Connective Tissue in Animals

Types of Connective Tissues in Animals. Classification of connective tissues. Cells, Extra cellular matrix and Fibres of connective tiissues.

1. CONNECTIVE TISSUE BY

2. INTRODUCTION Tissues of animal are classified into four major categories : epithelial, connective, muscle and nervous tissues . All these categories of tissues are organized to form organs and structures of animal body . Although each of the animals usually has these four kinds of tissues, the appearance and expression of all these tissues types may vary. Connective tissue is one of the four major categories of animal tissues that supports, joins and separate different forms of tissues and organs of the body. Cells of the connective tissue are more broadly apart from each other as compared to those in epithelial tissues. Connective tissues contains larger amount of extra-cellular matrix which is considerably absent in epithelial tissue

3. GENERAL FEATURES OF CONNECTIVE TISSUE Connective tissues are present in all part of the body excluding central nervous system. These tissues are never exposed to the outer environment. In their various forms, connective tissues have a variety of functions. Most of the connective tissues contain a lot of blood vessels (means they are highly vascular). They have receptors which can perceive pain, pressure, temperature, and other sensations. Connective tissue fills spaces between organs and tissues, and provides structural and metabolic support for other tissues and organs. Connective tissues consist of two chief components: extra-cellular matrix and cells. Extra-cellular matrix in connective tissues is the substances located in spaces between cells. The cells of connective tissues secrete extra-cellular fibres and account for the many of the functional properties of the tissue in addition to controlling the surrounding watery environment via specific proteoglycan molecules.

4. Various cells of connective tissues produced from embryonic cells called mesenchyme . Mesenchyme arises from mesoderm, an embryonic germ layer, and is composed of stellate or fusiform cells embedded in a gelatinous ground substance. Mesenchyme is the stem tissue of all the connective tissues of the body.

5. FUNCTIONS OF CONNECTIVE TISSUES Support and protection : The cells of connective tissue produce minerals and fibers that make up the bony structural framework in the body. As a result, it protects delicate organs, and covers and connects the other types of tissues. Transport : Fluid connective tissues such as blood and lymph efficiently carry substances from one area to another area of the body. Storage : Adipose cells in the connective tissues store fats a form of energy until it is required. Defense : It involves defense against microbes through the intercellular interactions and antibodies production by specialized cells of connective tissues.

6. COMPONENTS OF CONNECTIVE TISSUE Main components of connective tissue are (I) specialized cells and (II) extracellular matrix. The extracellular matrix is made up of fibres in a protein and polysaccharide matrix, secreted and organized by cells in the extracellular matrix . Variations in the composition of the extracellular matrix , determines the properties of the connective tissue . The cells sit in a matrix made up of glycoproteins , fibrous proteins and glycosoaminoglycans , which have been secreted by the fibroblasts, and the major component of the matrix, is in fact, water.

7. (I) Specialized cells in Connective Tissue 1. Fibroblasts: These are bulky and flat cells containing branching projections. Fibroblasts contain large and oval shaped nuclei with one or two conspicuous nucleoli . The active fibroblast contains a lot of rough endoplasmic reticulum necessary for production of collagen and elastin fibers . 2. Macrophages: It arises from a type of white blood cell termed as monocytes . Macrophages are not in regular shape and have short branching processes . At first, these cells are not active. After inflammation, they intensively turn into amoeboid and phagocytic stage. They directly engulf blood cells, bacteria, dead cells and debris digesting this material with powerful enzymes

8. Fixed macrophages exist in in a particular tissue; example includes alveolar macrophages in the lungs or spleenic macrophages in the spleen . Wandering macrophages have the ability to move throughout the tissue and gather at sites of infection or inflammation to carry on phagocytosis . 3. Plasma cells: These are small cells which arise from B lymphocyte, a type of white blood cell. Plasma cells release antibodies and proteins that attack or reduce the effect of foreign materials in the body.

9. 4. Mast cells: These are large cells (20-30μm) packed with intensely basophilic granules that most of the time obscure the nucleus. These cells also have mediators e. g. histamine, heparin and serotonin for instantaneous hypersensitivity. 5. Adipocytes : These are also called fat cells or adipose cells. These cells store triglycerides the form of fat. They are prevalent underneath to the skin and around organs for example heart and kidneys. 6. Leukocytes : These are white blood cells that move along with the connective tissues around blood vessels.

