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Connective tissue
Group of tissue that bind other tissues in the body
Composition of connective tissue
- Cells
- Matrix a. Ground substance b. Fibers
1. Cells
Specialized cells in connective tissue form and maintain the extracellular
Immature : blast - can reproduce and form the matrix Mature : cyte - reduce ability to divide and maintain matrix Bone remodeling : removal of existing bone by deposition of new bone bone by osteoblasts
Cells are grouped into โ Fixed cells โ Wandering cells
1. Fixed cells are
A. Fibrocyte/ fibroblast
โ Responsible for formation of fibers โ Spindle fusi formed (youngest) โ Lamellar โ Stellate starlike (oldest) โ Blasts - fibroblasts form fibers, osteoblasts form bones, chondroblasts form cartilage โ Cytes - fibrocytes, osteocytes, chondrocytes โ Extracellular fibers and ground substances
B. Fixed macrophage/ histiocytes
โ Involved in phagocytosis โ Agents โ Macrophage or histiocytes: phagocytic WBC most abundant in the loose connective tissue. Difficult to distinguish with fibroblasts unless they are performing phagocytic activity โ Phagocytosis of ECM components and debris โ Antigen processing and presentation to immune cells โ Secretion of growth factors, cytokines and other agents
C. Adipose/ fat cells
โ Adipocytes store triglycerides. When adipose cells predominant the connective tissue is called adipose tissue โ Store neutral fats
B. Mast cells
โ Resembles basophils โ Production of heparin (natural anticoagulant), histamine (promotes inflammation), and serotonin (vasoconstriction) โ Abundant along the blood vessels โ Pharmacologically active molecules
C. Plasma cells
โ Cells with cart wheel or checker board appearance โ Derived from B-lymphocytes โ Found to produce antibodies โ Found in abundance in loose connective tissue and lymphatic tissue of the respiratory and digestive tract โ Antibodies
D. Lymphocytes
โ Smallest of the free cells of connective tissue โ Involved in synthesis of plasma cells โ Various immune/ defense functions
E. Eosinophils
โ Accumulates in the blood and tissue during allergic reactions and sub acute conditions โ Modulate allergic/ vasoactive reactions and defense against parasites
F. Pigment cells
โ Resembles fibroblasts โ Contains pigment granules โ Dermal chromatophore (melamophore) โ Dermis of skin, retina, choroid and iris of eyeball โ Epidermal melanocytes: moles
- adipocytes - store triglycerides, insulate and cushion *Osteocytes (osteoblasts) - bone *Chondrocytes (chondroblasts) - cartilage *Leukocytes and erythrocytes - blood
- Matrix
Fibers
1. Collagen
โ Tough, thick and fibrous resembling microscopic ropes. Resist stretching and are very flexible, found in the bone, cartilage, tendons(muscles to bone), ligaments (bone to bone) โ Collagen type 1 โ Most abundant โ Bones, tendons, skin, fibrocartilage, organic part of bones and teeth
Ground substance
โ Between cells and fibers โ May be viscous( blood ), semisolid ( cartilage ), and solid ( bone ) โ Supports cell, binds them together, store water and provide medium for exchange of substances between the blood and cells โ Active role in how tissues develop, migrate, proliferate and change shape โ is found in all cavities and clefts between the fibres and cells of connective tissues
- Glycosaminoglycans โ GAGs/ hyaluronic acid chondroitin 4-sulfate / chondroitin 6-sulfate/ dermatan sulfate heparan sulfate
- Proteoglycans โ proteoglycans /protein core to which GAGs are covalently bound/ - aggrecan, syndecan, fibroglycan
- glycoproteins โ fibronectin, laminin, osteonectin, osteopontin, chondronectin..
