3.2- SS and Bones (Pt.2)

Endochondral Ossification (Steps)

Cartilage progressively replaced by bone, extending towards the ends (epiphyses). Bone simultaneously formed in periosteal and endosteal layers, to remodel the medullary cavity

Clavicle

Collar bone

Epiphyses

Located in the ends of developing long bones to allow for growth corresponding to the demands of the bone (indicate a bone is still growing)

Osteophyte

Spur, outgrowth or ridge that forms on a bone on vertebrae in old people

Endochondral Ossification

(cartilaginous bone formation), cartilage models of bones form from mesenchyme during the fetal period, and bone subsequently replaces most of the cartilage.

Nutrient Artery function

(one or more per bone) they arise outside the periosteum, pass through the shaft of a long bone via nutrient foramina, and split in the medullary cavity into longitudinal branches. These vessels supply the bone marrow, spongy bone, and deeper portions of the compact bone.

Fracture

A broken bone is termed a fracture (from Latin: 'break'). A fracture may be associated with stripping and/ or tearing of the periosteum (particularly if there is displacement of the bone ends). There is typically swelling from bleeding due to the rich blood supply (particularly of bone tissue and marrow). It is accompanied by severe pain due to the rich sensory nerve supply (particularly of periosteum).

What are the parts of a developing long bone?

A mature long bone is characterised by a shaft (between its proximal and distal ends). The corresponding part in a developing long bone is the termed the diaphysis (from Greek: 'between growth'). The termination of the diaphysis is the metaphysis ('changing growth'- site of high metabolic activity). An epiphysis ('upon growth') is the end of the developing bone, adjacent to a metaphysis.

What happens to the arteries at the end of a long bone after the growth plate disappears?

Anastomoses in ends of a long bone ;mature long bone no longer possesses epiphyses, metaphyses or a diaphysis (the parts of a developing long bone). The branches of articular arteries that correspond to epiphysial and metaphysial arteries are able to link ('anastomose') with each other because the intervening (avascular) hyaline cartilage of the growth plate has disappeared with epiphysial fusion.

Intramembranous Ossification (Step 1&2)

At about the 6th intrauterine week, intramembranous ossification commences. Mesenchyme condenses into a sheet of soft tissue (transforms into a network of soft trabeculae) Osteoblasts gather on the trabecular to form osteoid tissue (unclassified bone)

What do nutrient arteries bring into the primary centre?

Bring osteogenic cells (osteoblasts and osteoclasts)

Intramembranous bones

Broad, flat bones of the skull and clavicle; Begin as fibrous cartilage that later differentiates into osteoblasts.

What provides a clue to indicate the growing end of a long bone?

Direction of nutrient foramen; the major artery supplying a long bone is termed the nutrient artery. This artery occupies a passage (termed the nutrient foramen) penetrating the shaft of the bone through to the medullary cavity. The canal of nutrient foramen (when viewed from its outside opening) is directed away from the growing end. Differential longitudinal growth results in the nutrient artery taking an oblique path (from outside to inside) through the full thickness of the bone, while the bone is still growing (unequally). Equal growth would have resulted in the artery penetrating perpendicular to the shaft.

Simple Fracture

Does not rupture the skin. Fixed by immobilising limb- bone receives a rich blood supply, accelerating the repair process (and creating much bleeding at the time of injury). This vascularity enables numerous vessels to invade the fracture site during repair within the mass of connective tissue (termed callus) as a result of periosteal and endosteal proliferation. New bone is formed within the callus then subsequently remodelled. Uncomplicated fractures therefore tend to heal well, provided the bone ends are correctly aligned and immobilised. Healing is generally more rapid in children and in bones that are not weight bearing.

Mesenchyme

Embryonic connective tissue that arises from mesoderm. All bones are derived from mesenchyme (embryonic connective tissue)

______ start off as hyaline cartilage and then are replaced by bone tissue

Endochondral bones; forms models for future bones. Begins as hyalin cartilage, and is the centre for primary and secondary ossification

What determines difference in growth?

Epiphyseal Duration; the more time an epiphysis (and associated epiphysial plate) exists the greater the opportunity for growth in length at that site. No further longitudinal growth occurs after epiphysial fusion (with disappearance of the epiphysial plate). The earlier an epiphysis appears the later it tends to fuse. Epiphyses for larger bones tend to appear before (and fuse after) those for smaller bones. Within a large long bone the epiphysis for one end tends to appear before (and fuse after) that of the other end. More growth therefore occurs at one end (the 'growing end'). The first epiphyses to appear (at about birth) are for the lower end of the femur and the upper end of the tibia (the two longest bones in the body). Most lower limb growth in length occurs near the knee as these associated epiphyses also tend to be the last to fuse. Most upper limb growth in length occurs near the ends of the long bones at the shoulder and wrist. The first epiphyses to fuse are at the elbow.

What structure enables growth at the length of a long bone?

Epiphyseal growth plate

What is the remnant of an epiphyseal plate and its forensic significance?

Epiphyseal line; fusion of an epiphysis to a metaphysis is associated with disappearance of the epiphysial plate and cessation of further growth in length at this site. A scar, termed the 'epiphysial line', is the only remnant of the plate in a mature bone. Although not visible on the external surface, the epiphysial line can be seen in vertical sections and in some radiographs. Since epiphyses fuse in an ordered sequence, they can assist in determining the age of an individual from radiographic images or forensic skeletal examination. In the latter, a narrow cleft on the external surface of a bone indicates an epiphysis undergoing fusion. An epiphysial plate undergoing fusion resembles a fracture line. It may be differentiated from a fracture by X-ray of the corresponding bone on the other side of the body.

