Connective Tissue III Flashcards
The dominant feature of CT is that
most of the tissue components are extracellular
ECM components that largely determine the structure and function of each tissue
a. structural fibers which provide mechanical strength and resiliency
b. a hydrated gelatinous material called ground substance, in which the structural fibers are enmeshed
c. numerous other extracell macromolecules embedded within or diffusing through the ECM
_______ fibers are the most abundant structural fibers of the ECM and are composed of a large family of closely related proteins.
Collagen
The collagens are _______ proteins of _______ sequence to each other; collagen proteins aggregate to form _______
- fibrous
- very similar primary sequence to each other
- fibers of varying sizes and organizations
Each collagen molecule is composed of _______ intertwined polypeptide chains that form a fairly _______. Each polypeptide is called an _______. Assembly of these chains in different combination leads to the formation of _______
- three
- rigid rope-like triple helix
- alpha chain
- multimeric collagens of at least 17 types
Each collagen molecule can be _______ and _______ with other collagen molecules to form higher order fibrous structures. The many different forms of collagen lead to diversity of structural fibers.
- aligned
- cross-linked
Fibrillar collagen:
Some collagen molecules assemble in large bundles, called fibrils.
To form fibrils, collagen molecules are aligned _______, to generate _______, and they are stacked to generate fibril _______. These rope-like structures can have great _______ to resist tensile _______
- both head to tail
- length
- filbril thickness
- both head to tail
- strength
- stresses in tissues.
In the electron microscope collagen fibrils display a _______. Collagens that form these structures are the most abundant in the body (especially Type _______). Collagen fibrils can vary enormously in thickness. Collagen Type _______ is an abundant component of fibrillar collagen
- characteristic banding pattern
- I
- 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 collagen fibrils to other tissue components.
Network-forming collagen: what do they form? what do they assemble into? where are they found?
These collagens form very thin fibers (perhaps a few molecules thick) and assemble into interlaced networks that form porous sheets. Such collagens are found in the basal laminae, and also as anchoring fibers that attach basal lamina and cells to the extracellular matrix.
Some network-forming collagen function as important _______. Collagen Type _______ is a common component of the network-forming sheets in basal laminae.
- filtration barriers (as in the kidney)
- IV
Loose connective tissues contain thin collagen fibrils that are _______. Cell densities and ground substance components are relatively ________ in loose connective tissues. Blood and lymph capillaries, as well as nerves, are typically abundant in loose connective tissue.
- relatively sparse, and are arranged in irregular lattices
- high
- abundant
Dense connective tissues contain _______, and have a _______ number of cells. These tissues can have collagen bundles that are arranged in various “_______” orientations or in _______ sheets, such as in ligaments and tendons. These tissues also have _______ strength, and are found where tissues _______
- Thick collagen fibrils that are very abundant relative to ground substance
- low
- irregular
- parallel-organized
- great
- tissues must resist strong shear forces in particular directions, such as in tendons and ligaments.
Collagen is synthesized and modified _______cellularly, and then secreted and further modified _______cellularly. Collagen is made and secreted by cells of the _______. The final extracellular product is highly modified in a number of ways.
- intra
- extra
- the connective tissue family
Intracellular collagen modifications:
- 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 modifications:
- 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 _______. Elastic fibers contain the proteins_______ that assemble into _______
- distensibility and resiliency
- elastin and fibrillin
- stretchable and resilient fibers and sheets
Elastin is a _______ protein that exists in a predominantly _______ conformation (i.e. largely unstructured), that can be stretched upon exertion of force. Elastin monomers are secreted by _______ (in some cases, smooth muscle cells). Extracellularly, they form _______ and _______ where the molecules are highly cross-linked with each other to generate an extensive network. These elastin networks are interwoven with _______
- filamentous
- random coil
- fibroblasts
- filaments
- sheets
- fibrilin
fibrillin appears to help _______, and to _______. These elastic fibers can stretch and then _______
- organize the elastin elements in the fiber
- organize the elastic fibers with the other components of the extracellular matrix
- stretch and then recoil like a rubber band
