Connective Tissue

Question 1

What produces the extracellular matrix (ECM)?

Answer 1

Produced by CT

Question 2

What is the ECM?

Answer 2

Structural fibers; glycoproteins; and polysaccharides. Distinct for each type of CT. Largely determine structure and function of each tissue

Question 3

Why is CT important?

Answer 3

Mechanical strength. Control exchange of nutrients/ligands. Control the ECM.

Question 4

What is function of ECM

Answer 4

Control of epithelial cell polarization/shape. Guidance and regulation of cell migration through matrix. Controlcell proliferation; differentiation; metabolism. Defense/immune response/inflammation. Control tissue formation; organization; modification

Question 5

What are mesenchymal cells?

Answer 5

Precursors to all of the connective tissue family members; primarily function in embryogenesis but small numbers of them may persist through adulthood to function as stem cells for generation of new connective tissues.

Question 6

What are fibroblasts?

Answer 6

Pre-eminent cells of most connective tissues in the body

Question 7

What are myofibroblasts?

Answer 7

Derivatives of fibroblasts that are capable of smooth muscle-like function and are found in connective tissues that require a contractile function. Often generated at the site of wounds where their contractile function contributes to retraction and shrinkage of scar tissue.

Question 8

What are adipocytes?

Answer 8

Derivatives of fibroblasts and/or primitive mesenchymal cells. The main type of adipocyte found in adults functions to store fat as energy for other cell types; tissue containing these cells is called �white fat�. A distinct type of adipocyte is prominent in newborns/children; it contains many mitochondria that convert fatty acid into heat. Tissue with these cells is called �brown fat�.

Question 9

What are osteoblasts and osteocytes?

Answer 9

Cells that make bone

Question 10

What are chondrocytes?

Answer 10

Cells that make cartilage

Question 11

What do smooth muscles cells do with respect to the ECM?

Answer 11

Some (esp. those in the walls of blood vessels) make some of the extracellular matrix components in which they are imbedded. Some smooth muscle cells derive from the same types of precursors as other connective tissue cells (why they can synthesize and secrete similar types of ECM components).

Question 12

What are the immigrant blood-derived cells that are abundant in the CT?

Answer 12

Lymphocytes; macrophages; neutrophils/eosinophils; mast cells; osteoclasts

Question 13

What are lymphocytes important for?

Answer 13

Central to acquired immunity to foreign organisms/viruses/materials.

Question 14

What are macrophages?

Answer 14

Large phagocytotic cells. Engulf cells ECM; non-cellular material. Critical regulatory cells that secrete and respond to numerous extracellular signals. They can signal to stimulate endothelial cells to induce angiogenesis; immune cell migration and function; fibroblast activation; blood vessel permeability et al.

Question 15

What are neutrophils and eosinophils important for?

Answer 15

Defense against microorganisms

Question 16

What are mast cells important for? What are they derived from?

Answer 16

Secretory cells that (when stimulated by immune responses) release various substances including vasodilators that promote swelling in connective tissue; thus mast cells are important in edema and allergic hypersensitivities. Derived from basophils.

Question 17

What are osteoclasts important for? What are they similar to?

Answer 17

Phagocytic cells that appear to be derived from blood monocytes and are very similar to macrophages. However they specifically function in bone resorption and remodeling; not general phagocytosis.

Question 18

What are the main componenets of the ECM?

Answer 18

Structural fibers (provide mechanical strength). Ground substance (a gelantinous material where structural fibers are enmeshed). Many other ECM macromolecules

Question 19

What are the main types of structural fibers of the ECM?

Answer 19

Collagen (fibrillar; fibril-associated; network-forming) and elastic fibers

Question 20

What is the structure of each collage molecule?

Answer 20

Composed of 3 intertwined polypeptide chains that form a fairly rigid rope-like triple helix. Each polypeptide is called an alpha chain.

Question 21

What many different types of collagen are there? What is this largely determined by?

Answer 21

At least 17 types. Mostly dependent on different types and different combinations of alpha chains.

Question 22

Describe fibrils. What type of collagen is common here?

