special connective tissue of animals are -Reticular Tissue, Adipose Tissue, Brown fat tissue, Pigmented Connective Tissue
Reticular tissue
- It is composed of cells and reticular fibre network. The cells have stellate shape with processes which extend in all directions and joins those of wrapped by reticular fibres.
- The reticular tissue forms the frame work of organs like lymphatic glands; spleen, red marrow of bones. The reticular cells line the lymph sinuses in lymphatic glands or blood sinusoids in spleen, Liver Red marrow etc. These cells are actively phagocytic and form part of the Reticulo-endothelial system.
- It appears likely that the reticular cells may be of different types which cannot be distinguished by morphological means alone. Some of them have retained their embryonic or developmental tendencies and in red marrow give rise to erythrocytes and granulocytes in lymphoid tissue to lymphocytes etc and these primitive reticular cells as they are some times called are usually non-phagocytic.
- The reticular tissue forms the frame work of organs like lymphatic glands, spleen and red marrow of bones. The reticular cells line the lymph sinuses in lymphatic glands or blood sinusoids in spleen, liver red marrow etc. These cells are actively phagocytic and form part of the Reticulo-endothelial system.
Adipose tissue
- Fat is regarded as arising from specific cells (steatoblasts). Fat cells are found isolated or in groups in all areolar connective tissue but in which justifies the name adipose tissue. The largest deposits of fat are found in subcutaneous connective tissue (panniculus adiposus) in the kidney region in the mesenteries and mediastinum and in the cervical axillary and inguinal regions.
- Fat is different from other connective tissues, in that the cells and not the intercellular substance make up the bulk and determine the nature of the tissue. The large ovoid or spherical cells consist of peripheral cytoplasmic membrane enclosing a large fat droplet. The nucleus is flattened and surrounded by a small amount of cytoplasm and is usually found pressed against the cell wall.
- In sections, when the fat is dissolved out, the cells appear as empty rings or have a signet ring shape when the plane of section passes through the nucleus. This is so when they occur isolated or in small groups. But in denser masses due to pressure of adjacent calls they become polyhedral. Fat is usually arranged in groups or lobules, each lobule being separated from the other by areolar connective tissue. Delicate connective tissue passes between the cell and serves as bed for capillaries.
- Chemically fat contains esters of glycerol and certain fatty acids. It is not soluble in cold alcohol or water, but readily dissolves in xylol. That is why fat dissolves in ordinary preparations. But by special methods fat can be stained (e.g. black by Osmic acid by Sudan red III).
Brown fat tissue
- This is different from the common or white fat tissue. In rats and other rodents, it is highly developed and forms yellowish, lobated masses in certain parts of the body – between the scapulae, on the neck, in the mediastinum, in the inguinal region and elsewhere.
- Microscopically, latter name was given because this tissue was believed to play a peculiar role during hibernation. The brown fat contains a pigment which gives the tissue its colour.
- The fat cells assemble in groups separated by this network of collagenous or reticular fibres and numerous capillaries. The microscopic structure suggests an endocrine gland. While the common fat tissue loses or accumulates neutral fat with changes in the nutritional condition of the animal, these factors do not seem to affect the brown fat tissue.
Pigmented connective tissue
- The cells of this tissue occur in the chorioid and iris of the eye and in the corium of dark skinned animals.
- The cytoplasm is filled to a varying degree with brown or black pigment which is usually melanin. They are specialized cells, called as Melanocytes, irregular in outline with cytoplasmic processes.
Blood and nerve supply of connective tissue
Connective tissue received its blood supply from the vessels which pass through them and for which they form supporting bed. For dense connective tissue the supply is scanty.
Nerves are numerous in connective tissue. Some of them terminate in the tissue itself, but other go to epithelium or muscle. Tendons, fibrous membranes and periarticular connective tissue have special nerve endings.
