Histology - Cartilage + Bone

Connective tissue w/rigid extracellular matrix Chondrocytes (cells) with low metabolic activity Collagenous (tensile strength) and elastic fibers Chondroitin sulfate (ground substance) Development and growth of long bones Early fetal skeleton forms Supports soft tissues (ear + nose, respiratory system, moveable joints, intervertebral disks) Avascular (vasculature in adjacent perichondrium) No innervations No lymph vessels 75% water, forms a gel with ground substance that allows for diffusion of gases and nutrients

Mesenchyme

Develops from mesenchyme Chondroblasts for collagen fibrils Differentiation of cells to chondrocytes and separation by the matrix Perichondrium envelops cartilage Interstitial growth Appositional growth

Sheath of dense irregular connective tissue – with fibroblasts and vasculature, envelops cartilage Contains many undifferentiated cells which can differentiate into chondroblasts

Mitotic division of existing chondrocytes and production of new matrix (young cartilage)

Differentiation of new chondrocytes from stem cells (inner layer of perichondrium) and production of matrix at surface

Hyaline Elastic Fibrocartilage

Most common Type II collagen Appears blue/white In embryo: serves as skeleton until replaced by bone – acts as a template Epiphyseal plate in long bone growth Joint surfaces, nose, larynx, trachea, bronchi, ends of ribs adjacent to sternum Hyaline cartilage is covered by perichondrium - except over articular surfaces

Amorphous ground substance with proteoglycans – including chondroitin sulfate and kertain sulfate Basophilic Collagen fibers (20 nm) are very fine, appear structureless Territorial matrix adjacent to chondrocytes is rich in glycosaminoglycan and stains more basophilic than non-territorial matrix

Chondrocytes occupy small cavities in matrix (lacunae) Surface of cell irregular; holds onto matrix + allows for better nutrition Chondrocytes = basophilic – large amounts of ER, typical of protein producing cells Outer cells are elliptical w/long axis parallel to surface Large central nucleus Deeper chondocytes are round, may appear in groups of up to 8 – isogenous group (Cell nests), all offspring from one chondrocyte Lined up in rows in epiphyseal plate Often shrink in histological sections

Intramembranous ossification
endochondrial ossification

Small cavities in cartilage/bone matrix

Deeper round chondrocytes grouped – up to 8 cells – all offspring from same chondrocyte

Support w/flexibility Auricle of ear, external auditory canal, Eustachian tube, epiglottis, cuneiform cartilage of larynx Similar to hyaline cartilage – many elastic fibers visable Yellow in fresh sections – opaque Covered by perichondrium Matrix is much less homogeneous – extensive network around chrondrocytes

Tough support + tensile strength Intervertebral disks, tendon and ligament attachment to bone, pubic symphysis Combination of hyaline cartilage and dense regular connective tissue Merges with adjacent dense connective tissue or hyaline cartilage Chondrocytes in rows or groups Matrix appears acidophilic – lots of collagen No perichondrium A form of connective tissue transitional between dense connective tissue and hyaline cartilage Merges into neighboring tissues – typically tendons or articular hyaline cartilage Develops like connective tissue – initially fibroblasts are separated by fibrillar material, then they differentiate into chondrocytes and produce cartilage matrix