Week 9a Connective Tissue Structure and Function

connective tissue

group of tissues that demonstrates the “form follow function” idea, group of tissues with large extra-cellular components (meaning low cell density and more extracellular components like fibers, etc)

connective tissue proper

• dense or loose connective tissue

• can be regular or irregular

cartilage

• hyaline

• fibrocartilage

types of connective tissue

• connective tissue proper 

• cartilage 

• bone 

• blood 

• adipose (though atypical because not much extracellular components, rather HUGE intracellular elements- lipid droplets)

cells of connective tissue

• fibroblasts

• osteoblasts/cytes

• chondrocytes

• mesenchymal cells (pleurapotential stem cells, hang around to differentiate or proliferate to replace CT)

components of the extracellular matrix

• ground substance (GAGs, hyaluronic acid, fibronectin)

• fibers (collagen and elastin)

function of connective tissue

• primary: handle mechanical loads

• secondary: energy/mineral reserves (bone- largest reservoir of calcium), injury response (scar)

fibroblast 

• principle cell of most CT 

• synthesize different fibers and carbohydrates of ground substance

• secrete MMPs and TIMPS 

MMPs/matrix metalloprotienases

• approx 20 known human ones, examples are collagenases, gelatinases, stromelysins

• breaks down protiens

• activated by metals (Ca and Mg)

• overproduction involved in chronic inflammation- damages CT and may damage free nerve endings causes pain

TIMPS

• endogenous inhibitors: tissue inhibitors of matrix metalloproteinases

collagen

• fiber: glycoprotein

• assembled from procollagen subunits

• vitamin C is important component in its development

• as many as 10 types, tho type I most common and type II found in hyaline cartilage

reticular fibers 

• type III collagen

• narrow fibers, loosely arrange as a mesh 

• provide support to different cellular components 

type III collagen

• aka reticulin

• weaker and immature, eventually develops into type I

• develop in response to injury as repair tissue

elastic fibers 

• allow tissue to respond to distension and stretch (return back to original length- reformation)

• elastin component 

  • randomly coiled molecule

  • crosslinked

  • form fiber with fibriliin

proteoglycans

• core proteins bound to GAGs

• GAGs have high density of negative charges due to sulfate and carboxyl group- this attracts water since positive pole and forms a hydrated gel (amount of gel depends on the cell/tissue)

hyaluronic acid

• long, rigid GAG, not bound to proteoglycan

• also a key element of ground substance

loose connective tissue proper 

• irregular 

• sparse, thin fibers (collagen, reticular, elastin)

• abundant ground substance 

• mostly found beneath surface epithelia which is often a site of immune and or inflammatory reactions 

connective tissue proper

• dense CT with mostly fibers, few cells and little ground substance

• can be irregular or regular

  • irregular: no primary orientation of fibers

  • regular: tendon, ligament, ordered arrangement of fiber

• elastic CT: more elastin by proportion (lungs, aorta) but don’t even need much elastin

skin layers

• epidermis

• dermis

• subcutaneous (hypodermis)

epidermis

• most superficial later of skin, 0.06 to 0.6 mm

dermis 

• below the epidermis, 2-4 mm

• consists of 2 layers and is highly vascular with lymphatic vessels

  • papillary dermis 

  • reticular dermis 

subcutaneous

deepest layer of skin (hypodermis), very variable in thickness both within and across individuals, depends on adiposity

papillary dermis 

• layer of dermis that is anchored to the epidermis via basement membrane 

• loose irregular connective tissue 

reticular dermis

• layer of the dermis

• dense, irregular connective tissue

• contains fibroblasts, macrophages, and mast cells (have inflammatory function since slow to skin surface and may need to fight off foreign material)

function of irregularity of fibers in skin 

irregularity allows for flexibility in the skin that is due to the differences in forces and directions of forces that the skin comes in contact with, allows for some freedom of movement 

tendons

• bone to muscle

• some degree of vascularization and nerve supply

• immune cells and cytokines respond to injury and signal type III collagen formation- which is weaker and may increase the risk of reinjury

ligament

• bone to bone

• some have a direct blood supply and innervation (example is the PCL)

tendon and ligaments

• fibers and fibroblasts in parallel

• exhibit crimp

• produces toe region

ligament mechanics

stress strain curve, as force increased the deformation also increases until a yield point where enters the plastic region, and then ultimate failure point

cartilage

• matrix heavy

• 3 main type- hyaline, fibro-, elastic

• tend to be avascular (particulary hyaline)and aneural

hyaline cartilage examples

• intercostals- ribs

• trachea and bronchi

• articular cartilage at bone

• epiphysial plate

• primarily type II collagen

fibrocartilage examples 

• intervertebral discs 

• pubic symphysis 

• attach tendons to bones 

• more type I collagen

elastic cartilage examples

• external ear

• external auditory and custachian tubes

• cartilage in larynx

• tip of nose

• face, nose, ears, larynx

chondrocytes 

• cells of cartilage 

• actively produce matrix components 

• tends to decline with age- ground substance is greater than collagen, so the capacity to accommodate load and injury declines with age 

