Session 7: Bones, bone marrow, blood & blood vessels Flashcards
Describe the bones of the axial and appendicular skeleton
- 206 bones in total => 80 are axial and 126 are appendicular
- axial = skull, laryngeal skeleton, vertebral column & thoracic cage.
- appendicular = bones that attach to axial skeleton eg bones of shoulder, pelvis & limbs
What are the 2 types of bones?
Cancellous and compact/cortical bone
What is cancellous bone?
- Sponge-like tissue inside bones
- Forms networks of trabeculae (fine bony columns/plates)
- Spaces between trabeculae are filled with bone marrow
What is compact/cortical bone?
Hard outer bone
What are osteoblasts, and what do they do?
Cells derived from mesenchymal stem cells.
They form new bone by laying bone tissue.
How do osteoblasts turn into osteocytes?
Once the osteblasts has surrounded itself with bone matrix, it becomes trapped in lacuna and becomes and osteocyte.
What are osteocytes and what do they do?
They are mature bone cells formed from osteoblasts that maintain bone.
Due to restrictive space, they cannot produce bone tissue
What are the types of cells found in bone?
Osteoblasts, osteocytes, osteoblasts and haematopoietic cells in bone marrow that produce RBCs
What are osteoclasts? What do they do?
- Originate from haematopoietic stem cells
- They break down bone tissue through the release of acid to release hydroxyapatite crystals and collagenase.
- Remodel bone & regulate Ca2+ in blood
What processes is bone formed?
Endochondral ossification and intramembranous ossification
Describe the process of endochondral ossification.
- Produces long bones from a cartilage template
- Continued lengthening is by ossification at epiphyseal plates
- Appositional growth => growth at edges, increases bone width
How do long bones develop?
Long bones require cartilage template to develop by endochondral ossification
Describe the process of intra-membranous ossification.
- Formation of bone from clusters of mesenchymal stem cells in the centre of bone (trabecular of cancellous bone)
- Interstitial growth = growth in the middle, outwards which increases bone length
- Flat bone develops directly from mesenchymal tissue.
What is appositional growth?
Growing at the edges to increase bone width
What is interstitial growth?
Growth in the middle, outwards to increase bone length
Describe in 5 steps how bone trabeculae is formed.
- Osteoblast lays down bone tissue around itself
- Once surrounded by bone tissue, it becomes trapped within bone tissue and turns into osteocyte.
- Cement line = where new bone meets existing bone, more mineral is added so becomes bone and cement line moves
- Hydroxyapatite is deposited
- Osteoclasts resorbs (break down)
What are calcium crystals called?
Hydroxyapatite crystals
Describe the conversion of cancellous bone to cortical bone in 5 steps.
- Mesenchymal cells convert osteoblast that line recently formed trabeculae
- Lay down bone tissue that is mineralised
- Osteoblats trapped => forms into osteocytes
- Steps 1-3 are repeated
- Central mesenchymal cells convert into blood, & lymph vessels and nerves
What is ECM made up of?
Collagen 1, proteoglycans and glycoprotiens
What is the difference in structure between cancellous/cortical bone and cancellous bone?
Cortical/compact bone has Haversian and Volkmann’s canals whilst cancellous does not.
Describe the structure of cortical/compact bone.
Made up of packed osteons which are made up of Haversian canal and Volkmann’sc canal.
Carry blood vessels, lymphatic vells and nerves
What is the active form of Vitamin D called?
Calcitriol
What does Vitamin D3 (calcitriol) deficiency lead to?
Less calcium is absorbed in the small intestine.
Less calcium absorbed means bones are less dense & strong
How does reduced Ca2+ absorption lead to increased bone resorption and decreased bone mass?
- Due to low levels of Ca2+ parathyroid hormone (PTH) will continue to be released (until [Ca2+] is high again).
- PTH stimulates bone resorption.
- Increased and continuous PTH production and release increases bone resorption which leads to decrease bone mass and increased risk of fracture & breakage.
What occurs in osteogenesis imperfecta?
- Mutation in COL1A gene
- Incorrect synthesis of collagen 1 fibres during ossification
- Bones are weak and brittle and are at high risk of fracture.
Which age range does osteogenesis imperfecta occur in? How does it present
Mainly affects neonates & children
Presents as shortened height and stature
What is the difference between rickets and osteomalacia?
Rickets affects children whilst osteomalacia affects adults.
What causes rickets?
Vitamin D deficiency causing weakened bone development
How do patients with rickets present?
- Soft bones
- Shortened height stature
- Painful to walk
- Bowed legs
What causes osteomalacia?
Vitamin D deficiency => lower mineralisation (no or little hydroxyapatite => increased osteoid
What causes increased calcium resorption in osteomalacia?
- Kidney disease (kidney activates vitamin D so disease impairs ability)
- Protection from sunlight (reduced sunlight uptake = less vitamin D)
- Surgery of stomach or intestines (where Vitamin D is absorbed)
- Drugs - phenytoin prevents vitamin D absorption
- Low vitamin D/calcium-rich foods uptake in the diet => less Ca2+ absorbed -> increased bone resoption = weak & damaged bones
What is osteoporosis?
- Loss of bone matrix/tissue
- Loss of structural density & mineralisation
- Compression fractures
- Shortened stature
- Incomplete filling of osteoclasts resorption bays
What are the RFs for Type 1 primary osteoporosis?
- Postmenopausal women - reduced oestrogen causes increased osteoclast activity
What are the RFs for Type 2 osteoporosis?
- older men and women due to loss of osteoblasts function
- loss of oestrogen AND androgen
What are general RFs for osteoporosis?
- Insufficient calcium intake
- Lack of exercise - immobilisation of bone leads to accelerate bone loss, exercise maintains bone mass
- Smoking
What is achondroplasia?
- An inherited mutation in FGF3 receptor gene.
- FGF3 promotes collagen formation from cartilage => endochondral ossification is affected bu intra-membranous ossification is not affected
How does achondroplasia present?
- Short stature but normal-sized head & torso (flat bones unaffected)
- Long bones cannot lengthen properly due to impaired endochondral ossification
What are the 5 types of bones?
Long, short, flat, irregular and sesamoid
Describe long bones. What is their function?
- Longer than wide, appendicular skeleton including the femur and smaller bones of the finger.
- Function: support the weight of the body and facilitate movement
Describe short bones and their function.
As long as they are wide. Eg wrist and ankle joints
Function: provide stability and some movement\
Describe flat bones and their function.
Flattened and roughly parallel opposite edges. Eg in skull, thoracic cage (sternum and ribs) and pelvis (ilium)
Function = protects internal organs and provides large areas of attachment for muscles
Describe irregular bones and their function.
Vary in shape and structure, complex shape.
Functions = Protect internal organs, vertebrae, vertebral column, protect spinal cord, protects pelvis & important anchor points for muscle groups
Describe sesamoid bones and their function.
- Small, round bones in tendons, knees and feet eg patella
Function: Protects tendons from stress and damage from repeated wear and tear
Where is bone marrow found?
Between trabeculae in cancellous bone
Describe red marrow.
- Rich blood supply
- Full of developing blood cells
- Only found in spongy bone
Function is to replenish cells in the blood (haemopoiesis)
Describe yellow marrow.
- Full of adipocytes
- Poor blood supply
Function is to act as shock absorber & energy source. It can convert to red marrow.
Where is bone marrow found?
Ribs, vertebrae, sternum and bones of pelvis
