histology) cartilage and bone

8/4/2019 Histology) Cartilage and Bone

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CARTILAGEo Specialized form of connective tissueso Consists of cells :

Chondrocytes Extracellular fibers Gel-like Matrix

o The intercellular components predominates over the cells, which are isolated in smallcavities w/in the matrix

o Has no nerves or blood vessels of its own.o Collodial properties of its matrix are important to nutrition to its cells.o The matrix is also responsible for its firmness and resilience.o Axial and appendicular skeleton is first formed in cartilage models later replaced by bone.

Role of Cartilage in post-natal lifeo Growth of Long boneso Articular surface

Kinds of Cartilageo Hyaline - most common and most characteristico Elastico Fibrocartiloage

Distinguished on the amount of extracellular matrix, abundance of collagen or elastic fibers.

I.HYALINE CARTILAGE

A. Sites in adult1. Ventral ends of ribs, tracheal rings, larynx, joint surfaces of bones.

B. Elastic, semitransparent tissue with an opalescent bluish gray tintC. HISTOGENESIS

At sites of future cartilage formation in the embryo, mesenchymal cellswithdraw their processes and become overcrowded together in dense

aggregation called "Protochondral tissues" or centers of chondrofication.

Nuclei of the cells are very close together and cell boundaries are indistinct.

As the cells enlarge and differentiate, they secrete around themselves in a

metachromatic extracellular matrix.

D. Chondrocytes Lacuna(e) - space for chondrocytes

Elliptical immediately beneath the surface of the perichondrium Semicircular or angular in deeper layers

Conform to the shape of the lacunae they occupy.E. Cartlage Matrix

In fresh hyaline, matrix is homogeneous. Principal constituents of ECM - type II collagen and proteoglycans

Collagen fibrils are thin and lack crossbanding Not organized in bundles but form a loose meshwork throughout

the matrix.


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Proteoglycans Proteins - forms the backbone Carbohydrates - glycosaminoglycans, radiate from the core protein

in a bottle brush configuration.

Principal glycosaminoglycans Chondroitin sulfate and keratan sulfate

One end of molecule is bound to hyaluronic acid The molecular org of ECM in hydrated state is ideally suited to its function

on the weight bearing articular surfaces of bones.

F. Secretion of Matrix components Chondrocytes synthesize and secret the collagen and proteoglycans surrounding

matrix.

II.ELASTIC CARTILAGE

A. Sites1. External ear, walls of the external auditory and eustachian canals, epiglottis.

B. General Characteristics:1. Differs from the hyaline grossly in its yellowish color and its greater opacity and

elasticity.

2. Cells are similar to the hyaline.3. The interstitial substance differs from that hyaline cartilage by being permeated

by frequently branching fibers,

4. They form a network that is often so dense that the ground substance isobscured.

III.FIBROCARTILAGE

A. Sites1. Intervertebral discs2.

Certain articular surfaces: symphisis pubis

3. Ligamentum teres femoris4. Attachment of tendons to bones

B. General Characterisitcs:1. Encapulated chondrocytes lie singly or in pairs or aligned in rows between

bundles of collagen fibers

2. Matrix is inconspicuous except in immediate vicinity of the cells, where itspresence can be inferred from the characteristic form of the lacunae

3. It is clearly assc. w/ the connective tissue of the capsules and ligaments of joints.4. It is transitional form between cartilage and dense connective tissue and the

gradial form one to another

IV.Histophysiology

Joints - sustain great weight and allow the bone to move easily and smootly against oneanother.

Ear and resp passages - pliable and resistant framework that prevents collapse of thetubular organ

Makes possible bone growth in length.V.Some Diseases in Cartilage Deficiency


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A. Vitamin C deficiency - Scurvy Apparent in the gums.

B. Vitamin D Deficiency - Rickets Epiphyseal cartilages continue to proliferate but fail to calcify and the growing

bones become deformed by weight bearing.

Its growth in lengths is influenced by growth hormone.BONE

o May contain as many as 3 different regions.o A typical long bone has all three:

Tubular middle portion (Diaphysis): compact bone Metaphysis is the region where compact bone forms a shell around a mass of spongy or

cancellous bone. A long bone typically is capped by an epiphysis. Between the epiphysis and the

metaphysis is the epiphyseal plate, where a bone grows in length.o Articular Surfaces

On the articular surface of a long bone, a thin layer of hyaline cartilage covers the top ofthe compact bone.

Normally, the surfaces of these articular cartilage is extremely slippery.o Periosteum and Endosteum

Except on the articular surfaces, bone is covered with a dense irregular tissue called theperiosteum. The cells of the inner layer of the periosteum, called osteoblasts secret

bone constituents, giving the periosteum the ability to form a new bone. Both the marrow cavity and the surfaces on the spicules of spongy bone are lined with a

thin layer of cells called endosteum. Like the periosteum, the endosteum has osteogenic potential. The periosteum and endosteum are responsible for growth in diameter of the bone.

o Variations

Not all bones have two epiphysela plates. Ex. Most tarsal bones have a singleossification center.

Others have complex ossification centers that reflect complicated final grossmorphology.

I.Microscopic Structures of Bones

A. General Appearance1. A section of bone reveals a large amount of mineralized ECM arranged in

lamellae or plates.

