Bone cells, types and processes Flashcards
How does bone differ from other CT?
Calcium phosphate (CaPO4), sometimes called hydroxyapatite, which mineralises the extracellular matrix.
What gives bone its mechanical properties?
Calcium phosphate - great compressive strength
Collagen - great tensile strength to the bone
Describe osteoblasts?
Synthesise new bone - migrate over matrix and synthesise and deposit osteiod - matrix protein of bone
Major protein is collagen, contains smaller quantites of osteocalcin and osteopontin
Make bone by depositing calcium phosphate
Describe osteoclasts?
Multinucleate cells formed by fusion of progenitor cells of the monocyte/macrophage lineage
They move over the surface of the bone matrix and secrete acidic chemicals to dissolve it - this creates a pit on the surface of the cortical bone
Absorbs minerals - and thn releases them in the extracellular fluid
What is meant by resorption?
The process of bone breakdown and mineral uptake
What are osteocytes?
Trapped osteoblasts within the bone matrix
They are trapped within lacunae and become involved with signalling processes
Communicate with other osteocyctes via filipodia (projections) which extend through the canaliculi (microscopic canals between the lacunae of ossified bone) of the bone
Describe the distribution of bone within the adult human skeleton?
The adult human skeleton comprises 206 bones and within these there are 26 vertebrae, 64 bones in the upper limbs (32 each side) and 62 bones in the lower limbs. Many of these bones are contained within the hands and feet.
What is the axial skeleton?
The axial skeleton forms the longitudinal axis of the body
What is the appendicular skelton?
bones of the upper and lower limbs.
Describe the structure of a long bone
The diaphysis is the shaft of a long bone.
This flares out at each end into the metaphysis, which lies adjacent to the growth plate.
On the other side of the growth plate is the epiphysis. The articulating surfaces are covered with hyaline cartilage and the remainder of the bony surface is covered with periosteum.
The medullary cavity is lined with endosteum. The medullary cavity itself is full of red marrow in the child, which is actively involved in haematopoiesis, whereas in the adult there is a high fat content and the marrow appears yellow.
The nutrient artery supplies the marrow and enters the bone through a nutrient foramen, usually near the middle of the diaphysis.
Describe short bones?
As long as they are wide.
Located in the wrist (carpal) and ankle (tarsal) joints, short bones provide stability and, when working together, they facilitate a great range of movement
Describe flat bones?
The function of flat bones is to protect the internal organs such as the brain skull, heart (sternum and ribs), and pelvic organs (ilium, ischium, and pubis). Flat bones can also provide large areas of attachment for muscles.
Describe sesamoid bones?
Sesamoid bones are bones embedded in tendons and function to protect the tendons from stress and wear.
They also function to provide mechanical advantage to a muscle crossing a joint over a wide range of movement.
e.g. patella - provides mechanical advantage to the quadriceps.
Describe irregular bones?
Irregular bones vary in shape and structure and therefore do not fit into any other category (flat, short, long, or sesamoid).
They often have a complex shape, which helps protect internal organs. For example, the vertebrae protect the spinal cord.
Define processes ?
Processes are prominent projections of a bone. Processes may be divided into articulating or non-articulating.
What is a head process?
Rounded articular projection supported by a neck (e.g. head of humerus)
Describe the blood supply to bones?
Main supply is the nutrient artery which enters the diaphysis (shaft) of the bone
Also periosteal ateries which supply the periosteum (a dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints.) and the outer third of the cortex of the bone
Describe metaphyseal arteries and how their blood supply differs in children and adults?
Metaphyseal arteries are present in some bones (femur) - They enter at the site of attachment of the capsule
Children - metaphyseal arteries do not cross the growth plate meaning the secondary ossification centre in the epiphysis is completely dependant on the epiphyseal artery.
Adults - epiphysis fuses and an anastomosis (cross connection) formes between the epiphyseal and metaphyseal arteries
What is bone remodelling
Bone remodelling occurs in response to environmental factors (e.g. sustained application of a load) due to a change in the balance in activity between osteoblasts and osteoclasts.
