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Histology > Bone 1 > Flashcards

Bone 1 Flashcards

1
Q

How is the skeleton a dynamic living tissue

A

Respond o body demand changes for minerals eg pregnancy lactation
Haematopoiesis done by skeleton spec in bone marrow
Bone needed for Ca homeostasis
Mineral store involved in acid-base balance maintenance as release mineral salts into blood that act as buffer
Ltd fat storage in BM too

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2
Q

Topographical classification

A

Cranial skeleton
Post cranial skeleton
(Axial, appendicular)

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3
Q

Ontogeny based classification

A

Somatic (form in body wall)

Visceral (form from brachial arches)

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4
Q

Phylogeny based classification

A

Preformed in cart

Ossify directly in fibrous CT ie flat bones

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5
Q

Class of individual bones

A 
By shape:
Long
Flat
Irregular
Short
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6
Q

Bone components

A

Organic (dry 30-35%, live 30%)
Inorganic (d 65/70%, live 45%)
Water (d 0, live 25%)

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7
Q

Inorganic component

A

Mainly Ca and P in form of Calcium hydroxyapatite small amount of other salts eg CaF2 CaCO3 MgF2
Responsible for rigidity
If removed bones become bendy

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8
Q

Organic component

A

Mainly C1 95%
Some amorphous GS
C gives strength and resilience
If removed bones become brittle

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9
Q

Woven bone

A

Immature form
Primary bone tissue
C fibres laid in random orientation, not aligned along stress lines
Produced in rapid osteoid production eg foetal development fracture repair too

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10
Q

Lamellar bone

A

Mature replacement of woven in 2 forms compact & cancellous(spongy)
C fibres form regular pattern in cancel lamellae parallel in compact form concentric sheets around vascular channel

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11
Q

Cell types

A

Osteoprogenitor cells
Osteoblasts
Osteocytes
Osteoclasts

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12
Q

Osteoprogenitor cells

A

Mesenchymal cells lining bone cavities found in periosteum endosteum haversion channels and Volkmann canals
Differentiate in response to stimulus and give rise to bone producing cells

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13
Q

Osteoblasts

A

Bone producing cells
Synth organic part of bone matrix (osteoid) and facilitate matrix mineralisation
Cuboidal shape basophilic cyt when active look like epithelium
Act as partial barrier
Extensive rer and Golgi as active pro synth and excretion

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14
Q

Why is osteoblast barrier fx key

A

Osteoblast inhib

Sep ECF and bone fluid so mineral concs can be regulated

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15
Q

Osteocytes

A

Mature osteoblasts embedded in own secretion occupying lacuna
key in matrix maintenance
Stellate with less rer and Golgi as reduced metabolic activity than osteoblasts more condensed chromatin - less active DNA

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16
Q

How osteoclasts communicate

A

Numerous filopodia in small canaliculi that interact with each other via gap jctn allowing hormone and metabolite transport between cells

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17
Q

Osteoclasts

A

Myeloid progenitor lineage
(Monocytes in blood migrate to tissues and become osteoclasts or macrophages)
Giant mobile multinucleated cells acidophilic cut some rer and Golgi
Abundant mitochondria and lysosomes reflect bone resorption fx

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18
Q

How osteoclasts carry out bone resorption

A

In howships lacunae (make themselves) on bone matrix surface
Form enclosed area between themselves and matrix by folding membrane many times to create micro environment ideal for bone resorption

19
Q

Micro environment conditions for bone resorption

A

Low pH

High proteolytic enz conc

20
Q

Where is mineralisation detrimental

A

Most area of the body

21
Q

What inhibits mineralisation of soft tissue

A

Pyro phosphate (PP)

22
Q

How C1 is involved in mineralisation

A

C1 fibrils produced and packaged in rer and Golgi
Secreted by osteoblast at cell surface producing osteoid
In maturation phase C fibrils form polymers and line up forming hole zones.

