Connective Tissue PDF

Connective tissue One of the basic tissues of the body Connects various tissues of the body and gives them support Develops from mesoderm or mesenchyme Contains – cells, extracellular matrix (fibers and ground substance) 1) Cells Fibroblasts, adipose cells, macrophages Plasma ce...

Connective tissue One of the basic tissues of the body Connects various tissues of the body and gives them support Develops from mesoderm or mesenchyme Contains – cells, extracellular matrix (fibers and ground substance) 1) Cells Fibroblasts, adipose cells, macrophages Plasma cells, mast cells, mesenchymal cells Blood cells Fibroblasts: Most common cells of connective tissue in animals Responsible for production and maintenance of fibers and ground substance Spindle shaped cells with basophilic cytoplasm, oval / ellipitical nucleus and many processes Known as fibrocytes in the resting stage Adipose cells (adipocytes): Specialized for synthesis and storage of fat Have large lipid droplet Nucleus – flat, pushed to the periphery Cytoplasm is very thin Cells appear singly or more often in groups Macrophages: Also called histiocytes May be fusiform, stellate or spheroidal in shape Cytoplasm contains variety of granules and vacuoles Phagocytic in nature Plasma cells: Provide resistance to the body against diseases Specialized for the manufacture of antibodies against antigens Found abundant in lamina propria of digestive tract and respiratory tract Also found in the lymphoid tissue These cells have cart-wheel shaped nucleus Mast cells: Widely distributed in the connective tissue, also seen along the course of blood vessels Contain large number of granules in the cytoplasm Secrete histamine, heparin Undifferentiated mesenchymal cells: Multipotent stem cells that can differentiate into any cell type under proper stimulus Usually found along the blood vessels, also located in bone marrow Precursors of all types of cells Blood cells - Lymphocytes and neutrophils: Migrated from blood stream 2) Fibers are of 3 types Collagen, elastic and reticular fibers Collagen fibers They are inelastic and have great tensile strength Contain protein collagen Seen in all types of connective tissue Fibers run in bundles, The bundles split into branches Individual fibers are unbranched Synthesized by fibroblasts Each fiber contains fine subunits called tropocollagen Fresh fibers appear colorless When stained with heamatoxylin and eosin stain, they appear pink  Depending on the chemical composition, there are many types or grades of collagen fibers Type I collagen fibers – thickest fibers, seen in bones, tendons, dermis of skin Type II collagen fibers – found in the cartilages, vitreous body of eye Type III collagen fibers – seen in spleen, lymph nodes, bone marrow, also called reticular fibers Type IV collagen fibers –seen the basement membrane Type V collagen fibers – fetal tissues, blood vessels Elastic fibers Highly elastic, can be stretched to 150% of their resting length without breaking Found in the walls of large arteries Synthesized by fibroblasts Yellowish when they are in groups Contain protein called elastin Fibers usually run individually, branch and anastomose with each other When stained with heamatoxylin and eosin stain, they appear pink Reticular fibers Type III collagen fibers Seen in lymph node, spleen, thymus, liver, bone marrow, endocrine glands Fine branching fibers, form network - reticulum Cannot be stained with heamatoxylin and eosin stain Stained by silver staining methods 3) Ground substance: Semisolid gel also known as intercellular substance Cells and fibers are embedded in it Consists of water, carbohydrates and proteins Carbohydrates in the form of mucopolysaccharides (glycosaminoglycans) Proteins in the form of glycoprotein  Functions of connective tissue Providing structural support Compartmentalization Aiding in the defense and protection of the body Forming the site for storage of fat Transport  Classification of connective tissue Depending upon the type and proportion of cells, fibers and ground substance it can be classified into:  CONNECTIVE TISSUE PROPER => Binds Loose connective tissue – Areolar Tissue (Protects and binds deeper tissue) – Adipose Tissue (Fat) – Myxomatous Tissue – Reticular Tissue (Lymph Organs) Dense connective tissue – Regular Dense Connective Tissue (Ligaments and Tendons) – Irregular Dense connective Tissue (Binds epidermis to skin) – Elastic (Aorta)  SUPPORTING CONNECTIVE TISSUE => Protection/Structure Cartilage - Elastic (Ears) - Hyaline (Ribs) - Fibrocartilage (Vertebral Discs) Bone  FLUID CONNECTIVE TISSUE => Transport Blood Lymph CONNECTIVE TISSUE PROPER Areolar connective tissue Loose connective tissue:  Areolar tissue: e.g. superficial fascia Contains bundles of collagen fibres, and scattered individual elastic fibres Most of the cells present are fibroblast cells  Adipose tissue: e.g. mesentery Contains groups of adipose cells with collagen fibers When adipose tissue is stained with haematoxylin and eosin stain the fat cells appear empty, since the fat in the lipid droplet dissolved during staining Cells have thin cytoplasm and peripherally placed nucleus Adipose tissue  Myxomatous tissue: e.g. umbilical cord, vitreous body of eyeball Fetal or embryonic type of connective tissue Contains plenty of ground substance with hydrated mucosubstances, fine meshwork of collagen fibers, with fibroblasts  Reticular tissue: e.g. spleen, lymph node, thymus, liver Contains network of reticular fibers Dense