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Anatomy of the limbs > Development and growth of bone > Flashcards

Development and growth of bone Flashcards

1
Q

What are the functions of bone?

A
  • Support the body shape
  • Provide a system of levers for muscle action
  • Protect the internal organs (e.g. rib cage, pelvic girdle, skull)
  • A site of blood cell formation (blood marrow)
  • A mineral storage pool (>98% of all calcium in the body is stored within bones
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2
Q

What are the mechanical properties of bone and what contributes to them?

A

Bone has a cable-like flexibility and resistance to tension, because of the framework of collagen and other bone proteins

Bones have pillar-like stiffness and resistance to compression conferred due to collagen containing crystalline mineral (hydroxyapatite)

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3
Q

What are the 2 main types of bone, their structures and when are they found?

A

Woven bone – immature type of bone
Seen during development and repair of fractures – quite irregular

Lamella bone – mature type of bone
Layered bone so more regular arrangement

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4
Q

What is lamellar bone in the cortex of the shaft? (shaft is main part of bone aka diaphysis)

A

compact bone

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5
Q

What is lamellar bone in the head and margins of the interior of the shaft?

A

spongy bone

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6
Q

How is lamellar bone arranged?

A
  • There is an outer, hard layer of compact lamellar bone (cortical bone)
  • There is an inner layer of interlacing struts of lamellar bone (cancellous/trabecular/spongy bone)
  • Trabecular bone looks irregular, but it is still made up of lamellar bone
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7
Q

What are osteons?

A

Structures found in compact bone - they are concentric circle of bone with osteoblasts in between. There is a central canal which contains blood vessels and lymph vessles

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8
Q

What connects the osteons?

A

canaliculi

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9
Q

Describe the structure of trabecular bone

A
  • It is still lamellar bone

- Trabeculae, although irregularly arranged, are made of lamellar bone

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10
Q

How are osteocytes arranged in bone?

A

They are arranged in rings and layers. Everything else is calcified bone, which is calcium salts and osteoid (bone protein with lots of collagen in it).

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11
Q

Describe the blood supply in bones

A
  • Bones are solid and structural, but they have a very rich blood supply
  • When damaged, bones will bleed a lot
  • There are lots of little blood vessels from the surface (the periosteum)
  • There are larger vessels that come in via nutrient foramina – arteries and veins can pass through these
  • There are also epiphyseal and metaphyseal vessels
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12
Q

What is the periosteum?

Describe its structure and role

A

The outer surface of the bone

  • A layer of cellular connective tissue, also fibrous
  • Has a key role in bone growth and repair
  • Very goof blood and sensory nerve supply
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13
Q

What matures to become and osteoblast and is this a reversible process?

A
  • An osteogenic cell -> osteoblast -> osteocyte

- Osteocytes, if in a region where bone has become damaged, free up from the bone case and revert back to osteoblasts

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14
Q

What do osteoclasts do?

A
  • They produce acid to dissolve calcium salts
  • They remodel bone when needed
  • Break down bones if they are not used gradually
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15
Q

When does bone development begin and end?

A

6 weeks of foetal life, and continues into adulthood

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16
Q

What are the two types of ossification (making bone)?

A
  • intramembranous

- endochondral

17
Q

What is intramembranous ossification - when does it happen?

A
  • This occurs where there is existing vascular connective tissue and mesenchymal cells
  • Bone matrix (ostein) is deposited around the collagen
  • Bone matrix begins to mineralise, to form woven bone, which later remodels to lamellar bone
18
Q

What is the process of intramembranous ossification?

A

STEP 1: Development of ossification at the centre

STEP 2: Calcification

STEP 3: Formation of trabecular bone

STEP 4: Development of the periosteum

19
Q

What is endochondral ossification - when does it occur and what happens during it?

A

Majority of bones formed like this

  • This occurs within existing foetal cartilage models
  • The cartilage calcifies and chondrocytes die
  • You get periosteal osteoclasts, which cut channels for sprouting vessels
  • Osteoblasts, which enter with vessels to build bone around them
20
Q

What are the three main parts of long bone?

A

epiphysis (head)
metaphysis
diaphysis (shaft)

21
Q

How does bone development occur in long bone and why?

A
  • Long bones must support forces whilst growing so the shaft must ossify first followed by the epiphyses
  • Growth continues by ossifcation at growing cartilage plates
  • Growth stops when the cartilage growth ceases and plate is overrun by ossification
22
Q

What will be seen in the hands of a child that isn’t in an adult?

A

When you compare the hand of an adult and child, we can see that in the child’s wrist, epiphyses ossify in the 2nd year of life. The gaps between bones are normal – it’s the growth plates. Epiphyseal plates (dark) remain cartilaginous until growth ceases, after puberty.

23
Q

Describe the adaptability of bone

A
  • Bone can grow without comprising its support functions, and can repair when fractured
  • Bone increases or decreases bulk and density, in response to pattern of use
  • Bone can alter its external and internal shape in response to pattern of use (remodelling)
24
Q

What enables bone to grow well and remodel?

A
  • Bone has a large blood supply – cells are never far from nutrients and oxygen
  • Osteocytes maintain bone matrix, but can activate osteoblasts for new bone building
  • Osteoclasts are giant cells specialised for destruction of bone matrix
25
Q

How does bone elongate?

A
  • Cartilaginous epiphyseal plates in between the heads and the shaft produce cells, that will calcify and gradually elongate the bone
26
Q

Describe how the bone develops to form osteons and space for blood vessels - increasing bone diameter

A
  1. Ridges in periosteum create grooves for periosteal blood vessels
  2. Periosteal ridges fuse, forming an endosteum-lined tunnel
  3. Osteoblasts in endosteum build new concentric lamellae inward toward the centre, forming a new osteon
  4. Bone grows outwards as osteoblasts in the periosteum bind new circumferential lamellae
  5. Osteon formation repeats as new periosteal ridges fold over blood vessels
27
Q

What are some types of fractures?

A
  • transverse
  • oblique
  • spiral
  • comminuted
  • segmental
  • avulsed
  • impacted
  • greenstick
  • torus
28
Q

How does a fracture heal?

A

Bleeding is an important part of the process. The haematoma becomes infiltrated by fibrous matrix, immune cells and GF. You begin to get activation of osteo-progenitor cells producing new blood cells. You get connective tissue forming, which produces a reactive cartilage. The cartilage will ossify (initially as immature bone, and later it will remodel to become mature).

29
Q

What are the 3 main steps in fracture healing?

A
  1. Early fracture healing
  2. Fracture repair phase: woven bone formation
  3. Late fracture repair – reactive cartilage undergoing endochondral ossification
30
Q

What happens when blood calcium levels are high?

A
  • Calcitonin is released by parafollicular thyroid cells
  • The breakdown of bone matrix by osteoclasts is inhibited
  • Uptake of calcium into the bone matrix is thus promoted
31
Q

What happens when blood calcium levels are low?

A
  • Parathyroid hormone is released by chief cells of the parathyroid glands
  • Osteoclast bone resorption activity is promotes
  • There is increased calcium reabsorption by the kidneys
32
Q

Endochondral ossification and bone elongation

A
  1. Cartilage model forms and grows
  2. Primary ossification centre forms
  3. Medullary cavity forms and develops
  4. Secondary ossification centre forms
  5. Epiphyseal plate forms which is a cartilage plate that enables bone elongation growth
33
Q

Which type of ossification occurs in bones at the base of skull and long bones?

A

Endochondral

Anatomy of the limbs (5 decks)

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