FUNCTION: Its main role is to store energy in the form of fat , although it also cushions and insulates the body + Adipose tissue also serves as an important endocrine organ  by producing hormones such as leptin , resistin , and the cytokine TNFα
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Lecture 6 GenMed_2nd semester
Tissues - definition, their origin and classification
Connective and supporting tissue - general characteristics, components and classification of them
The connective tissue proper - types, chief distribution, and function
Supporting tissues: cartilage and bone - types, chief distribution, and function
are of three kinds distinguishable by their appearance and chemical reaction: collagenous or white, reticular, and elastic
White or collagenous fibers
are the most common
posses little elasticity, but offer great resistance to pulling force (several hundred kg/cm2).
w hite fibers are dissolved by weak acids, and yield gelatin when boiled
Fibers are 1- 1 2 m in thickness and consist of bundles of smaller parallel
Fibrils 0.3-0.5 m thick by electron microscope it ha s shown that each fibril
Microfibrils (unit fibers of collagen) having diameter 40 to 100 nm
Microfibrils reveal characteristic periodic cross bandings with an interval 64 nm in the mature microfibrils . E ach microfibril is made up of long polypeptide chains that consist of tropocollagen
in tissue sections fibers are colored pink to red by H.E., more specifically they are stained by acid fuchsin (red) and anilin blue
macromolecule of tropocollage occurrence: in all types of connective and suppurting tissue 280x1,5 nm thickness 1- 20 m structure of fiber: structure of fiber: FIB RE S are of three kinds : collagen or white, reticular, and elastic White or collagen fib re s are the most common , posses little elasticity, but offer great resistance to pulling force (several hundred kg/cm 2 ) , w hite fibers are dissolved by weak acids, and yield gelatin when boiled
Characteristic of these fibers is elasticity , are branched and form networks, d. cca 1 m,
f ib re s are composed of glycoprotein microfibrils and albumoid elastin (protein) that shows remarkable resistance to hot water, acids and alkalis
b y electron microscopy elastic fibers consist of peripheral collection of thin tubular fibrils of 10 nm diameter that surround the central amorphous component
e lastic fibers occur singly or in the form of sheets
Electron micrographs of developing elastic fibers. A: In early stages of formation, developing fibers consist of numerous small glycoprotein microfibrils. B: With further development, amorphous aggregates of elastin are found among the microfibrils. C: The amorphous elastin accumulates, ultimately occupying the center of an elastic fiber delineated by microfibrils. Note the collagen fibrils, seen in cross section.
Reticular cells are branching cells the processes of which are generally in contact with each othe r . t wo type s of reticular cells are known nonphagocytic and phagocytic cells t he former produce reticular fibres, the latter take part in breakdown of the erythrocytes ( eg., in the spleen).
Fat (adipose) cells or adipocytes relatively large cells (diameter 40 to 50 mm) of oval shape t wo types of adipose cells are described: univacuolar fat cells (white) with one single large lipid droplet , the cytoplasm is reduced to only a thin rim, the nucleus is flat multivacuolar fat cells (brown) that contain numerous small droplets of oil, their nucleus is located always centrally in histological sections the lipid content of adipocytes is dissolved during dehydration and cells seem to be vacuolated.