10. (II) Extracellular Matrix in Connective Tissue The cells of connective tissue are interspersed in a large volume of extra-cellular matrix. This extra-cellular matrix (ECM) is secreted by the cells. It constitutes protein fibers interpose in an amorphous mixture of large protein-polysaccharide molecules termed as ground substance . The followings are description of two major components of extracellular materials: ( i ) ground substance and (ii) fibres.

11. Ground Substance: Ground substance is the part of the extracellular matrix that occupies the spaces between the cells and fibers . It may be fluid, semi fluid, jellylike or calcified. Functions of ground substance are followed as : It supports cells and helps in connecting cell to cell. Helps in water storage. Works as an exchanging medium between the blood and cells. It has an important role in which ways tissues develop, migrate, proliferate, and change shape, and in what ways they perform their metabolic functions.

12. CONNECTIVE TISSUE FIBERS Collagen fibres: These fibres are very strong and resist pulling forces, but they are not stiff, which allows tissue flexibility. The properties of different types of collagen fibres vary from tissue to tissue . Chemically, collagen fibres consist of the protein collagen, which is the most abundant protein in our body. Elastic fibres: Elastic fibers contain the protein elastin surrounded by a glycoprotein named fibrillin , which adds strength and stability. They are branched and wavy and after stretching will return to their original length. Reticular fibres: Reticular fibers (reticulum, a network), the least common of the three, are thinner than collagen fibers and commonly form a branching, interwoven framework in various organs . give support in the walls of blood vessels and form a network surrounding the cells in some tissues, such as areolar connective tissue, adipose tissue, nerve fibres, and smooth muscle tissue.

13. COLLAGEN FIBERS RETICULAR FIBERS ELASTIC FIBERS

14. CLASSIFICATION OF CONNECTIVE TISSUES Basically, Connective tissue can be classified on the basis of their maturity i.e. ( A) Embryonic and (B ) Mature connective tissue. Followings are details about each type of Connective tissue.

15. EMBRYONIC CONNECTIVE TISSUES Embryonic connective tissues are present basically in the embryo (human which is being developed during initial two months of pregnancy), and in the fetus (human which is being developed during pregnancy period of third month till birth). These are of two types, mesenchyme and mucous connective tissue .

16. Mesenchyme These cells are not regular in shape and embedded in semifluid ground substance which is composed of delicate reticular fibers . Location : It is located almost exclusively under skin and along developing bones of embryo; some in adult connective tissue, especially along blood vessels. Function: It forms almost all other types of connective tissue.

17. MESENCHYME

18. Mucous (or mucoid ) connective tissue It is widely scattered fibroblasts embedded in gelatinous and characteristically abundant ground substance consists of fine collagen fibers . It also is transitorily encountered as a stage in the differentiation of mesenchyme into mature connective tissue . Location: It is chiefly located in fetus . Function: It forms the umbilical cord.

19. MATURE CONNECTIVE TISSUES

20. Loose Connective Tissues Loose connective tissues are the packing material in human body. The fibres of loose connective tissues are loosely arranged between cells. Loose connective tissue forms a layer that separates the skin from underlying muscles, providing both padding and a considerable amount of independent movement.

21. Areolar connective tissue It is one among the most abundant connective tissues in the body. It consists of fibers (collagen, elastic, reticular) arranged randomly and several kind of cells such as fibroblasts , macrophages , plasma cells, adipocytes , mast cells, and a few white blood cells, embedded in semi-fluid ground substance viz. hyaluronic acid, chondroitin sulfate , dermatan sulfate , and keratan sulfate . Location : It is known as packing material of the body as it is found in nearly every body structure. It is present in subcutaneous layer deep to skin, papillary region of dermis, lamina propria of mucous membranes, near blood vessels, nerves, and body organs . Function : It provides strength, elasticity and support to the different body parts.

22. Adipose connective tissue Adipose tissue or fat is a loose connective tissue containing large numbers of fat cells, or adipocytes . It contains cells or adipocytes arise from fibroblasts which are modified to store triglycerides as conspicuous and centrally located fat droplets . (a) White Adipose tissue : This composes 20 to 25 % of the body weight in healthy adults. The amount of adipose tissue in an individual is determined the balance between energy intake and expenditure . It is found supporting the kidneys and the eyes, between muscle fibres and under the skin, where it acts as a thermal insulator and energy store. (b) Brown Adipose tissue : This (BAT) is characteristically found in the fetus and newborn. It includes most abundant capillary network and several pigmented mitochondria that are responsible for aerobic cellular respiration. When brown tissue is metabolised, it produce less energy and considerably more heat than other fat, contributing to the maintenance of body temperature. In some adults it is present in small amounts . Location: It is present in subcutaneous layer inner to skin, surrounding heart (Fig. 6) and kidneys, yellow bone marrow, stuffing around joints. It fills bony socket behind the eyeball. It dominates extensive areas of loose connective tissue in the pericardial and peritoneal (abdominal) cavities. Function : It provides insulation that slows heat loss through skin.It provides another source of padding and shock absorption for the body . It stores energy in the form of fat; maintains and protects organs . In newborns, BAT produces heat to maintain proper body temperature.