connective tissue: Reticular tissue with reticular fibres (eg lymph node  Regular dense connective tissue: e.g. tendons of muscles Collagen fibers are arranged regularly in bundles with fibroblast cells  Irregular dense connective tissue: eg dermis of skin contains a dense irregular network of collagen and elastic fibre bundles  SUPPORTING CONNECTIVE TISSUE  Cartilages Cartilage is a specialized, supportive type of connective tissue which has the ability to resist compressive forces, enhance bone resilience and provide support on bony areas where there is need for flexibility. Forms the skeletal basis of some parts of the body e.g. auricle of ear, outer part of nose It can be bent, and returns to original form when the force is removed Composition of the cartilage:  Cartilage contains – cells and extracellular matrix  Matrix is made up of ground substance and fibers  Cartilage is covered by a covering called perichondrium  The perichondrium contains 2 layers - Outer fibrous layer which contains collagen fibers - Inner cellular or chondrogenic layer which contains chondroblast cells Cells Mature cartilage cells are called chondrocytes – located in the spaces called lacunae within the matrix Young cartilage cells are called chondroblasts, located in the perichondrium Matrix Made up of ground substance and fibers - Ground substance Semisolid gel Contains water, carbohydrates in the form of muco-polysaccharides, proteins in the form glycoproteins - Fibers Collagen and elastic fibers  Classification of cartilages Based on the visibility and nature of fibers in the matrix, they are classified into 3 types: Hyaline cartilage Elastic cartilage Fibrocartilage  Hyaline cartilage E.g. costal cartilage, thyroid cartilage, trachea Has a covering called perichondrium which contains fibrous and chondrogenic (cellular) layers Hyaline cartilage contains cartilage cells and matrix Cartilage cells are chondrocyte and chondroblast Fibrous layer Chondrogenic Chondrocytes - located in the Layer (with spaces called lacunae chondroblasts) Chondrocytes found in groups of 2-8 cells - cell nests Chondrocytes produce the matrix  Matrix: Matrix contains collagen fibers and ground substance (made up of mucopolysaccharides, proteoglycans and glycoproteins) Matrix appears homogeneous, has affinity for basic dyes Freshly prepared matrix around chondrocytes stains dark and called territorial matrix The remaining matrix looks lightly stained and called interterritorial matrix Collagen fibers are not seen as a distinct entity since the refractive index of ground substance and collagen fibers is same  Hyaline cartilage Territorial matrix Inter territorial matrix Elastic cartilage This type of cartilage has elasticity, comes back to its natural size after being stretched E.g. auricle of ear, epiglottis Has a covering called perichondrium which contains fibrous and cellular layers Chondrocytes are present singly or in small groups Matrix contains plenty of branching elastic fibres  Fibrocartilage Also known as white fibrocartilage E.g. intervertebral disc, pubic symphysis Perichondrium is absent Matrix contains bundles of collagen fibres Chondrocytes appear singly and arranged in rows between bundles of collagen fibres  Bones Bone is the hardest form of connective tissue It provides protection to internal organs and supports the body. Highly vascular, living tissue which makes up most of the skeleton The matrix is calcified by the deposition of calcium phosphate Has regenerative capacity The human skeleton contains 206 bones  Functions of bone Provides support and shape to the body Protects vital organs of the body (heart, brain) Helps in transmission of the body weight Provides attachment to muscles and act as levers of the joints helping in locomotion Storehouse for calcium salts Involved in erythropoiesis (red blood cell production)  Classification of bones According to their position: Axial bones: Bones forming the axis of the body e.g. skull, vertebrae, sternum, ribs. Appendicular bones: Bones of the limbs e.g. scapula, humerus, femur According to size, shape and consistency: Long bones: Have three parts – upper end, lower end and shaft Ends of the bones take part in forming joints e.g. humerus and femur Short bones: Small cuboid shaped bones e.g. carpal and tarsal bones Flat bones: These bones are expanded and flat e.g. sternum, scapula, ribs Irregular bones: Irregular shaped without proper outline E.g. vertebrae Pneumatic bones: Bones with hollow spaces which contain air (sinuses) E.g. Maxilla, frontal bone Sesamoid bone: Develop within the tendons of some muscles Develop where the tendons cross the ends of long bones Minimize the friction between the tendon and the bone e.g. Patella (develops in the tendon of quadriceps femoris muscle) According to development: Membranous bones: Bones develop from the membrane formed by the mesenchymal tissue (connective tissue of embryo) e.g. clavicle, most of the bones of skull Cartilaginous bones: Mesenchymal tissue first transformed into a cartilage, which later becomes bone e.g. humerus, femur According to the structure:  Compact bones (lamellar bones): Contains bony plates which are arranged compactly e.g. shaft of long bones  Spongy bones (cancellous bones): Made up of bony plates which are arranged irregularly Plenty of spaces separate the bony plates which gives a spongy appearance e.g. ends of long bones, flat bones Parts of a developing long bone:  Diaphysis: Part which develops into shaft, develops from primary ossification