Mobile cells : h istiocytes , mast cells, plasma cells leukocytes H istiocytes (macrophages) are irregularly shaped cells with processes that usually are short and blunt , nucleus is ovoid, sometimes indented, and smaller and more densely staining than that of the fibroblast , n ucleoli are not conspicuous t he cytoplasm stains dark macrophages are capable of amoeboid movement and phagocytosis Mast cells (role in defense, allergy and anyphylaxis) are irregularly oval in outline and occasionally have short pseudopodia (locomotion for the cell), an indication of their slow mobility cells contain cytoplasmic granules that are refractile and water-soluble and stain with basic and metachromatic dyes (as methylene blue or azure A) contain heparin and also histamine an serotonin
M esenchyme unspecialized connective tissue from where all connective tissues derive composed of mesenchymal cells whose processes are in contact and of a ground substance that is fluid and usually without fibrils it occurs during first weeks of embryonic life
Loose (areolar) connective tissue consists of cells, fibers and ground substance MOBILE CELLS C ells - f ibroblasts and (histiocytes , plasma cells, mast cells, and leukocytes Fibers - c ollagen fibers very prominent and run in different directions; elastic fibers and small number of reticular fibers are present too, a ground substance is relatively fluid like it occurs within parenchymal organs (kidney, epididymis, glands etc.) a n d in tubular organs as a part of the mucosa and submucosa )
consists of the close packing of fibers; cells are proportionally fewer compared with loose
connective tissue and amorphous ground substance is reduced.
I n dependence on direction of tension forces, two types of DCT occur:
d ense irregular connective tissue
d ense regular connective tissue
D ense irregular connective tissue C ells - fibroblasts F ibers are mainly collagen, but elastic and reticular may occur, too . Fibers are interlacing to form a coarse, tough felt-work. Fibers are inter-woven and without regular orientation (tension s exert in all directions) basis of most fasciae , the dermis of the skin, the fibrous capsules of some organs and the sclera of the eyeball
Dense irregullar collagenous tissue distribution: capsules, reticular layer of the dermis
D ense regular connective tissue fibers show an orderly parallel arrangement (tensions subject only in one direction) it forms tendons, ligaments and aponeuroses i n tendons, the collagenous fibers are only present and run parallel , few cells (fibroblasts) that are usually aligned in rows between the fibers ( on cross sections, the cells appear stellate in shape with long cytoplasmic processes extending between the collagenous bundles ) a morphous ground substance is present only in a small amount
Mucous tissue cells are stellate fibroblasts with anastomosing processes that lie in a mucoid jelly-like mass, the fibers are of only collagen type as Wharton' s jelly in the umbilical cord and as dental pulp of the deciduous teeth
Reticular tissue composed of reticular cells and reticular fibers , amorphous ground substance is negligible Cells are stellate with long cytoplasmic extensions , large and pale nucle us and abundant basophilic cytoplasm Fibers are in close appositions to cells and form more or less complicated network D istribution : forms the framework of lymphatic organs and bone marrow
Elastic tissue cells, fibers and not great amount of the ground substance C ells are typical fibroblasts, sparsely scattered with nuclei markedly flattened F ibers are mostly elastic and parallel oriented; a small number of reticular fibers was also described is occurred as the ligamenta flava, the true vocal cords, the ligamentum nuchae
Adipose tissue white adipose tissue (univacuolar) brown adipose tissue (multivacuolar) Cell; aggregated fat cells + scarsely fibroblasts, eosinophils, and mast cells Fibers; c ell s are surrounded by a web of fine reticular fibers t he closely packed fat cells form lobules in and between the m there is a rich network of blood capillaries
- fibers can be solely collagenous or a combination of collagenous and elastic depending upon the cartilage type
- the surface of the hyaline and elastic cartilage is enveloped by a connective tissue membrane - the perichondrium , from which the growth and nutrition of cartilage is provided
t he fibrocartilage has no perichondrium
Classification of the cartilage:
yellow or elastic cartilage
w hite (fibrous) cartilage or fibrocartilage – no perichondrium
is firm and slightly bluish
i n the microscope, its matrix appears clear (glasslike) because fibers and ground substance have the same staining capacity and refractive index
