Cartilage and Bone Histology

chondroblasts

secrete extracellular matrix, including type 2 collagen, located near periphery and smaller

chondrocyte

maint. cell, in middle of cartilage, bigger and eye-ball like

lacuna

small space with ECM that houses the chondrocyte

isogenous group

chondrocytes and blasts that have undergone mitosis and sit together in groups of two or more

perichondreum

two layers of dense connective tissue, that support cartilage

outer fibrous = fibrocytes

inner chondrogenic layer = stem cells and chondroblasts

Hyaline, fibro, and elastic

what are the three types of cartilage?

hyaline cartilage

most common type, strong, flexible, resists compression, helps with bone growth

repiratory system, ribs, epiphysis

where do we find hyaline cartilage?

perichondreum, glassy matrix with unseen type 2 collagen

how does hyaline cartilage appear histologically?

territorial matrix

matrix surrounding the lacuna that stains darkly bc of proteins and it being newer

interterritorial matrix

lighter in color, surrounding the territorial matrix

elastic cartilage

hyaline cartilage with visible elastic fibers in the ECM, has lacunae, isogenous groups, and perichondreum

ear, epiglottis, larynx

examples of where you can find elastic cartilage

fibrocartilage

hyaline cartilage + dense CT, consisting of type 1 and 2 collagen, fibrocytes, and chrondrocytes, and NO perichondreum

intervertebral discs, meniscus, pubic symphysis, and bone repair

locations of where you would find fibrocartilage

interstitial cartilage growth process

starts in chrondrocyte’s center

undegoes mitosis

matrix between the cells start pushing away from each other

budding from the middle

appositional cartilage growth

mesenchymal cell in the chondrogenic layer

transitions to chondroblast

produces ECM

transitions to chondrocyte in the lacuna

bone CT

creates bone, ECM contains type 1 collagen + inorganic minerals

protects internal organs, storesand releases fat, makes blood, stores and releases minerals, attachment site for m. to create movement, supports the body

functions of the bone

eosinophilic collagen

basophilic nuclei of hemopoietic cells

white blobs of adipose

bone histology appearance

osteoprogenitor cells

stem cells that mature into osteoblasts, located in periosteum and endosteum, squamous shape

osteoblast

bone building cell, cuboidal shape, comes from osteoprogenitor cell and becomes an osteocyte

osteocyte

maintains bone, connects to each other via extensions, exchanges stuff via gap junctions

osteoclast

bone breaking cell that is a derivative of monocyte, large and multinucleated, found in depressions called “Howships lacuna”

2 layers of fibrous CT on external surface

outer layer: anchors tendons, ligaments, and neurovasculature to bone

inner layer: osteoprogenitors, osteoblasts, appositional growth leads to external circumferential lamellae

periosteum contents

lines internal open surfaces of bone tissue

thinner than periosteum

reticular fibers

creates internal circumferential lamellae

endosteum

compact bone

osteon, hard compact structure on the outside of bone under the periosteum

concentric lamellae

different directions of osteoblasts secreting osteoid therefore increasing strength

dark spider like structures with osteocytes

compact bone histology

central canal

central hole in complact bone histology that is the site for neurovacular shit, lined with endosteum, surronded by collagen

interstitial lamellae

in between osteons, remnants for remodelling

perforating canal 

in compact bone, runs from the periosteum perpendicularly to the osteons, and gives rise to the central canal

spongy bone

deep to compact bone, only associated with endosteum, made of trabeculae, looks spongey, bone marrow fills space with trabeculae, lack osteons

osteoblasts lay down ECM based on stress, collagen appears long, cannaliculi run towards marrow cavity

how does spongy bone react to stress?

woven bone stains more basophilic

what bone type stains more basophilic, woven or lamellar?

intramembranous ossification

begins with mesenchyme and created woven bone then lamellar

echondral ossification

starts with hyaline cartilage and then creates woven bone and then lamellar

mesenchyme arranges in sheets

cells differentiates into osteoblasts and starts forming CT

mesenchyme surrounding bones develops into periosteum

steps to intramembranous ossification

starts with hyaline cartilage model

ECM begins to calcify triggering bone cells to come in and add more matrix

secondary ossification

(some cartilage remains for continued growth during childhood “epiphyseal plate”)

steps to echondral ossification

appositional bone growth

periosteum adds (blasts)

endosteum removes (clasts)

interstitial bone growth

epiphyseal plate (hyaline cartilage) provides substrate to do so

diaphysis

body/shaft of the bone, has medullary/marrow cavity

epiphysis

ends of the bone that articulate with other bones, lined with hyaline cartilage

metaphysis

between the epiphysis and the diaphysis, has epiphyseal growth plate 

zone of rest

epiphyseal plate that is closest to epiphysis made of mostly hyaline cartilage

zone of proliferation

chondrocytes undergo mitosis, and stacking of columns

zone of hypertrophy

chondrocytes balloon out

zone of calcification

chondrocytes die, cartilage ECM calcifies

zone of ossification

osteoblasts come and attach to calcified ECM, secretion begins

fibrous joint

connects bone with dense fibrous CT, slight to no movement

cartilaginous joint

bones connected by hyaline or fibrocartilage, limited movement

synovial joint

joint is surrounded by a capsule extension of each bone’s periosteum, articular cartilage lines ends of bones