Lecture 3 Specialized Connective Tissues PDF

Specialized Connective Tissues A. Adipose tissue: -composed of fat cells (in loose or IR-DCT) - higher in females than in males - important regulators of energy metabolism - major signalling and endocrine function (leptin) - thermal insulation - fill up spaces, “shock absorb...

Specialized Connective Tissues A. Adipose tissue: -composed of fat cells (in loose or IR-DCT) - higher in females than in males - important regulators of energy metabolism - major signalling and endocrine function (leptin) - thermal insulation - fill up spaces, “shock absorber” (cushion) Two types: 1. Adipocytes of white, unilocular adipose tissue contain one large lipid droplet. 2. Adipocytes of brown, multilocular adipose tissue contain many lipid droplets. Adipose Cells - mesenchymal derivatives specialized as storage depots for lipids. Development of white and brown adipocytes 1. White adipose tissue – storage of lipids (neutral fats) - large cell, 50 -150 um, with one large droplet of lipid - Post-fixation with osmium tetroxide Routine H/E staining Cryosectioning Uptake and Mobilization of Lipids 2. Brown adipose tissue – due to the high number of mitochondria in the cytoplasm and the large number of blood capillaries. - Adipocytes of brown fat contain many small lipid inclusions and are therefore called multilocular. - heat production; limited in distribution (In adults it is found only in scattered areas, especially around the kidneys and adrenal glands, the aorta, and mediastinum. DISTRIBUTION OF BROWN ADIPOSE TISSUE -In Newborn: -2-5% of body weight -BLACK AREAS (brown adipose tissues) -SHADED AREAS (white + brown adipose)  A BROWN ADIPOCYTE 1. Polygonal cells enclosed in BL 2. 15 – 25 μm 3. Multilocular (plurivacuolar) varied sizes 4. Centrally- eccentrically located nucleus and 1 -2 nucleoli 5. Cytoplasm with numerous large round mitochondria with long transversal cristae, small Golgi app., sER, rER, free ribosomes, abundant lipid droplets. 6. Capillaries and adrenergic nerve endings come in contact with every cell. 7. Why brown? Cytochrome of mitochondria and lipochrome within lipid droplets! Also vascularized! -A protein (UCP-1 or thermogenenin) in the mitochondria decouples the oxidation of fatty acids from the generation of ATP, thus the cells generate heat (backflow of protons- bypassing the ATP synthetase system) - activated by neurotransmitter; faster metabolism than white fat. Thermogenesis – generation of heat in hibernating animals and human infants. → maintains body temperature  Specialized Connective Tissue B. Cartilage - with chondrocytes surrounded by ECM - chondrocytes occur singly or in isogenous groups (2-8 cells) - cells in lacunae within the matrix - matrix is a network of collagenous and/or elastic fibers in ground substance enriched with GAGs and proteoglycans. - does not contain vessels or nerves - surrounded by a layer of DCT (perichondrium)  Three types: 1. hyaline cartilage,- the most common form, type II collagen is the principal collagen type. 2. Elastic cartilage - the more pliable and distensible elastic cartilage possesses, in addition to collagen type II, an abundance of elastic fibers within its matrix. 3. Fibrocartilage - present in regions of the body subjected to pulling forces, characterized by a matrix containing a dense network of coarse type I collagen fibers. Chondrocyte function is hormone dependent: - Synthesis of sulfated GAGs is accelerated by growth hormone, thyroxine, and testosterone ; synthesis is slowed down by by cortisone, hydrocortisone, and estradiol. -Somatotropin targets the liver = IGF-1 that acts on cartilage cells to promote growth. 