Connective Tissue Cells Document PDF

Connective tissue(CT)  Connective tissue provides a matrix that supports and physically connects other tissues and cells together to form the organs of the body. The interstitial fluid of connective tissue gives metabolic support to cells as the medium for diffusion of nutrients and waste...

Connective tissue(CT)  Connective tissue provides a matrix that supports and physically connects other tissues and cells together to form the organs of the body. The interstitial fluid of connective tissue gives metabolic support to cells as the medium for diffusion of nutrients and waste products. All connective tissues originate from embryonic mesenchyme, a tissue developing mainly from the middle layer of the embryo, the mesoderm.  The connective tissue is formed of: 1. connective tissue cells 2. connective tissue fibers 3. connective tissue matrix  Types Of Connective Tissue According to the nature of the intercellular matrix we have three types of connective tissue: 1. connective tissue proper which has a soft matrix 2. cartilage which has a rubbery matrix 3. bone which has a solid matrix  Connective Tissue Proper It is called connective because it supports, binds and connects various tissues and organs. The connective tissue is formed of: C.T. Cells C.T. Fibers Soft matrix or ground substance  Types of connective tissue proper 1. Areolar C.T 2. Adipose C.T 3. Yellow elastic C.T 4. White collagenous C.T 5. Mucoid C.T 6. Reticular C.T  Types Of Connective Tissue Cells They are of two types: 1. Resident (Fixed) C.T. Cells As: Fibroblast, Fixed macrophages, Adipocytes, Mesenchymal Cells. 2. Transient (Wandering) C.T. Cells As: Mast Cells, Plasma Cells, Leukocytes, Melanocyte. Fibroblast are the most common cells in connective tissue proper, produce and maintain most of the tissue’s extracellular components. They are developed from mesenchymal cells and from pericytes. * It has a large, ovoid, euchromatic nucleus and a prominent nucleolus * It is very numerous in areolar C.T. * It is a branched cell with multiple process. * It has basophilic cytoplasm.  * The cytoplasm is rich in RNA, endoplasmic reticulum, golgi apparatus and mitochondria. * Fibroblast can divide. Functions of Fibroblast: * They form collagen, elastin and reticulin substances in order to form C.T. fibers. * They can also form the mucoprotein of the C.T. matrix.  * Their number increases during healing of wounds and in case of C.T. damage. * Fibroblast change into Myofibroblast which can close wounds during injuries.  Fibrocyte, are the mature cells of fibroblasts. * They are small spindle-shaped cells with dense nuclei. * They have acidophilic cytoplasm with few cell organelles. * They cannot divide.  Macrophages( Mononuclear Phagocytic System) They have highly developed phagocytic ability and specialize in turnover of protein fibers and removal of apoptotic cells, tissue debris, or other particulate material, being especially abundant at sites of inflammation. Size and shape vary considerably,  * They are a branched cells with many processes. * They have irregular cell membranes duo to presence of pseudopodia. * Their cytoplasm is not clear and is rich in lysosomes. It is basophilic in staining and is rich in cell inclusions and it contains also phagocytosed particles. * The nucleus is small, it may be indented or kidney-shaped. It is very rich in chromatin and is darkly stained.  This character differentiate it from fibroblast which has a pale faintly stained basophilic nucleus.  Macrophages are present in the connective tissue of most organs and are sometimes referred to by pathologists as histiocytes.” * Histiocyte cells can be stained with vital stain as Trypan blue In the TEM, macrophages are shown to have a characteristic irregular surface with pleats, protrusions, and indentations, features related to their active pinocytotic and phagocytic activities. They generally have well-developed Golgi complexes and many lysosomes.  Macrophages derive from circulating blood monocytes. Monocytes cross the epithelial wall of small venules to enter connective tissue, where they differentiate, mature, and acquire the morphologic features of macrophages. Monocytes formed in the yolk sac during early embryonic development circulate and become resident in developing organs throughout the body except the brain, comprising a group of related cells called the mononuclear phagocyte system.  Many of these macrophage-like cells with prominent functions in various organs have specialized names. All are long-living cells, surviving with relative inactivity in tissues for months or years. During inflammation and tissue repair which follow organ damage, macrophages become activated and play a very important role. Under such conditions these cells increase in number, mainly in the connective tissue stroma, both by proliferation and by recruiting additional monocytes formed in the bone marrow.  Adipocytes or fat cells, are found in the connective tissue of many organs. These large, mesenchymal derived cells are specialized for cytoplasmic storage of lipid as neutral fats, or less commonly for the production of heat. Tissue with a large population of adipocytes, called adipose connective tissue, serves to cushion and insulate the skin and other organs.  