Write briefly about the following:
(i) Ciliated epithelium, (ii) Adipose tissue, (iii) Spongy bone, (iv) Dense bone, (v) Replacing bone, (vi) Investing bone, (vii) Haemopoiesis
(i) Ciliated epithelium: This epithelium consists of columnar or cuboidal cells. Columnar cell possesses delicate and hair like projection (cilia) at their free surfaces. They occur in urinary tubules, fallopian tubes, trachea and kidney tubules.
Adipose tissue : It is a specialised form of aerolar tissue where it contains mainly fat cells or adipocytes. They are believed to be the modified fibroblasts. Besides fibroblasts, the matrix also contains macrophages, collagen fibres and elastic fibres. This tissue lies beneath the skin, around kidney and in mesentery and bone marrow. It synthesis, stores and metabolises fat and forms insulating layer beneath the skin.
(iii) Spongy bone : In this bone, there is no concentric organisation like the Haversian system. The bone marrow cavities are large and irregularly arranged. It contains network of many fine irregular bony plates called trabeculae. Each trabeculae is composed of many irregularly arranged lamellae with lacunae between them.
(iv) Dense bone: It is comparatively hard and compact bone where haversian canals occur between the concentric lamellae of bony matrix. The lacunae containing osteocytes are found within the two lamellae. Haversian canals supply blood vessels and nerves to the bone.
(v) Replacing bones : These bones are synthesized by the replacement of cartilagenous cell (chondriocy tes) by the bony cells (osteocytes) e.g., humerus bone.
(vi) Investing bone : This bone is synthesized by the transformation of connective tissues into the investing bone e.g., bones of skull.
(vii) Haemopoiesis : It is the formation of new
erythrocytes from the haemopoietic tissue. The haemopoietic tissue in the young foetus is liver and spleen whereas in the adults, it is the bone marrow of long bones. The haemopoietic tissue synthesises millions of RBCs every minute and its excess lot is stored in the spleen.