Bone Flashcards
Describe the functions of bone
o Mechanical - Support and attachment for muscles, tendons, ligaments and joints.
o Protective - Protects internal organs
o Metabolic -Mineral reservoir for calcium and phosphate homeostasis
o Haematopoiesis - Support blood formation
Describe the development of bone as the result of endochondral or intramembranous ossification
Endochondral Ossification
• Bone forms as cartilage first during 3rd month of development
• Blood vessels and osteogenic cells invade the cartilage framework.
• The cartilage remains as growth plates (1o cartilaginous joint), in long growing bones
• Growth plates fuse (at approx. 18 in females, 21 in males)
Intramembranous Ossification
• Bone forms as a fibrous plate
• Bone cells differentiate from fibroblasts and haemopoietic precursors.
• No cartilaginous phase!
Where does haematopoiesis take place in bones?
Cancellous (trabecular) bone is highly vascularised and frequently contains red bone marrow where haematopoiesis, the production of blood cells, occurs.
Describe the composition of bone
Bone is composed of: o Water (20%) o Protein (35%) • Collagen type I (Provides toughness) • Growth factor proteins • Other organic matrix proteins o Minerals • Hydroxyapatite (Provides rigidity)
Describe the gross anatomy of bones
• Compact bone/cortical bone
• Spongy (trabecular/cancellous) bone
• Blood vessels - in trabecular bone
• Medullary cavity
• Bone marrow – site of haemopoiesis and fat storage, in medullary cavity
• Membranes
– Periosteum - a dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints
– Endosteum - a thin vascular membrane of connective tissue that lines the surface of the bony tissue that forms the medullary cavity of long bones.
What is the fundamental functional unit of cortical bone
The osteon or haversian system is the fundamental functional unit of much compact bone.
Each osteon consists of concentric layers, or lamellae, of compact bone tissue that surround a central canal, the Haversian canal, and is surrounded by the cement line.
Describe the 6 main types of bone, giving examples of each
Long - femur, humerus Short - phalanges, metatarsals Flat - scapula, ribs, sternum Sesamoid - patella Irregular - patella, vertebrae, carpals, tarsals Sutural - in cranium
Recognise that bone is composed of cortical and trabecular elements.
The epiphyses of long bones are composed of trabecular (spongey) bone.
This acts as a softer interface at joints.
The diaphysis of long bones is made up of cortical bone. This bone is denser and is arranged into Haversian Systems, from the way the collagen molecules form fibrils, which then form fibres and finally, sheets.
This structure gives the bone its strength.
Describe the cells involved in bone maintenance and renewal and their functions.
Osteoclasts are the bone resorbing cells. They are derived from a haemopoietic lineage.
Osteoblasts are responsible for laying down more bone. These come from a mesenchymal lineage.
Bones are constantly monitored and remodelled to keep them at peak strength. Osteoclasts will absorb any area of bone that has been damaged, and then osteoblasts will lay down new bone in the same area.
Osteocytes are derived from the differentiation of Osteoblasts. They act as sensors of mechanical pressure and damage.
Describe the lineage of osteoblasts and osteoclasts
Osteoblasts - mesenchymal
Osteoclast - haematopoietic
Osteocytes - derived from differentiated osteoblasts
Their differentiation is regulated by specific regulatory molecules.
