i Tii TiConnective TissuesConnective Tissues

Aj U i i f S i & T h lAj U i i f S i & T h lAjman University of Science & TechnologyAjman University of Science & TechnologyFaculty of DentistryFaculty of Dentistryy f yy f y

Histology & Cell BiologyHistology & Cell Biology08 01 11208 01 11208 01 11208 01 112

Dr. AlDr. Al--Moutassem Billah KhairMoutassem Billah KhairKK

Connective TissuesConnective TissuesConnective tissue is the term traditionally applied to a basic type of

tissue of mesodermal origin which provides structural and metabolic supportf h i d h h h b dfor other tissues and organs throughout the body.

Connective tissues usually contain blood vessels and mediate theexchange of nutrients metabolites and waste products between tissues andexchange of nutrients, metabolites and waste products between tissues andthe circulatory system.

All connective tissues contain isolated cells surrounded by extracellularA y xmaterial “matrix” which is synthesized by own cells.

Connective tissue viscosity and tensile strength vary according to thearrangement of their extracellular matrix fibrous and amorphous components(fibrinogen, collagen, proteoglycans …).

C i i i f i di h id f f i f hiConnective tissues, in fact, indicate the wide range of function of thistype of tissue “supporting tissue”.

Connective tissue locationsConnective tissue locationsConnective tissue locationsConnective tissue locations

Connective tissues are omnipresent in the body. Every organ iscomposed of, or ensheathed by, at least some connective tissue.p f, y,They bind epithelial tissues to the subjacent structures of the body and holdthe parenchymal epithelial cells together to form the organ (lungs, liver, …).

They bind skeletal muscles together and attach them to bones by tendons orattach bones to bones by ligaments.

They form robust capsules of organs such as the liver and spleen.

They surround the central nervous system by a sheath, and some exist in andd i h l d liaround peripheral nerves and ganglia.

Other are specialized connective tissues “bone, cartilage & peripheral blood.

Connective tissue functionsConnective tissue functions

Connective tissues have variety of functions like

They bind tissues and organs of the bodyThey bind tissues and organs of the body.

They provide tough physical support (dermis) and the source oft t il t th (li t & t d )great tensile strength (ligament & tendon).

They have important metabolic roles such as the storage of fat( hi di i ) d l i f b d i h(white adipose tissue) and regulation of body temperature in thenewborn (brown adipose tissue).

Some of the cells of connective tissue form the major part of thebody’s defenses against pathogenic microorganisms.

They are largely involved in the processes of tissue repair.

Connective tissue componentsConnective tissue components

All connective tissues consist of cells, extracellular fibers andA f , x famorphous ground substance.

The cells of connective tissue:The cells of connective tissue:1. Cells responsible for synthesis and maintenance of the extracellular material.

They are derived from precursor cells in primitive mesenchyme. The types areThey are derived from precursor cells in primitive mesenchyme. The types arefibroblasts, chondroblasts, osteoblasts and odontoblasts. They produce fibersand ground substance.

2. Cells responsible for the storage and metabolism of fat, adipocytes.

3. Cells with defense and immune functions. This group of cells includes thell h & l h ll l llmast cells, macrophages & mononuclear phagocyte system cells, plasma cells

as well as all types of white blood cells.

Mesenchyme cells are relativelyunspecialized and are capable ofunspecialized and are capable ofdifferentiation into all connectivetissue cell types.

They have an irregular, stellate orfusiform shape with delicateb hi t l i t ibranching cytoplasmic extensions.The nuclei are oval with visiblenucleoli.

Some mesenchymal cells remain infully mature supporting tissue &provide a pluripotential source ofcells.

Active fibroblasts arestellate shape withpextensive cytoplasmicprocesses.

They containlarge nucleus withprominent nucleolusprominent nucleolus,and many cytoplasmicorganelles, which isthe evidence of activeprotein synthesis.

Mature fibroblast or fibrocyte issmaller than the active fibroblasts.

The cell is long and thin with finecytoplasmic processes.

The cytoplasm is greatly reduced involume and the nucleus isvolume and the nucleus iscondensed and elongated in thedirection of the collagen fibers.f g f

The main function is to maintainthe integrity of supporting tissueby continuous slow turnover of theextracellular material.

Mast cells are darkly stained because of theircytoplasmic granules. They are involved in defensecytoplasmic g anules. They a e involved in defensefunction and promote an increase in vascularpermeability.

