Connective Tissue - Fixed Cells PDF

Dubai Medical College Histology Department Prof. Dr. Nadia M El Rouby Fixed CT cells 1. Fibroblast and Fibrocyte Fibroblast develops from pericytes and undifferentiated mesenchymal cells. When fibroblast becomes mature and less active...

Dubai Medical College Histology Department Prof. Dr. Nadia M El Rouby Fixed CT cells 1. Fibroblast and Fibrocyte Fibroblast develops from pericytes and undifferentiated mesenchymal cells. When fibroblast becomes mature and less active it changes into fibrocyte. Fibroblast (fiber-forming cell) can form the C.T. fibers and C.T. matrix. Site: It is numerous in areolar C.T. It is a branched cell with multiple cell processes and basophilic cytoplasm (?). The nucleus is vesicular (?). Fibroblast may change into a contractile cell (myofibroblast) which is rich in contractile filaments, so it helps in wound closure during healing. 1  Dubai Medical College Histology Department Prof. Dr. Nadia M El Rouby Functions: *They form collagen, elastin and reticulin proteins that polymerize to form the corresponding C.T. fibers. *They can also form the mucoprotein (organic component) of the C.T. matrix. *Their number increases during healing of wounds and in cases of C.T. damage. *Fibroblasts can change into contractile cells called myofibroblast that contract to help in closure of wounds. 2. Fixed Macrophages or Histeocytes Their origin is blood monocytes after their migration to C.T. They are motile cells. They are branched cells with multiple processes (pseudopodia). As they have pseudopodia, they are motile. These pseudopodia make the cell membrane irregular. Their cytoplasm is basophilic. It is rich in lysosomes and phagocytosed particles. The nucleus is indented, or kidney shaped. It is very rich in hetrochromatin so it is dark. This character differentiates it from fibroblast that has pale nucleus. The cells can be stained with vital stain as Trypan blue or black Indian ink. 2  Dubai Medical College Histology Department Prof. Dr. Nadia M El Rouby Functions: *They form the mono-nuclear phagocytic system which present all over the body. *They play an important role in the defense mechanism of the body. *They can trap, and transport antigens so act as antigen presenting cell. *They can engulf bacteria and old blood cells. *They can clean wounds from foreign bodies and debris. *Some macrophages join with each other to form multinucleated giant cells known as Foreign Body Giant Cell. 3. Adipose Cell or Fat Cell or Adipocyte: It is derived from mesenchymal cell after accumulation of fat droplets in its cytoplasm. There are two types of adipocytes: A) unilocular fat cell: It is a large oval cell with flat peripheral nucleus (signet ring appearance). The cell contains a large globule of fat which is surrounded with a small amount 3  Dubai Medical College Histology Department Prof. Dr. Nadia M El Rouby of cytoplasm. The cells are present mainly in the adipose C.T. & around blood vessels. In H and E-stained sections, fat cells appear as oval empty spaces because fat dissolves during preparation leaving a space. Fat cells can be stained orange with Sudan III or stained black with osmic acid or Sudan black. Functions: * Storage of fat * Support certain organs as kidneys & aorta. * Heat insulation. 4  Dubai Medical College Histology Department Prof. Dr. Nadia M El Rouby B) Multilocular adipocyte These cells are present in new-born. The cytoplasm contains many fat globules and huge number of mitochondria. Nucleus is rounded. The main function is heat production. Multilocular adipocytes present in newborn for heat production due to excessive heat loss resulting from immaturity of heat regulating center of the brain. Sites: they are usually present mainly in the neck, shoulders, back, axilla and para-aortic regions. 4. The Mesenchymal Cell = UMC It is an embryonic branched cell with a large oval nucleus and basophilic cytoplasm. It is present mainly in embryonic tissue. Function: It can differentiate itself into other types of C.T. cell. 5. pericytes They are pale branched cells with long cytoplasmic processes. They present immediately external to the endothelium of blood capillaries and small venules (pericytes = peri- around). They are considered mesenchymal cells which persist during adult life. Functions: *Pericytes can give rise to both fibroblasts and 5  Dubai Medical College Histology Department Prof. Dr. Nadia M El Rouby smooth muscle cells. *They play an important role in connective tissue and blood vessels process of healing. *Pericytes may be modified to form myoepithelial cells 1. Endothelial cells They line the inner surface of the blood capillaries and blood vessels constituting their endothelium. In adults they are considered as connective tissue cells. Functions: 1. They synthesize type IV collagen. 2. They can divide to form new capillaries in tissue damage. 3. They produce their own basal lamina. 2. Reticular Cells They are presented in the reticular C.T. They are modified fibroblasts that secrete reticular fibers. They are branched cells with a small oval nucleus and many processes which are attached with the reticular fibers and other reticular cells to form a network of reticular C.T. Functions: They form the stroma (background) of glands, organs and bone marrow. They remove cellular debris from lymphatic organs. 6