connective tissue overview collagen ecm structure and type of fibers

What defines connective tissue and what makes it different from epithelial tissue

Connective tissue is a heterogeneous group of tissues characterized by the presence of abundant extracellular matrix (ECM) separating relatively few cells.

This is the main difference from epithelial tissue:

• epithelium → many tightly packed cells + little ECM;

• connective tissue → fewer cells + abundant ECM.

The ECM determines the tissue’s mechanical and functional properties.

All connective tissues share:

• a common embryological origin,

• cells embedded in ECM,

• structural, trophic, protective, and reparative functions.

Examples include:

• loose connective tissue,

• dense connective tissue,

• adipose tissue,

• cartilage,

• bone,

• blood.

What are the two major components of connective tissue?

What are the two major components of connective tissue?

A:

Connective tissue is composed of:

1. cells;

2. extracellular matrix (ECM).

The ECM is subdivided into:

• ground substance;

• fibers.

Fibers include:

• collagen fibers,

• reticular fibers,

• elastic fibers.

The relative proportions of cells, fibers, and ground substance determine the appearance and function of each connective tissue type.

What is the embryological origin of connective tissue? And in the head region?

the head region, some connective tissues derive from neural crest ectomesenchyme.

All the other from the mesoderm

The embryonic precursor of connective tissue is called mesenchyme.

Mesenchymal stem cells are multipotent and can differentiate into:

• fibroblasts,

• adipocytes,

• chondrocytes,

• osteoblasts,

• smooth muscle cells.

Describe mesenchyme histologically.

Cells are star haped

Oval nuclei

Long cytoplasmtic processes

Ecm is rich in hyalu, water and reticular fibers

Which are the functions of the connective tissue

1. Structural and organizational : stroma of organs supporting frameweok that organizes funcitonal cells ( parenchyma)

2. Trophic

3. Defense

4. Repair

What is the structural and organizational function of connective tissue?

• supports organs,

• organizes tissues into lobules and compartments,

• surrounds vessels and nerves,

• mechanically stabilizes tissues.

Examples:

• connective tissue septa in pancreas,

• reticular framework in lymphoid organs,

• endomysium/perimysium in muscle.

What is the trophic function of connective tissue?

Most connective tissues are vascularized and provide nutrients and oxygen to surrounding tissues.

Functions:

• transport nutrients,

• remove waste,

• support blood vessels.

This is especially important because epithelia are avascular and depend on underlying connective tissue for diffusion.

What is the defense function of connective tissue?

Connective tissue contains many immune and inflammatory cells:

• macrophages,

• mast cells,

• plasma cells,

• lymphocytes,

• neutrophils.

What is the repair function of connective tissue?

Fibroblasts:

• proliferate,

• synthesize collagen,

• produce scar tissue.

Repair occurs in stages:

1. inflammation;

2. tissue formation;

3. remodeling.

Excessive repair may lead to fibrosis.

What is ground substance?

Ground substance is the hydrated amorphous component of ECM occupying the space between cells and fibers.

It contains:

• water,

• ions,

• gases,

• metabolites,

• glycosaminoglycans (GAGs),

• proteoglycans,

• glycoproteins.

Functions:

• diffusion,

• support,

• cushioning,

• signaling.

: Why is ground substance highly hydrated?

Ground substance contains negatively charged GAGs.

These negative charges attract:

• sodium ions,

• water molecules.

This creates hydrated gels that:

• resist compression,

• facilitate diffusion,

• maintain tissue hydration.

What are glycosaminoglycans (GAGs)?

What are the functions of GAGs?

Why do GAGs stain with basic dyes?

GAGs are long unbranched polysaccharides composed of repeating disaccharide units.

They contain:

• sulfate groups,

• carboxyl groups.

This makes them highly negatively charged (polyanions).

What are the functions of GAGs?

A:

Functions:

• attract water,

• form hydrated gels,

• resist compression,

• regulate diffusion,

• bind growth factors,

GAGs are highly negatively charged due to sulfate and carboxyl groups.

