Bone Structure And Function Flashcards
5 functions of bones are:
Structural function
Mobility and strength
Support- ligaments and muscles can attach to them
Protection- of internal organs
Production and storage of minerals like calcium and phosphates
Other points:
Posture
Produces blood cells in red bone marrow at ends of bones
Produces and stores fats in yellow bone marrow in shafts
Typical long bone key points
Proximal and distal epiphysis covered in articular cartilage
Epiphysis area has the spongy / trabecular bone
Diaphysis area is the shaft of bone covered in compact / cortical bone
Hole in middle of diaphysis is medullary cavity, containing blood vessels and bone marrow and connective tissue and endosteum layer is covered in osteoprogenitor cells
Nutrient artery in nutrient foramen
Metaphysis adjoins diaphysis to epiphysis. Metaphysis separates epiphyseal plates which fully grown - become epiphyseal line
Periosteum layer covers all of long bone except cartilage.
Outer layer is dense irregular CT + enables attachment of ligaments and tendons
Inner layer has osteoprogenitor cells
BONE AS CONNECTIVE TISSUE
Bone is firm and slightly flexible
Matrix is collagen fibres and ground substance
Resists hard and compressive forces but has some give
Bone is :
25% water
25% collagen
50% crystallised mineral salts like calcium hydroxyapatite
Hard but brittle
Light per unit volume
Possess 4 types of cells: Osteoprogenitor Osteocytes Osteoblasts Osteoclasts
What are two types of Osseous tissue?
Compact / cortical bone
Spongy/ trabecular/ cancellous bone
COMPACT TISSUE
80% of total bone mass Solid hard layer on all bones External layer of all long bones Gives bones strength Withstands pressure vertically but not laterally/ transverse
SPONGY BONE
20% of total bone mass
Found within epiphysis of long bones and inner parts of axial skeleton
Honeycomb network
Lightness to bones
Good at shock absorption (redistributes pressures and stresses in a number of directions)
COMPACT BONE MORE DETAIL
Denser and less flexible
Osteon = concentric lamellae rings of calcified matrix around vertically oriented vessels. Can be called Haversian systems too.
Many osteons along diaphysis
Compact bone withstands great pressure vertically.
Osteons keep bones hard and receive nutrients from body and waste disposal.
Between osteons there is more lamellae.
Separating lamellae is lacunae (small depression in the bone)- has extracellular fluid and osteocytes.
Osteocytes =mature bone cells. Osteoblasts laid down the collagen fibres into cross cross formation, get trapped then turn into osteocytes.
Osteocytes in lacunae have canaliculi (projections) to connect to osteocytes in other lacunae about what must happen.
What is an osteon?
Functional unit of compact bone with collagen fibres laid down into rings of concentric lamellae and in criss cross formation with vertical blood vessels
What is osteocytes?
Osteocytes is mature bone cell that has canaliculi to connect to other osteocytes
What is osteoblast?
Cells which lay down new bone tissue into concentric rings of lamellae
What is lacuna?
Depression within a bone containing extracellular fluid and osteocytes
Canaliculus
Projection from one osteocytes to another to communicate and receive nutrients and remove waste
Spongy / trabecular bone
Found in epiphysis and in axial skeleton like rib, skull and in between vertebrae
Osteoblasts lay down collagen fibres along lines of stress
Lattice like
Light
Spongy bone deals with stresses in different directions and gives strength
Stress can be transferred in many projections
Holes in spongy bone makes it light, although they do contain blood vessels, red bone marrow and extracellular fluid.
Osteocytes in lacunae on surface of trabeculae and nutrients pass through canaliculi projections.
Spongy bone - converts to compact bone by osteoblasts
OSTEOPROGENITOR CELLS
Undifferentiated cells
Make new bone when required
When stimulated they divide and daughter cells are osteoblasts
Found in endosteum and inner layer of periosteum
OSTEOBLASTS
Came from osteoprogenitor cells
Build matrix and collagen fibres.
Cannot divide
Build a system of bone and get trapped within it. They become osteocytes.
Found on surface of bone as osteoblasts + sit in lacunae once they are osteocytes
OSTEOCYTES
In lacunae as mature bone cells
Maintain bone via communication
Canaliculi projections
Communication about nutrients within blood
Tells whether blasts or clasts need to perform more action
OSTEOCLASTS
Have ruffled border
Large and come from monocytes
Clear up bone + reabsorb the bone
Attach to surface of bone, create a seal then re,ease enzymes / acids to break down bone and reabsorb debris
Release minerals back into bloodstream eg, calcium
On surface of bone
Rate of clearing, reabsorption and release of minerals depends on instructions from osteocytes
Remodelling
Remodelling - coupling between osteoblast makingnew bone cell and osteoclast clearing
Uncoupling - one acts more than other
Eg osteoporosis (more osteoclast than blast activity)
Why we need to know?
Bones constantly remodelled in childhood and adolescence
Cell activity in bone , removal and replacement at same site is remodelling - needs coupling
How a bone gets longer
New cartilage produced on epiphyseal side of plate
Cartilage replaced and old cartilage converted into bone
Age 18-25, bone stops producing cartilage and collagen at growth plates and amount of bone to grow bones stops as well
Bones growth in width
Blood vessels in bones stimulates osteoblasts to produce more bone on surface of bones to make them wider.
So length = cartilage
Width= osteoblasts and blood vessel
Bone growth issues
LOP BB
Low bone density (osteoporosis) uncoupling
Osteogenesis imperfecta- genetic, low collagen production. Brittle bones + may fracture, may harm growth plates
Pagets disease of bone- Bone regeneration speeds up but not produced correctly so is weak
Bone cancer- metastatic (secondary cancer growth)
Bone infections- Trauma or surgery. Osteomyelitis, increased by recent fracture, injury or diabetes etc
Blood supply to bones
People Neevr Make Eggs
Periosteal arteries- through periosteum Volkmann’s canals. Supplies blood to osteons of compact bone (outer)
Nutrient artery- in nutrient foramen within diaphysis , supplies medullary cavity and inner compact bone
Metaphyseal arteries- enters through metaphysis to supply spongy bone and bone marrow
Epiphyseal arteries- through epiphyses + supplies spongy bone and bone marrow
Bone remodelling affected by:
Call Me A Hippy G
Calcium and phosphate levels
Mechanical stress
Age
Hormones
Genetics and environmental factors
AGE
Demineralisation of bones - 1% each year after 40
Women age 40-45 are worse (up to 8% per year), loss of oestrogen
HRT keep levels of oestrogen up and prevent osteoporosis
Osteoporosis
MECHANICAL STRESS
Weight bearing needed to develop and heal
Muscle pulls on bone, mechanical stress + bone remodels
Relate to weight bearing of patient
Lack of weightbearing reduces bone mineral density
12 weeks non weight bearing reduces bone min density by 1/2
Elderly may not get back to original bone density after fracture
Other factors
Black people= larger bone density
Asian people = bone density issues
Women more likely
Genetic factors
ENVIRONMENTAL=
Calcium deficiency: osteoblasts will receive info that not enough calcium so clasts break down bone to re,ease more calcium into blood - lose bone mineral density
Calcium also needed in blood clotting
800-1000 mg a day
After menopause: 1000-1200mg a day
Calcium:
Muscle contractions and heart beat
Strengthens bone and teeth
Clotting blood
Vitamins D and K absorb calcium
