Connective Tissue Flashcards
Ross & Pawlina - Connective Tissue
what is connective tissue?
connective tissue consists of cells and extracellular matrix (ECM).
connective tissueforms a vast and continuous compartment throughout the body. bounded by basal or external laminae of various epithelia, muscle cells and nerve supporting cells.
what is ECM?
ExtraCellular Matrix includes structural fibrils and specialised proteins that constitue the ground substance.
what are the types of connective tissue - plus subtypes?
embryonic connective tissue
- mesenchyme connective tissue - mucous connective tissue
connective tissue proper
- loose connective tissue
- dense connective tissue
- regular
- irregular
specialised connective tissue:
- bone, cartilage, blood, adipose tissue, lymphatic tissue
what is embryonic connective tissue?
embryonic connective tissue is present in the embryo and within the umbilical cord. it is classified into two subtypes:
- mesenchyme
- mucous connective tissue
mesoderm, the middle germ embryonic layer, gives rise to much of the connective tissues of the body.
what is mesenchyme?
where is it found?
what is the appearance of cells found in mesenchyme?
mesenchyme is a subtype of embryonic connective tissue.
it is found in the embryo.
mesenchyme contains small, spindle-shaped cells, uniform in appearance.
the processes extend and contact similar processes of neighbouring cells, forming a 3-D cellular network. the extracellular space is occupied by a viscous ground substance.
what is mucous connective tissue?
where is it found?
describe…
mucous connective tissue is a subtype of embryonic connective tissue and present in the umbilical cord.
it consists of a specialised, gelatinlike ECM; its ground substance referred to Wharton’s jelly.
the spindle-shaped cells are widely separated and appear much like fibroblasts in the near term umbilical cord.
what is Wharton’s jelly?
Wharton’s jelly is used in reference to the ground substance in the ECM of mucous connective tissue.
It is so called due to the gelatinlike nature of the ECM.
how can the connective tissue proper be classified into general subtypes? (alternative names)
- plus further subdivisions
- Loose connective tissue (areolar tissue)
- Dense connective tissue: subdivided based on organisation of collagen fibres into:
- dense irregular connective tissue
- dense regular connective tissue
Describe areolar tissue
areolar tissue is another name for loose connective tissue.
it is characterised by loosely arranged fibres and abundant cells of various types
thin sparse collagen fibres with an abundant ground substance
the ground substance had a viscous gel-like consistancy; playing an important role in the diffusion of oxygen and nutrients from the small vessels that course through this tissue type.
most cell types found in loose connective tissue are transient wandering cells that migrate from local blood vessels in responce to specific stimuli.
where is loose connective tissue primarily located?
loose connective tissue is found beneath the epithelia that covers body surfaces and line the internal surfaces of the body
describe dense irregular connective tissue…
DICT is characterised by abundant fibres and few cells.
cells are sparse and typically of a single type, fibroblast.
DICT also contains little ground substance
the fibres are arranged in bundles orientated in various directions that can withstand stresses on organs or structures.
what is the function of Dense irregular connective tissue and where is it found?
hollow organs possess a distinct layer of DICT called the submucosa in which the fibre bundles course in varying planes.
this allows the organ to resist excessive stretching and distentiopn
DICT is also found in skin, the reticular/depp layer of the dermis. providing resistance to tearing.
describe Dense regular connective tissue…
where is it found?
DRCT is characterised by highly ordered and densely packed arrays of fibers and cells.
DRCT is the main functional component of tendons/ligaments/aponeuroses.
fibers of DRCT are the prominent feature and as with DICT contain little ground substance.
the fibers are arranged in parallel array and are densely packed to provide maximum strength.
the cells that maintain and produce the fibers are packed and aligned between the fiber bundles.
what are tendons?
what are the cells that produce the collagen fibers called in tendons?
tendons are a form of dense regular connective tissue
tendons are cordlike structures that attach muscle to bone.
they consist of parallel bundlesof collagen fibers.
fibroblasts (tendinocytes) lie betwqeen the rows of fibers.
describe the structure of a tendon…
the tendon is made up of parallel collagen fibre bundles and tendinocytes.
the tendinocytes are surrounded by specialised ExtraCellular Matrix that separates them from the load-bearing collagen fibers.
the matrix is surrounded by a thin connective tissue capsule - the epitendineum
the fiber bundles are separated into fasicles by the endotendineum which is continuous with the epitendineum. the endotendineum contains small blood vessels and nerves of the tendon.
what are ligaments?
ligaments are a type of dense regular connective tissue
ligaments consist of fibers and fibroblasts arranged in parallel.
ligaments join bone to bone
what are aponeuroses?
aponeuroses are a type of dense regular connective tissue
aponeuroses resemble broad, flattened tendons
the bundles of collagen are arranged in multiple layers, each layer perpendicular to the one before it.
what are the three principle types of connective tissue fibers?
connective tissue fibers are of 3 principle types:
1. collagen fibers 2. reticular fibers 3. elastic fibers.
what is the most abundant type of fibers of the 3 connective tissue fibers? - what are their main attributes?
collagen fibers - high tensile strength and flexible
what does a collagen fiber contain?
a collagen fiber is made up of fine, thread-like subunits called collagen fibrils
what are the characteristics of collagen fibrils?
collagen fibrils are uniform in diameter, but may differ in size at differnet locations - diameter can measure up to 300nm
collagen fibrils are a 68nm banding pattern. the banding pattern reflects the structire of the subunit , the collagen molecule.
why does the collagen fibril have a 68nm banding pattern?
the 68nm reflects the collagen molecules that make up the collagen fibril
what is a collagen molecule?
what causes there to be different types of collagen?
a collagen molecule is 300nm in length and 1.5nm thick.
each collagen molecule is a triple helix composed of 3 interwined polypeptide alpha chains.
the alpha chains that constitue the helix are not all alike, and may vary in size from 600 to 3000 amino acids.
a collagen type is classified by the combination of 3 aplha chain that intertwine to form a collagen molecule.
