specialized fibroblasts; produce reticular fibers made of type III collagen; produce supporting network for organs that change size/shape
unilocular adipose tissue
"common ""yellow fat;"" color from dissolved carotenoids; main fat type in adults; one large lipid molecule in center"
multilocular adipose tissue
"""brown fat;"" color from mitochondrial carotenoids and capillaries; common in newborns and hibernating animals; important in non-shivering thermogenesis; lipids organized into droplets"
proteoglycan structure
brush-shaped structure with rod-shaped protein core and negatively charged GAG extensions; retain water
glycoprotein structure
globular proteins with branched monosaccharides
aggrecan
largest proteoglycan; involved in hydration of collagen extracellular matrix; abundant in loose connective tissue
decorin
a type of proteoglycan; involved in collagen fibrillogenesis and cell signaling
versican
a type of proteoglycan; binds to fibulin; involved in cell-cell and cell-matrix interactions
syndecan
a type of proteoglycan; binds extracellular matrix and intracellular actin
secondary structure of collagen
alpha helical organization
tertiary structure of collagen
triple helical organization; coiled-coil; glycines to the inside
quarternary structure of collagen
microfibrils and fibrils aligned rod-like oligomers
aminoacid composition of collagen
33% glycine; 10% proline; 10% hydroxyproline
procollagen
precursor to tropocollagen; terminal propeptides have not yet been cleaved; synthesized collagen fibers have been assembled and hydroxylated; ready for export out of cell
tropocollagen
product once terminal propeptides have been cleaved from procollagen; occurs extracellularly
lacunar region of collagen fibril
light-colored striated area between collagen fibers; makes up about 90% of collagen length
overlapping region of collagen fibril
dark-colored striated area in which collagen fibers overlap; makes up about 10% of collagen length
lysyl oxidase
an extracellular enzyme that is involved in the cross-linking of collagen fibers
Ehlers-Danlos Type IV deficiency
results from haploinsufficiency; faulty transcription of collagen type III; results in aortic and/or intestinal rupture
Ehlers-Danlos Type VI deficiency
results from enzymatic insufficiency; faulty lysine hydroxylation; results in augmented skin elasticity and rupture of eyeball
Ehlers-Danlos Type VII deficiency
results from enzymatic insufficiency; decrease in procollagen peptidase activity; results in increased articular motion and joint dislocation
scurvy
results from enzymatic insufficiency; lack of vitamin c - cofactor for proline hydroxilase; results in hemorrhages and ulceration of gums
osteogenesis imperfecta
dominant negative mechanism of transmission; change in one nucleotide for the collagen I gene causes misfolding of proteins; results in spontaneous fractures and cardiac insufficiency
haploinsufficiency
occurs when a diploid organism has only one functional copy of a gene
dominant negative mutations
a mutation that reduces the functioning or stability of other related proteins
lysine hydroxylase deficiency
disrupts fross-linking of collagen fibers; results in hypermotility of joints and easy bruising and poor wound healing and scarring
reticular fibers
composed of collagen type III; thin and branching
elastic fibers
thin fibers made up of the glycoprotein fibrillin; form sparse networks interspersed with collagen; confer elasticity and resilience to many tissues; found in large arteries and lungs and skin and ligaments and tendons
Marfan syndrome
autosomal dominant disorder; caused by mutations in the fibrillin gene; can lead to death by aortic rupture
cutis laxa
caused by mutations in the elastin gene; causes loose skin and can cause emphysema and heart problems
associative elements
glycoproteins that link fibers in ECM with cellular receptors; include fibronectin and laminin and tenascin and entactin
integrins
receptors that mediate attachment between a cell and its environment; anchor cells to the ECM
cartilage
semi-rigid form of avascular connective tissue; characterized by predominant ground substance/ECM
chondrocytes
connective tissue cells found in cartilage; synthesize and produce extracellular matrix
hyaline cartilage
the most common form of cartilage; transparent and smooth; smooth texture ideal for articulations; primarily composed of type II collagen
fibrocartilage
combination of dense connective tissue and cartilage; has cells in individual lacunae arranged in rows; found where resistance to shearing and compressing forces are required; high combination of collagen I fibers
elastic cartilage
a flexible and elastic cartilage; many elastic fibers; cells closely packed and disorganized; found in ear and nose and epiglottis
osteoclasts
multi-nucleated giant cells involved in the resporption and remodeling of bone; derived from monocytes
osteocytes
mature bone cells; develop from osteoblasts that have secreted matrix; sit in lacunae of bone
osteoblasts
bone cells found at the surface of bone; synthesize organic components of matrix
osteoid
"unmineralized matrix; ""pre-bone"""
lacunae of bone
cavities in the lamellae of bone in which osteocytes reside
canaliculi
thin cylindrical spaces that perforate bone matrix; allow for exchanges between osteocytes and blood capillaries
cell processes
allow for biochemical coupling of osteocytes; rely upon gap junctions
Howship lacunae
enzymatically etched depressions in which osteoclasts lie; formed during the process of resorption
bone resorption process
osteoclasts attach to bone surface via integrins and seal area to be degraded; osteoclasts release HCl to degrade minerals; osteoclasts release protesases to degrade collagen
ruffled border
irregular projections formed by the border of active osteoclasts against bone matrix
osteopetrosis
a condition mediated by defective osteoclast activity; leads to excessively hard and brittle bones and increased propensity for bone fractures
Paget's disease
a condition initially marked by excessive large osteoclast activity
matrix vesicles
foci for deposition of hydroxyapatite; site of mineralization; contain alkaline phosphatase
osteomalacia
deficient bone mineralization in adults
rickets
deficient bone mineralization in children
cancellous bone
porous bone; has large surface area for mineral exchange; adds support without weight; also called trabecular or spongy bone
trabecular bone
porous bone; has large surface area for mineral exchange; adds support without weight; also called cancellous or spongy bone
spongy bone
porous bone; has large surface area for mineral exchange; adds support without weight; also called cancellous or trabecular bone
compact bone
"dense areas of bone without cavities
cortical bone
"dense areas of bone without cavities
medullary cavity
central marrow-containing cavity of the bone; confers resistance without weight
osteon
the structural unit of bone; also called the Haversian system
Haversian system
the structural unit of bone; also called the osteon
cement line
a collagen-rich layer defining the outer boundary of an osteon
Volksmann's canal
tubes that run perpendicular to Haversian canals; connect Haversian canals
collagen
the most abundant protein in the human body; makes up 30% of dry weight; has a mainly structural function
layers of elastin produced by smooth muscles; found in arteries
elastin production
secreted by fibroblasts in connective tissue and smooth muscle cells in blood vessels
basement membrane
structural attachment site for overlaying epithelia and underlying connective tissue; synthesized by epithelial cells
functions of connective tissue
support and packing; transport; storage; defense; repair
perichondrium
a layer of dense connective tissue that surrounds cartilage in most places; forms an interface between cartilage and tissue; harbors vascular supply; not present in fibrocartilage
interstitial growth
a type of chondrogenesis in which preexisting chondrocytes divide mitotically
appositional growth
a type of chondrogenesis in which perichondrial cells differentiate into chondrocytes
intramembranous ossification
a method of bone formation in which osteoblasts differentiate directly from mesenchyme and begin secreting osteoid; occurs in bones of the face and skull
endochondral ossification
a method of bone formation in which the matrix of preexisting hyaline cartilage is eroded and replaced by osteoblasts producing osteoid
Haversian canal
a series of concentric circular tubes in an osteon; contain blood vessels and nerves