EMBRYONIC CONNECTIVE TISSUE CONNECTIVE TISSUE PROPER

ADIPOSE TISSUE

q Adult connective tissuesØConnective tissue proper§ Loose (alveolar) § Reticular§ Dense irregular§ Dense regularü Collagenousü Elastic§ Adipose

q Embryonic connective tissues ØMesenchymal ØMucous

q Specialized connective tissues ØSupporting tissues § Cartilage § Bone § Blood

Categories of connective tissues

CONNECTIVE TISSUES Ø They have the same origin – mesenchyme and the same structure

(cells and extracellular matrix), Ø Unlike epithelial cells, connective tissue cells are widely seperated

by components of extracellular matrix.

Cells of connective tissue + extracellular matrix (ECM)

Epithelial tissue

Closely aggregated polyhedral cells and very little extracellular matrix Epithelia are derived from all germinal layers

Connectivetissue

Connective tissue is composed of two elements: ØCells ØExtracelullar matrix [ECM] ü Fibers −collagen fibers, elastic fibers, reticular fibers ü Ground substance

Extracellular matrix = Fibers + ground substance

Cells of connective tissues (CTs)v Connective tissue proper − fibroblasts, fibrocytes v Adipose tissue – adipoblasts, adipocytes v Cartilage – chondroblasts, chondrocytes v Bone – osteoblasts, osteocytes v Blood – formed elements (erytrocytes, leukocytes)

Cells of Connective Tissue (CT) proper

ØThe cells spend all their live in the tissue

§ Fibroblasts – originate from undifferentiated mesenchymal cells, produce ECM components, can proliferate

§ Fibrocytes – quiescent fibroblasts

Two stages of activity

The active cells The quiescent cells

↓ ↓Fibroblasts Fibrocytes

Fibroblasts _ Fibrocytes ü Fibroblasts § the most common cells

in connective tissue § branched cytoplasm § ovoid, large and pale

staining nucleus with nucleolus § rich in RER and well developed Golgi complex § responsible for the

synthesis of ECM components§produce the growth

factors § proliferate when the

additional fibroblasts are required

ü Fibrocytes § smaller than

fibroblasts§ fewer processes § smaller, darker,

elongated nucleus § small amount of

RER

The function of connective tissues

Ø Providing structural support Ø Serving as a medium for exchange Ø Aiding in the defense and protection of the body Ø Forming a site for storage of fat

The function of connective tissue proper

Ø Forms the capsules of organs and membranes that enveloped the central nervous system (meninges)

Ø Forms trabeculae and walls inside several organs – components of the stroma within organs

Ø Medium for exchange of metabolic waste, nutrients and oxygen between the blood and many of cells in the body

The cells which reside in the tissue

§ Macrophages§ Mast cells§ Plasma cells§ Leukocytes

Macrophages → the Mononuclear Phagocyte System ØMorphological features reflect functional activity of macrophages: § they have pseudopodia, only in macrophages § irregular surface with and protrusions – pinocytotic and

phagocytic activities§ oval or kidney-shaped nucleus located centrally § well-developed Golgi complex, many lysosomes, prominent

rough endoplasmic reticulum (RER)

ü Macrophages derive from monocytes of blood

ØMacrophages are long-living cells, can proliferate locally. The cells are distributed throughout the body, and in certain region have special names: § histocytes – the connective tissue proper § Kupffer cells – the liver § microglia cells – the central nervous system § osteoclasts – the bone

φ 10 – 30 µm

Macrophages functionsØ phagocytosis of foreign substances and bacteria Ø antigen processing and presentation to other cells

(Antigen Presenting Cells – APC) Ø secretion of cytokines and other molecules § enzymes, eg. collagenase Ø removing cell debris and damaged extracellular components

Ø Macrophages when stimulated § may increase in size and are arrangement in clusters forming epithelioid

cells;§ may fuse to form multinuclear giant cellsØ Epithelioid cells and giant cells are found only in pathological conditions.