i n the adult , chondrocytes are arranged in groups, composed of 2 , 4 , or 8 cells that are of the same origin (cells of each group have been derived from the same parent cell) s uch cell groups are termed isogenous groups or cell nests
f ibrous component is represented by very fine collagenous fibers that form a feltwork Semitransparent opalescent cartilage that forms most of the fetal skeleton and that consists of cells that synthesize a surrounding matrix of hyaluronic acid, collagen, and protein; in the adult, it is found in the trachea, larynx, and joint surfaces . several isogeneous groups may unite in complexes termed as territoria between territoria the matrix stains slightly and is called as interterritorial matrix perichondrium
Elastic cartilage is usually yellowish in colour and opa que and more flexible than hyaline c hondrocytes are numerous and scattered singly or in small isogenous groups of two or three cells that are surrounded by capsules of the intercellular substance , fibers: elastic and collagenous th e matrix (intercellular substance) shows characteristic fibrillar appearance in H.E. preparations this is caused by presence of elastic fibers that are never totally masked by amorphous ground substance elastic fibers may be visualized by special dyes as orcein or resorcin- fuchsin
White (fibrous) cartilage or fibrocartilage – NO PERICHONDRIUM is a transitional t issue between hyaline cartilage and dense fibrous connective tissue of tendons and ligaments the intercellular substance is composed of thick bundles of collagenous fibers running parallel with one another , c hondrocytes are not numerous, rounded and are arranged singly or in pairs in rows between bundles of collagenous fibers t he amorphous ground substance is inconspicuous and found only in the immediate vicinity of the chondrocytes f ibrocartilage has no true perichondrium
According to relation to the lamella e, vascular channels of two types are
distinguished in the compact bone:
the Haversian canals located in the centers of haversian systems, they are
20 to 100 m in diameter and contain one or two blood vessels
the Volkmann's canals - they are not surrounded by concentrically
arranged lamellae and traverse the bone in direction perpendicular or oblique
to the Haversian canals
function of Volkmann's canals - connect Haversian canals with one other and
provide their communication with the free surface of bone or with the marrow
SPONGY BONE composed of lamellae
a s the trabeculae of spongy/ cancellous bone are relatively thin, they may not contain complete haversian systems but only superficial or circumferential lamellae
OSSIFICATION Bones first appear as condensation of mesenchymal cells that form bone models. Most flat bones develop in mesenchyme within pre-existing membranosus sheaths; this type of osteogenesis is called intramembranous bone formation. Mesenchymal models of most limb bones are transformed into cartilage bone models which later become ossified by endochondral bone formation. Bone develops in 2 types of connective tissue; MESENCHYME & CARTILAGE INTRAMEMBRANOUS OSSIFICATION This type of bone formation occurs in the mesenchyme that has formed a membranous sheath. The mesenchyme condense and become highly vascular, some cells differentiate into OSTEOBLAST and begins to deposit intercellular substances – osteoid tissue or prebone. Calcium-phosphate is then deposited and the osteoblast are trapped in the matrix and become OSTEOCYTES , in contact by long cytoplasmic processes. The bone is developed around bloodvessels forming osteons, haversian sys. Some osteoblast remains on the surface to continue to lay down layers. Between the plates the bone remains spongy. In the spongy bone OSTEOCLASTS remove bone.
INTRACARTILAGINOUS OSSIFICATION This type of bone formation occurs in the preexisting cartilaginous models. In a long bone the primary center of ossification occurs in the diaphysis. Here the cartilage cells increase in size, the matrix becomes calcified and the cells die. Pericondrium ---- Periosteum. Invasion of vascular connective tissue from the periosteum breaks up the cartilage. Some invading cells differentiate into hemiopoietic cells other cells differentiate into OSTEOBLASTS. About the time of birth, a secondary ossification center appears,(epiphysis) of long bones. Periosteal buds carry mesenchyme and blood vessels in and the process is similar to that occurring in a primary ossification center. The cartilage between the primary and secondary ossification centers is called the epiphyseal plate , and it continues to form new cartilage, which is replaced by bone, a process that results in an increase in length of the bone. Growth continues until the individual is about 21 years old or until the cartilage in the plate is replaced by bone. The point of union of the primary and secondary ossification centers is called the epiphyseal line.