in the body called macrophages. • They are almost as numerous as fibroblasts in loose connective tissue and are more abundant in richly vascularized areas.
Generally they are irregular shaped cells with processes, which usually are short and blunt. Occasionally they may exhibit long, slender branching processes. They are relatively larger cells (15-20um in diameter). Their nuclei are ovoid, usually indented and heterochromatic. Nucleolus is present but not so conspicuous. The cytoplasm is mildly basophilic and typically has a frothy appearance under the light microscope. Ultrastructurally, macrophages contain numerous lysosomes, which digest ingested material.
The macrophage is derived from the blood-borne monocyte, which migrates into tissue and differentiates into this phagocytic cell. • Here it is stained blue after gobbling up trypan blue stain. • Look for the irregular cell border and numerous phagosomes.
ALLAH SubhanahuTa`ala has enabled macrophages to multiply mitotically to some extent, but he develops them largely from haemopoeitic stem cells in the bone marrow, circulates in the blood as monocytes before sending them to their final extravascular sites through the venule walls.
There are two types of macrophages: Stationary or fixed macrophages: Attached to fibers of the matrix. They are irregular with many filopodia. Motile or nomadic macrophages: Free with in the matrix. They are of a more rounded and regular form.
Macrophages are important phagocytes, forming part of the macrophage system. They are also able to dispose of dead or moribund cells prior to tissue regeneration. Because of their mobility and phagocytic activity, they are able to act as scavengers, engulfing extravasated blood cells, dead cells, bacteria, and foreign bodies.
Fat cells • There are two types of fat cells: • Unilocular fat cells • Multilocular fat cell.
Mast cells • ALLAH Rab-ur-Ezzat has blessed us with very important type of defense cells called mast cells. • They are widely distributed in loose connective tissues and often preset in the fibrous capsules of certain organs such as liver. • They are characteristically numerous in relations to blood vessels and nerves.
Mast cells are irregularly oval in outline, about 12um in diameter, with short pseudopodia, an indication of their slow mobility. • The nucleus is centrally placed and relatively small. • They are easily identified by large number of prominent Cytoplasmic granules. • Mast cells also contain a well developed Golgi apparatus and scanty endoplasmic reticulum.