Multinuclear giant cells

Mast cells

Ø Oval to round connective tissue cells Ø The cytoplasm is filled with basophilic secretory granules Ø Small, spherical nucleus, situated centrally

v Secretory granules of mast cells § they contain biological active substances: ü histamine - promotes an increase in vascular permeabilityü heparin - (sulfated glycosaminoglycan is blood anticoagulant)ü neutral proteases ü chemotactic factor for eosinophils

§ substances not stored in the granules: ü leukotriens (C4, D4, E4)

φ 10 – 13 µm

derive from cells of the bone marrow

q The connective tissue mast cells§ skin and peritoneal cavity

q The mucosal mast cells§ the connective tissue of the intestinal

mucosa and lungs

Mast cells

vThe surface of mast cells contains specific receptors for immunoglobulin E(IgE), a type of immunoglobulin produced by plasma cells

Leukocytes

Diapedesis

or white blood cells Øthe wandering cells of connective

tissue Øthey migrate through the walls of

capillaries and postcapillary venules from the blood to connective tissue (diapedesis)

v Granulocytes

v B and T Lymphocytes

ØPlasma cells

Ø B lymphocyte → plasma cell → synthesis of immunoglobulins

Ø large, ovoid cells with basophilic cytoplasm, very well developed RER, The Golgi complex

Ø spherical nucleus, placed eccentrically Ø average of live is short, 10 – 20 days.

Adipose cells

Ø Adipose cells, adipocytes, fat cells § the connective tissue cells for

storage of neutral fats or for the production of heat

The extracellular matrix

ØFibers § Collagen fibers § Elastic fibers § Reticular fibers

ØGround substance § Glycosaminoglycans (GAGs)§ Proteoglicans § Multiadhesive glycoproteins

Fibers

v Collagen fibers ü are formed by protein collagen ü the collagen is the most abundance protein in the human body (30% of dry weight) ü the collagens belong to a family of more than 25 members, produced by several

cells type üare acidophilic; stain pink with eosin, blue with Mallory’s stain

eosin Mallory’s

ØThe cell type responsible for collagen synthesis§ fibroblasts, chondrocytes, osteoblasts § odontoblasts § endothelial cells § vascular smooth muscle cells

ØThe collagen profile • the principal amino acids – glycine (33.5%), proline (12%), hydroxyproline (10%) • amino acids that are characteristic of the collagen – hydroxyproline and hydroxylysine

Collagen types

v Type I − the abundant: skin, tendon, bone, dentinv Type II − cartilage, vitreous bodyv Type III − skin, muscle, blood vesselsv Type IV − all basement membranes v Type V − fetal tissue, skin, bone, placentav Type VII – epithelia – anchors skin epidermal basal lamina to underlying stroma

(anchoring fibrils)

Collagen is a protein polymer composed of monomeric units of the proteinTropocollagen

Tropocollagen Three α chains

§ elongated protein 280 nm in length and 1.5 nm in width

Structural arrangement of collagen: 1) Collagen is arranged into microfibrils.2) Microfibrils are arranged into fibrils.3) Fibrils are grouped into a fiber.4) Fibers are grouped into a collagen bundle

Collagen synthesis

v Hydroxylation of proline and lysine§ peptidyl proline hydroxylase § peptidyl lysine hydroxylase Co-factors: O2, Fe, vit. C

v Glycosylation of hydroxylysine § transferases Mn

v Removing of registration peptides § procollagen peptidases § tropocollagen

v Formation of covalent cross-links between tropocollagen molecules § lysyl oxidase Cu and O2 ions

v Procollagen synthesis § Registration peptides on both

amino-terminal and carboxy-terminal ends

§ precursor of tropocollagen

Vitamin C (ascorbic acid) deficiency leads to the scurvy, disease characterizedby the degeneration of connective tissue. Scurvy characterized by bleddinggums and loose teeth among other symptomsVitamin C deficiency → abnormal hydroxylation of procollagen → synthesis ofdefective collagen

Reticular fibers

Øconsist mainly of type III collagen Øextremely thinØstain black by impregnation with silver salts – agyrophylic fibers

ØLocalization § are particularly abundant in smooth muscle tissue§ endoneurium § spleen, lymph nodes, bone marrow § constitute a network around the cells of parenchymal organ, eg. liver,

endocrine glands § the wall of arteries

Reticular fibers

Elastic fibers Ø Elastin – the main component + microfibrillsØ Proelastin - precursor of elastin Ø Elastin is rich in glycin and proline Ø Contains two unusual amino acids – desmosine and

isodesmosine formed between four lysinesØ has rubberlike qualities Ø stains brown with orcein and violet with

resorcine-fuchsin

v Elastoblasts § Fibroblasts § Chondrocytes § Vascular SMC § Endothelial cells

They are composed of an amorphous elastin surrounded by a microfibrillar component consisting of fibrillin

The elastic fibers system

ØOxytalan fibers§ zonule fibers of the eye § dermis q do not contain elastin q consist of a bundle of 10nm

microfibrils composed of glycoproteins: fibromodulin I and II, and fibrillin.

