4: cartilage, bone and disorders

trachea

thin wall. rigid tube ringed by C shaped hyaline cartilage.

chondrocytes position

exist in lacunae which is rimmed by strongly basophilic (blue) territorial matrix with high conc of acidic sulphated GAGs secreted by chondrocytes

GAGs (glycosaminoglycans)

unbranched chains of glycoproteins. most common is hyaluronic acid

Hyaline matrix. why is it glassy?

matrix between chondrocytes (inter-territorial matrix) contains more collagen fibrils and less GAG. highly hydrated and hence does not stain strongly. gives it a glassy appearance

articular cartilage

hyaline covers the surfaces of bones where they come together to form joints. gets nutrients from synovial fluids.

why hyaline (esp articular) does not heal well

low capacity of chondrocytes for replication; poor blood supply

major long bone in the upper limb and major bone in lower limb whose articular ends covered in hyaline

upper: humerus, radius, ulna

lower limb:

femur, tibia, fibula

theory behind using hyaluronic acid injections for osteoarthiritis

HA major component of synovial fluid and help lubricate joint and reduce pain

malignant tumours of cartilage called

chondrosarcomas.

sarcoma

cancer of mesenchymal origin

smoking on morphology of respiratory epithelium

metaplasia. epithelium changes from pseudostratified columnar to stratified squamous

explain why PAS identifies goblet cells effectively

identify glycoproteins, stains mucins in goblets

adenocarcinoma

tumour of glandular resp epithelium

smoking on cilia of resp epithelium

paralysis. infection. increased exposure of epithelium to carcinogens

single nucleotide polymorphism

variation in a DNA sequence occurring when a single nucleotide in a genome is altered

insertions and deletions

additions or losses of nucleotide pairs in a gene

histology of elastic cartilage

dense aggregations are eosinophilic. dark pink bundles against lighter pink of ECM

Perichondrium

Dense irregular connective tissue membrane covering cartilage

why is respitory epithelium unique in epiglottis

particularly thick.

two major components of elastic fibres

elastin and fibrillin

epiglottis unique feature and why

SSNKE buccal epithelium on one side and PSCE on the respiratory side. this is because it is normally in an upright position and resp e is continuous with the airway . epiglottis closes to cover trachea on swallowing and the aspect lined with SSNKE provides protection from abrasion from boluss

elastic cartilage location

epiglottis, outer ear, auditory tube, external auditory meatus

cartilage is maintained by what type of growth

appositional: differentiation of stem cells from supporting CT (chondroblasts in perichondrium) and interstitial: division of cells within a tissue (chondrocytes within a cartilage)

Fibrocartilage

comprised of DRCT and hyaline cartilage and contains fibroblasts as well as chondrocytes.

cartilage that contains fibrous bundles of t1 collagen, such as that of the intervertebral disks in the spinal cord. sternoclavicular and temporomandibular joints.

intervertebral disk

trabecular bone, skeletal muscle. inside, annulus fibrosus (fibrocartilage). nucleus pulposus

fibrocartilage adaptation for its position

shock absorbance, resistance to shearing

what structures hold the annulus fibrosus in place

ligaments

what is the nucleus pulposus comprised and what is its function

gel matrix (water and hyaluronic acid) acts as a shock absorber

Slipped (herniated) disc

displacement of nucleus pulposus due to weakness of annulus fibrosus (which cracks with age and under excess force) displaced disk can put pressure on adjacent nerves.

ground bone

Osteons-

Central Canal (haversian)- middle dark hole

osteocytes in Lacunae- (black dots)

Canaliculi- spider web allows communication between lacunae

intersitial lamella- outside

outer lamella of osteon

Osteon

structural unit of compact bone. slender cytoplasmic processes that reach to adjacent osteocytes via canaliculi. processes connect via gap junctions to allow for passage of nutrients. connect to haversian canals.

canaliculi

Hairlike canals that connect lacunae to each other and the central canal provides channel for osteocyte communication

haversian canals

blood, lymph and nerve channels

Volkmann (perforating) canals

transverse canals that connect haversian canals

interstitial lamellae

fill spaces between osteons. remnants of old osteons created during remodelling

how does lamellar in bone contribute to bone strength

lamella are organised into different planes to provide increased strength with slippage planes between lamellae to allow some degree of flexion before a bone breaks.