1. Hyaline cartilage – most common type; serves as temporary support during the embryonic stage, to be replaced by bones. - located in the articular surfaces of the movable joints, in the walls of larger respiratory passages (nose, larynx, trachea, bronchi), in the ventral ends of ribs, and in the epiphyseal plate (responsible for the longitudinal growth of bone. ECM– proteoglycan + glycoproteins fibers =contains primarily type II collagen, although small amounts of collagen types VI and IX are also present. - proteoglycans = chondroitin 4-sulfate, chondroitin 6-sulfate, and keratan sulfate, covalently linked to core proteins. - structural multiadhesive glycoprotein chondronectin. Interaction of molecules forming the matrix: The Trachea Low mag of hyaline cartilage Perichondrium Chondroblasts Chondrocytes in cell nests TEM of chondrocyte TEM stained to show GAGs in cartilage matrix 2. Elastic cartilage -found in the auricle of the ear, the walls of the external auditory canals, the auditory (eustachian) tubes, the epiglottis, and the cuneiform cartilage in the larynx. Elastic cartilage – darker staining matrix  Elastic cartilage – elastin fibers in the matrix Perichondrium Chondroblasts Chondrocytes High mag of elastic cartilage 3. Fibrocartilage - intermediate between dense connective tissue and hyaline cartilage; found in intervertebral disks, in attachments of certain ligaments, and in the pubic symphysis. - contains chondrocytes, either singly or in isogenous aggregates, arranged axially, in long rows separated by coarse collagen type I fibers and less proteoglycans than other forms of cartilage. - it is richer in collagen type I, the fibrocartilage matrix is more acidophilic. Pubic symphysis Intervertebral disc Diagram of intervertebral joints  Intervertebral joint - composed of fibrocartilage primarily. - the peripheral annulus fibrosus rich in bundles of type I collagen - central nucleus pulposus with a gel-like matrix rich in hyaluronic acid N = nucleus pulposa  Specialized Connective Tissues C. Blood – fluid connective tissue; due to its mesenchymal origin of cells Plasma = fluid extracellular material Formed elements = RBC, WBC, platelets BLOOD CELLS: Erythrocytes (RBC) – 99% of formed elements; no nucleus but with hemoglobin; remarkably elastic ; biconcave disk ; suspended in isotonic medium. White blood cells : Granular - neutrophils, basophils and eosinophils Agranular – monocytes and lymphocytes Normal range of WBC: ~ 60% neutrophils (50% - 70%) ~ 3% eosinophils (>0% - 5%) ~ 0.5% basophils (>0% - 2%) ~ 5% monocytes (1% - 9%) ~ 30% lymphocytes (20% - 40%) Granular Leukocytes 1. Neutrophil (polymorphonuclear leukocytes) – 12-15 um in diameter; - invade sites of infection ; phagocytosis; one-week lifespan 2. Eosinophil – nuclei with two lobes; cytoplasm with specific granules that stain red or pink with eosin. - with granules that contain an electron-dense proteinacaeous crystal MBP – major basic protein (Cytotoxin) - with histaminase and arylsulfatase - phagocytose antibody-antigen complexes 3. Basophil – 2-3 lobed nucleus; specific granules stained deeply bluish with heparin, histamine, lysosomal enzymes and leukotrienes. - important in inflammatory response 4. Lymphocytes – both nucleus and cytoplasm stain blue 5. Monocytes – kidney-shaped nucleus with granules 6. Platelets – do not contain nuclei; fragments of large thrombocyte precursor cells (megakaryocytes); assist in hemostasis - smaller due to division of cytoplasm into two zones : outer hyalomere and inner granulomere a. Primary aggregation b. Secondary aggregation c. Blood coagulation d. Clot retraction and clot removal - plasmin  Specialized Connective Tissues D. Bones - primary functions: mechanical and metabolic Mechanical - support and protection, acts as lever during muscle contraction/movement. Metabolic – reservoir of calcium, phosphate and other ions (released or stored). STRUCTURE: - calcified bone matrix (mineralized) - three cell types: 1. osteocytes – in lacunae between bone lamellae 2. osteoblasts – for the synthesis of organic components of the matrix 3. osteoclasts – involved in the resorption and remodelling of bones.  