B - THE CONNECTIVE TISSUES
These tissues arise from the mesoderm only and, in contrast to the epithelia tissues, they have a large amount of intercellular substance or matrix among their cells. They are never to be found on surface, and they do not rest on a basement membrane. Their main function is to connect other tissues or organ together or support them. Their ground substance is either solid or fluid and accordingly they are classified into three main groups:
The connective tissues proper.
The skeletal tissues.
The vascular tissues.
The Connective Tissues Proper .
The tissues that belong to this category are divided into two general subtypes :-
I) Loose connective tissue
II) Dense connective tissue
I- Loose connective tissue: - Is characterized by loosely arranged fibers and an abundance of cells, there are four subtypes in this category;
(a) Areolar connective tissue. Note the white or collagenous fibers which are wavy , do not branch and run in bundles; and the yellow or elastic fibers which are thinner, run singly and branch to form a network . the following cell types : the fibrocytes which secrete the fibers and have branched irregular forms and clear cytoplasm ; the mast cells which secrete the ground substance and have a distinctly granular cytoplasm ; the large amoeboid macrophages ; the fat cells full of fat droplets ; and the small plasma cells with eccentric nuclei . Some white blood cells , such as some eosinophils and lymphocytes , may also be found in small numbers . Note the clear, amorphous and homogeneous matrix
(b) Reticular connective tissue. Examine a section of the spleen or of a lymph gland and note the reticular tissue in it , with branching and anastomosing reticular fibers .
(c) Adipose connective tissue. Examine a section of the fat body of the toad and note the adipose connective tissue with predominant fat cells
loaded with fat globules .
