MA2 - Connective Tissue Flashcards
What are the four components of connective tissue?
fixed (resident) cells; wandering (immune) cells; fibers; ground substance (stuff between cells and fibers)
Describe the features of ordinary connective tissue. (3)
soft; pliable; has diverse collection of cells
Describe the features of bone. (3)
mineralized; stiff; has bone cells (i.e. osteocytes, osteoblasts, etc.)
Describe the features of cartilage. (4)
firm; NOT mineralized; type of type II collagen matrix; has cartilage cells
Describe the characteristic features of areolar connective tissue.
abundant ground substance; wandering (immune) cells; sparse mixture of elastic fibers (type I) and collagen fibers (type III)
What is the function of the abundant ground substance in areolar connective tissue? (2)
slows diffusion and hinders movement of invading microorganisms; provides lubrication
Give two example locations of areolar connective tissue.
underlies epithelia (i.e. lamina propria or papillary dermis); surrounds blood vessels
What are the characteristic features of reticular connective tissue?
reticular (branching) fibers (type III collagen)
What is the function of reticular fibers in reticular connective tissue?
fibers produce a network that provides support for parenchymal cells.
What are the three types of loose connective tissue (few fibers, many cells)?
areolar connective tissue; reticular connective tissue; adipose tissue
Give three example locations of reticular connective tissue.
bone marrow; lymph nodes; spleen
What are the two characteristic features of adipose tissue?
abundant adipocytes; abundant vasculature
What are the functions of adipocytes? (3)
store energy; generate heat; provide cushioning
What are the three types of adipose tissue?
brown adipose tissue; white adipose tissue; beige adipose tissue
What is the function of brown adipose tissue?
consumes energy to make heat
What is the function of white adipose tissue? (2)
stores energy; provides cushioning
What is the function of beige adipose tissue? (2)
derived from white adipose tissue; consumes energy to make heat
What are the two types of dense connective tissue (many fibers, few cells)?
dense regular connective tissue; dense irregular connective tissue
What is the primary difference between loose and dense connective tissue?
loose = few fibers, many cells; dense = many fibers, few cells
Describe the features of dense regular connective tissue.
mostly type I collagen fibers arranged in non-random directions
Describe the function of dense regular connective tissue.
provides strong connection in direction of fibers
Give two examples of dense regular connective tissue.
cornea; tendons + ligaments
Describe the features of dense irregular connective tissue.
rich in type I collagen fibers aligned in multiple directions
Describe the function of dense irregular connective tissue. (2)
serves to protect other tissue; provides strong internal support
Give two examples of where you can find dense irregular connective tissue.
organ capsules; dermis
What are the three subtypes of dense irregular connective tissue?
fibrous connective; fibroelastic connective; fibromuscular connective
Describe the properties of fibrous connective tissue. (2)
stiff; fibers dominated by collagens
Describe the properties of fibroelastic connective tissue. (2)
elastic; type I collagen + elastic fibers
Describe the properties of fibromuscular connective tissue. (2)
contractile; collagen + smooth muscle fibers
What is the most common type of dense connective tissue?
dense irregular connective tissue
Describe the features of brown adipocytes. (2)
abundant mitochondria; many lipid droplets
Describe the metabolic rate of brown adipocytes.
very metabolically active because of high rate of fatty acid consumption in mitochondria
Brown adipocytes express what protein that allows them to generate heat?
express uncoupling protein (UCP1), which allows protons to leak across inner mitochondrial membrane, generating heat
Brown adipocytes are associated with what vascular structure?
associate with numerous blood capillaries to transfer heat
Brown adipocytes are most and least abundant in
most abundant in newborns, least abundant in adults
Describe the features of white adipocytes. (2)
few mitochondria; only one very large lipid droplet
Describe the metabolic rate of white adipocytes.
less metabolically active than brown adipocytes, probably because they’re primarily used for energy storage
White adipocytes produce
endocrine factors (adipokines) to regulate whole body energy metabolism
Under what conditions can white adipocytes become metabolically active?
