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:

1. The connective tissues proper. 2. The skeletal tissues. 3. The vascular tissues.

1. 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 .

oblasts, all lying embedded in an extensive emifluid or gelatinous matrix.

(d) Mucous connective tissue. Examine a T.S. of the umbilical cord of a placental mammal and not the mucous connective tissue with few white fibers and stellate cells or fibrs

E : elastic fiber,C : collagen fibers

II-Dense connective tissue:-Can further subclassified into: -

1- Dense irregular connective tissue, which characterized by an abundance of fibers and few cells (example the dermis in skin)

C: collagen,F: fibers , D: duct of sweat gland, E: elastic fibers

2-Dense regular connective tissue ,which characterized by ordered and densely packed in parallel arrays of fibers .This can subdivided into: (a) Fibrous connective tissue. Examine an L.S. of a tendon and note the

) Elastic connective tissue .xamine an

of the gam

dense connective tissue in it with white fibers running in bundles along the length of section. The yellow fibers are few.

b(E

L.S.

lientu

m nuchae of and note the numerous branching and yellow fibers؛ the white bers are few.

fi

2-

The S

Elastic fiber (1 BV :blood vesse

, areolar co .t. ; elastic ) l . C: collagen fibers . D: duct of sweat gland . E: elastic fibers

keletal Tissues: These tissues compose the skeleton. They are either cartilage or bone. I-Cartilage Is a specialized form of connective tissue in which the extracellular matrix has a firm consistency, it is essential for the development and the growth of long bones, It consist of cells (Chondrocytes) and an extensive extracellular matrix composed of fibers nd ground substance. The cells are located in cavities called lacuna, also it

a capsule like sheath of dense ue. Three forms of cartilage have evolved,each exhibiting

atrix composition.

yaline Cartilage. Examine a T. S. of the trachea of the rabbit. Note the matrix is solid and clear, and that the chondroblasts or chondrocytes

either singly or in-groups of twos, fours or rarely eighths. Note in a clear capsule or lacuna and

asurrounded by the perichondrium which is connective tissvariations m (1)- Hthatare arranged that the single or group of chondroblasts lieshe presence the perichondrium. t

A, B,C progressive stages in chondrocytes differentiation Ca : calcium deposits Cap: capsule Ch : cG :gL :laLi :liP : Asterisk, capsule of a lacuna, but with lacuna but with

,

hondrocytes lycogen cuna pid perichondrium

lacuna and contained chondrocyte not included within the

) - Elastic cartilage.Has a matrix rich in yellow fibers and surrounded by perichondrium it is found in the ear pinna and epiglottis of mammals.

(c

C:cartilage ,F Arrow, lacuna

: fibroblast ,

AT: adipose tissue ,E : elastic fiber, EC: elastic cartilage , MG: mucous gland

(b)- Fibrous cartilage. Has matrix rich in white fibers and there is no perichondrium, it is found in the

ntervertebral discs in mammals. ie