Loose connective tissue contains, in addition tofibroblasts (F), leucocytes of different typesf y f ff y(Lymphocyte, Eosinophils, Neutophils) macrophages (M)and plasma cells (P).

The fibers of connective tissue: The fibers of connective tissue:

They are of two main types, collagen (including reticulin) and elastin. Theblood contains an extracellular fibrous component called fibrinogen, which isconverted into actual fibers of fibrin when blood clotsconverted into actual fibers of fibrin when blood clots.

1. Collagen is the main fiber type found in most connective tissues and is themost abundant protein in the human body.p y

Collagen fibers are flexible and have a remarkably high tensile strength.

Collagen is secreted into the extracellular matrix in the form of tropocollagenwhich consists of three polypeptide α chains (two α1 & one α2) boundtogether to form a helical structure. In he extracellular matrix, thet ll l l l i t f ll fib il th lltropocollagen molecules polymerize to form collagen fibrils, then collagenfibrils aggregate to form fibers.

The fibers of connective tissue

The fibers of connective tissue

Collagen fibfibers

The fibers of connective tissue: f f

Th h i th t f th h li t ll lik d di t diffThe α chains that form the helix are not all alike, and according to differencesin α chains, as many as 16 different types of collagen have been identified.These various collagen are classified by Roman numerals on the basis ofg f y R fchronology of discovery. The main types can be classified as follows:

- Collagen that form long fibrils: Type I (skin, tendon, bone, dentin), type II(cartilage, vitreous body), type III (skin, muscles, blood vessels), type V (fetalskin, skin, bone, placenta, most interstitial tissues), type XI (cartilage).

C ll h f k T IV (b b )- Collagen that forms networks: Type IV (basement membranes)

- Collagen that forms anchoring fibrils: Type VII (basal lamina).

Fib il i t d ll T IX ( til it b d ) t XII- Fibril-associated collagens: Type IX (cartilage, vitreous body), type XII(embryonic tendon & skin), type XIV (fetal skin & tendon).

The fibers of connective tissue: The fibers of connective tissue:

2. Reticular fibers are closely related to collagen fibers, in that they both consistof collagen fibrils The reticular fiber is composed of type III collagen & mayof collagen fibrils. The reticular fiber is composed of type III collagen & mayalso be type IV collagen.

They are formed by loosely packed, thin fibrils bound together by smallThey are formed by loosely packed, thin fibrils bound together by smallinterfibrillar bridges. The fibrils do not bundle to form thick fibers.

They are arranged in a mesh-like pattern or network in loose connectivetissue, around glands & smooth muscles, bone marrow and lymphoid organs.

The fibers of connective tissue: The fibers of connective tissue:

3. Elastic fibers are composed of three types, oxytalan, elaudin and elastic.3. Elastic fibe s a e composed of th ee types, oxytalan, elaudin and elastic.Elastin is a rubber-like material which is arranged as fibers &/ordiscontinuous sheets in the extracellular matrix particularly of skin, lungand blood vessels where it confers the properties of stretching and elasticrecoil.

Th ar t i all thi r tha llag fib r a d arra g d i a bra hi gThey are typically thinner than collagen fibers and arranged in a branchingpattern to form a three-dimensional network.

They are interwoven with collagen to limit the distensibility of the tissueThey are interwoven with collagen to limit the distensibility of the tissueand to prevent tearing from excessive stretching.

The fibers of connective tissue The fibers of connective tissue

Elastic fibers

The ground substance of connective tissue:

- Ground substance is an amorphous transparent material, that occupies theb h ll d fib d h h i f i fl id lspace between the cells and fibers, and has the properties of a semi-fluid gel.

- Ground substance (G. S.) is a highly hydrated, mixture of glycosaminoglycansin the form of hyaluronic acid and proteoglycansin the form of hyaluronic acid and proteoglycans.

- These huge molecules are entangled and electrostatically linked to oneanother and their water of hydration, to form a flexible gel through whichf y , f f x g gmetabolites may diffuse.

- The size of the spaces between the glycosaminoglycan molecules and thenature of electrostatic changes determine the permeability characteristics ofany particular connective tissue.

G S h i l i i f d b h fib i f h- G. S. mechanical properties are reinforced by the fibrous proteins of theextracellular matrix to which its components are also bound.