ØElaunin fibers§ around sweet glands § dermis q irregular deposits of

elastin between the microfibrils

ØElastic fibers§ the wall of large arteries § connective tissues q elastin located

centrally and thin sheath of microfibrils

q the most numerous component of the system

Microfibrils

Elastin

Ground substance

Øhighly hydrated, colorless and transparent complex mixture of macromolecules Øit fills the space between cells and fibers Øit is viscous and acts as lubricant and barrier to the penetration of invaders

v Glycosaminoglycans (GAGs)v Proteoglycans v Multiadhesive glycoproteins

Glycosaminoglycans (GAGs)

Øcalled mucopolysaccharides

- dermatan sulfate - chondroitin sulfate - keratan sulfate - heparan sulfate- hyaluronic acid

Øwith the exception of hyaluronic acid GAGs are bound covalently to a protein core, forming proteoglycans

Øwith the exception of hyaluronic acid all other GAGs are sulfated ØGAGs are intensely hydrophilic and act as polyanions

Proteoglycans Ø are composed of a core protein associated with the four main GAGs (without

hyaluronic acid) Ø proteoglycan (monomer) is three-dimensional structure (can be pictured as test

tube brush)

Proteoglycan monomer

Core protein

q Proteoglycans of extracellular matrix (ECM) § aggrecan – the most important, the

dominant in cartilage § syndecan, fibroglycan

v Proteoglycans are degradated by several cell types (lysosomal enzymes). Lysosomal enzymes deficiency causes several disorders in humans(eg. Mucopolysaccharidoses )

Proteoglycan aggregates

Schematic representation of the proteoglycan aggrecan

Functions: ü structural component of ECM ü anchoring cells to the ECM ü as extracellular and surface

proteoglycans bind many protein growth factors (TGF-β→ transforming growth factor)

Multiadhesive glycoproteins

Ø play an important role in the interaction between neighboring adult and embryonic cells

Ø play role in the adhesion of cells to their substrate

Protein

v Fibronectin § the product of fibroblasts and epithelial cells § has sites to bind cells, collagen and GAGs

v Laminin § participates in the adhesion of epithelial cells to basal lamina

v Matrix receptors are cell-surface molecules. Cells bind to collagen, fibronectin, laminin

§ Integrins – transmembrane linker proteins, interact with the cytoskeleton

v Intracellular proteins – the interaction between integrins, ECM, cytoskeleton elements

§ Paxilin§ Vinculin§ Talin

Embryonic connective tissues Mesenchyme

Ø The precursor embryonic tissue for all types of connective tissue Ø Stellate undifferentiated cells and ground substance Ø The lack of fibers Ø Under specific stimuli the cells differentiate into the cells of connective tissue -

fibroblasts, adipoblasts, chondroblasts, osteoblasts, blood cells

Ø Mucous connective tissue § has a abundance of ground substance rich in hyaluronic acid § is jellylike tissue containing very few collagen fibers type I and type III § the cells – mainly fibroblasts§ is found in umbilical cord and is referred to as Wharton’s jelly § is found in the pulp of young teeth

Umbilical cord

Embryonic connective tissues Mucous

Adult connective tissues The connective tissue proper

Loose connective tissue

ØLoose connective tissue § the very common type of connective tissue § fills spaces between groups of muscle cells, supports epithelial tissue, forms

layer around lymphatic and blood vessels. § is found in dermis, hypodermis, mucous membranes § has delicate consistency, well vascularized, not very resistant to

stress

Ø Reticular connective tissue § consists of reticular fibers (type III collagen) and specialized fibroblasts named

reticular cells § reticular tissue creates the special microenvironment for hematopoietic organs

and lymphoid organs (bone marrow, lymph nodes, spleen), and envelops certain cells (eg. hepatocytes)

