Locomotor - bone and the skeleton Flashcards
What is bone?
Osseous living tissue containing specialised cells and a matrix of:
- 60% mineral salts (hydroxyapetite)
-35% collagen (type I)
- 4% water
-1% proteoglycan
What are the functions of bone?
Housing stem cells (bone marrow)
Provide structural support and locomotion
Acting as a reservoir of minerals
Providing protection of underlying structures
Bufferin excessive pH changes in the blood
Production of blood cells
Regulating electrolyte body balance (Ca and P ions)
What classifies a long bone?
Classified as longer than it is wide, adapted to work as a lever.
What is the end of the long bone?
Called an epiphysis.
Rounded and covered with articular cartilage, which sits on top of subcondral bone and below a layer of cortical bone.
This is supplied by red bone marrow.
What is the middle of the long bone?
Called the diaphysis.
Formed of cortical bone surrounding a medullary cavity. It is filled with yellow bone marrow and has own blood supply via vessels through the nutrient foramen.
What is the metaphysis?
Between the diaphysis and epiphysis. Where the epiphyseal plate sits.
What makes up the medullary cavity?
Lined by the endosteum - single layer of cells
Is osteogenic and osteolytic.
What covers the outside of the bone?
Periosteum covers it. 2-layers for protection and site of sensory nerves, blood and lymphatic vessels.
What are short/irregular bones?
Short - same width and length
Irregular - complex shapes
No medullary cavity
Develop from single site of ossification
What are flat bones?
Thin and broad bones found where extensive organ protection is required or broad surface for muscle attachment.
No medullary cavity
2 layers of bone surrounding air or trabecular
Whats an example of long bones?
Arm bones
-humerus, ulna, radius, metacarpals and phalanges
Leg bones
-femur, tibia, fibia, metatarsals and phalanges
What are examples of short bones?
Tarsals, carpals and patella
What are examples of irregular bones?
Vertebrae, sacrum (middle of the pelvis where joins vertebrae), coccyx and some bones of the skull
What are examples of flat bones?
Thoracic cage
Pectoral girdle (scapular, collar bones and ribs)
Pelvis (ilium, iscium and pubis)
Some skull bones
What are examples of sesamoid bone?
Patella bone
Bones near joins in knees, hands and feet
What is the blood supply of bones?
Cortical - well vascularised via arteries that enter the bone via nutrient foramen in the diaphysis. Supply the calcified cartilage.
Travels horizontally via Volksmann canals and vertically via Haversian canals.
What are osteons?
Layers of lamella bone and osteocytes around the blood vessels.
What is lamella formed of?
Cortical bone (type I collagen), twists in opposite directions,
What gives lamella its strength?
Collagen orientation
-Transverse: compression
-Longitudinal: tension
Structural integrity gives some reisitance to twisting
What are the two types of bones formed?
Lamella - regular, strong bone slowly produced during growth/remodelling
Woven bone - weak, irregular bone, produced rapidly in early life/healing. It’s gradually replaced by lamella bone.
What are osteoblasts?
They form bone matrix (osteogenic activity).
Cuboidal cells found in periosteum secrete osteoid which becomes bone matrix/osteocytes when trapped
What are osteocytes?
Formed bone matrix, maintain bone structure and influenced by environment. Important with:
-Maintenance of local matrix and acts as mechanoreceptors
-Resorb material during passive bone resorption and Ca/O homeostasis
-Communicate between osteocytes and osteoblasts
What are osteoclasts?
Absorb bone matrix via enzymes and hydrogen ions. Look like large multinucleated cells. Originate from haematopoietic tissue.
What is endochrondrial ossification?
- Bone is formed onto a temporary cartilage model
- The model grows (zones of proliferation), then chondrocytes mature and hypertrophy, and growing cartilage model calcifies
- As this happens chrondrocytes start to die. Fragmented calcified matrix left behind acts as structural framework
- Blood vessels and chrondrocytes invade and osteoblasts lay down bone matrix
In foetus the primary ossification centre forms in diaphysis and a secondary in epiphysis. All replaced by cartilage, except epiphyseal plate which stays open till maturity.
How do the chondrocytes develop?
Proliferation > Maturation > Growth > Death
Limited supply
What is intramembranous ossification?
Direct formation of bones within the mesenchyme by direct osteoblast differentation.
No cartilage template
Examples are flat bones
How do bones grow in width?
Osteoblasts on periosteum grow outwards
Osteoclasts on endosteum maintain medullary cavity
What is bone modelling?
The bone shape changing in response to the loads imposed on it.
Wolff’s Law - bones adapt based on stress and demands placed on it
What is bone re-modelling?
The lifelong cyclical process of bone addition and removal to maintain the structure by repairing microdamage and mineral homeostasis (e.g. exercise).