23. Reticular connective tissue It consists of fine interlocking network of reticular fibres (thin form of collagen fiber ) and reticular cells. Location : It is present in liver, spleen, lymph nodes; red bone marrow; reticular lamina of basement membrane ; around blood vessels and muscles. Function : It forms stroma (supporting framework) of organs; binds smooth muscle tissue cells; filters and eliminates damaged blood cells on spleen and microorganisms in lymph nodes.

24. Reticular Connective Tissue

25. Dense Connective Tissues It contain more fibres, which are thicker and more densely packed, but have noticeably less number cells than loose connective tissues. Dense connective tissues consist mostly of collagen fibers ; they may also be called fibrous, or collagenous tissues. Dense connective tissues are tough, strong, and durable. They resist tension and distortion and interconnect bones and muscles.

26. Dense regular connective tissue In dense regular connective tissue, the collagen fibers are parallel to each other, packed tightly, and aligned with the forces applied to the tissue . Tendons are cords of dense regular connective tissue that attach skeletal muscles to bones. Their collagen fibers run along the length of the tendon and transfer the pull of the contracting muscle to the bone . Ligaments resemble tendons but connect one bone to another . Ligaments often contain elastic fibers as well as collagen fibers and thus can tolerate a modest amount of stretching . Aponeuroses are layers of tendon like materials which join muscle to muscle and muscle to bone. Location : It is present as Tendons, Ligaments and Aponeuroses in the body . Function : It provides strong attachment between various structures. Tissue structure withstands pulling ( tension) along long axis of fibers .

27. Dense irregular connective tissue Dense irregular connective tissue contains an interwoven meshwork of collagen fibers with a few fibroblasts . This structural pattern provides support to areas subjected to stresses from many directions and gives skin its strength. Location: It occurs in sheets, such as fasciae (tissue beneath skin and around muscles and other organs ), reticular (deeper) region of dermis of skin, fibrous pericardium of heart, periosteum of bone , perichondrium of cartilage, joint capsules, membrane capsules around various organs (kidneys, liver, testes , lymph nodes, valves of heart. Function: It provides pulling (tensile) strength in many directions .

28. Elastic connective tissue It is predominantly elastic fibers with fibroblasts between fibers and yellowish in colour. Location : It is found in lung tissue, walls of elastic arteries, trachea, bronchial tubes, vocal cords , suspensory ligaments of penis and some ligaments between vertebrae. Function : It allows stretching of various organs. It is sturdy and move back to original shape after being stretched. Elasticity is important for normal functioning of lung tissue and elastic arteries.

29. SUPPORTING CONNECTIVE TISSUE Supporting connective tissues includes cartilage and bone. These tissues constitute a strong framework which supports the rest parts of the body. These connective tissues are composed of the extra-cellular matrix rich in fibers . In some cases, it contains deposits of insoluble calcium salts.

30. CARTILAGE Cartilage composed of a dense network of collagen and elastic fibers which are embedded in the chondroitin sulfate , a jelly like ground substance. Cartilage can tolerate noticeably more stress than loose and dense connective tissues. The strength of cartilage is owing to its collagen fibers , and its resilience is owing to chondroitin sulfate . Cells of mature cartilage, termed chondrocytes , prevail singly or in groups within spaces termed as lacunae in the extracellular matrix . A covering of dense irregular connective tissue termed as perichondrium surrounds the surface of most cartilage. Perichondrium has blood vessel and nervous system and is the source of cartilage cells. Because cartilage contains no blood supply, it repairs slowly subsequent to an injury.

31. Hyaline cartilage It consists of a resilient gel as ground substance and appears in the body as a bluish- white, shiny substance . It constitutes very thin collagen fibers are not easily visible in microscope. Prominent chondrocytes are found in lacunae surrounded by perichondrium . Location : Most abundant cartilage in body. It is prevalent at ends of long bones, anterior end of ribs, nose , parts of larynx, trachea, bronchi, bronchial tubes, embryonic and fetal skeleton. Function : It forms smooth surfaces for movement at joints It provides flexibility and support. It is weakest type of cartilage.

