Lecture 13 & 14 - Bone & Bone Marrow Flashcards
What are some bone functions?
- Protect important/delicate tissues
- Hemopoiesis
- Mineral storage (Ca and Phosphate)
Desc. the structure of cancellous (spongy) and compact bone
Cancellous:
- Network of fine bony columns (trabeculae)
- Spaces filled w bone marrow
- Osteocytes trapped within lacunae
Compact:
- Form external surfaces
What are the types of ossification?
- Endochondral ossification: Formation of long bones from cartilage at epiphyseal plates
[appositional (at edges) growth] - Intra-membranous ossification: Formation of bone from mesenchymal stem cells in centre of cancellous bone (trabecular)
[interstitial (middle) growth]
Desc. the bone formation in utero
- Flat bone develops directly from mesenchymal tissue by intra-membranous ossification
[Skull, jaw, scapula] - Long bones require cartilage template develop by endochondral ossification
[femur, humerus]
Desc. intramembranous ossification in parietal (irregular bone of the skull) bone
- Mineral deposits within trabeculae radiate outwards from a central point
State function of
- Osteoblasts
- Osteocyte
- Periosteum
- Osteo clasts
- Osteoblasts: Synthesise bone, lay down osteoid
- Osteocyte: Osteoblasts trapped in extracellular matrix. Canaliculi supply nutrients
- Periosteum: Attached to bone by collagen fibres known as Sharpey’s fibres. Outer layer contain fibroblasts, inner layer is MSC (diff. to form osteoblasts)
[form most outer layer of bone] - Osteoclasts: Resorption of bone –> initiate bone remodelling
How to identify osteoclasts?
- Function is bone resorption
- Lie in a depression and has multiple nuclei
How does cancellous bone turn into cortical (dense) bone?
*X in ILO
- MSC converts into osteoblasts
- Lays down osteoid that is mineralised
- Osteoblasts gets trapped- osteocyte
- Form lamellae
- Central MSC turn into blood vessels, lymph vessels and nerves
What is the function of Volkmann’s canals?
- Connect osteon to osteon
Diff. btw immature and mature bone is?
- Immature bone osteocytes is in random arrangement, mature is arranged in lamellae of osteons
What are the starting points for bone remodelling?
Resorption canal (centre)
Diff of mature bone structure in compact and cancellous bone
- Compact: Haversian canal (blood vessel, lymph vessel and nerves), Volkmann’s canal (osteon to osteon)
[found in medullary /diaphysis region] - Spongy: No Harversian/Volkmann’s canals, osteoclasts at edge
[found in epiphysis, edge]
Where does bone strength come from?
- Great tensile strength from cortical bone
lamellae are able to slip to resist fracture
What are the steps in bone remodelling (yellow slide) and what triggers it?
- Steps:
1. Osteoclasts make wide tunnel (cutting cone)
2. Osteoblasts make small tunnel (closing cone) - Exercise stimulates bone remodelling
What is osteoid?
- Laid down by osteoblasts
- Unmineralized bone (90% collagen, 10% ground substance)
NOT BONE!!
What are the factors that affect bone stability?
- Activity of osteocytes:
- Can act like osteoblasts and lay down osteoid in lacunae
- Can act like osteoclasts and degrade bone (osteocytic osteolysis), ⬆️by PTH - Activity of osteoblasts (main):
- Stimulated by calcitonin (via IGF-1), oestrogen, testosterone, thyroid hormone, vit A - Activity of osteoclasts (main):
- ⬆️by PTH, release Ca2+ into bone
- Calcitonin inhibit PTH at PTH receptor - Nutrition:
- Vit D3 produces calcitriol (calcium absorption)
- Vit C: synthesis of collagen
- Vit K and B12: synthesis of bone proteins
What is osteogenesis imperfecta? Symptoms? Who does it usually affect?
- Mutation in COL1A gene, autosomal dominant
- Abnormal collagen 1 formed
- Symptoms: short stature, weak bones (⬆️fracture), blue sclera
- Mainly affects neonates and children
What is rickets? Caused by what? Symptoms?
- Mainly affects children
- Vit D deficiency –> poor Ca mobilisation and ineffective mineralisation of collagen 1
- Leads to weakened bone dev., short stature, waddling gait
What is osteomalacia? Caused by what? Symptoms?
- Rickets in adults
- Vit D deficiency –> lower mineralisation and increase osteoids
- Increased calcium resorption
- Occurs in Vit D & Ca deficiency, women cover up skin, pregnant women, phenytoin (drugs) prevent vit D absorption
What are the types of osteoporosis? Caused by what?
