connective and non-functional supportive framework of a cell or tissue or organ


the functional part of a cell or tissue or organ (as compared to the stroma)

extracellular matrix

made up of protein fibers and ground substance

ground substance

a hydrophilic complex of anionic macromolecules and multiadhesive glycoproteins that stabilizes the extracellular matrix

protein fibers


structure of loose/areolar connective tissue

few cells; disorganized fibers; abundant ground substance; little tensile strength

structure of dense regular connective tissue

abundant collagen fibers arranged in the same direction

structure of dense irregular connective tissue

predominant collagen fibers loosely arranged in bundles w/o specific orientation

function of loose/areolar connective tissue

holds blood; supports epithelium; arena for immune function and nutrient exchange

function of dense regular connective tissue

mechanical coordination and support; withstand stress from one particular direction

function of dense irregular connective tissue

mechanical support and integrity; withstand stress from many directions


outer layer of skin; consists of epithelium plus loose connective tissue


layer of dense irregular connective tissue underlying the epidermis


connects bone to bone; made up of dense regular connective tissue


connects bone to muscle; made up of dense regular connective tissue

cornea structure

composed of alternating lamellae of collagen I fibers arranged perpendicularly for mechanical strength and transparency

migratory CT cells

derived from hemtopoeitic stem cells; include immune cells and osteoclasts

resident CT cells

derived from undifferentiated mesenchymal cells; include stationary connective tissue cells


most abundant connective tissue cell type; secrete collagen & elastin & proteoglycans & associative proteins & growth factors; produce fibers; repair injured connective tissue

reticular cells

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


largest proteoglycan; involved in hydration of collagen extracellular matrix; abundant in loose connective tissue


a type of proteoglycan; involved in collagen fibrillogenesis and cell signaling


a type of proteoglycan; binds to fibulin; involved in cell-cell and cell-matrix interactions


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


precursor to tropocollagen; terminal propeptides have not yet been cleaved; synthesized collagen fibers have been assembled and hydroxylated; ready for export out of cell


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


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


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


receptors that mediate attachment between a cell and its environment; anchor cells to the ECM


semi-rigid form of avascular connective tissue; characterized by predominant ground substance/ECM


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


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


multi-nucleated giant cells involved in the resporption and remodeling of bone; derived from monocytes


mature bone cells; develop from osteoblasts that have secreted matrix; sit in lacunae of bone


bone cells found at the surface of bone; synthesize organic components of matrix


unmineralized matrix; ""pre-bone

lacunae of bone

cavities in the lamellae of bone in which osteocytes reside


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


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


deficient bone mineralization in adults


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


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


the most abundant protein in the human body; makes up 30% of dry weight; has a mainly structural function

types of collagens

fibril-forming collagens; network-forming collagens; fibril-associated collagens; transmembrane collagens; anchoring fibril-forming collagens

fenestrated layers

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


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