Answer 22

Formed by aligning collagen molecules head to tail. They are long and the collagen can be stacked to generate thickness. Rope-like. Have great strength to resist tensile stress. Collage type I is abundant in fibrils and this (and other collagens that generate fibrils) is most abundant type in body

Question 23

What are fibril-associated collagens?

Answer 23

On the surgace of collagen fibers. Thought to link collagen fibrils to each other or to link collage fibrils to other tissue components.

Question 24

What are network-forming collagens? What type of collagen is common?

Answer 24

Form very thin fibers and assemble into interlaced networks that form porous sheets. Found in the basal laminae and also as anchoring fibers that attach basal lamina/cells to ECM. Can function as important filtration barriers (E.G. in the kidney). Collagen type IV is a common component

Question 25

What are some intracellular modification of collagen?

Answer 25

Post-translationally glycosylated and hydroxylated on select amino acid residues. Assembled into a triple helix

Question 26

What are some extracellular modification of collagen?

Answer 26

N- and C- termini are cleaved by proteases (N-telo peptides). This causes: formation of bundles and end-to-end polymers of the collagen fibrils. Chemical cross-links catalyzed by enzymes (increase the tensile strength of bundles)

Question 27

What are n-telo peptides and why are they important?

Answer 27

N-terminal fragments of collagen. Clinically important because their levels in urine and blood are used to diagnose important connective tissue and bone disease. Proteolytic release of these fragments is important to initiate the formation of budles/fibrils and cross-linkage

Question 28

Which proteins are found in elastic fibers? What do they do?

Answer 28

Elastin and fibrillin. Assemble into stretchable and resilient fibers and sheets.

Question 29

What is the structure of elastin?

Answer 29

Filamentous protein that exists in a predominantly random/unstructured coil conformation. Can be stretched upon exertion of force

Question 30

Which cells secrete elatin?

Answer 30

Fibroblasts

Question 31

What does fibrillin do in the elastic fibers?

Answer 31

It is interwoven with elastin and appears to help organize it.

Question 32

What are the major components of ground substance?

Answer 32

Proteoglycans; other secreted proteins/glycoproteins; inorganic and small organic solutes; water

Question 33

What is the structure of proteoglycans?

Answer 33

Contain a protein core attached to very large acidic polysaccharides called glycosaminoglycans (GAGs)

Question 34

What are GAGs?

Answer 34

Long polymers of polysaccharides. Typically contain hundreds to thousands of sugar residues. Most are attached to proteins; hyaluronic acid is exception

Question 35

How are proteoglycans different from other glycoproteins?

Answer 35

Because their GAG chains can be up to 95% of their mass

Question 36

What 3 properties of GAGs are relevant to their function?

Answer 36

1) Highly negatively charged (so very hydrophilic) 2) Their rigid extended structure causes them to readily form gels. This gels promote hydration of ground substance and can act as selective sieves with varying pore sizes. Also serves to resist large compression forces. 3) Some can also bind to and activate/inactive other proteins (like growth factors and ECM modifying enzymes)

Question 37

What are some examples of the other secreted proteins and glycoproteins in the ground substance?

Answer 37

Include proteases that process collagen; growth factors; ligands; enzymes

Question 38

When a wound occurs; what do CT cells do to promote inflammation and blood clotting?

Answer 38

CT fibroblasts; mast cells; etc. release signaling compounds that increase water perm. of capillary endothelia; increase cellular permeability of endothelia; attract migration of white cells to the site of the would (chemotaxis); stimulate proliferation of fibroblasts and differentiation of monocytes into macrophages

Question 39

Which cells secrete hystamine? What does it do?

Answer 39

Secreted by mast cells. Thought to promote endothelial permeabilization

Question 40

Which cells secrete cytokines? What do they do?

Answer 40

Secreted by white blood cell derivatives and fibroblasts. They promote several of the inflammation/blood clotting processes. Can also signal long distance to hematopoietic tissue to stimulate productions of more white blood cells

Question 41

What cells in the ECM are involved in new tissue formation?

Answer 41

Fibroblasts (divide and secrete ECM components); cytokines and other growth factors; many signals from macrophages et. al trigger new blood vessel growth (angiogenesis)