28 different collagen types have been identified (I to XXVIII)
a collagen molecule may by homotrimeric (3 identical alpha chains) or hetrotrimeric (2/3 genetically distinct alpha chains)
what are the classes of collagens that have been identified (6)?
- fibrillar collagens (type I, II, III, V, XI)
- fibril-associated collagens with interupted triple helices (FACITs)
- hexagonal network-forming collagens (type VIII, X)
- transmembe collagens
- multiplexins
- basement membne forming collagens (type IV, VI, VII)
where does the biosynthesis of collagen take place?
both inside and outside the cell
what are the biosynthetic intracellular events involved in producing collagen?
- collagen alpha chains are synthesised in the rER as long precursors - preprocollagen - and discharged into the rER cisternae
- in the rER cisternae, a number of posttranslational modifications of preprocollagen molecules occurs to produce procollagen:
- 7 modifications inc: triple helix formation, addition of hsp47 - folded procollagen is passed to the golgi and associates into small bundles. packed into secretory vesicles and transported to the cell surface
what are the biosyntheic extracellular events involved in producing collagen?
- procollagen is secreted from the cell and converted into a mature collagen molecule by procollagen peptidase associated with the membrane of the cell, which cleaves the uncoiled ends of the procollagen
- the collagen molecules align to form fibrils, regulated by the cell and other collagen types (V, IX)
what ways is collagen degraded?
proteoltic and phagocytic pathways
in what ways can intial fragementation of insoluble collagen molecules occur?
- mechanical wear
- free radicals
- proteinase cleavage
what is proteoltic degradation pathway of collagen?
occurs extracellularly through the activity of metric metalloproteinases (MMPs)
In general, undenatured collagen molecules are resistant to MMPs
What are MMPs?
what are the types of MMPs?
matrix metalloproteinases
MMPs are synthesysed and secreted by the cells of the connective tissue into the ECM (also by epithelial and cancer cells)
collagenases (degrades type I, II , III, X)
gelatinases (degrades most types of degraded collagen)
matrilysins (degrades type IV (basement membrane collagen))
what is the phagocytic degradation pathway of collagen?
phagocytic degradation occurs intracellularly and involves macrophages (also some types of fibroblasts) to remove the components of the ECM
what are reticular fibers?
features and function…
reticular fibers provide a supporting framework for the constituents of various tissue and organs.
the reticular fibers consist of collagen fibrils - composed of type III collagen molecules.
what do the fibrils of reticular fibers exhibit?
68nm banding pattern
narrow diameter, about 20nm
tend not to bundle to form thick fibers
exhibit a branching pattern
where is reticular fibres most prominent?
reticular fibers are most prominent in early development and initial stages of wound healing and scar tissue formation where they provide early mechanical strength tot he newly synthesised ECM. gradually replaced by stronger type I collagen
in loose connective tissue, reticular fiber networks are found at the boundary of connective tissue and epithelium, as well as surrounding adipocytes, small blood vessels, nerves and muscle fibers (endomysium).
what are elastic fibers?
composition and functions
elastic fibers allow tissues to strech and distend.
elastic fibers are typically thinner that collagen fibers and are arranged in a branching pattern to form a 3D network, interwoven with collagen fibers to limit the distensibility and preventing tearing to the tissue.
elastic fibers are produced by many of the same cells that produce collagen and reticular fibers.
elastic fibers are composed of two structural components:
1. elastin: central core 2. fibrillin-1: surrounding network
what are the structural components of elastic fibers?
- elastin
2. fibrillin-1
what is the extracelluar matrix?
ECM is a complex and intricate structural netwrok that surrounds and supports cells within the connective tissue.
ECM contains a variety of fibers formed from different structural proteins, as well as the ground substance; multiadhesive glycoproteins, proteolycans and glycoaminoglycans.
what is the function of the ECM?
the ECM provides mechanical support, structural support and influences the communication in the tissue.
the ECM functions as a biochemical barrier and plays a role in regulating metabolic functions of the cells surrounded by the matrix.
what is the ground substance? components…
- multiadhesive glycoproteins
- proteoglycans
- glycoaminoglycans
the ground substance is a viscous, clear substance with a high water content
what are the types of resident cells found in connective tissue?
- fibroblasts
- macrophages
- adipocytes
- mast cells
- adult stem cells
what are the types of wandering/transient cells of connective tissue?
- lymphocytes
- basophils
- neutrophiles
- eosinophils
- plasma cells
- monocytes
what are the characteristics of fibroblasts?
only the nucleus of the fibroblast is usually seen in standard preparations.
the nucleus is elongated disk shape
when active, meaning the fibroblast is producing ECM material, the cytoplasm of the cell is more extensive and may display basophilia due to increased amounts of rER
fibroblasts contain abundant rER and golgi apparatus.
what is the main function of fibroblasts?
fibroblasts are responsible for the synthesis of collagen, elastic and reticular fibers, as well as the complex carbohydrates of the ground substance
these produces can be synthesised simultaneously in one fibroblast cell