in response to cold temperature → become converted into beige adipocytes
Describe the features of beige adipocytes.
though derived from white adipocytes, they have abundant mitochondria and produce uncoupling protein like brown adipocytes
How can brown adipocytes be recognized in section?
eosinophilic cytosol w/ many small lipid droplets
Macrophages are derived from
monocytes or embryonic precursors
What is the function of macrophages? (2)
function as innate immune system sentinels; phagocytose debris
When activated by an immune response, what do macrophages produce?
chemotactic factors that recruit granulocytes (i.e. neutrophils); pyrogens that increase body temperature
What are the components of the mononuclear phagocytic system? (3)
wandering monocytes; resident macrophages; dendritic cells
What are histiocytes?
resident macrophages in ordinary connective tissue
What are Kupffer cells?
resident macrophages in liver sinusoids
What are nurse cells?
macrophages in bone barrow
What are microglia?
macrophages of the CNS
What are dust cells?
alveolar macrophages of the lung
Mast cells are derived from
bone marrow progenitors
What is the function of mast cells?
serve as innate and adaptive immune system sentinels
Where are mast cells frequently found?
found in connective tissue that is subjacent to an epithelium or near a blood vessel/nerve
How can mast cells be identified in section? (2)
have round nuclei; have uniformly-sized granules that stain reddish-purple with toluidine blue OR basophilic with H&E
What are plasma cells?
terminally differentiated B lymphocytes (B cells)
What do plasma cells produce?
antibodies via constitutive secretion (IgA/IgG/IgE)
How can plasma cells be recognized in section? (2)
off-center, heterochromatic circular nucleus + large, highly basophilic cytoplasm
Plasma cells are particularly abundant in what tissue structures? (4)
lamina propria; lymph nodes; spleen; bone marrow
Plasma cells produce IgA in what tissue structure?
lamina propria
What do fibroblasts synthesize?
fibers; ground substances of extracellular matrix
In addition to synthesizing fibers, what is an additional function of fibroblasts?
bind to and remodel extracellular matrices
Fibroblasts can differentiate into
myofibroblasts, in response to a need for wound healing
How can fibroblasts be identified in section?
highly elongated, usually along the axis of the fiber they’re attaching to
How can you differentiate between a fibroblast and a myofibroblast in section?
myofibroblasts have a darker cytosol due to increased numbers of ribosomes
Myofibroblasts principally express what protein?
smooth muscle actin
What are the three principal types of bone cells?
osteoblasts; osteoclasts; osteocytes
What are the three principal types of cartilage cells?
chondroblasts; chondroclasts; chondocytes
What are mesenchymal stem cells?
multipotent stem cells that can produce adipocytes, fibroblasts, bone cells, etc.
Where are mesenchymal stem cells found?
in most connective tissues
Where do mesenchymal stem cells originate?
believed to originate in bone marrow
What is the function of mesenchymal stem cells? (2)
tissue repair; inflammation response
What are the fixed (resident) cells? (6)
brown adipocytes; white adipocytes; macrophages; mast cells; plasma cells; fibroblasts [mnemonic: BWMMPF]
Most wandering lymphocytes can be classified as
T cells, but a small fraction are B cells
How can lymphocytes be recognized in section?
small size; thin rim of basophilic cytosol; heterochromatic nucleus
What are the two primary types of granulocytes?
neutrophils; eosinophils
What is the function of neutrophils?
principal defenders against bacterial infections by phagocytosing bacteria
How can neutrophils be identified in section? (2)
highly segmented nuclei (in contrast to eosinophils, which have bi-lobed nuclei) + pale cytosol
What is the function of eosinophils?
defend against parasitic infections; can also cause allergic reactions
How can eosinophils be identified in section?
bi-lobed nuclei
Dendritic cells are derived from
bone marrow progenitors or monocytes
Upon activation, what do dendritic cells do?
