Days 4+5: CT, Collagen, ECM Flashcards
1
Q
functions of connective tissue
A
- Binding other tissue types together
- Structural cohesion
- Resist forces
- Protect
- Energy reservoirs
- Transport nutrients
- Controlling the passage of fluids, the migration of cells, and the spread of infections
2
Q
classifications of connective tissue
A
Connective tissue proper: structural framework of organs, form the stroma
-
loose (areolar) connective tissue (most widespread CT)
- thin fibers, many cells (includes plasma, mast, fibroblast, lymphocytes, etc)
- tissue is pliable, well-vascularized, and only slightly resistant to tensile forces
-
dense irregular connective tissue
- __thick fibers, few cells (mostly fibroblasts)
Special: have a unique function based on a modification in either the cells, fibers, or ground substance
- dense regular connective tissue: only found in ligaments and tendons, in tendons, the fibroblast may be called tendinocytes
3
Q
embryonic precursor of connective tissue cells
A
- mesenchymal stem cells (MSCs) are precusors of the “resident” cells of adult connective tissues:
- fibroblast
- myofibroblasts
- chondroblast
- osteoblast
- adipocyte
- unilocular
- multilocular
- fibroblast
- In the fetus, CT is known as “fetal mesenchymal tissue”
- originates from embryonic mesoderm layer
4
Q
fibroblast
A
- native cell to the CT
- produces/degrades fibers + ground substance of matrix
- can undergo mitosis
- has overall fusiform shape and thin protoplasmic processes, which may contact the processes of other fibroblasts
- nuceli are very thin, basophilic, and elongated
- synthesize, secrete, and organize all the fibers of connective tissue, as well as most of the interfibrillar ground substance
- fibroblasts that are actively repairing or forming new connective tissue have more cytoplasm than ones involved in ongoing low-level matrix turnover of established connective tissue
- can trans-differentiation into other mesenchyme-derived cells (adipocyte, chondroblast, osteoblast)
Myofibroblasts
- modified, similar to fibroblasts and smooth muscle cells
- basophilic cytoplasms (lots of prot generation)
- abundant in areas of wound healing
5
Q
adipocytes
A
- lipid storage & mobilization
- mesenchymal origin
unilocular:
- triglycerides fuse, a blood supply heavily supplies, the dominant extracellular structural elements are reticular fibers
- secrete chem factors that relay the state of energy storage to brain, liver, muscle, etc
multilocular:
- thermogenic and direct innervation by sympathetic nervous system controls metabolism of its stored fatty acids
- distrubuted near the scapula, clavicle, and along vertebral column
6
Q
macrophage
A
- frothy appearance due to vacuole contents
- cell born in BM, resides in CT
- circulate blood as monocytes, after 40 hrs, enter the CT and increase in size, lysosomal content, and endocytic capacity
- some serve as antigen-presenting cells: process antigens and present to lymphocytes to stimulate the immune response
7
Q
plasma cell
A
- when antigenically stimulated, B-lymphocytes undergo mitotic division, plasma cell clones that synthesize and secrete abs against the antigen
- they are the effector cells of B-lymphocytes, producing antibodies against one specific antigenic epitope
- end stage cells, short lifespan
- usually not present in blood stream
- no secretion granules because the release of product (antibodies) is constitutive
- morphology:
- oval to round shape (12 um in diameter)
- cytoplasm is basophilic, with no intracellular granules
- nucleus is eccentric (away from cell center)
- pale cytocentrum (cell center) that corresponds to location of Golgi
- nucleus is
8
Q
mast cell
A
- large cell, central oval nucleus, metachromatic (may be red) granules (take on color separate from stain)
- granules contain pharmacologic agents that create inflammation
- can appear red in H&E, and dark blue in other preparations
- can be confused with eosinophils, but differ in nuclear morphology
- long-lived, enhances WBC response through inflammation
- antibodies of IgE class are associated with mast cell plasma membrane
- enables rapid response to antigens (allergens specifically)
- functionally related to basopils
9
Q
extracellular matrix components
A
- Role of the ECM is to distribute stresses of movement + gravity while maintaining the body shape
Comprised of:
- insoluble protein fibers
- collagen
- reticular fibers
- elastic fibers
- interfibrillar ground substance
- made up of soluble complexes, composed of long carbohyrate polymers linked to protein molecules that attract + bind to water
- the resident cells (fibroblasts, chondrocytes, osteoblasts) produce both the fibers and ground substance
10
Q
collagens
A
- long, stiff, triple-stranded helical structures
- three polypeptide alpha chains twist around to form triple helices
- type I:
- most common and abundant fiber of CT
- composed of fibrils (made of staggered tropocollagen molecules)
- aggregate as their density increases
- type II:
- supports cartilage matrix
- type III (reticular fibers):
- smaller, more flexible than type I
- eosinophilic, agyrophilic (stained with silver treatments)
- type IV
- major component of basal/external lamina
11
Q
elastic fibers
A
- occurs in tissues that need to be strong + elastic
- comprised of elastin (hydrophobic protein) and held in place by surrounding scaffolding of tiny fibrils
- stain lightly with eosin, special stains are required to render them visible for light microscopy
- ie, resorcin fuchsin, Verhoeff’s stain
- fibers branch, but do not provide supporting network for cells like reticular fibers do
12
Q
fibrosis
A
- the pathological accumulation of dense type I collagen
- early fibrosis (forming granulation tissue): primarily type III collagen that is replaced by type I
- occurs as a backup process to prevent fluid loss after an epithelial wound if re-epithelialization is not successful
-
cyst: when occurs internal to a CT compartment
- common when glands are damaged / lose exit to epithelium
-
scarring: elevated type III collagen
- keloid:
- raised, collagen is laid down perpendicularly to epithelium, interfering with re-epithelialization
- low myofibroblast count
- hypertrophic:
- flat, collagen parallel to surface
- higher myofibroblast count
- keloid:
13
Q
edema
A
- ground substance pathology
- extracellular fluid normally arises from plasma filtered through vascular endothelium and leaves through lymphatics
- disturbances in the amount of fluid leaving the tissue causes edema d/t extracellular fluid accumulation
14
Q
primary + secondary structure of collagen
A
- alpha chains of collagen (2 identical alpha 1, one alpha 2 chain) comprised of:
- 33% glycine
- 17% proline (half are hydroxylated)
- many lysines in collagen are also hydroxylated
- mature collagen doesn’t usually contain cysteine
- repetitive structure with tandemly repeating sequence: Gly-X-Y (usually X: Pro, Y: Hydroxyproline)
- has alternating regions of polar/nonpolar
- (Glyc-Pro-Y) (Gly-X-Y) (Gly-Pro-Y)
- Gly-Pro-Y: usually non-polar
- Gly-X-Y: polar d/t polar aa in X/Y position
- (Glyc-Pro-Y) (Gly-X-Y) (Gly-Pro-Y)
- assembly of collagen triple helix (procollagen) requires further processing + assembly to become mature collage
15
Q
primary + secondary structure of elastin
A
- in all tissues that require elasticity
- single, non-glycosylated molecule
- 33% Gly, 50% Pro
- synthesized as 70kDa monomer (tropoelastin)
- secreted into extracellular fluid, where is cross-linked (by lysyl oxidase) to form highly insoluble elastin fibers
- slow turnover, catalyzed by elastase
- does not form a regular secondary structure
- stretched (longitudinally): becomes more ordered
- released: relaxes back to non-stretched configuration