32. Fibrous cartilage Cells of fibrous cartilage are chondrocytes that are scattered between visibly thick bundles of collagen fibers within the extracellular matrix. It lacks perichondrium . Location : It is prevalent in pubic symphysis , intervertebral discs, menisci (cartilage pads) of knee , portions of tendons that insert into cartilage. Function : It support and joins structures together. Strength and rigidity compose it as the strongest type of cartilage.

33. Elastic cartilage Chondrocytes are embedded in fine network of elastic fibers within extracellular matrix. It has perichondrium . It is also termed as yellow cartilage . Location : It forms lid on top of larynx, parts of external ear (auricle), auditory tubes. Function : It gives strength and elasticity and maintains shape of certain structures.

34. BONE TISSUE Cartilage, joint, and bones make up the skeletal system. The skeletal system supports soft tissues, protects delicate structures, and works with skeletal muscles to generate movement. Bones store calcium and Phosphorus , contain red bone marrow, which generates blood cells and contain yellow bone marrow, a storage site for triglycerides . Bones are organs comprised of many different connective tissues. These include bone or osseous tissue, periosteum , red and yellow bone marrow and endosteum . Location : Compact and spongy bones tissue constitute the various parts of bones of the body. Function : It provides support, protection and storage . It contains blood forming tissue . It provides levers that act with muscle tissue to enable movement.

35. Compact B one Compact bone comprised of tightly packed osteons or haversian systems. The osteon contains a central canal termed as osteonic ( haversian ) canal that is enclosed by concentric rings (lamellae) of matrix. Mature bone cells ( osteocytes ) are placed in spaces between the rings of matrix termed as lacunae. Small channels termed as canaliculi radiate from the lacunae to the central osteonic ( haversian ) canal to give passageways by the hard matrix. The osteonic canals constitute blood vessels and nerves which are parallel to the long axis of the bone. These blood vessels interlinked through the way of perforating canals with vessels on the surface of the bone. In compact bone, the haversian systems are packed closely together to form a solid mass.

36. Spongy ( Cancellous ) Bone Spongy bone is lighter and less dense than compact bone. It contains plates ( trabeculae ) and bars of bone neighbouring to small and irregular cavities which have red bone marrow. The canaliculi attach to the neighbouring cavities, instead of a central haversian canal, to receive their blood supply. The trabeculae are organized to give maximum strength. The trabeculae of spongy bone follow the lines of stress and can realign if the direction of stress changes.

37. FLUID CONNECTIVE TISSUE Fluid connective tissues include blood and lymph which are characteristic collections of cells in a fluid extracellular matrix . Under normal conditions, the proteins dissolved in this watery matrix do not form large insoluble fibers . In blood, the watery matrix is called plasma.

38. Blood Tissue Blood tissue is a connective tissue having liquid extra-cellular matrix and formed elements. The extra-cellular matrix is termed as blood plasma. The blood plasma is pale yellow fluid which consists generally of water with a wide variety of dissolved materials (e.g. nutrients, wastes, enzymes, plasma proteins, hormones , respiratory gases, and ions). Suspended in the blood plasma are formed elements—red blood cells, white blood cells and platelets. Red blood cells carry oxygen to various body cells and remove some carbon dioxide from them. White blood cells are responsible for phagocytosis , immunity, and allergic responses. Platelets participate in clotting of blood

39. Red Blood Cell Platelets White Blood Cell

40. Location : It is located within blood vessels, within chambers of heart Function : ( i ) Red blood cells carry oxygen and few carbon dioxide. ( ii) White blood cells carry on phagocytosis and mediate allergic reactions and immune system responses . ( iii) Platelets are essential for blood clotting .

41. Lymph Lymph is the extra-cellular fluid that moves in lymphatic vessels. This is the connective tissue which comprised of various forms of cells in a transparent liquid extracellular matrix that resembles to blood plasma although contains much less protein. The c omposition of lymph varies from one part of body to another . For example, lymph leaving lymph nodes includes many lymphocytes, a type of white blood cell, in contrast to lymph from the small intestine, which has a high content of newly absorbed dietary lipids. The three main forms of lymphocyte are thymus cells (T cells), B cells (bursa-derived cells) and natural killer ( NK) cells. Lymphocytes have characteristically large. Location : It is located within lymphatic vessels. Function : It facilitates the immune system to the body.

42. Basophil Neutrophil Monocyte Eosinophil