migrate to lymph nodes and stimulate T cells
Describe the process of collagen synthesis. (5)
fibrillar collagen synthesized as preprocollagen in RER → P and K residues of preprocollagen hydroxylated in ER → glycosylation allows preprocollagen to form coiled-coil trimers called procollagen → globular ends of procollagen cleaved to form tropocollagen → tropocollagen + lysyl oxidase = crosslinked tropocollagen in fibrils → fibrils become fibers
Differentiate between preprocollagen and procollagen.
procollagen = hydroxylated + trimerized form of preprocollagen before secretion
Differentiate between procollagen and tropocollagen.
tropocollagen = secreted + cleaved form of procollagen but before assembly into fibers
Type I collagen is mainly synthesized by
fibroblasts
Type I collagen can be best visualized using what stain?
Masson’s trichrome
Describe the structure of Type I collagen.
large banded fibrils and fibers that can be combined into bundles
Describe the structure of Type II collagen.
banded fibrils but smaller than Type I collagen fibrils
Describe the distribution of Type I collagen.
typically found in bone, tendon, submucosa, dermis
Describe the distribution of Type II collagen.
very restricted distribution — only found in cartilage or part of eye
Type II collagen is synthesized by
chondrocytes of cartilage
Describe the structure of Type III collagen. (2)
banded fibrils but smaller than Type I collagen fibrils; BRANCHED
Describe the distribution of Type III collagen.
wide distribution — most common type of collagen in reticular connective tissue
Type III collagen is best visualized with what stain?
silver staining
Describe the structure of Type IV collagen.
does not form fibrils, but a meshwork/gel instead
Describe the distribution of Type IV collagen. (2)
present in basal laminae of epithelial cells; external laminae of muscle cells
Type IV collagen is made by (2)
epithelial cells (basal laminae) or muscle cells (external laminae)
Elastic fibers and elastic lamellae are comprised of
fibrillin; elastin
Describe the properties of fibrillin.
forms a microfibrillar structure that surrounds elastic fibers and lamellae; templates deposition of elastin
Describe the function of elastin.
forms amorphous core of elastic fibers and lamellae
Elastins are crosslinked together by
aldehydes made by lysyl oxidase
Describe the structure of elastin in the presence and absence of tension.
under force = protein elongates; without tension = random coil structure
Describe the composition and activity of elastic fibers in the lungs.
highly branched elastic fibers that recoil during exhalation to contract airways
Describe the composition and activity of elastic fibers in the dermis.
thick and thin elastic fibers that give skin its resiliency
Describe how elastic lamellae are utilized in vasculature.
lamellae form layers in arteries and arterioles where they reduce systole pressure (via expansion) and contribute to diastole (via recoil)
What is ground substance?
filler between cells and fibers of connective tissue
What is the function of ground substance? (2)
cushions/lubricates the aqueous passages of connective tissue; binds water and increases viscosity
Describe how ground substance stains.
stains poorly by both H&E and EM
What are proteoglycans?
highly glycosylated proteins comprised of core protein w/ many large glycosaminoglycans (GAGs) attached
In proteoglycans, what drives function?
the glycosaminoglycans (GAGs)
Describe the structure of glycosaminoglycans.
long chains of repeating disaccharides, some of which are sulfated, increasing their negative charge
What is a consequence of the negative charge of glycosaminoglycans?
they bind to water and repel each other, allowing them to fill space and resist compression
How do proteoglycans function in signaling?
they can bind to growth factors, which prevents their diffusion (i.e. helps prevent movement of paracrine factors into circulation)
Describe the properties of glycoproteins.
less glycosylated than proteoglycans and their function is therefore dominated by the protein part, not the carbohydrate part
What are the two primary glycoproteins?
fibronectin; laminin
Describe the function of fibronectin.
promotes covering of wounds by epithelial cells after injury
Fibronectin binds to (4)
collagen; proteoglycans; fibrin; integrin of cells
Laminin is made by
epithelial and muscle cells
Laminin exists in association with
type IV collagen
What is the function of laminin?
associates epithelial and muscle cell with underlying connective tissue
What is the glycocalyx?
the combination of proteoglycans that have transmembrane domains and are embedded in the plasma membranes of cells
