Tissues + Structures - Bones Flashcards
What is bone?
Type of dense connective tissue with cells and fibres embedded in a calcified ground substance (bone matrix).
How do cells of bone receive nutrition?
Minute channels have been developed in bone matrix so that each osteocyte (bone cell) can receive nutritive substances.
What are bone canaliculi?
Microscopic canals between the lacunae of ossfied bone - osteocytes project into these canals.
What is a haversian canal?
Larger canal inside osteocyte in which canaliculi communicate to.
What happens during bone development?
Matrix is laid down in concentric layers (lamellae) around the capillaries.
What are volkmann’s canals?
Channels that run at right angles to the haversian canals and contain anastomosing vessels between haversian capillaries.
What are the two macroscopic forms of bone?
- Compact.
- Cancellous.
What is compact bone?
Hard and dense bone. Resembles ivory. True ivory is dentine.
What is cancellous bone?
Sponge-work of traveculae that is arranged in a real pattern best adapted to resist the local strains and stresses.
What is the moulding of bone?
Resorption of existing bone by phagocytic osteoclasts and deposition of new bone by osteoblasts.
Is there microscopic difference between the two types of bone?
No difference.
What type are long bones?
Cancellous - spongy.
What do cancellous bones contain?
Marrow - red or yellow.
What sort of marrow do we have at birth?
Predominantly red marrow - active haemopoiesis. As we get older red marrow is replaced by fatty yellow marrow (red marrow atrophies).
Where is red marrow found in adults?
Axial bones.
Where is yellow marrow found in adults?
Limb bones.
What is periosteum?
Thick layer of fibrous tissue that covers the outer layer of bone particularly where the blood vessels run.
Is the periosteum osteogenic?
Yes - the periosteum can basically create new bone. Its deeper cells can differentiate into osteoblasts when required.
What is the deeper layer of periosteum known as?
Osteogenic layer.
Where does new bone occur?
Under the periosteum.
How does periosteum connect to underlying bone?
Sharpey’s fibres.
Where will you see sharpey’s fibres strongly?
Over the attachments of tendons and ligaments.
Where does perisotuem not cover?
Articulating surfaces of the bones in synovial joints - it is reflected from the articular marjins to join the capsule of the joint.
What is endosteum?
Single-layer that lines inner bone surfaces (marrow cavity and vascular canals).
What does endosteum do?
Endosteum is osteogenic and is the main contributor to making new bones.
What are osteogenic cells also known as?
Osteochondrogenic.
What is the difference between osteogenic and osteochondrogenic?
- Osteogenic = cells seen in well vascularised bone.
- Osteochondrogenic = cells seen in avascularised bone, they don’t produce new bone but produce hyaline cartilage.
What is the fracture callus?
Fracture site + mass of inflammatory tissue and bone forming cells.
What nerves supply subcutaneous periosteum?
Nerves of overlying skin.
What nerves supply deeper periosteum layers?
Motor branches to nearby muscles.
What is the arterial supply of the shafts of the long bone?
Branches from the periosteum, especially numerous beneath muscular and ligamentous attachments.
What supplies the epiphysis?
Circulus vasculosus of the joint.
What are veins like in cancellous red marrow bones?
Large.
What are veins like in compact bone?
They run with the arteries in volkmann’s canal.
How does bone develop?
Two processes:
1. Intramembranous ossification.
2. Endochondral ossification - cartilage.
Where does each ossification occur?
- Intramembranous - bones of the vault of the skull, face, clavicle.
- Endochondral - long bones of the skeleton.
What happens in intramembranous ossification?
Osteoblasts lay down bone in fibrous tissue. No cartialge precursor. Growth of thickness of other bones (subperiosteal ossification) is also by intramembranous ossification.
What happens in endochondral ossification?
Pre existing hyaline cartilage of model is destroyed AND replaced by bone.
In endochondral ossification what cells destroy bone?
Osteoclasts.
In endochondral ossification what cells replace bone?
Osteoblasts.
When does endochondral ossification occur?
During years of growth - constant. It occurs even if the original bone was made endochondral or intramembranous. It also occurs in the callus of fracture sites.
What is the primary centre of ossification?
The site where bone first forms.
Where is the primary centre of ossification in long bones?
Centre of the shaft = diaphysis.
When does the diaphysis first occur?
8th week of pregnancy (intra-uterine life).
What are the end of the bones called?
Epiphyses.
What happens to the epiphyses (end of the bones) in terms of ossification?
They are cartilaginous and start the process of ossification much later, normally after birth. Hence why you can still see epiphyseal plate of cartilage in XRAYS.
What is secondary cartilage?
Cartilage that develops in certain membrane bones e.g. head of mandible and ends of clavicle. They are ossified in membrane.
What covers the articular surfaces of membrane bones?
Fibrocartilgae - identical with the intra-articular disc in structure. Between these bundles of tissue are many cells.
What is the difference between sencondary cartilage and hyaline cartilage?
The cells in secondary cartilage are larger and more tightly packed and the matrix is more fibrous.
What is the purpose of secondary cartilage?
To provide a cartilage surface for membrane bones that would otherwise not have any cartilaginous ends.
What is a sesamoid bone?
Bone that is small and is embedded with a tenon or muscle.
Where do you find sesamoid bones?
Certain tendons where they glide over adjacent bone e.g. patella, tendons of flexor pollicis brevis in hand and feet.
What are the type of sesamoid bones?
- Fibrous.
- Cartilaginous.
- Bony nodules.
- Mixture of the above.
What is the purpose of sesamoid bones?
No reason.