Basic dyes bind these negative charges strongly.

This explains:

• basophilia,

• metachromasia.

What is metachromasia

Metachromasia is the phenomenon in which a dye changes color when bound to highly negatively charged molecules such as sulfated GAGs.

Example:

• toluidine blue normally stains blue;

• in cartilage matrix or mast cell granules it appears purple

Where is chondroitin sulfate found?

contributes to resistance against compression

1. Bone

2. 2. Cartilage

3. 3. Heart valves

Where is dermatan sulfate found?

1. Skin

2. Tendons

3. Blood vessesl

4. TENSILE STRENGHT AND FLEXIBILITY

Where is keratan sulfate found?

Keratan sulfate is found in:

• cornea,

• cartilage,

• bone.

Important for hydration and transparency of the cornea.

Why is hyaluronic acid unique among GAGs?

Where is hyaluronic acid found?

What are the properties of hyaluronic acid?

Hylauronic acid is unique in the gags

1. DOES OT HAVE SULFATE GROUP

2. IT IS OT ATTCHED TO CORE PROTEIN so it exists as a free carbohydrate chian

3. The functions: as it is very hdrayted and a long polymer and it is hard to compress it severs as shock abosbrtion, lubriication as we can find in the loose connective tissue and in synovial fluid and also it support cells migration as we can find in the embryonic menechyme

What are proteoglycans?

Proeto: coro protein

To which is attahced

Glycan: gag some can have one gag some hundreds

Ex. AGGREGAN IN CARTILAEGE

They form aggregates with gags, they allow to resist compression and regulate diffusion as they TRAP WATER.

And bind to gf

What are multiadhesive glycoproteins

They are multifunctional ECM proteins that connect:

• ECM components together;

• cells to ECM.

Main examples:

• fibronectin,

• laminin.

Q: What is fibronectin?

Fibronectin is a glycoprotein that bind

Collagen, fibrins and integrins

Fibronectin allows cell adhesion

Migation and WOUND HEALING

WHAT IS LAMININ

Laminin is a major glycoprotein of the basal lamina.

Bind type IV collagen and integrins

ORGANIZES BASAL LAMINA AND ANCHORS EPITHELIAL CELLS

COLLAGEN FIBERS FUNCTIONS AND APPEARANCE?

Collagen fibers are the most abundant connective tissue fibers.

Functions:

Tensile strenght

Resisteance to traction

They are:

• thick,

• eosinophilic,

• wavy,

• arranged in bundles.

Describe collagen structural organizatio

This hierarchical organization gives enormous tensile strength.

1,apha chain

Triple helix ( tropocollagen)

1. fibrils;

2. fibers;

3. bundles.

Tropocollagen is the basic collagen molecule formed by three intertwined alpha chains arranged in a triple helix

Q: Why are glycine and proline important in collagen?

Glycine is small fits inside the triple elox

Proline allow stabilization of the helix through h bonds

What is the main bandining pattern for collagen fibirils and how is it formed?

68 nm bandin patter

Arrangement of collagen molecule in bundles in a a quarter stagger arrangement overlap and gap zone

The alternating pattern produces the characteristic 68 nm striations visible under electron microscopy.

Which cells synthesize collagen?

The major producers are fibroblasts in connective tissue proper

But also OSTEOBLAST CONDROBALSTS AND SMOOTH MUSCLE CELLS

What are the intracellular steps of collagen synthesis?

1. Synthesisi of pro alpha chains in the er

2. 2. HYRDROXYLATION OF PROLINE AND LYSINE for which essential vitamin c

3. Formation of tropocolaggen

4. Golgi

5. Exocitosis

Why is vitamin C essential for collagen synthesis?

Vitamin C is required for hydroxylation of:

• proline,

• lysine.

Hydroxylation stabilizes the collagen triple helix.

Without vitamin C:

• collagen becomes weak,

• connective tissue integrity is impaired.

