Glossary of Anatomy Chapter 6: Bones

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Layer of dense irregular connective tissue that acts like a girdle to resist outward expansion when cartilage is compressed. Contains the blood vessels from which nutrients diffuse through the matrix to reach cartilage cells.
Hyaline Cartilage
Most abundant cartilage.

Only fibres are collagen fibres.

Includes articular cartilages, costal cartilages, respiratory cartilages, and nasal cartilages.
Elastic Cartilages
Cartilage which contains stretchy elastic fibres to stand up to repeated bending.

Found only in the external ear and epiglottis.
Highly compressible cartilage with great tensile strength. Consists of parallel rows of chondrocytes alternating with thick collagen fibres.

Occur in sites that are subjected to both heavy pressure and stretch.
Appositional Growth
Growth in which cartilage-forming cells in the surrounding perichondrium secrete new matrix against the external face of the existing cartilage tissue.
Interstitial Growth
Formation of new cartilage in which the lacunae-bound chondrocytes divide and secrete new matrix, expanding the cartilage from within.
Long Bones
Bones which are longer than they are wide.

Includes all limb bones but the patella, carpals, and tarsals.
Short Bones
Roughly cube-shaped bones.
Sesamoid Bones
Type of short bone that forms in a tendon.

(eg: patella)
Flat Bones
Thin, flattened, somewhat curved bones.

Includes sternum, scapulae, ribs, and most skull bones.
Irregular Bones
Bones that have complicated shapes which cannot fit into another class.

(eg: vertebrae, coxal bones)
Functions of bones (5)
Support, protection, levers for movement, mineral storage, blood cell formation (hematopoiesis)
Compact Bone
Dense, smooth-and-solid-looking bone.
Spongy Bone
Bone that consists of a honeycomb of small needle-like pieces (trabeculae).
The "shaft" of a long bone.
Medullary Cavity
The central marrow cavity of the long bones. Contains yellow bone marrow (fat).
The end of a long bone, which is covered with a thin layer of hyaline/articular cartilage.
Epiphyseal Line
The space between the diaphysis and epiphyses which represents a remnant of the epiphyseal plate.
Epiphyseal Plate
A disc of hyaline cartilage that grows during childhood to lengthen to bone.
A double-layered membrane which covers the external surface of the entire bone, except for the joint surfaces.

Outer layer = dense irregular connective tissue (fibrous layer)

Inner layer = osteogenic layer containing osteoblasts and osteoclasts
Bone-forming cells
Bone-destroying cells
Nutrient Foramen
Opening in a bone through which nerve fibres, lymphatic vessels, and blood vessels travel.
Perforating/Sharpey's Fibres
Collagen fibres which secure the periosteum to the underlying bone.
Connective tissue membrane lining the internal bone surfaces.
Spongy bone in flat bones.
Red Marrow
Hematopoietic tissue found within the trabecular cavities of spongy bone of long bones and in the diploe of flat bones.

(Yellow marrow in the medullary cavity can revert to red marrow if a person becomes very anemic).
Osteon / Haversion System
The structural unit of compact bone.

An elongated cylinder oriented parallel to the long axis of the bone.

Acts as a weight-bearing pillar.
Concentric layers which make up the osteon.

The collagen fibres in adjacent layers run in opposite directions to withstand torsion stresses.
Central/Haversion Canal
Hollow tunnel through the core of each osteon which contains small blood vessels and nerve fibres.
Perforating/Volkmann's Canal
Tunnels in compact bone lying at right angles to the long axis of the bone that connect the blood and nerve supply of the periosteum to those in the central canals and the medullary cavity.
Mature bone cells.
Small spaces in the bone which house the osteocytes.
Hairlike canals which connect the lacunae to one another and to the central canal.

Nutrients reach the osteocytes of spongy bone by diffusing through the canaliculi from capillaries in the endosteum surrounding the trabeculae.
The organic part of the bone matrix. Includes ground substance and collagen fibres, both of which are secreted by the osteoblasts.

Lends flexibility and tensile strength to bone.
Inorganic portion of the bone, which consists largely of mineral salts.

Tightly packed crystals account for the bone's exceptional hardness.
Bone formation.
Intramembranous Ossification
Formation of a bone from a fibrous membrane.

All bones formed by this process are flat bones.
Endochondral Ossification
Bone development by replacing hyaline cartilage.

Forms almost all bones of the skeleton below the base of the skull, with the exception of the clavicles.
Intramembranous Ossification Method
Fibrous connective tissue membranes formed by mesenchymal cells are the supporting structures on which ossification begins at about week 8 of development.

(1) An ossification centre appears in the fibrous connective tissue membrane.
(2) Bone matrix is secreted within the fibrous membrane.
(3) Woven bone and periosteum form.
(4) Bone collar of compact bone forms and red marrow appears.
Endochondral Ossification Method
(1) A bone collar forms around the diaphysis of the hyaline cartilage model.

(2) Cartilage in the centre of the diaphysis calcifies and then cavitates.

(3) The periosteal bud invades the internal cavities and spongy bone forms.

(4) The diaphysis elongates and a medullary cavity forms.

(5) Secondary ossification centres appear in the epiphyses, and they ossify.
Periosteal Bud
Group of fibres which invade the spongy bone, including a nutrient artery and vein, lymphatics, nerve fibres, red marrow elements, osteoblasts, and osteoclasts.
Growth of Length in Postnatal Long Bones
Cells at the top of the epiphyseal plate divide quickly, pushing the epiphysis away from the diaphysis.

Older chondrocytes die and deteriorate, and the cartilage matrix calcifies. This leaves long spicules of calcified cartilage at the epiphysis-diaphysis junction.

These become part of the osteogenic zone and are invaded by marrow elements from the medullary cavity.

Spicule tips are eventually digested by osteoclasts, allowing the medullary cavity to grow longer.

Epiphyseal plate closure occurs when the chondroblasts of the epiphyseal plates divide less often and are replaced entirely by bone.
Postnatal Long Bone Growth in Width
Appositional growth.

Osteoblasts beneath the periosteum secrete bone matrix on the external bone surface as osteoclasts on the endosteal surface of the diaphysis remove bone.

There is normally less breaking down then building up, which thickens the bone.
Hormonal Regulation of Bone Growth
Growth hormone (modulated by thyroid hormones) ensures that the skeleton has proper proportions as it grows.

Sex hormones promote the growth spurt of adolescence, but prolonged exposure to them induces epiphyseal plate closure and the halt of bone growth.
"Slivers" of material making up spongy bone.
Thinning of bones caused by osteoclasts operating at a higher rate than osteoblasts.
Breakdown of bone via osteoclasts.

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