Topic 3.2: Muscoloskeletal - Skeletal system and bones

functions of skeletal system - list (6)

1. Support -> structural framework for the body -> attachment point for tendons of muscles

2. Protection - > encloses visceral organs

3. Movement -> skeletal muscles attach to bone -> contraction pulls on bone to produce movement

4. Mineral homeostasis -> stores minerals like NaCl and Ca2+ which can be released into blood on demand

5. Blood cell production -> red bone marrow within bones produces RBCs

6. Triglyceride storage -> yellow bone marrow stores triglycerides

division of skeletal system (2)

axial → bones of head, neck and trunk (~80)

appendicular → bones of limbs including pectoral and pelvic girdle (~126)

composition of bone (4)

form of connective tissue → ECM surrounding widely separated cells

35% organic components -> eg. collagen

65% inorganic hydroxyapatites -> eg. calcium phosphate, calcium carbonate 

Composition allows bones to be strong and resilient -> minerals resist compression, collagen resists tension

compact bone - summary

dense and forms outer shell of all bones

Surrounds spongey bone or medullary cavity

Hollow pillars of bone matrix containing nerves and blood vessels

Composed of repeating structural units (osteons) -> consist of concentric lamellae arranged around central Haversian canal

Blood vessels and nerves = contained within Harversian canal

spongey bone - summary (5)

also called trabecular

always inside outer layer of compact bone

Not organised into osteons -> consist of lamellae which are arranged into thin lines (traveculae)

Organised into lines of compressive stress and tensile stress -> aligned to assist with weight bearing

Filled with red or yellow bone marrow as well as medullary cavity

periosteum - summary (2)

dense layer of vascular connective tissue that envelopes bones except at surface of joints

Attached to underlying bone via perforating fibres of collage -> extend into bone's extracellular matrix

general structure of bones (3)

compact bone sandwiching spongey bone

periosteum surrounding except at surface of joints

classifications of bones - list (4)

1. long bones

2. short bones

3. flat bones

4. irregular bones

classifications of bones - long bones (2 + examples)

longer than they are wide

bear a lot of weight

femur and humerus

classifications of bones - short bones (3 + examples)

similar width to length

stability and support with little movement

Sesamoid bones = special type that forms in a tendon

carpal bones of wrist

classifications of bones - flat bones (2 + examples)

thin, flattened usually a bit curved

protect vital organs and provide surfaces for large muscle attachment

sternum and skull bones

classifications of bones - irregular bones (1 + examples)

don’t fit into other categories because of complicated shapes

vertebrae

gross anatomy of long bones - left

proximal epiphysis

metaphysis

diaphysis

metaphysis

distal epiphysis

gross anatomy of long bones - top right

articular cartilage

spongey bone → red bone marrow

red bone marrow

epiphyseal line

gross anatomy of long bones - bottom right

compact bone

endosteum

nutrient artery

medullary cavity → contains yellow bone marrow in adults

periosteum

articular cartilage

main structural regions of long bones (3)

Diaphysis = shaft of long bone -> long axis of bone

Epiphysis = proximal and distal ends

Metaphysis = regions between epiphysis and diaphysis

main structural regions of long bones - metaphysis in adults vs children

epiphyseal growth plate of hyaline cartilage in growing bone

epiphyseal line in adults

anatomy of long bones - membranes (2)

periosteum → outer double-layer fibrous covering entire surface except at joints

endosteum → thin membrane that lines medullary cavity, internal bone surfaces, trabecular and canals of compact bones

anatomy of long bones - vasculature (2)

Marrow cavity (medullary) = hollow space within diaphysis that contains yellow (fat) marrow and blood vessels

Nutrient artery = located outside of periosteum but heads into centre of bone towards medullary cavity

anatomy of long bones - articular cartilage def

hyaline cartilage covering the joint surface

blood supply of bone tissue and periosteum (3)

Periosteal arteries supply periosteum and outer compact bone -> enters through many small canals and perforates into compact bone

Nutrient artery enters via nutrient foramen at centre of diaphysis -> enters medullary cavity, courses

Ends of long bone = supplied by epiphyseal and metaphyseal arteries

nerves of bone tissue and periosteum

nerves accompany blood vessels

veins carry blood away from bone and accompany arteries → rich sensory nerve supply to periosteum

very sensitive to tearing and tension

bone growth and remodelling cells (2)

Osteoblasts = bone-building cells

• Synthesise and secrete collagen fibres, organic components, to built extracellular matrix of bone

• Initiate calcification

Osteoclasts = break down bone ECM -> bone resorption

• Release lysosomal enzymes and acids to digest proteins and mineral components of ECM

ossification - def

bone formation

bone development from mesenchyme processes - list (2)

1. intramembranous ossification → directly from mesenchyme

2. endochondral ossification → from cartilage derived from mesenchyme

intramembranous ossification - summary (2)

Mesenchymal models of bone form during the embryonic period

Direct ossification occurs in foetal development

endochondral ossification - summary (2)

Cartilage models of bones form from mesenchyme during foetal period

Bone replaces cartilage

intramembranous ossification - steps (4)

1. Development of ossification centre

   • Chemical signalling tells mesenchymal cells to cluster together and differentiate