23
Q

How long is the maturation phase

A

Several days

24
Q

How is amorphous CaPO4 salts involved in mineralisation

A

The salts precipitate into the hole zones formed
Forming initial mineralisation sites
Ca salt deposition maybe accelerated by osteoblast ability to conc them in intracytoplasmic vesicles which are released into the ECM along with high alkaline phosphatase (ALKP) levels

25
Q

ALKP fx

A

Breaks down PP allowing for mineralisation

26
Q

Calcitonin as bone mineralisation regulator

A

Hormone secreted by C cells of the thyroid gland (tones down blood calcium)
Inhib osteoclast fx so reduce bone resorption and reduce Ca released into plasma

27
Q

Parathyroid hormone (PTH) role in bone mineralisation regulation

A

Hormones secreted by chief cells of PTgland
Interact directly with osteoblasts and increase RANK ligand and reduce osteoprotegerin (OPG) release
Indirectly stimulate osteoclast activity leading to incr bone resorption

28
Q

2 mechanisms of bone formation

A

Endochondral ossification

Within a membrane of CT

29
Q

Skeleton fx

A

Structure & support for the body
Permit locomotion
Scaffold for muscle and teeth attachment
Carries vital organs and so is optimised for protection in some areas but this an compromise movement eg skull
Other areas balance between movement and protection eg thorax

30
Q

Intramembranous formation

A

Source of most flat bones
Many primary ossification centres form in fibrous CT when mesenchymal cells diff into osteoblasts which produce osteoid and mineralisation ensues
Cells trapped and mature. Islands of dev bone spicules form and after a while fuse and woven bone is produced with Areas of trapped CT

31
Q

In intramembranous ossification how do blood vessels etc permeate it

A

The trapped CT areas are penetrated by blood vessels and undiff mesenchyme cells which give rise to the BM
Bones grow radially and fuse replacing original CT

32
Q

New born skull formation

A

Fontanelles are soft areas of the skull that correspond to unossified areas. Post birth bone formation in flat bones incr and outstrips bone resorption esp at int/external surfaces forming 2 compact bone layers with a cancellous centre (diploe) other mesenchyme cells give rise to end/periosteum

33
Q

How is periosteum of skull specialised

A

Outer fuses with the deep scalp layers

Inner constitutes the dura mater (outermost brain membrane)

34
Q

Endochondral ossification

A

Mainly responsible for short and long bone formation

35
Q

Endochondral ossification step 1

A

Small hyaline cart model formed

36
Q

Endochondral ossification stage 2 internal

A

Chondrocytes in shaft enlarge, surrounding cart resorbed and only thin trabeculae of cart left which are calcified. Therefore death of Chondrocytes leaving large spaces.

37
Q

Endochondral ossification stage 2 external

A

Simultaneously perichondrium of shaft dev osteogenic potential becomes periosteum and bone collar formed around shaft by intramembranous ossification
This adds to degen of Chondrocytes cutting of nutritional supply

38
Q

Endochondral ossification stage 3

A

Blood vessels invade empty spaces via channels in the bone collar made by osteoclasts
Primitive mesenchyme cells follow and diff into osteoblasts and blood forming cells of BM

39
Q

Endochondral ossification stage 4

A

Osteoblasts form layer on the surface of calcified cartilage remnants and start to produce woven bone

40
Q

Endochondral ossification stage 5

A

2 ends of cartilage model now sep by primary ossification in centre of shaft
2 cart ends grow in diameter forming epiphyses and each develop a secondary ossification centre

41
Q

Endochondral ossification stage 6

A

Interface between shaft and epiphysis that continues to undergoes regressive changes then ossification leading to elongated bony diaphyseal shaft formation with semilunar cartilage epiphysis at each end
Interphase between the two is the growth plate

42
Q

Endochondral ossification stage 7

A

Within GP cartilage proliferate continuously leading to bone elongation

43
Q

Endochondral ossification stage 8

A

At each end a layer of hyaline remains which becomes art cart

44
Q

Endochondral ossification stage 9

A

Woven bone remodelled under influence of fxal stress into lamellae bone formin cortical layer of compact with cancellous centre

Histology (10 decks)

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