Functions of Bones ▪ Provides protection for internal organs, such as the brain, heart, lung, bladder, and reproductive organs. Provides supporting framework for the body (e.g., long bones for limbs and skull for the support of brain and framework for facial features). Enables body movements in conjunction with the muscles and nervous system. Produces blood cells (hematopoiesis) within the medullary cavity of long bones and cancellous bone. Provides a calcium and phosphorus reserve for the body. Provides detoxifi cation for stored heavy metals in the bone tissues. Removes these toxic materials from blood, thereby reducing damage to other organs and tissues. Provides sound transduction in the middle ear (auditory ossicles: malleus, incus, and stapes). Bone cells: Osteoblasts - responsible for the synthesis of the organic components of bone matrix, and deposition of the inorganic components of bone also depends on viable osteoblasts. -- located exclusively at the surfaces of bonematrix -cuboidal to columnar shape and basophilic cytoplasm during matrix synthesis. Relationship of three cells types and the calcified matrix -secrete collagen I, GPs, proteoglycan (with affinity to Ca ions-osteocalcin); matrix vesicles- with enzymes to hydrolyze PO4. Osteocytes - with long cytoplasmic processes surrounded by calcified matrix; within lacunae with canaliculi; reduced RER and Golgi apparatus; condensed nuclear chromatin; death = resorption of calcified matrix. Ground bone Osteoclasts – large, multinucleated cells; found along resorption bays or Howship lacunae Hormone-dependent (calcitonin and PTH) BONE MATRIX: 1. Inorganic components: - hydroxyapatite - bicarbonate, citrate, Mg, K, Na - noncrystal CaPO4 hydration shell – water + ions around crystals 2. Organic components – collagen type I + GS GS = proteoglycans + multiadhesive glycoproteins (osteonectin) - calcium-binding glycoproteins = osteocalcin  Periosteum & Endosteum Periosteum – outer layer (covers bone) and provides osteoprogenitor cells. external part –dense CT (fibrous) connected with ligaments, and other CT. - with blood supply Endosteum - single very thin layer of connective tissue, with flattened osteoprogenitor cells and osteoblasts. - covers the small spicules or trabeculae of bone that project into the marrow cavities.  Periosteum & Endosteum For the nutrition of bone cells and supply of new osteoblasts. Perforating fibers or Sharpey’s – connects the periosteum to the matrix. TYPES OF BONES: 1. Compact bone 2. Cancellous (spongy bone) SHAPES/FORM: Long bones : epiphysis diaphysis Flat bones : two layers of plates (compact) - thicker layer of spongy bone= diploe eg. calvaria (skull) Based on development: 1. Primary or woven - rich in osteocytes; random bundles of collagen 2. Secondary or lamellar - matrix organized in lamellae Primary bone Secondary bone  Osteogenesis 1. Intramembranous ossification - osteoblasts differentiate directly from mesenchyme and begin secreting osteoid. 2. Endochondral ossification - the matrix of preexisting hyaline cartilage is eroded and replaced by osteoblasts producing osteoid. Intramembranous Ossification – flat bones, eg. ossification centers of the skull INTRAMEMBRANOUS OSSIFICATION Endochondral Ossification – hyaline cartilage as template or model; eg long and short bones A plate of epiphyseal cartilage is divided into five zones: 1. Resting zone consists of hyaline cartilage with typical chondrocytes. 2. Proliferative zone, chondrocytes divide rapidly and form columns of stacked cells parallel to the long axis of the bone. 3. Hypertrophic cartilage zone - swollen chondrocytes whose cytoplasm has accumulated glycogen. Hypertrophy compresses the matrix into thin septa between the chondrocytes. 4. Calcified cartilage zone, loss of the chondrocytes by apoptosis is accompanied by calcification of the septa of cartilage matrix by the formation of hydroxyapatite crystals. 5. Ossification zone, bone tissue first appears. Capillaries and osteoprogenitor cells originating from the periosteum invade the cavities left by the chondrocytes. Metabolic role of Bone: -Hormones: calcitonin and PTH - nutritional deficiencies: calcium, vitamin D -Children – rickets - Adults – osteomalacia - osteoporosis JOINTS: 1. Diarthroses- permits free bone movement. 2. Synarthroses – limited movement. Synostoses – joined by bone tissue; no movement Synchondroses – joined by hyaline cartilage Syndesmoses – joined by interosseous ligaments/ fibrocartilage Diarthrosis: Synovial membrane Synoviocytes – type A = macrophage like - type B = fibroblast –like cells.  ARTICULAR CARTILAGE Without perichondrium