Primary:
Type 1
- Postmenopausal women (⬇️oestrogen –> ⬇️stimulation of osteoblasts to lay down osteoid, osteoclasts activity greater)
- Due to ⬆️osteoclasts
Type 2
- Older men and women
- Loss of osteoblast func (senile osteo.)
- Loss of oestrogen & androgen
- Incomplete filling of osteoclast resorption
Secondary:
- Due to drug therapy (corticosteroids)
- Due to malnutrition, prolonged immobilisation (affect bone remodelling)
- Due to metabolic bone disease (hyperparathyroidism)
Risk factors of osteoporosis are
- Insufficient Ca intake (recommended 700mg/day)
- Reduce exercise: maintain bone mass
- Smoking
What is achondroplasia? Results in what
- Autosomal dominant inheritance in FGF3 (fibroblast growth factor) receptor gene
- FGF promotes collagen formation from cartilage (endochondral ossification affected)
- Results in short stature (normal size head & torso), long bones X lengthen properly
Structure, example and function of long bones
- Longer than wide
- Eg: Femur, humerus, radius, tibia, metacarpal (hand), metatarsal (feet), phalanges (fingers n toes)
- Located mostly appendicular skeleton
- Func: Support weight of body & facilitate movement
Structure, example and function of short bones
- Length = width
- Eg: Carpals & tarsals (wrist and ankle joints)
- Provide stability & movement
Structure, example and function of flat bones
- Flattened
- Eg: Skull (cranial bones), thoracic cage (sternum and ribs), pelvis, scapula
- Protect internal organs, large area of attachment for muscles
Structure, example and function of irregular bones
- Vary in shape and structure
- E.g vertebrae and sacrum (pelvis)
- Protect internal organs, vertebrae protect spinal cord, provide anchor points for muscle
Structure, example and function of sesamoid bones
- Embedded in tendon
- E.g patella (develop after birth, when start walking)
- Protect tendon from stress and dmg (wear and tear)
Desc 2 types of marrow in spongy bone
Red marrow:
- Rich blood supply
- Hemopoiesis
Yellow marrow:
- Adipocytes (shock absorber, insulation, energy reserve, can convert to red marrow)
- Poor blood supply
How do maturing cells leave the bone?
- Through sinusoids: endothelial cell fenestrations
- Platelets: megakaryocytes released fragments of cells through apocrine secretion directly into blood
How is the flow in capillaries controlled? What function?
- Controlled by precapillary sphincters
- Controls fluid exchange btw capillaries and body tissues, large cells X pass thru
Define vein. Desc 3 layers and features
- Vein: Transport blood from body tissue to heart
- Tunica intima (endothelium), media (smooth muscle & elastic fibre), externa (elastic fibrous capsule)
- Has fibroelastic cartilaginous valves
- Pump blood under low pressure and against gravity
Desc vein type
- Pulmonary
- Systemic
- Superficial
- Deep
- Oxygenated blood from lungs to left atrium
- De-oxy from body to right atrium
- Close to surface of skin
- Deep btw tissue
*venules smallest vein, inferior vena cava biggest
Define artery. Desc 3 layers and features
- Blood away from heart
- Tunica intima (elastic membrane, non-fenestrated endothelium), media (thick smooth muscle, elastic fibres), adventitia/externa (collagen and elastic fibres: allow artery to stretch but prevents overexpansion)
- Small lumen
What are collateral blood vessels?
*sometimes referred to as communicating blood vessels
- Arteries formed when there is blockage to provide alternative path for arterial blood
- Generated due to ischaemia (reduced blood flow)
What is structure and function of pericyte?
not in ILO
Structure:
- Immature ‘smooth-muscle like’ cell
- Key component of capillaries
- Contractile properties
- Blood-brain barrier
Function:
- Differentiate into endothelial cell
- Mantain tight capillaries
How long does it take for RBC to mature upon entering general blood circulation?
1-2 days
Where would osteoprogenitor cells usually be found?
In periosteum–> diff into osteoblasts at external surface
What component of bone impedes distribution of nutrients to osteocytes?
- Extracellular matrix
- Canaliculi supply
Desc hypertension effect on each layer of artery/vein
- Intima: artherosclerotic plaque formation, reduce lumen size
- Media: hypertrophy of smooth muscle cell (become larger)
- Externa: dmg extracellular matrix –> become larger/allow artery to stretch prevent over