After exocytosisi of collagen how do they become mature fibers

Cleavage of procollagen peptide

Fibrillogenesis And assembly

What is scurvy and why does it occur?

Scurvy is caused by vitamin C deficiency.

Without vitamin C:

• collagen hydroxylation fails,

• collagen becomes unstable.

Clinical manifestations:

• bleeding gums,

• fragile vessels,

• poor wound healing,

• tooth loss,

• weak scar formation,

• impaired bone formation.

Where is type I collagen found?

Type I collagen is the one found the most it privides very high tensile sterght

1. Bone

2. Dermis

3. Tendons

4. Dentin

5. FIBROcartilage

Where is type II collagen found?

Mainly in cartilage

Helps in resisting pressure

Forming fine fibirils adapted to resist compression

Where is type III collagen found?

Forms RETICULAR FIBERS

1, liver

Lymphoid organs

Spleen

Bone marrow

Around vessels

Type IV collagen

Type Iv is the collagen bound to the glycoprotein laminintherephore is the main component of the BASAL LAMINA here you do not have fibrils but NETWROKD

Which kind of collage is in the dermis, bone and tendons

Type I for hugh tensile strenght

Type of collage for sleppn, lympooid organs, bone marrow and aorund blood vessels

Type 3 for reticular fibers

Which kind of collagen is not in fibrils but it forms netwroks

Type IV in the basal lamina assoicated with lamins

Which kind of collagen is in the cartilage and which is fibrocartilage

In fibrocartilage high tensile strenght is needed so is type I

In nornal cartilage is type II forming fine fibrils that are used for pressure resistance and compression

What is Ehlers-Danlos syndrome?

Ehlers-Danlos syndromes are inherited disorders caused by defects in collagen synthesis or processing.

Clinical features:

• hyperextensible skin,

• joint hypermobility,

• vessel fragility,

• poor wound healing,

• abnormal scars.

The pathology results from defective connective tissue strength.

What are reticular fibers?

Reticular fibers are thin branching fibers composed mainly of type III collagen.

They form delicate meshworks supporting soft tissues infact it is found in liver, slepp, bone marrow ecc.

What are the functions of reticular fibers?

Is essential for flexibile tissue That need structural support and have cellular movement

Where are reticular fibers found?

Reticular fibers are found in:

• lymph nodes,

• spleen,

• liver,

• bone marrow,

• around adipocytes,

• around capillaries,

• around muscle fibers.

Why are reticular fibers ideal for lymphoid organs?

Reticular fibers form delicate branching meshworks.

This provides:

• structural support;

• free movement for immune cells.

Thick collagen bundles would impair cell migration.

What are elastic fibers?

Elastic fibers are connective tissue fibers specialized for elasticity and recoil.

They allow tissues to:

• stretch;

• return to original shape.( recoil)

What are elastic fibers composed of?

What are desmosine and isodesmosine?

They have a elastin core

Elastin is rich in glycine and proline and it is hydrophibic forming RANDOM COILS that allow stretching and recoling

Fibillin

Glycoprotein to stabilize elastin

Desmosine and isodesmosine

Create covalent cross linkbetween elastic molecules.!

Where are elastic fibers abundant and how do they appear histologically

Abundant in 1. Skin 2, vocal cords, 3, aorta 4,.large arteries 5. LIGAMENTUM FLAVUM

Apparently as dark wavy braching fibers

How is the structure of elastic fibers in large arteries?

Elastic fibers here are arrangened in CONCENTRIC FENESTRAED LAMAELLAE in the tunica media ( muscle tissue) to allow EXPANSION during systole and recoil in diastole

Why do elastic fibers recoil after stretching?

As elastin is rich in glycine and proline and it is hydrophobic it allows to have random coils that then go back to original

also with the stabiliziation by fibrillin

What is Marfan syndrome?

Marfan syndrome is caused by mutations in fibrillin-1.

Consequences:

• defective elastic fiber organization,

• weak connective tissue.

Clinical features:

• tall stature,

• long limbs,

• lens dislocation,

• aortic aneurysm.