   • Osteoblasts secrete organic extracellular matrix

2. Calcification

   • Calcium and other mineral salts are deposited and ECM calcifies

3. Formation of trabecular

   • ECM develops into trabeculae that fuse to form spongey bone around blood vessels

4. Development of periosteum and compact bone

   • Mesenchyme at periphery of the bone develops into the periosteum

   • Periphery of spongey bone will become compact bone tissue

intramembranous ossification - example bones (5)

• Flats bones of skull

• facial bones

• mandible

• medial part of clavicle

• hardening of fontanelles

endochondral ossification of long bones - steps (6)

1. Development of cartilage model

   • Mesenchymal cells develops into chondroblasts -> form hyaline cartilage model

2. Growth of cartilage model via cell division of chondrocytes

3. Development of primary ossification centre

   • At mid-region of cartilage model, cartilage hypertrophies and calcifies → periosteal capillaries grow into calcified cartilage to supply interior

   • Nutrients supplied by capillaries initiates primary ossification centre → becomes diaphysis

4. Development of medullary

   • As primary ossification centre grows towards end of bone, osteoclasts breakdown some of newly formed bone -> forms medullary cavity

5. Development of secondary ossification centres

   • Branches of epiphyseal artery enter still forming bone of proximal and distal epiphyseal -> blood supply triggers development of secondary ossification centre in ends of long bones

6. Formation of articular cartilage and epiphyseal plate

   • Spongey bones remains in interior bone rather than being broken down by osteoclasts

   • Bone growth occurs from the articular cartilage in the epiphyseal plate

bone growth in adolescence to adulthood (3)

Bone growth occurs in length and diameter until ~25 years -> only in diameter past 25

To avoid altering joint, bone growth occurs from diaphyseal side of epiphyseal plate -> avoid changing shape of epiphysis

Epiphyseal plate begins like as epiphyseal cartilage that allows bone to grow in length and ossifies once bone length is achieved

longitudinal bone growth - summary steps (2)

1. Interstitial growth of cartilage on epiphyseal side of epiphyseal plate via chondrocyte proliferation

2. Replacement of cartilage on diaphyseal side with bone via endochondral ossification

epiphyseal plate - zones (4)

1. resting cartilage

2. proliferating cartilage

3. hypertrophic cartilage

4. calcified cartilage

epiphyseal plate - zones of resting cartilage

Small, scattered chondrocytes

cells don’t function in cell growth but act as anchor for epiphysis to already formed bone

epiphyseal plate - zones of proliferating cartilage (3)

Chondrocytes slightly larger than those in resting cartilage and undergo interstitial growth

Cells arranged like stacks of coins

Divide and replace those that die at diaphysis side

epiphyseal plate - zones of hypertrophic cartilage

Mainly matured chondrocytes arranged into columns

epiphyseal plate - zones of calcified cartilage (2)

Very thin (usually one cell thick) and consists of dead chondrocytes -> ECM has calcified so chondrocytes dead

Osteoclasts dissolve calcified cartilage whilst osteoblasts and capillaries invade area -> bone

appearance of epiphyseal plate in juvenile vs adult bones

appears as darker bone in juvenile bones

epiphyseal cartilage no longer visible in adults (faint line remains)

appositional bone growth - summary (3)

Growth in width/ thickness

new bone deposited on outer surface whilst older bone lining medullary cavity destroyed

Medullary cavity enlarges as bone increases in thickness -> osteoblasts become osteoclasts and destroy bone

bone remodelling rates (3)

differ between bones and parts of same bone

5-7% of bone mass is recycled every week

Spongey bone replaced every 3-4 years

Compact bone replaced every 10 years

bone remodelling - summary process

combination of bone deposit by osteoblasts and bone resorption by osteoclasts

bone remodelling - purpose (2)

to maintain proper bone proportions during growth

change shape in response to mechanical stress

factors affecting bone growth and remodelling (4)

vitamins and minerals → calcium hardens bone ECM and Vit D increases calcium absorption

exercise → weight bearing activities stimulate osteoblasts

hormones → estrogen and testosterone stimulate bone deposition by osteoblasts

age → demineralisation due to decreasing hormone levels as activity of osteoclasts outpaces osteoblasts

types of bone markings - list (3)

1. sites of muscle and ligament attachment

2. projections that help form joints

3. depressions and openings for passage of nerves and vessels

types of bone markings - sites of muscle and ligament attachment

Created by stress of muscles pulling on bone

Eg. gluteal tuberosity on femur -> attachment for the gluteus maximus

types of bone markings - projections that help to form joints

Special shapes that connect together whilst still allowing movement

Eg. radius and ulna articulate with humerus but still allow flexion and extension of elbow

types of bone markings - depressions and openings for passage of nerves and vessels

Lots in skull for cranial nerves, carotid arteries and jugular veins passing in and out of skill

Eg. foramen magnum (occipital bone) -> passageway for spinal cord

types of bone markings - sites of muscle and ligament attachment examples (8)

1. tuberosity

2. crest

3. trochanter

4. line

5. tubercle

6. epicondyle

7. spine

8. process

types of bone markings - projections that help to form joints examples (4)

1. head

2. facet

3. condyle

4. ramus

types of bone markings - depressions and openings for passage of nerves and vessels examples (7)

1. grove

2. fissure

3. foramen

4. notch

5. meatus

6. sinus

7. fossa