tumours of bone cells. why are they rare but tumours are found in bone

osteosarcomas. tumours of lung and breast frequently metastasize to bone

flat bones

sternum, scapulae, ribs, (most) skull bones, clavicle

irregular bones

vertebrae, bones of pelvis (ileum, sacrum and coccyx but don't form from membranes of mesenchymal tissue), facial bones

long bones

phalanges, metacarpals, femur, humerus

sesmoid bones

patellas

short

carpals, talus, calcaneus

endrochondral ossification

bone is formed from hyaline cartilage template. most bones. ends of long bones remain covered by hyaline cartilage. not covered by perichondrium.

growth at epiphyseal plate

resting chondrocytes proliferate, forming columns. chondrocytes increase in size in the zone of hypertrophic cartilage and begin to calcify. breakdown in zone of cartilage degeneration before osteoblasts recruited to sites of calcified cartilage to begin bone formation (zone of ossification)

Rickets

Vitamin D deficiency in children

achondroplasia

autosomal dominant. lethal in homozygous form. results from mutations in fibroblast growth factor 3 gene. leads to decreased endochondral ossification, reduced proliferation of chondrocytes, decreased cellular hypertrophy and decreased cartilage matrix production. and premature closure of growth plates causing shortened long bones

pituitary dwarfism

diminished stature as a consequence of reduced activity at epiphyseal growth plates resulting from underactive pituitary gland before puberty

lack of growth hormone.

acromegaly

excess of GH post puberty. not gigantism bc growth plates have closed. periosteal growth. appositional. hands and feet are broadened.

Gigantism

a condition produced by hypersecretion of growth hormone pre-puberty.

intramembranous ossification

most flat bones. condensation of mesenchymal CT. begins in ossifications centres where mesenchymal progenitors develop into osteoblasts. secrete osteoid that becomes calcified to form spicules of woven bone

principle component of osteoid

t1 collagen

progenitor are osteoblasts

mesenchymal CT

immediate progenitor cell type of osteoclasts

monocytes. arise from fusion of macrophages

osteogenesis imperfecta

genetic abnormalities in t1 collagen synth. tII may die around time of birth from multiple fractures. legal importance bc confusion with multiple fractures caused by deliberate injury

vitamin d importance

dietary and synth under influence of UV. normal ossification. absence causes poorly mineralised. pliable matrix known as osteoid. bend under body weight. rickets

osteomalacia

adult rickets. vitamin D or calcium deficiency. bone pain, back ache, muscle weakness, increased risk of fracture.

bone become pliable during remodelling. individuals who are unable to go outdoors and whos diet lacks VD.

osteoporosis

more women and elderly ; >50. loss of bone matric and structural density. fractures of spine, hip and wrist. DEXA scan for bone density. post menopausal .

manifestation of achondroplasia

short limbs in proximal, normal trunk, enlarged skull vault, small face. sporadic mutation.

Paget's disease

a bone disease of unknown cause characterized by the excessive breakdown of bone tissue, followed by abnormal bone formation. skull, spine, legs. infection/genetics.

Menisci

flattened, shock-absorbing pads of fibrocartilage between the articulating surfaces of some joints

entheses

where tendons or ligaments join bone. fibrocartilage.

elastic cartilage

matrix comprised of t2 collagen, GAGs and elastic fibres

Fibrocartilage components

matrix t1 and t2 collagen

hyaline components

t2 collagen and abundant GAG for nutrients

proginator cells of cartilage

fibrous outer perichondrium

fracture repair

torn vessels bleed forming a haematoma. clot removed by macrophages ad replaced by a mass of procallus tissue comprised of fibroblasts and collagen. callus invaded by blood vessels and osteoblasts. fibrocartilage replaced by woven bone. woven bone remodelled as compact and spongy bone.

fracture repair type of ossification

endochondrial and intramembranous

osteoclasts

fused macrophages that destroy bone

osteocytes

a bone cell, formed when an osteoblast becomes embedded in the matrix it has secreted. trapped in lucunae

osteoblasts

deposit osteoid

Chondrocytes

Cells that secrete cartilage. trapped in lacunae

compact bone

Hard, dense bone tissue covered in periosteum. osteons. lamellar organisation. t1 and calcium hydroxyapatite.