Compound Fracture

If fractured bone is exposed to the air (by laceration of overlying skin or mucous membrane, eg. from sharp bone fragments) it is termed a 'compound' fracture and has a significant risk of infection. Fixed using tools

What particularly impairs normal bone growth?

In children and adolescents, injury to an epiphysis (resulting in displacement or separation of an epiphysial plate) or a fracture extending through the epiphysial plate carries special significance. Damage to an epiphysis or epiphysial plate will tend to impair subsequent growth. Bone infections (spread from the blood stream) tend to occur at the metaphysis (a site of vulnerable blood supply) and may also lead to damage of the adjacent epiphysial plate. Interruption of blood supply to the adjacent epiphysis or metaphysis will similarly tend to impair normal growth.

During bone development in utero, osteoblasts promote what type of ossification?

Intramembranous Ossification; some bones develop from a fibrous tissue precursor, by intramembranous ossification. These bones include the flat bones of the skull as well as parts of the clavicle and mandible. Despite the different precursor (and process), bone formed via intramembranous ossification is identical with that formed via intracartilaginous ossification.

Arteries supplying a long bone (4)

Nutrient vessels Periosteal vessels Metaphyseal Epiphyseal

Intramembranous Ossification (Step 3&4)

Osteoclasts remodel the centre they say to contain marrow spaces and osteoblasts remodel the surface they say to form compact bone Mesenchyme at the surface gives rise to periosteum

Secondary Ossification Centre

SOC appear in the middle of each epiphysis then invade the cartilage model between the joint surface and the growth plate. Secondary centres of ossification are growth centres typically located in the ends of the cartilage model for long bones. They occur only at one end of a small long bone (eg. digits and ribs) but at both ends of the large long bones (those associated with the elbow and knee joints). Almost all secondary centres appear after birth (females generally at an earlier age than males). Although secondary centres tend to appear at different times for different sites, the vast majority have appeared well before puberty. Blood vessels, together with osteoblasts, invade each secondary centre. The (epiphysial) arteries are derived from separate sources to that of the primary centre (which is from the nutrient artery). Hyaline articular cartilage is retained at joint surfaces after the bone has completed ossification.

What arteries supply the developing ends of a long bone?

The ends of a developing long bone typically receive sets of metaphysial and epiphysial arteries. Epiphysial and metaphysial arteries are 'end arteries' because the cartilaginous plate is avascular and forms a barrier preventing communication between them (until epiphysial fusion). Interruption of blood supply from these arteries endangers the adjacent epiphysis or metaphysis (and may impair normal growth). Occasionally an interruption of blood supply may occur to a particular epiphysis, resulting in death of bone (necrosis).

Epiphyseal Growth Plate (disk)

The epiphysial (growth) plate is a plate of hyaline cartilage in the epiphysis, between the epiphysis and the metaphysis. The epiphysial plate produces new bone at its metaphysial surface (where it is supplied by metaphysial arteries). Growth in length therefore occurs at the metaphysial surface of a epiphysial plate. The epiphysial plate disappears (along with the capacity for growth in length at this site) when the epiphysis fuses with the metaphysis. Fusion occurs after the commencement of adolescence (females generally at an earlier age than males). Although epiphyses at different sites tend to fuse at different times, the vast majority have fused by the end of adolescence.

Primary Ossification Centre

The primary ossification centre commences near the diaphysis, then extends along it to reach the metaphysis. Ossification commences at a primary centre. This generally occurs in the middle of each cartilage (or membranous) model. At about the 8th week hyaline cartilage starts being transformed into bone at primary centres (those for the larger bones tending to appear first). By birth the vast majority of primary centres have appeared (except for the short bones in the hand and most of those in the foot). Unlike cartilage, bone requires a blood supply as the calcified matrix does not allow diffusion. In addition, a blood supply is required to transform cartilage to bone. Blood vessels (branches off nutrient artery and tributaries of nutrient vein) invade the primary centre together with cells that subsequently form bone (osteoblasts).

What arteries supply the shaft of a long bone and what is the effect of removing the periosteum?

The shaft of a long bone receives a single large nutrient (medullary) artery via a nutrient foramen extending obliquely to the medullary cavity (directed away from the growing end) to supply the bone marrow and inner compact bone. It divides into superior and inferior medullary branches (directed towards both ends). The shaft of a long bone also receives multiple small periosteal arteries that supply the periosteum and outer compact bone. Although these arteries link with branches of the nutrient artery, extensive stripping of the periosteum (eg. during surgery) may deprive directly underlying compact bone of blood supply.

What are the two major types of epiphyses?

The two major types of epiphyses are 'pressure' and 'traction' epiphyses. Pressure epiphyses are associated with joints. They enable growth of the apposed articular surfaces while being subjected to compression. Traction epiphyses associated with bony prominences enable growth where strong attachments pull on them.

By what process do most bones ossify?

The vast majority of bones develop from a hyaline cartilage precursor, by intracartilaginous (endochondral) ossification where a cartilage model is progressively replaced by bone.

Ossification

process of bone formation during which cartilage is replaced by bone

When do bones first appear in the human foetus?

they say 6-8 weeks of intrauterine life