Adipocytes specialize in concentrating triglycerides as lipid droplet(s), with other cells normally accumulating relatively little lipid. Adipocytes are active cells metabolically, responding to both nervous and hormonal stimuli. They release hormones and various other important substances and adipose tissue is now recognized as an endocrine organ at the center of nutritional homeostasis  There are 2 different types of adipocytes: Uni-locular adipocytes: they are more common type specialized for fat storage, consists of cells each containing one large cytoplasmic droplet of whitish yellow fat. Nucleus peripheral and crescent like and sometimes said to have a signet-ring appearance, with the lipid droplet displacing and flattening the nucleus against the cell membrane  Multi-locular adipocytes: These cells have multiple lipid droplets interspersed among abundant mitochondria, which helps give this tissue a darker appearance. Brown adipocytes release heat and function to warm the blood. Both types of adipose tissue have a rich blood supply and the adipocytes, unlike other cells of connective tissue proper, are individually surrounded by a thin external lamina containing type IV collagen. Nucleus central and round  Plasma cells are B-lymphocyte-derived, produce antibody. They are large, oval cells have basophilic cytoplasm rich in RER and a large Golgi apparatus near the nucleus that may appear pale in routine histologic preparations (-ve Golgi image). The nucleus is spherical and eccentric. Nuclei have prominent nucleolus and peripheral heterochromatin that resemble cartwheel or clock-face.  Their average life span is only 10-20 days. They are derived from B lymphocytes and are responsible for the synthesis of immunoglobulin antibodies. Each antibody is specific for the one antigen that stimulated the clone of B cells and reacts only with that antigen or molecules. The results of the antibody-antigen reaction are variable, but they usually neutralize harmful effects caused by antigens. Bound antigen antibody complexes are quickly removed from tissues by phagocytosis.  Mast cells, They are small cells, develop in bone marrow and differentiate in connective tissue. Mast cells are large, ovoid, connective tissue cells (20 to 30 mu in diameter) with a spherical nucleus and cytoplasm filled with large, intensely basophilic granules. They are not easily identified in human tissue sections unless special fixatives are used to preserve the granules such as toluidine blue.  It stains the granules intensely and metachromatically because they contain heparin, a highly sulfated proteoglycan and histamine. The cytoplasm displays small amounts of rER, mitochondria, and a Golgi apparatus. The cell surface contains numerous microvilli and folds. The nuclei of mast cells are usually present at one side(not central).  Types of mast cells: 1- Heparin secretory Mast cells which are present in the C.T. of skin. They secrete Heparin which is an anticoagulant. 2- Histamine secretory mast cells which present under the mucosa of respiratory and digestive tracts, they secrete histamine. It can contract smooth muscles, dilate blood capillaries and increase the capillary permeability. – The surface of both types of mast cells contains specific receptors for IgE.  Functions of mast cells: - They are considered as Paracrine cells, they secrete heparin or histamine. - They release chemical mediators as immediate hypersensitivity factors which may cause anaphylactic shock.  Undifferentiated mesenchymal cells, All connective tissues originate from embryonic mesenchyme, a tissue developing mainly from the middle layer of the embryo, the mesoderm. Mesenchymal cells are undifferentiated and have large nuclei, with prominent nucleoli and fine chromatin. They are often said to be “spindle-shaped,” with their scant cytoplasm extended as two or more thin cytoplasmic processes. The embryonic mesenchyme includes stem cells for other tissues such as blood, the vascular endothelium, and muscle  Leukocytes ,leave blood by migrating between the endothelial cells of venules to enter connective tissue. This process increases greatly during inflammation. Inflammation begins with the local release of chemical mediators from various cells, the ECM and blood plasma proteins. These substances act on local blood vessels, mast cells, macrophages, and other cells to induce events characteristic of inflammation.  Most leukocytes function in connective tissue only for a few hours or days and then undergo apoptosis. However, as some lymphocytes and phagocytic antigen-presenting cells normally leave the interstitial fluid of connective tissue, enter blood or lymph, and move to selected lymphoid organs  Pigment cells and Melanocytes, the pigment cell precursor is called the melanoblast and the mature pigment cell is called the melanocyte. There are two types of pigment produced by melanocytes, eumelanin (brown or black) and pheomelanin (yellow/red). Melanocytes are neural crest-derived cells located in the bottom layer (the stratum Basale) of the skin's epidermis, the middle layer of the eye (the uvea), the inner ear, vaginal epithelium, meninges, bones, and heart.  Melanin is a dark pigment primarily responsible for skin color. Once synthesized, melanin is contained in special organelles called melanosomes which can be transported to nearby keratinocytes to induce pigmentation. Thus darker skin tones have more melanosomes present than lighter skin tones. Functionally, melanin serves as protection against UV radiation DOPA test is used to differentiate between melanocytes and pigmented cells