LECTURE - Connective Tissue, Cartilage, Bone, and Skin Flashcards
What is connective tissue?
- basic tissue type of mesodermal origin
- provides structural and metabolic support for other tissues/organs throughout body:
> loose ‘packing material’ bw cells - dense structural support
- exchange of nutrients, metabolites, and waste products
- energy storage and thermal regulation
- immune system
- tissue repair
responsible for tensile strength
collagen
main fiber in CT; most abundant protein in body
collagen
- polymers of tropocollagen
type I collagen
fibrous connective tissue
type II collagen
hyaline cartilage
type III collagen
- reticulin
- supporting meshwork
- silver stain positive
type IV collagen
basement membranes
type VII collagen
anchoring fibrils
protein responsible for stretch/recoil
elastin
- skin, lung, blood vessels
- synthesized by fibroblasts
- tropoelastin
- requires presence of structural glycoprotein = fibrillin
gel-like material that allows pasage of molecules through connective tisue
ground substance
- consists of glycosaminoglycans
glycosaminoglycans
- long unbranched polysaccharide chain => small mass, large vol
- negatively-charged hydrophilic side groups = extracellular fluid
- ex: Hyaluronic acid
interface between CT and parenchymal cells (epithelium)
basement membrane
- lamina lucia, lamina densa, lamina fibroreticularis
white fat
- large lipid droplets
- 20-25% of body weight in normal well-nourished adults
- energy store, thermal insulator, shock absorber
brown fat
- small lipid droplets
- abundant mitochondria
- non-shivering thermogenesis (mitochondria uncoupling)
- hibernating animals, newborn mammals
rigid protective and supporting framework; deposition of calcium salts within collagen and matrix
bone
smooth articular surface at ends of bone structural support in special areas (eg, ears), new bone formation
cartilage
joints
composite structures joining bones and permitting varying degrees of movement
- ligaments: bone-to-bone connections (stabilize joints); ACL
- tendons: bone-to-muscle connections (move joints); Achilles’ tendon
cartilage
semi-rigid nature due to predominant ground substance within ECM
different types of cartilage vary in amount and nature of fibers:
- hyaline: few fibers; lots of ECM
- fibrocartilage: abndant collagen fibres
- elastic: elastic fibers
development of cartilage
precursor chondroblasts grow and synthesize ground substance/fibers => trapped mature chondrocytes maintain cartilage matrix
hyaline cartilage
- nasal septum
- larynx
- tracheal rings
- most articular surface
- sternal ends of ribs
- developing skeleton
- found where we need flexibility*
fibrocartilage
- intervertebral discs
- pubic symphysis
- some joints
- alternating layers of hyaline cartilage and dense collagen
- tensile strength
elastic cartilage
- external ear/auditory canal
- epiglottis
- parts of larynx
- walls of Eustachian tubes
- similar hyaline but with numerous elastic fibers (stained black due to affinity for silver salts)
osteoid
ECM (type I collagen) that become mineralized calcium hydroxyapatite
synthesize osteoid, line up on surface of bone
osteoblasts
inactive osteoblasts trapped within bone
osteocytes
multinucleated phagocytes that erode bone and facilitate resorption/remodeling
osteoclasts
trabeculae
network of fine irregular plates within cancellous (medullary bone)
components of long bones
- compact (cortical): dense walls of diaphysis (shaft)
- cancellous (medullary) bone: central medullary cavity; network of fine irregular plates called trabeculae
- periosteum: dense fibrous layer covering external surface
- joint surfaces protected by hyaline cartilage
diarthrosis
- synovial joint
- joins bones or cartilage with a fibrous joint capsule that is continuous with the periosteum of the joined bones
- constitutes the outer boundary of a synovial cavity, and surrounds the bones’ articulating surfaces.