spongy bone

no harversian or volkmanns canals. osteocytes in lacuna between lamellae (more irregular than cortical). remodelling by osteoblasts/clasts located on surface of trabeculae

trabecular organisation; high turnover rate, not covered by periosteum, lamellar organisation, niche for bone marrow, osteocytes in lacunae

how can decalcified bone be stained by h&e

because t1 collagen left behind

reduce of gravitational force on bone

bone reabsorption increases,

bone resist fracture

rigidity and flexibility. lamellae can slip relative to eachother to help disperse forces

sport on bone

hypertrophy of corticol bone

remodelling unit

cutting cone of osteoclasts, reversal zone of containing osteoprogenitors, closing cone where osteoblasts secrete osteoid accompanied by angiogenesis.

gigantism

increased structure as a result of enhanced activity of epiphyseal growth plate stimulated by over active pituitary before puberty

t1 osteoporosis

loss of bone density as a result of overactive osteoclasts following menopause

sex hormones effect on ossification

precocious sexual maturity (can be due to tumour producing growth hormones) retards bone growth because of premature closure of epiphyseal growth plates. if sex hormones are deficient, epiphyseal plates may persist later into life, leading to prolongued bone growth and tall stature.

Osteoporosis t2

loss of bone density due to diminished osteoblast function with age

thyroid hormones on bone

neonatal hypothyroidism: intellectual impairment, short stature. heel prick.

describe bone formation by intramembranous ossification

method by which most flat bones are formed. condensations of embryonic mesenchymal cells at ossification centres. these cells differentiate into osteoprogenitor cells which proliferate to form layer of osteoblasts. secrete osteoid that calcifies to form woven bone, neighbouring ossification centres fuse and undergo mature remodelling to form mature bone

rheumatoid arthritis

can run in families. affects joints of hand and wrist and small joints of feet. systemic causing fatigue, malaise and depression. chronic autoimmune disorder in which the joints and some organs of other body systems are attacked.

Osteoarthritis

inflammation of the bones and joints as a result of cartilage damage. most common. increased risk with obesity. degenerative disorder. knees and hips

endochondral ossification describe process

method most bones esp long bones are formed. takes place within hyaline cartilage. late in first trimester, periosteal bone collar surrounds cartilaginous template causing cartilage to become ischaemic. degenerating cartilage invaded by new blood vessles and osteoprogenitors to create a primary ossification centre, osteoblasts deposit osteoid which undergoes mineralisation. remodelling of the resulting woven bone leads to formation of mature bone, around time of birth, secondary ossification centres form in epiphyses. separate an epiphyseal growth plate which allows the bone to grow until puberty when growth plate closes

what type of bone is disproportionately affected in osteoporosis

spongy

most common fractures in osteoporosis

neck of femur and vertebrae

risk factor in development of osteoporosis

smoking, family history, low dietary calcium intake and mobility

what age does bone mass reach its peak

25-35

secondary osteoporosis

loss of bone density as a result of disease (multiple myeloma) or long term steroid usage

how many genes contribute to development of osteoporosis

polygenic many genes

Bisphosphonates

inhibit bone resorption used in osteoporosis. two phosphate groups that bind calcium ions allowing drug to accumulate at bony surfaces. bisphosphonates taken up by osteoclasts and reduce bone loss by reducing their action.

cell produce ECM

chondroblasts

types of cartilage

hyaline: ECM, proteoglycans. HA. T2 collagen

elastic: similary but elastic fibres

fibrocartilage: similar to hyaline but matrix contains abundant T1 collagen

Describe hyaline cartilage

covered by fibrous perichondrium, except articular surfaces of synovial joints. abundant ECM and t2 collagen which forms fibrils that don't form into fibres. large amounts of HA hyaline is well hydrated. pliant and reliable under pressure. large ration of GAGs to collagen in ECM facilitates diffusion of subtances between chondrocytes and BV surrounding the cartilage.

hyaline cartilage growth

perichondrium allow oppositional growth.

chondroblasts become chondrocytes.

dividing cells form a isogenous group. lay down more territorial matrix and separate leading to interstitial growth. pressure and stress to cartilage creates mechanical, electrical and chemical signals that increase chondrocyte activity.

epiphyseal plate

formed by hyaline. chondrocytes undergo cell division and hypertrophy followed by death and ossification by invading osteoblasts.

Fibrocartilage in intervertebral disc shock absorbing

annulus fibrosus, chondrocytes in lacunae are embedded in large bundles of T1 collagen fibres. more cartilaginous matrix in pubic symphysis or menisci.