2. W/in the lammelae exist small lacunae and anastomosing network of miniaturecanaliculi. The lacunae are occupied by living osteocytes and delicate cell

processes from these osteocytes called the canaliculi.

3. The mineralized matrix prevents free diffusion so that the osteocytes areconnected to the blood vessels in the bone via the canaliculi.

B. Lamellar Patterns - bone lamallae in compact bones are arrg in 3 differentcompartments.

1. Along the periosteal and endosteal surfaces of a long bone there arecircumferential lamellae.


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2. Throughout the mass of the compact bone, lamellae are arrangement in 4-20concentric layers around a vascular space. These cylindrical units called

Haversian Systems run parallel to the long axis of the bone.

3. Interstitial Systems are irregular arrgangements of lamellae. These often areroughly triangular or quadrangular.

C. Vascular Channels1. Haversian Canals

a. Always surrounded by concentrically arranged lamellae, where the longaxis of the cylinder of lamellae is parallel to the long axis of the blood

vessel. Even in cases where the Haversian Canals branch into Y-Shaped

Haversian Systems, lamellae maintain their concentric arrangement.

2. Volkmann's Canalsa. Occur where blood vessels form the periosteum penetrate compact bone,

crossing Haversian Systems in their descent into it. Therefore, Volkmann's

Canals have their long axis perpendicular, or nearly perpendicular, to the

lamellae of the Haversian Systems.

Cancellous bone is composed of small numbers of lamellae w/c are not closelyarranged into form like Haversian Systems. Instead, lamellae lie close to blood vessels

and the endosteum, and they receive their nutrition by direct diffusion.

D. Periosteal Variations1. While a bone growth in diameter, the inner layer of the periosteum is cuboidal

layer of cells loosely arranged in a sheet. These osteoblasts are active in bone

formation; they secrete uncalcified fiber and amorphous matrix, w/c

subsequently calcify to form compact bone.

2. Once a bone reaches its full diameter, osteoblasts become quiescent and areindistinguishable from the other densely packed fibroblasts that comprise the

periosteum.3. Dense bundles of collagen fibers become incarcerated in the bony matrix of a

growing bone. These Sharpey's fibers anchor the periosteum firmly to the

underlying bone.

The endosteum is similar to the layer of osteoblasts but is somewhat thinner. Like

osteoblasts, the cells of endosteum can secrete bone.

II.Cytologic Structure of Bone

A. Cell Types in Growing Bone1. Osteoprogenitor Cells

a. Relatively undifferentiated cells that commonly undergo mitosis.b. Has a pale staining oval nucleu and an acidophillic or faintly basophillic

cytoplasm.

c. Found near all free surfaces of bone including periosteum andendosteum. They ling Haversian Canals and are found on trabeculae of

degenerating cartilage at the epiphyseal plate of a growing bone.

2. Pseoblastsa. Avtively secret bone matrix. Typical of cells that make collagen for export,

they have a large amount of rough ER and therefor basophillic cytoplasm.


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b. The nucleus of the osteoblasts is prominent and contain a large basophillicnucleolus.

c. The Golgi Apparatus is well developed.3. Osteocytes

a. Somewhat similar to osteoblasts. Becaus it is less active in matrixsecretion. Its RER and GA are less prominent than those of osteoblast

b. Although less active, they are not inert. They respond rapidly toparathyroid hormone during regulation of serum calcium concentration

and they can secret matrix.

c. Occupy lacunae in the solid matrix.4. Osteoclasts

a. Large multinuclear cells formed by the fusion of mononuclear cells.b. Numerous mitochondria and prominent GA.c. Secrete acid hydrolases and certain ions that cause the breakdown of

bone.

B. Interconversion of Cell Types.1. Osteoprogenitor cells can differentiate into osteoblasts.2. Osteoblasts can also differentiate into osteocytes.

C. Chemical Composition of Bone1. Inorganic Salts - complex calcium phosphate. Other components of the mineral

are calcium carbonate, citrate, flouride, magnesium and sodium.

D. Bone also contains such glycosaminoglycans as Keratan Sulfate, Chondroitin Sulfate andHyaluronic Acid.

E. Bone contains Type I CollagenIII.Formation of Bone

A. Intramembranous Ossification - calcification of mesenchymal tissue. Flate bones of the skull; condensations of mesenchymal cells occur near blood

vessels. Osteoblasts secret ostoidthat mineralize.

B. Endochondral ossification Long bones in the extremities, bones in the pelvis, vertebral column, base of the

skull.

C. Osteoblasts secrete bone organic matrix w/c later is mineralized.IV.Function of Bone

A. Calcium Storage1. Calcium is essential for cell adhesion, membrane permeability, muscle

contraction and blood clotting.

2. Hormones that affect Calcium exchange between blood and bone:a. Parathyroid Hormone (PTH)

i. Breaks down bone for circulationb. Calcitonin

i. Depresses bone resorption and is antagonistic to the effects of PTH3. Regulation of Maturation and Growth:

a. Gonadal hormonesi. Female - ovaries

ii. Male - Testis


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b. Growth hormonesi. Secreted by anterior pituitary gland

histology) cartilage and bone

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