• tend to localize in nests or lacunae 

cartilage matrix

• thin, sparse type II collagen fibrils

• GAGs (hyaluronic acid, chondroitin sulfate, keratan sulfate)

• H2O accounts for about 70%, most is tightly bound to GAGs. gives resilience and resistance to compression

intermittent compression of cartilage

• “milking”

• critical to nutrition, waste removal

synovial joint (diathrosis)

• joint with capsule

• inner lining has synovial membrane which secretes synovial fluid

  • behaves like epithelium bc adapted to secrete

  • lacks the structural hallmarks of epithelium tho

• secretes proteoglycans and hyaluronic acid

synovial fluid

• filtrate of plasma, hyaluronic acids, and GAG complexes

• combined with hyaline cartilage, produces a very low friction environment, allows for smooth movement and less shear

• important for joints that bear a lot of weight

bone 

• mineralized CT 

• reservoir for Ca and PO3- (calcium and phosphate)

• functions in structure, movement, protection, mineral homeostasis, hematopoiesis (blood cell synthesis)

compact and cancellous bone

• good blood supply and innervated

• aka cortical and trabeculae bone

• combination provides strength flexibilty, and limited weight

osteocyte

• mature bone cell

• isolates in its own lacunae with canaliculi to get blood supply

periosteum

• tough fibrous connective tissue around surface of bone

• highly vascular

• highly innervated

• anchored by Sharpey’s fibers

• hurts if damages (this is where we feel pain when we break a bone)

cells of bones 

• osteoprogenitors- periosteal and endosteal, divide, differentiate, and proliferate 

• osteocytes- mature osteoblast, maintains matrix 

• osteoblasts- immature osteocyte, active, secretes matrix and involved in mineralization 

• osteoclasts- large, multinucleate, phagocytic cells, bone resorption 

matrix of bone

• osteoid- type I collagen and glycoproteins

• hydroxyapatite- calcium and phophate salts, 60% of the mature matrix

osteogenesis imperfecta

• issues with osteoid in the matrix (less and fewer than normal), increases risk of fractures

• ex: Mr Glass from that movie

endochondral ossification

• bone formation

• bones built on a cartilage model

• axial growth continues until closure of epiphyseal plate

• flat bones tho are via intramembranous ossification that may continue throughout life

bone remodeling 

• occurs throughout life 

• regular breakdown/replacement of osteocytes and bone mineral 

• bone deposition occurs at sites of injury or stress 

  • phone bone (bone formation on back of skull bc of looking down at phone all the time), osteophytes (kinda like bone spurs)

bone pathology

pathology in matrix, bone mass and density, or mineralization of bone, examples include:

• osteoporosis/penia

• osteopetrosis

• ostomalacia

osteopetrosis

bone pathology characterized bu excess mineralization- bones get heavy and dense, the mineral crystal aren’t formed right and end up making the bones brittle

osteomalacia

• (bone softening)- exhibits matrix demineralization, but not reduction of bone mass

osteoporosis/penia

• net reaabsoption will reduce bone mass, loss of matrix, low bone mass

  • numerous risk factors but exact cause unknown

fracture healing of bone

• bone does not actually heal

  • other cell/tissue types are activate to make new bone to unite ends of the break

  • periosteum and marrow

• re-engage endochonral ossification (normally rapid in healthy tissue)

  • problems include malunion, nonunion, or critical defect

role of periosteum in fracture healing

cells divide and about half move to clot and become osteoblasts

role of marrow in fracture healing

cells dedifferentiate, form procallus (blastema) and later become cartilage

critical defect of bone 

2.5-6 cm, bone can’t recover from this gap in bone on its own 

adipose tissue

• more cellular, less matrix than other CT

• white and brown

• hypertrophy and hyperplasia- post mitotic

  • precursors differentiate into new adipocytes (adipogenesis)

• highly vascular

white adipose tissue

• energy depot

• structural support by dispersing load over bony prominences

• beige-ing: takes on aspects of brown adipose and may be a consequence of aerobic exercise

brown adipose tissue

• minimal in adults (if at all)

• increased mitochondria

  • increase rate of fat oxidation 

• thermogenic 

• uncoupling- uncouple oxidation from phoshorylation- still do the ETC but don’t phsophorylate ATP, instead use energy to make heat 

white adipose tissue variability 

• gene expression differences between depots (subcutaneous vs visceral)

• diet and exercise effects on morphology