CARTILAGE AND BONE

• How many bones do humans have?

  206 bones
• T OR F : bones and cartilages are organs

  TRUE
• Cartilage and bone tissues

  • special types of dense regular connective tissue.
  • relatively few cells and abundant intercellular substance
  • their cells, called chondrocytes and osteocytes, respectively, are inside cavities called Iacunae
  • Their intercellular substance (matrix) is also firmer or harder.
  • IS of cartilage - is gelatinous, albeit firm,
  • IS of bone - is calcified, hence, rigid and hard.
• Cartilage (Gristle)

  • types: hyaline, elastic, and fibrous
  • no blood vessels, lymph vessels, or nerves
  • chondrocytes are nourished by diffusion of nutrients from the surrounding tissues.
• Hyaline Cartilage

  • most abundant type of cartilage
  • glistening, smooth, and pearly white in fresh specimens.
  • forms the bulk of the skeleton of the fetus in-utero.
  • axial and appendicular skeleton are first formed out here
  • location: joints, sternal ends of ribs, some parts of respiratory system and external ear, and tendons and ligaments
  • consists of cells (chondrocytes) that are inside cavities (lacunae) which are embedded in the in the intercellular substance (cartilage matrix).
• Chondrocyte (Cartilage Cell)

  • RHP - cytoplasm shrinks a little
  • young
  • elliptical in shape w their long axes parallel to cartilage surface
  • capable of mitosis
  • daughter cells are called isogenous cells
  • mature - larger and rounder
  • cytoplasm is finely granular and basophilic
  • limited number of mitochondria
  • well developed RER and Golgi complex
  • inclusions: fat droplets and glycogen granules
  • nucleus is ovoid
• Cartilage Matrix

  • consists of an amorphous ground substance where extracellular fibers are embedded.
• water

  • 70% - 80% of wet weight of tissue
• Ground substance of cartilage matrix

  • mostly made up of proteoglycans
  • intensely basophilic because of GAGs
  • 50 um in thickness, as capsule of the chondrocytes, also called territorial matrix
  • interterritorial matrix - area in between the territorial matrices
  • pericellular capsule
  • innermost (1-3 um) layer of the territorial matrix resembles a basal lamina
  • protects the chondrocyte against mechanical stress.
  • also contains some non-collagenic proteins and glycoproteins, notably chondronectin, which is a fribronectin-like substance that promotes the adherence of collagen fibers to cell surface
• Extracellular Fibers of cartilage matrix

  • type II collagen fibers
  • 40% of the dry weight of tissue
  • thinner than type I collagen
  • H&E - not distinguishable
• Elastic Cartilage

  • flexible than hyaline cartilage and is yellowish in fresh specimens.
  • present in the auricle and external acoustic meatus of the ear, auditory tube, epiglottis, and some other parts of the larynx.
  • matrix is less abundant
  • contains a considerable quantity of elastic fibers.
  • account for the pliability and yellowish color of the tissue
• Fibrous Cartilage

  • can withstand greater stress
  • white in fresh specimens
  • make up the intervertebral discs, articular discs, and glenoid and acetabular labra
  • loc: tendons and ligaments
  • collagen fibers are thick because the content is type I
  • regarded as a transitional stage between dense regular connective tissue and cartilage.
  • acidophilic
  • a relative paucity of ground substance.
• Perichondrium

  • notable the articular cartilages
  • is special because it has chondrogenic potency (i.e.,ability to form cartilage)
  • consists of an outer layer (fibrous layer) that blends with the surrounding tissue, and an inner, more cellular layer (chondrogenic layer) that adheres to the cartilage
  • cells of the chondrogenic layer apposed to the surface of thecartilage are stem cells, called osteoprogenitor cells, which can transform into chondroblasts
• Chondroblasts

  • are cells that synthesize the precursors of the extracellular fibers and the other organic constituents of cartilage matrix.
  • When they get surrounded by the matrix they secreted, they acquire lacunae and transform into chondrocytes.
• Bone