Reticular cell

Reticular fibers

Dense connective tissue (CT)Øis adapted to offer resistance and protection Øthere are fewer cells than loose connective tissue and high amount of collagen fibers

ØDense irregular CT§ the collagen fibers are arranged in bundles without a definite orientation § provide resistance to stress from all directions § is found in dermis

Collagen fibers Fibrocytes

ØDense regular CT (collagenous)§ the collagen bundles are arranged in the definite pattern § it is found in tendons

§ the collagen fibers have parallel, closely packed bundles of collagen separated by a small quantity of intracellular ground substance § fibrocytes have elongated nuclei parallel to the fibers § the cytoplasm of fibroblasts stains the same color as the

fibers

Tendon

Collagen fibers

Nuclei of fibrocytes

Ø Dense regular CT (elastic) § is composed of bundles of thick parallel elastic fibers § the spaces between the fibers are occupied by thin collagen fibers and flattened

fibroblasts § is found in yellow ligaments of the vertebral column, suspensory ligament of the penis

Aorta

Elastic laminae beetwen themvascular smooth muscle cells

fibrocytes

Adipose tissue

ØSpecial type of the connective tissue with predomination of adipose cells(adipocytes, fat cells)

ü Adipocytes § as isolated cells, in small aggregates (adipose tissue)

Adipose tissue

v Unilocular adipose tissue (common or yelow)

v Multilocular adipose tissue (brown)

Adipose tissue is found in a variety of places such as:1] the hypodermis2] surrounding and protecting certain organs3] the medullary cavity of long bones

Functions:1] stores energy2] contributes to the thermal

insulation of the body 3] protects delicate organs from

mechanical trauma

Unilocular (common or yelow) adipose tissue

ØThe color varies from white to dark yelow (depends on diet – carotenoids) ØThe distribution is determined by age and sex § in the newborn has uniform thickness in the body § its distribution is partly regulated by sex hormones and adrenocortical hormones

(different distribution in male and female body)

Spherical, isolated cell

Lipid droplet

Nucleus

Cytoplasm

Signet ring cells

Lipids are removedin routine

histological techniques

Polyhedral cells in

adipose tissue Sudan III

Unilocular (common or yelow) adipose tissue

Vimentin intermediate filament

Basal lamina

φ 50 – 150 µmØCytoplasm§ Golgi complex § mitochondria § poorly developed RER§ SER § free polyribosomes § pinocytotic vesicles

v Adipose tissue ü is richly vascularized

Unilocular (common or yelow) adipose tissue

ØLarge depot of energy for organism Ø Metabolism of adipose tissue is regulated by hormones

Adipose tissue as a secretory organ

Ø enzymes – lipoprotein lipase Ø leptin Ø adiponectin Ø adipsin ØTNFα (Tumor Necrosis Factor α) Ø source of estrogen (estrone) in postmenopausal women

Multilocular adipose tissue (brown fat)

ØMultilocular tissue cells are polygonal and smaller thanunilocular adipose cells

ØThe cytoplasm contains § great number of lipid droplets of various sizes § spherical and central nucleus § numerous mitochondria with abundant long cristae

(containing colored cytochromes) ØThe cells receive direct sympathetic innervation ØThe tissue is rich in capillaries

Distribution of multilocular adipose tissue

Ø In humans the tissue is important mainly in the first postnatal life (produces heat and protects the newborn against cold)

ØIt is greatly reduced in adulthoodØThe tissue is more abundant in hibernating animals – hibernating gland

In human newborn the multilocular adipose tissue constitutes 2 - 5% of the body weight

v Mainly around the shoulder blades and kidneys

Function of the multilocular adipose tissue

ØThe main function is to produce heat ØThe production is stimulated when human newborn or animals are exposed to

the cold environment ØMitochondria of multilocular adipocytes contain transmembrane protein –

thermogenin → heat production (temperature of tissue is elevated)

Slides

v Mesenchyme

Embryo head

ØMucous tissue

The umbilical cord - Warthon’s jelly

Arteries

Vein

ØLoose connective tissue ü Nuclei of fibrocytes and others cells ü Collagen fibers ü Elastic fibers

Elastic fibers

Collagen fibers

ØDense connective tissue

v Dense regular CT v Dense irregular CT

Tendon Skin

ØAdipose tissue

Sudan III

Signet ring cells