centre  Epiphysis: Forms ends of the bone, develops from secondary ossification centre  Epiphysial plate (disc) or physis or growth plate: Cartilage separating the epiphysis and diaphysis  Metaphysis: Part of diaphysis adjacent to epiphysial plate Region where active growth is seen Ossification of bones: The process of bone formation All bones develop from the mesenchymal tissue of embryo Types of ossification:  Membranous ossification: Mesenchyme of embryo directly transformed into bone e.g. mandible, clavicle, and bones of roof of skull  Cartilaginous ossification: Mesenchyme first transformed into a cartilage model, which later ossified to bone e. g. humerus, femur Ossification of a long bone: Begins in one or more areas of future long bone model These areas are called centers of ossification  Primary center of ossification: Appears in the main part of the bone Part which develops from this center is called diaphysis which later forms the shaft Primary center of ossification usually appears before birth  Secondary center of ossification: Appear at the ends of the bone usually after birth Part of long bone which develops from the secondary center is called epiphysis  Structure of Bone Bone is covered externally by Periosteum Interior of the bone contains a cavity – called medullary cavity which is filled with bone marrow Solid outer part of bone is known as compact bone Inner part of bone is known as spongy bone which contains interconnecting plates of bone called trabeculae Periosteum Double-layered membrane covering the external surface of the entire bone except at the articular surfaces Richly supplied with nerve fibers, lymphatic vessels and blood vessels Has 2 layers Outer fibrous layer made of dense irregular connective tissue (collagen fibres) Inner cellular layer contains osteoprogenitor cells and osteoblast cells Endosteum: – Membrane which lines the internal surface of bone, cavities in the bone – Its made up layer of flat cells (osteoprogenitor cells) – Also contains osteoclasts and osteoblast cells Bone contains bone cells and bone matrix  Bone Matrix or osteiod : Composed of organic and inorganic matter - Organic matter: Collagen fibers - produced by the osteoblast cells - Inorganic matter: Formed by crystals of calcium phosphate – Hydroxyapatite crystals Association of hydroxyapatite with collagen fibers is responsible for the hardness of bone Also contains smaller amounts of magnesium, fluoride, and sodium  Bone cells Osteoblast, Osteocyte, Osteoclast Osteoblasts: Bone forming cells, located on the surfaces of bone and endosteum Responsible for the synthesis of organic components of the bone matrix Osteocytes: Inactive osteoblasts trapped within formed bone, may assist in nutrition of bone Mature bone cells occupying the lacunae in the bone matrix They possess long thin cytoplasmic processes which are located in the cylindrical canals in the bone matrix called canaliculi  Bone cells Osteoclasts: Large, multi- nucleated bone removing cells Situated mainly at the endosteum Derived from blood monocytes which are derived from haemopeoitic cells in the bone marrow. Stick to the surface of bone, and break down the bone matrix Structure of compact bone: OL – Outer circumferential lamella IL – Inner circumferential lamella Compact bone contains plates of HS – Haversian system bone tissue called lamellae HC- Haversian canal There are spaces situated between the lamellae called lacunae These lacunae contain osteocytes Canaliculi extend from the lacunae Concentric into the lamellae lamella These canaliculi contain processes Interstitial lamella of osteocytes There are four types of bony lamellae - Concentric lamellae - Interstitial lamellae - Outer and inner circumferential lamellae Concentric lamellae: These are concentric plates of bony tissue around the Haversian canal Osteon (Haversian system): Haversian canal and concentric lamellae surrounding it are known as Osteon These are cylindrical structures which run parallel to long axis of bone Osteons are separated from each other by interstitial lamellae Haversian (central) canals: Run in the center of cylinders of concentric lamellae Run in longitudinal direction Contain blood vessels, nerves and lymphatics of bone Each Haversian canal of an osteon communicates with the marrow cavity, the periosteum and with each other through transverse or oblique Periosteum canals called Volkmann’s (perforating) canals Interstitial lamellae: Irregular lamellae situated between the concentric lamellae Outer circumferential lamellae: Lamellae parallel to periosteum Inner circumferential lamellae: Lamellae parallel to endosteum Interstitial lamella Osteocyte in the lacuna Volkmann’s canal Haversian canal Concentric lamella  Structure of spongy bone Consists of a series of interconnecting plates of bone — the trabeculae The spaces between the trabeculae are filled with bone marrow Trabeculae are lined by endosteum The lamellae are not arranged concentrically around a central canal, but run parallel to one another Osteocytes sit in lacunae between lamellae Spongy bone - Bone marrow: Vascular connective tissue present in the medullary cavity and spaces of spongy bone Two types of bone marrow – red and yellow bone marrow At birth red bone marrow is present throughout the skeleton After 5 years the red bone marrow is gradually replaced in the long bones by the yellow bone marrow Red bone marrow is actively involved in production of blood cells Yellow bone marrow contains large quantity of fat cells