  • comprise the bulk of the adult skeleton form a rigid framework
  • protect vital organs
  • serve as levers for muscles, and as storehouses for calcium and
  • phosphorus
  • they house bone marrow
  • types: long, short, flat, irregular, and sesamoid bones
• Long bones

  • are confined to the extremities
  • is tubular and consists of a body or shaft and two ends (proximal and distal epiphyses)
  • shaft - shaft has a hollow core (medullary cavity)
  • epiphyses - articulate with other bones and are covered on their articulating surfaces by hyaline cartilage (articular cartilage).
• Short bones

  • cuboidal and are confined to the wrist and ankle
• Flat bones

  • typified by the sternum, scapulae, and many bones of the skull.
• Irregular bones

  • include the vertebrae, hip bones, and the bones of the skull that are not flat
• Sesamoid bones

  • develop in tendons
  • ex. patella and knee cap
  • form of unnamed small nodules
• compact bone (cortical, dense)

  • appears like a solid mass
  • outer casing
  • 75% to 80% of body's total skeletal mass
• spongy bone (cancellous)

  • numerous spaces or cavities
  • inner region
  • minimal air sinuses
  • more volume than compact bone
  • 20% to 25% of body's total skeletal mass
• osteogenic

  • ability to form bone
• Periosteum

  • outer layer (fibrous layer)that blends with the surrounding tissue, and an inner, more cellular layer (osteogenic layer) that adheres to the bone.
• Osteoprogenitor cells

  • cells of the osteogenic layer that abut the surface of the bone
• Sharpey's fibers

  • bundles of collagen fibers from the periosteum get trapped within the bone matrix and form distinct structural entities
  • firmly anchor the periosteum to the bone
• Endosteum

  • lines all the medullary, marrow, and vascular cavities of bones
  • thinner than periosteum
  • single layer of osteoprogenitor cells
• In both spongy and compact bones, the intercellular substance (bone matrix), which is very hard, is arranged in thin layers ~lamellae) that are about 3 to 7 um thick each.
• cavities (lacunae)
• small canals (canaliculi)
• A lacuna is occupied by a cells (osteocyte)
• Spongy bone

  • consists of numerous small interconnecting bone fragments (spicules; trabeculae) that form the framework of a very complex system of spaces (bone marrow cavities)
  • the osteocytes derive nutrients and oxygen, either directly or indirectly, from the blood vessels
• Compact bone

  • lamellae are organized and arranged in any of three ways: Haversian systems, interstitial lamellae, or circumferential lamellae
• Haversian systems or osteons

  • make up the bulk of compact bones.
  • consists of several bone lamellae
  • outer boundary - delineated by a cement line made up of a thin layer of mineralized matrix and collagen fibers.
  • Haversian canals of neighboring Haversian systems are connected to each other by transverse channels called Volkmann's canals
• Haversian and Volkmann's canals

  • both canals contain blood vessels and nerves and are lined by endosteum.
  • are able to deliver nutrients, oxygen, and other needed substance . They can also remove metabolic waste products and carbon dioxide from all the osteocytes in all the Haversian systems.
• Interstitial lamellae

  • bone lamellae that are not arranged around a Haversian canal in between Haversian systems
  • remnants of Haversian systems that are being resorbed or broken down
• Circumferential lamellae

  • third category of lammelar arrangement in compact bone
  • are most developed in long bones.
  • types: outer circumferential lamellae and inner circumferential lamellae
• Bone matrix

  • consists of an amorphous ground substance where extracellular fibers are embedded.
• Ground Substance of Bone

  • consists mainly of water
  • its structural components are made up of:
  • inorganic minerals (about two-thirds of the dry weight of bone)
  • organic substances. (remaining third)
• Inorganic Minerals in the Ground Substance of Bone

  • consist mainly of calcium and phophorus
  • form crystals very similar to those of calcium hydroxyapatite (Ca10(PO4)(OH)2)
  • electron micrograph - crystals seen immersed in the ground substance and lying at regular intervals alongside the collagen fibers
  • bicarbonate, citrate, magnesium, potassium, and sodium