Connective tissue classificationConnective tissue classification

Cl ifi i i b d h i i d i i f hClassification is based on the composition and organization of thecellular and extracellular components and on special functions.

lI. General connective tissue proper:

Loose (areolar) connective tissue

Dense connective tissue: regular , irregular

II. Special connective tissue proper:p p p

Adipose tissue, reticular tissue, elastic tissue, mucous tissue

III Supporting (specialized) connective tissue:III. Supporting (specialized) connective tissue:

Cartilage, bone, peripheral blood.

Connective Connective Connective Connective tissue tissue classificationclassificationclassificationclassification

Loose connective tissue: Loose connective tissue:

- Loose connective tissue is characterized by loosely arranged fibers and anabundance of cells. The fibers are thin and relatively sparse. The groundsubstance is abundant and occupies more volume than fiberssubstance is abundant and occupies more volume than fibers.

- It has a viscous to gel-like consistency and is important in the diffusion ofoxygen and nutrients from the small vessels that course through this tissue asyg f gwell as the diffusion of metabolites back to the vessels.

- The primary location is beneath those epithelia that cover the body surfaces.It is also present around glands and smallest vessels.

- Its location represents the initial site in which antigens and other foreignb t h i t d ith li l f b h ll d dsubstances having entered an epithelial surface can be challenged and

destroyed. Thus, it is the site of inflammatory and allergic or immune reactions.

Examples of location: mesenteries, lamina propriaand the adventitial layer of blood vessels.and the adventitial laye of blood vessels.

Fibers: collagen (C), reticular and elastic fibers (E).

Loose connective tissue contains a variety of cells, whichcan include resident fibroblasts (F) macrophages (M) mastcan include resident fibroblasts (F), macrophages (M), mastcells, plasma cells (P) and leukocytes (L, N, Eo).

Dense connective tissue:

- Dense connective tissue have more fibers per unit volume than loosei i I i f ll d li l d bconnective tissue. It contains fewer cells and little ground substance.

- Dense connective tissue can be divided into regular and irregular according tothe arrangement of the fibersthe arrangement of the fibers.

A. Dense regular connective tissue is characterized by ordered and denselypacked arrays of fibers and cells. It is the main functional component ofp k y f f f p ftendons, ligaments, aponeuroses and in the stroma of the cornea.

Tendons are cord-like structures that join muscles to bone.

They consist of parallel bundles of collagen fibers (type I) between which arerows of fibroblasts (tendinocytes).

The tendon is surrounded by a thin connective tissue capsule, theepitendineum, which is a dense irregular connective tissue.

Dense connective connective tissue: Dense

regular connective tissue from

a tendon

Dense connective tissue:

Ligaments join bone to bone. They are similar to tendons, in that theyi fib d fib bl d i ll l b h fib lcontain fibers and fibroblasts arranged in parallel, but the fibers are less

regularly arranged than those in tendons.

Collagen is the major extracellular fiber of most ligamentsCollagen is the major extracellular fiber of most ligaments.

Some of the ligaments associated with the spinal column contain considerablenumbers of elastic fibers and few collagen fibers. These ligaments are calledf f f g f gelastic ligaments (yellow ligaments).

Aponeuroses are much like broad flattened tendons. Instead of all of thefibers lying in parallel arrays, the fibers of aponeuroses are arranged inmultiple layers.

Th b dl f ll fib i h f h l d i lThe bundles of collagen fibers in each of the layers are arranged in regulararrays and tend to be arranged at 90 o angles to the neighboring layers.

B. Dense irregular connective tissue is characterized byan abundance of fibers and few cells. Cells arean abundance of fibe s and few cells. Cells a etypically fibroblasts.

It exists in the dermis of the skin, capsules of organs(liver, spleen, …) and in the periosteum surroundingbones.

It provides significant strength because of the highproportion of collagen fibers.

The fibers are arranged in bundles oriented invari dir ti t with ta d tr t whi h avarious directions to withstand stresses to which anorgan or structure may be subjected.

Reticular tissue:

Reticular tissue forms a delicatesupporting framework for manysupporting framework for manyhighly cellular organs such asendocrine glands, lymph nodes, thesmall vascular channels of liver,spleen, bone marrow and thymus.

Reticular tissue is a specializedloose connective tissue consisting ofreticular fibers reticulin with areticular fibers, reticulin, with arich coat of glycoproteins.

