connective tissue 1 C Flashcards
Fibrillar collagen:
Some collagen molecules assemble in large bundles, called fibrils.
How are fibrillar collagen bundles formed?
collagen molecules are aligned both head to tail, to generate length (up to several hundred um long), and they are stacked to generate fibril thickness. These rope-like structures can have great strength to resist tensile stresses in tissues.
Collagen fibrils size:
can vary enormously in thickness
_____ is an abundant component of fibrillar collagen
Collagen Type I
Fibril-associated collagen:
These collagens decorate the surfaces of collagen fibrils, and are thought to link collagen fibrils to each other, or to link collage fibrils to other tissue components.
Network-forming collagen form _____
very thin fibers (perhaps a few molecules thick) and assemble into interlaced networks that form porous sheets.
network forming collagens are found:
in the basal laminae, and also as anchoring fibers that attach basal lamina and cells to the extracellular matrix.
Some of the network forming collagens function ____
as important filtration barriers (as in the kidney).
net working forming collagen type
Collagen Type IV is a common component of the network-forming sheets in basal laminae
Loose connective tissues contain ____.
thin collagen fibrils that are relatively sparse, and are arranged in irregular lattices
where are loose connective tissues found?
Blood and lymph capillaries, as well as nerves, are typically abundant in loose connective tissue.
Dense connective tissues contain:
- thick collagen fibrils that are very abundant relative to ground substance
- have a low number of cells.
- can have collagen bundles that are arranged in various “irregular” orientations
- or arranged in parallel organized sheets like in ligaments and tendons
dense CT are found
These tissues also have great strength, and are found where tissues must resist strong shear forces in particular directions, such as in tendons and ligaments
Collagen is synthesized and modified ____
intracellularly, and then secreted and further modified extracellularly.
Collagen is made and secreted by cells of the ___
connective tissue family.
Intracellular collagen synthesis and modification
- Collagen polypeptides are synthesized on the ER and translocated during synthesis to the ER lumen
- Collagens are post-translationally modified (they are glycosylated and hydroxylated on selected amino acid residues)
- The individual polypeptides are assembled into a triple helix
extracellular collagen synthesis and modification
- The N- and C-termini of collagen are cleaved by specific proteases. The N-terminal fragments that are generated are called N-telo peptides. The N-telo peptides are 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:
- Formation of bundles and end-to-end polymers of the collagen fibrils
- Enzymes catalyze chemical cross-links between collagen molecules. These covalent cross-links can increase the tensile strength of the bundles
Elastic fibers are found in ____.
connective tissues that require distensibility and resiliency
Elastic fibers contain the proteins ____ .
elastin and fibrillin that assemble into stretchable and resilient fibers and sheets.
Elastin is a
filamentous protein that exists in a predominantly random coil conformation (i.e. largely unstructured), that can be stretched upon exertion of force
Elastin monomers, like collagen, are secreted by ______
fibroblasts (in some cases, smooth muscle cells).
Extracellularly, elastic fibers form ______
filaments and sheets where the molecules are highly cross-linked with each other to generate an extensive network.
These elastin networks are interwoven with ____
filamentous protein, fibrillin, which appears to help organize the elastin elements in the fiber, and to organize the elastic fibers with the other components of the extracellular matrix. These elastic fibers can stretch and then recoil like a rubber band.
ground substance
The structural fibers of the extracellular matrix are enmeshed in hydrated aqueous gelatinous material.
major component of ground substance:
- proteoglycans
- other secreted proteins and glycoproteins
- inorganic and small organic solutes
- water
Proteoglycans contain _______.
a protein core attached to very large acidic polysaccharides, called glycosaminoglycans (GAGs)`
GAGs are _____
long polymers of carbohydrate molecules (polysaccharides). These molecules typically contain hundreds to thousands of sugar residues.
There are several different GAGs; most are ______
covalently attached to proteins, but some like hyaluronic acid are not attached to a protein core.
Proteoglycans are
different from other glycoproteins because the GAG chains can be up to 95% of their mass.
Three properties of GAGs are relevant to their function:
(1) they are highly negatively charged.
(2) Their rigid extended structure causes them to readily form gels. (3) Some proteoglycans can also bind to and inactivate or activate other proteins, particularly growth factors and ECM modifying enzymes.
Because GAG’s are very negative, they are
very hydrophilic
GAGs promote _____.
hydration of the ground substance to allow diffusion of small metabolites but tend to inhibit the movement of large structures (like bacteria)
Because GAGs promote hydration, they can function as:
selective sieves by forming gels of varying pore sizes.
It also creates a high swelling (turgor) pressure that allows the ECM to resist large compression forces (in contrast to collagen which functions to resist stretching forces).
Other secreted proteins and glycoproteins include
- proteases that process collagen and other types of proteins
- a variety of other extracellular enzymes
- growth factors
- other polypeptide ligands involved in cell signaling
Inorganic and small organic solutes: including
- ions
- carbohydrates
- lipid vesicles
- aggregates
- non-protein signaling ligands.
___ helps to maintain the hydration of ECM
gags