non-synovial joints
- limited movement
- syndesmoses (dense fibrous tissue): sutures between bones of skull
> replaced by bone with age => synostoses - synchondrosis (hyaline): connection between first rib and sternum (little it of movement)
- symphyses (fibrocartilage): pubic symphysis, intervertebral discs
tough, flexible straps/cords of collagen fibers that connect muscles to bone
tendons
largest organ in body (weight, SA)
SKIN
- marked site-specific function
functions of the skin
- protection (UV, chemical, thermal, mechanical)
- sensation (touch, pressure, pain, temperature)
- thermoregulation (heat loss, retention)
- metabolic functions (vit D3 synthesis)
- physical appearance (skin, hair, nails)
three main layers of the skin
- epidermis: stratified squamous epithelium; produces a surface layer of protein = keratin
- dermis: fibrocollagenous and elastic tissue, blood vessels, nerves, sensory receptors; skin appendages (mainly here)= hair follicles, sweat glands, sebaceous glands
- subcutis/hypodermis: mainly adipose tissue, larger blood vessels that supply dermis
epidermis
self-regenerating stratified squamous epithelium
- keratin, melanocytes, Langerhans cells Merkel cells
dermis
- horizontally arranged collagen ad elastic fibres, fibroblasts
- blood vessels, sensory organs
- skin appendages (eg: eccrine gland and ducts)
subcutis
adipose tissue
dermal collagen extensions
layers of the epidermis
- stratum corneum = lack nuclei
- stratum lucidum
- stratum granulosum = kerattohyaline granules
- stratum spinosum = cytokeratin -> tonofibrils, desmosomes
- stratum basale = mitotic figures
‘prickle cell layer’
- stratum spinosum
- bundles of tonofibrils converge into numerous desmosomes that form contacts between adjacent kerainocytes
melanocytes
- derived from migrating neural crest cells
- positive with S100 stain
- produce melanin for skin/hair pigmentation, UV protection
- scattered in basal layer (stratum basale); more numerous in sun-exposed sites
- similar in # between light and dark-skinned individuals; differences in synthetic activity (more active cells in darker indivs)
hair follicles
- for thermoregulation, display
- three phases:
> active growth (ANAGEN)
> involution (catagen)
> resting (telogen)
sebaceous glands
- secrete sebum (waterproofing)
- majority associated with hair follicles; exceptions = nipple-areola, eyelids, buccal/labial mucosa
- surround hair follicle and discharge holocrine lipid secretions or sebum onto hair shaft
- arrector pili muscle inserts below sebaceous glands
eccrine glands
- secrete sweat (thermoregulation)
- widespread (esp. palms, soles, forehead, axilla)
- coiled secretory glands: deep dermis/upper subcutis; outer layer of contractile myoepithelial cells
- eccrine ducts: double layer of epithelial cells, inner cuboidal; microvilli lining lumen, biochemically active (modify water, NaCl composition of sweat)
apocrine glands
- scent production in animals (less in humans)
- mainly nipple-areola, axilla, groin
- large glands w/ dilated lumen, eosinophilic budding with apical budding, myoepithelial cell layer
- secrete into adjacent hair follicle viaduct similar to sweat glands
- viscid milky secretion => becomes malodorous after action of skin commensal bacteria (not functional until puberty)
epidermal skin appendages (4)
- hair follicles
- sebaceous glans
- eccrine glands
- apocrine glands
overall skin thickness depends on these layers
dermis and subcutis
> eyelids: both layers thin
> buttocks/back: dermis thick, subcutis usually thick
- collagen and elastic fibers; progressive degeneration of upper dermal collagen and elastin with age = wrinkling + loss of texture
- dermis = skin appendages, most vascular supply + nerves, sensory endings
Layers of dermis
- papillary dermis: > fine interlacing collagen and elastin > small vessels, lymphatics and fine nerve twigs - reticular dermis: > larger collagen bundles and elastin fibres > larger vessels and nerves > skin appendages > widely variable thickness
composed of predominantly mature adipose tissue
subcutis
- partially compartmentalized by vertical fibrous septa from lower dermis
- some sites contain anagen hair follicles (scalp), apocrine glands (axilla, groin), eccrine (palms, soles), skeletal muscle (face)
what skin layer derives its name from abundant desmosomes present?
stratum spinosum
surround hair follicle and discharge holocrine lipid secretions onto hair shaft
sebaceous glands
- arrector pili muscle inserts below sebaceous gland