Reticular cells resemble fibroblastsfwith long processes morphologicallysimilar to mesenchymal cells.

Elastic tissue:Ela ti ti i r t i th ll li a t f thElastic tissue is present in the yellow ligaments of thevertebral column and in the suspensory ligament of thepenis. Also, some of body tissues contain large amount ofp , f y g felastic fiber like the wall of elastic arteries & dermis.

Dermis of the skin

Elastic tissue:d f b dl f h k l f b hIt is composed of bundles of thick elastic fibers with

thin collagen fibers and flattened fibroblasts. Theabundance of elastic fibers gives it a typical yellow colorabundance of elastic fibers gives it a typical yellow colorand great elasticity.

Large artery

H A tHuman Aorta

Mucous tissue: Mucous tissue:

Mucous tissue is the principalf h bili l dcomponent of the umbilical cord

“Wharton’s jelly” and, also, found inthe pulp of young teeth.the pulp of young teeth.

Mucous tissue is a jellylike tissuecontaining very few fibers and thecells are mainly fibroblasts.

Mucous tissue has an abundance ofd b d l fground substance composed mainly of

hyaluronic acid.Mucous tissue of an embryo

Adipose tissue: p

- The cells, adipocytes, are adapted for the storage of fat.

- Adipocytes are found in isolation or in clumps throughout loose connectivetissue or may form the main cell type as in adipose tissue.

- The fat stored within adipocytes is derived from three main sources:

Dietary fat circulating in the blood stream as chylomicrons

Triglycerides synthesized in the liver and transported in blood

Triglycerides synthesized from glucose within adipocytes

- Adipose tissue acts as a temporary store of substances for the energy-derivingprocesses of almost all tissues, and, therefore, generally has rich blood supply.

Th rat f fat d iti a d tili ati ithi adi ti d t r i d- The rate of fat deposition and utilization within adipose tissue determinedby dietary intake and expenditure.

Adipose tissue: Adipose tissue:

- Adipose tissue of two types that have different locations, structures, colors,and pathologic characteristics.

A White adipose tissue “unilocular” is distributed throughout the bodyA. White adipose tissue unilocular is distributed throughout the bodyespecially in the deep layer of the skin, the breasts, over the abdomen, aroundthe hips and buttocks.p

Unilocular adipose tissue accounts for about 25% of the normal weight infemale and 20% in male.

In addition to being an important energy store, white adipose tissue acts as athermal insulator under the skin and functions as a cushion against

h i l h k i h it d kid d Adi timechanical shock in such sites as around kidneys and eyes. Adipose tissueinfiltrates the mesenteries and the omentum in varying degrees.

White adipose tissue is composed of large polyhedral cells(50-150 µm) and small amount of extracellular matrixµ fcontaining reticular fibers. It is subdivided into incompletelobules by septa of connective tissue containing blood vessels.

Adipocytes contain a single central fat vacuole that is notbounded by a plasma membrane, but appear to be boundedbounded by a plasma memb ane, but appea to be boundedby a regularly spaced array of 9 nm diameter filaments. Thenucleus flat and unremarkable peripherally located.

The cell cytoplasm is reduced to a small peripheral rimaround the fat droplet containing the usual array ofa ound the fat d oplet containing the usual a ay oforganelles.

A rich network of blood capillaries is found in between cell.

Adipocytes in loose connective tissue

B. Brown adipose tissue “multilocular” highly specializedtype that is found in newborn mammals and somey fhibernating animals, where it plays an important part inbody temperature regulation. In human adults, only small

t f b di ti f damounts of brown adipose tissue are found.

The cells of brown adipose tissue are smaller than those of white adiposetissue. The nucleus of a mature multilocular adipocyte is typically in aneccentric position within the cell, but it is not flattened, as is the nucleus of a

hit di twhite adipocyte.

Its color is due to cytochromes in its extraordinary abundant mitochondria.

Brown adipose tissue is subdivided into lobules by partitions of connectiveBrown adipose tissue is subdivided into lobules by partitions of connectivetissue, but the connective tissue stroma between individual cells within thelobules is sparse.p

The tissue has an exceedingly rich blood capillaries that enhance its color.

Brown adipose tissue is present in large amounts in the newborn, because ofthe high surface-to-mass ratio in the newborn that results in excessive heatloss.