Classification of connective tissue
A. Connective tissue B. Connective tissue with special properties C. Specialized type of connective tissue
Functions include โ Packing and anchoring materials โ Binds tissues and organs. โ General Function: connects tissues & organs. โ Ground Subs: fluid/liquid โ Loose Variety โ Dense Variety
1. Loose variety
โ Loose Areolar/Fibroelastic CT โ Made up of loosely arranged fibers โ Forms the Tunica Propia of most ET โ Cells-fibroblast (predominant), โ Fibers- Collagenous (prominent) โ Reticular/ Elastic (few) โ Vascular
โ Macrophage
Gel-like matrix with all three fiber types; cells, fibroblasts, macrophages, mast cells and some white blood cells. Wraps and cushions organs; macrophages phagocytize bacteria; important role in inflammation; holds and conveys tissue fluid. Widely distributed under epithelia of body, surrounding capillaries
- Loose connective tissue โ lesser fibers with numerous ground substance and water, appear disorganized, loose network of fibers on which many fixed and wandering cells are suspended โ most common cells are fibroblasts, primary fibers are collagen fibers โ provides attachment of the skin to underlying tissues and provides nourishment โ epithelial basement membrane rests on loose connective tissue
Has three types
A. Areolar โ Made up of loosely arranged fibers โ Forms the Tunica Propia of most ET โ Cells-fibroblast (predominant), Macrophage, mast cells โ Fibers- Collagenous (prominent) - Reticular/ Elastic(few) โ Vascular
B. Adipose โ Matrix as in areolar but very sparse, closely lacked adipocytes, have nucleus pushed to the side by large fat droplet โ Provides reserve food fuel, insulates against heat loss, supports and protects organs โ Located under the skin, around kidneys and eyeballs, within abdomen, in breast
C. Reticular โ Network of reticular fibers in a typical loose ground substance, reticular cells lie on the network โ Fibers form a soft internal skeleton(stroma) supports other cell types including white blood cells, mast cells, and macrophages
โ Dense fibrous โ Offers firmness & resistance
- Cells- fibroblast in tendon Tendon cells
- Fibers- Collagenous fibers
- Distribution: tendons, fasciae, aponeuroses, white ligaments, capsule of organs.
The tissue appears yellowish due to elastic fibers. Cells - fibroblast in parallel rows Fibers - elastic fibers in parallel strands & coarser than areolar CT Vascular Distribution: ligamenta flava of vertebral column, true vocal cords, stylohyoid ligaments, suspensory ligament of penis, ligamentum nuchai of animals & scarpaโs fascia of the human anterior abdominal wall
Specialized connective tissue
Cartilage - composed of chondrocytes, dense network of collagen fibers, elastic fibers with an extensive matrix (proteoglycans) โ -provides support, resist tension and compression โ no blood supply thus heals slowly
3 types:
1. Hyaline cartilage
โ most abundant โ covers the end of bones where they form joints, rings of the respiratory tract, nasal cartilage, costal cartilage โ Provides tissue with smooth surface for easy movement โ Type II collagen and aggrecan โ Numerous chondrocytes
โ (+) perichondrium except at epiphyses and articular cartilage โ Locations: โ Bronchial tubes โ Larynx โ Costal cartilage
2. Fibrocartilage
โ has large amounts of collagen fibers, resist pulling, tearing forces. โ found in the intervertebral discs of some joints such the knee & jaw joints, symphysis pubis โ Transitory structure between dense fibrous CT & hyaline cartilage โ No perichondrium โ With collagenous fibers โ With chondrocytes arranged in rows โ Avascular โ Distribution: intervertebral disk, symphysis pubis, ligamentum teres femores
3. Elastic cartilage
โ contains elastic fibers in addition to collagen โ provides flexible support โ found in the external ear, epiglottis, auditory tubes Possesses a perichondrium โ Fibrous layer of perichondrium is regular connective tissue. โ Numerous branching elastic fibers within its matrix โ Dominant cell: Fibrocyte , Chondrocytes, chondroblasts โ Fxn: Flexible shape, support soft tissues โ Loc: External ear , epiglottis and other laryngeal
Function
- Provides support & framework to the body
- Protects vital organs. (skull encloses the brain)
- Responsible for storing such as calcium
- Encloses bone marrow which is responsible for the production of blood cells
- Attachment of muscles and tendons
According to Histological Structure of Compact Bones โ Found in the outer surface of all bones, a shaft of diaphysis (slender part of bone) of long bones, appears as solid mass. โ Spongy or Cancellous Bones โ Formed in epiphysis (ends of long bones), of the flat bones of the skull & face, in middle & inner portion of all other bones โ Found only as a thin portion inside the diaphysis of long bones but constitutes a greater part of the epiphysis
Histology of compact bone
โ Osteon โ the structural unit of compact bone
โ Lamellae โ column-like matrix tubes composed of collagen and crystals of bone salts
โ Central canal (Haversian canal) -canal containing blood vessels and nerves
โ Lacunae - cavities in bone containing osteocytes
โ Canaliculi - hairlike canals that connect lacunae to each other and the central canal
โ Perforating canal (Volkmannโs) โ channels lies to the central canal, connecting blood and nerve supply of the periosteum to the central canal
