Lecture One - Bones Flashcards
Define the axial and appendicular skeleton.
The axial skeleton consists of the bones of the skull (cranium), vertebral comumn, ribs and sternum.
The appendicular skeleton consists of the bones of the upper and lower limbs.
Define cartalige.
Cartilage is an avasular form of connective tissue consisting of extracellular fibers embedded in a matrix that contains cells localized in small cavities.
In heavy weight baring areas or areas prone to pulling forces, the amount of collagen is greatly increased and the cartilage is almost inextensible. In contrast, areas which experience less stress contain smaller amounts of collagen and cartilage containing elastic fibres.
Cartilage is nourished by diffusion and has not blood vessels, lymphatics or nerves.
What are the functions of cartalige?
Support soft tissues.
Provide a smooth, gliding surface for bone articulations at joints.
Enable the development and growth of long bones.
What are the three types of cartilage?
Hyaline:
Most common, matrix contains a moderate amount of collagen fibers (e.g. articular surfaces on bones).
Elastic:
Matrix contains collages fibres along with a large number of elastic fibres (e.g. external ear).
Fibrocartilage:
Matrix contains a limited number of cells and ground substance amidst a substantial amount of collagen fibres (e.g. intervertebral discs).
Define bone.
Bone is calcified, living, connective tissue that forms the majority of the skeleton.
Consists of intercellular calcified matrix, which also contains collagen fibers, and several types of cells within the martix.
What are the functions of bone?
Supportive structures for the body.
Protectors of vital organs.
Reservoirs of calcium and phosphorus.
Levers on which muscles act to procuce movement.
Containers for blood producing cells.
Define compact and spoungy bone.
Compact, dense or cortical bone is dense bone that forms the outer shell of all bones and surrounds spongy bone.
Spongy or trabecular bone consists of spicules of bone enclosing cavities containing blood forming cells (marrow).
Between the meshes of the spongy bone is the bone marrow or medulla.
In the flat bones of the skull, the compact material is called the external and the internal laminae (compact bone), and in between them is the diploe (spongy bone).
What are the bones as classified by their shape?
Long bones and tubular (e.g. humerous, femur).
Short bones are cuboidal (e.g. bones int he wrist and ankle).
Flat bones consist of two compact bone plates separated by spongy bones (e.g. skull).
Irregular bones are bones with various shapes (e.g. bones of the face).
Sesamoid bones are round or oval bones that develope in tendons e.g. the knee cap).
What is the periostium?
The periosteum is a fibrous connective tissue membrane that covers all bones exept for the parts in the joints where articular cartilage is present.
The periostium can form new bone.
This membrane recieves blood vessels whoes branches supply the outer layers of compact bone. A bone stripped of its periosteum will not survive.
Describe how bones are vasculer and innervated.
Bones are vascular and are innervated.
Generally an adjacent artery gives off a nutrient artery, usually one per bone, that directly enters the internal cavity of the bone and supplies the marrow, spongy bone and inner layers of compact bone. Plus, all bones, except in the area of a joint where articular cartilage is present, are covered by the periosteum.
Nerves accompany the cessels that supply the bone and the periosteum.
Most of the nerves passing into the internal cavity with the nutrient artery are vasomotor fibers that regulate blood flow.
Bone itself has few sensory nerve fibers.
On the other hand, the periosteum is supplued with numberous sensory nerve fibers and is very sensitive to any type of injury.
How to bones form?
Bone formation (osteogensis) is based on the activity of osteoblasts, which are specialized mesenchymal cells. Osteoblasts secrete an intercellular substance, osteoid, which consists initially of soft ground substance and collagen fibers.
Osteoblases develop into osteocytes, the definitive bone cells.
At the same time multinucleated osteoclasts develop, these bone-degrading cells are associated with the absorption and remodeling of bone.
Intramembranous ossification (osteogenesis membranacea):
Development of bone from connective tissue. Connective tissue contains many mesenchymal cells that develop via osteoblasts into osteocytes. At the same time osteoclasts develope and collagen fibers also appear.
The original bone is membrane bone and is later remodeled into lamellar bone. The skull cap, the facial bones and the clavicles develop as intramembranous bones.
Chondral ossification (osteogenisis cartilaginea):
Requires preformed parts of skeletal cartilage, which will then become replaced by bone.
Growth is possible only as long as cartilage still remains. The prerequisit for repalcement bone formation is the presence of chondroclasts, these are differentiated conective tissue cells that degrade cartilage and thus anable the osteoblasts to form bone. Tw types of replacement bone formation are recognised - endochondral and perichondral ossification.
This is a helpful basic explination of ossification.
